vot. 72351 design and development of a new...
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VOT. 72351
DESIGN AND DEVELOPMENT OF A NEW CNG (COMPRESSED NATURAL GAS) ENGINE
REKABENTUK DAN PEMBANGUNAN ENJIN CNG BARU
Dr. ROSLI ABU BAKAR
PUSAT PENGURUSAN PENYELIDIKAN UNIVERSITI TEKNOLOGI MALAYSIA
2002
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VOT. 72351
DESIGN AND DEVELOPMENT OF A NEW CNG
(COMPRESSED NATURAL GAS) ENGINE
REKABENTUK DAN PEMBANGUNAN ENJIN CNG BARU
Dr. ROSLI ABU BAKAR
RESEARCH VOTE NO: 72351
PUSAT PENGURUSAN PENYELIDIKAN UNIVERSITI TEKNOLOGI MALAYSIA
2002
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Abstrak
REKABENTUK DAN PEMBANGUNAN ENJIN BARU CNG
(GAS ASLI TERMAMPAT)
(Katakunci: Prestasi Enjin, CNG,emisi, system masukan)
Pencarian untuk menggunakan bahan api alternatif dalam enjin pembakaran
dalam semakin menjadi subjek yang diminati pada masa kini. CNG (Gas Asli
Termampat), suatu gas asli berbentuk gas, telah dikenali sebagai bahan api yang
menjanjikan kebaikan yang mencukupi dibandingkan dengan petrol dan diesel.
Tetapi, enjin CNG sama ada dalam bentuk bahan api-dual, bahan api-tunggal, atau
enjin khas CNG memberi prestasi yang kurang dibandingkan kepada petrol. Kuasa
keluaran rendah adalah disebabkan kekurangan dalam kecekapan volumetrik , halaju
nyalaan rendah dan ketiadaan sejatan bahan api. Pelbagai kajian telah dijalankan ke
atas enjin CNG. Tetapi, modifikasi di dalam kebuk pembakaran adalah sangat sukar
dan memerlukan kos yang tinggi. Kawasan pada masukan adalah lebih mudah ,
murah dan boleh diterima oleh pembeli kenderaan. Sebagai, tambahan, kecekapan
volumetrik enjin pembakaran dalam adalah fungsi konfigurasi kuat pancarongga
kemasukan
Aliran bertekanan dan turbulen adalah keadaan masukan ideal untuk operasi
CNG. Keadaan ini akan meningkatkan kecekapan volumetrik dan meningkatkan
halaju nyalaan. Pengajian akan membuat rekabentuk sebuah pencampur dan alat
pusaran yang menghasilkan kombinasi aliran bertekanan dan turbulen pada proses
masukan. Satu kombinasi teknik simulasi dan eksperimental telah dijalankan dalam
menghasilkan system canggih ini Langkah eksperimen ini diperlukan untuk
membuat engin CNG asas dan ujikaji prestasi system masukan. Simulasi dilakukan
pada fasa rekabentuk untuk memperolehi pencampur dan alat pusaran. Sebuah
pencampur penyelidikan yang menggabungkan prinsip pembakar-venturi dengan
tiga pembolehubah: 2,4,8 dan 16 lubang mengelilingi kawasan campuran, sudut
input ( 300 , 400,500 and 600) dan sudut output (200, 300 , 400 and 500). Alat pusaran
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mempunyai dua pembolehubah; nombor revolusi (1, 1.5, and 2) dan sudut satah (150,
300 , 450 and 600). Semua model telah difabrikasi dan diuji dalam rig ujikaji.
Pada umumnya didapati bahawa pencampur dan alat pusaran terbukti dapat
memperbaiki nisbah pusaran dan keadaan tekanan di dalam pancarongga masukan.
Penggunaan sistem masukan termaju dapat memperbaiki prestasi enjin CNG secara
par kepada petrol.
Penyelidik Utama: Dr. Rosli Abu Bakar (Head)
Mr. Mardani Ali Sera Mr. Sin Kwan Leong
E-mail : [email protected]
Tel. No.: 07-5534752 Vote No.: 72351
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Abstract
DESIGN AND DEVELOPMENT OF A NEW CNG (COMPRESSED NATURAL GAS) ENGINE
(Keywords: Engine performance, CNG, emission, intake system)
The search to implement alternative fuels used in internal combustion
engines are becoming the subjects of interest nowadays. CNG (compressed natural
gas), a gaseous form of natural gas, has been recognized as one of the promising
alternative fuel due to its substantial benefits compared to gasoline and diesel.
However, the CNG engine, either in dual-fuel, bi-fuel or dedicated forms has lower
performance compared to that of gasoline. This low power output is principally due
to loss in volumetric efficiency, low flame speed and absence of fuel evaporation.
Many studies have been carried out on CNG engine research. However, modification
inside the combustion chamber is too complicated and costly. Area in the intake
system is simpler, cheaper and may also commercially acceptable by the car buyer.
In addition, volumetric efficiency of reciprocating internal combustion engines is a
strong function of intake manifold configuration.
The pressurised and turbulent flow is an ideal intake condition for CNG
operation. These conditions will increase the volumetric efficiency and increase the
flame speed. This study comes up with a design of mixer and a swirl-device that
produced the combination of pressurised and turbulent flow in the intake process. A
combination of experimental and simulation technique were involved in producing
this advanced system. Experimental steps were needed to acquire basic CNG engine
and intake system performance test. The simulation approach was implemented in
design phase, especially in producing appropriate mixer and swirl-device. A research
mixer that combined a venturi-burner principles with three variables; 2,4,8 and 16
number of hole surrounding the mixing arena, input angles (300, 400,500 and 600) and
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output angles (200, 300, 400 and 500). A swirl-device has two variable; numbers of
revolution (1, 1.5, and 2) and angle of plane (150, 300, 450 and 600). All models then
fabricated and tested in a CNG engine performance test rig.
In general it was found that the mixer and the swirl-device proven to improve
the swirl ratio and pressure condition inside the intake manifold. The implementation
of advanced intake system is able to improve the CNG engine performance par to
that of gasoline.
Key Researchers: Dr. Rosli Abu Bakar (Head)
Mr. Mardani Ali Sera Mr. Sin Kwan Leong
E-mail: [email protected]
Tel. No.: 07-5534752 Vote No.: 72351
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CHAPTER I
INTRODUCTION
1.1 Compressed Natural Gas Engine
The search and the strategy to implement alternative fuels used in internal
combustion engines are becoming the subjects of interest nowadays. Most of the
concerns are driven by two factors: environmental effects and energy independence
from petroleum based fuel. It has been well known that gasoline and diesel, severely
affected the environment quality through its exhaust emissions. Besides, this
conventional fuel also identified as an un-renewable source of energy. As a result,
lots of countries and car manufacturers put priority in the effort to seek a cleaner,
affordable and better quality of alternative fuels.
CNG (compressed natural gas), a gaseous form of natural gas, has been
recognized as one of the promising alternative fuel due to its substantial benefits
compared to gasoline and diesel. These include lower fuel cost, higher octane and,
most certainly, cleaner exhaust emissions. Therefore, the number of vehicle powered
by CNG engine growing rapidly.
However, the CNG engine, either in dual-fuel, bi-fuel or dedicated forms has
lower performance compared to that of gasoline. This low power output is
principally due to loss in volumetric efficiency, low flame speed and absence of fuel
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evaporation. Hence, systematic studies have been carried out to improve techniques
and components in producing optimum CNG engine.
This study will concentrate on enhance the intake system to improve the CNG
engine performance. This advanced system is proposed to produce fast burn
combustion and increasing the volumetric efficiency of the engine that will promote
a comparable CNG engine performance compared to gasoline and diesel engine.
1.2 Research Background
Up to now, most of the CNG engines are simply conversions from either petrol
or diesel, which are far from the optimal design (Duan, 1996). Experimental testing
on Honda CNG Civic GX 1.6L showed a 12% reduction in power and a 13 %
reduction in torque at Wide Open Throttle (WOT) compared to gasoline operation
(Suga, Knight and Arai, 1997). The torque and power in Ford CNG Crown Victoria
also decreases approximately 12% (Lapetz et al, 1995). Maxwell and Jones (1995)
recorded that the average power and torque loss of CNG compared to gasoline is in
the range of 3 to 19.7% and 1.6 to 21.6%, respectively.
Research in CNG engine essentially focused on three main areas: intake process,
combustion system and exhaust treatment. Many efforts were put in designs and
operate appropriate systems in combustion process. Johansson and Olsson (1995)
developed combustion chambers that generate turbulent flow for CNG operation.
The results showed that there is a high correlation between in cylinder turbulence
and rate of heat release in the combustion process. Among the turbulent flow, Ando
findings (1996) confirmed that tumble is simpler as a system compare than that of
swirl. Turbulent flow produced by squishing also improved the burning rates, which
resulted in improvement of thermal efficiency (Evan, 1996).
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However, as this study not only considers about the novel of the products but
also based on the philosophy adding small, useful and economical devices without
major modification, modification inside the combustion chamber is too complicated
and costly. For this reason, area in the intake system is simpler, cheaper and may
also commercially acceptable by the car buyer. Since volumetric efficiency of
reciprocating internal combustion engines is a strong function of intake manifold
configuration (Pearson, 1990), the intake process might also give a great contribution
toward increasing the CNG engine performance.
The pressurised and turbulent flow is an ideal intake condition for CNG
operation. These conditions will increase the volumetric efficiency and increase the
flame speed. So far the implementation of turbocharged or supercharged is the
common practice. Nevertheless, this means added a new system that will increase
the power weight ratio of the vehicle. Moreover, the installation of a new system will
occupy more space that in the compartment, that is already jam-packed with CNG
conversion unit. Thus, instead of utilize the charged equipment; this study comes up
with a design of mixer and swirled-device that produced the combination of
pressurised and turbulent flow in the intake process.
1.3 The Objective and Scopes of the Research
The goal of the present research will focus on developing an advanced intake
system for CNG fuelled engine. This advanced system will be based on a new mixer
and swirled-device that implement pressurised and turbulent flow. To complete the
research objective the following scopes should be required:
1. To determine factors affecting the pressurised and turbulent flow in the intake
process
2. To design and fabricate the mixer and swirl devices based on the pressurised and
turbulent parameter
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3. To simulate the mixer and swirl devices designed
4. To build the rig for engine testing purposed
5. To set up the measurement system including the data acquisition system
6. To test the recommended design of mixer and swirl devices
7. To test and analyse the new design in terms of engine performance
1.4 Research Design And Methodology
The research methodology of this study will encompass the three steps:
1. Design and simulate the new design on mixer and swirl device.
2. Analyse and fabricate the recommended new designs.
3. Validate the designs in term of pressure and turbulent parameter in a transparent
model rig.
4. Test the final designs in term of engine performance.
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CHAPTER II
LITERATURE REVIEW
The internal combustion engines have served mankind for over two and a half
centuries. The first marketable engine, a coal gas-air mixture that has no compression
stroke produced between 1860 and 1865 in sizes up to six horsepower. During that
time efficiency was at best about 5 percent. In 1876, Nicolaus Otto proposed the basic
four-stroke engine, which obtained thermal efficiencies of up to 14 percent
(Heywood, 1988). Since then, the improvement in automotive technology goes on.
Not only in term of technology but also in the effect of this technology product, the
vehicles, on the social life.
Nowadays, the automotive industry is one of the biggest businesses in the
modern history. In 1999, there were about 750 million vehicles worldwide. As much
as 55.8 millions sold around the world in year 2000 (Kompas, 2001). On the
technology, the implementations of new technologies increase the efficiency. To date,
35 percent efficiency is a common value for a standard engine.
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2.1 Automotive Technology Trend
Up to now, research on engine development can be simplified in three mottos:
lighter, better and friendlier. Lighter means reducing the overall vehicle weight. The
rule is the lighter the lesser the fuel consumed. In this area, plastics, aluminium and
the use of carbon-fibre were a part of the research. Based on De Cicco (1999) work
(see table 1), the implementation of CFD modelling may also reduce the drag
coefficient of the car thereby increasing the fuel economy up to 10%.
Better represent on the implementation advanced technologies such as direct
injection, swirl and tumble flow; variable and higher compression ratios, a new
transmission and lean burn technology. These are a part of focus areas to improve
engine efficiency in conventional power-train. Lean burn technology is one of the
mature and attractive means of improving thermal efficiency (Purcell, 2000).
Advanced power train is also explored. Nakamura et al (1991) listed the Stirling
engine and dynamic gas turbine as two promising candidates in producing high
thermal efficiency and less pollutant engines besides the electric and fuel cell
technology. Poulton (1994), also included the two-stroke engine as an alternative
engine for road vehicle in the future.
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Table 1: Technological Options for Improving
Vehicle Fuel Economy (DeCico, J., 1999)
TECHNOLOGY TYPE FUEL ECONOMY IMPROVEMENT* LOAD REDUCTION
Mass (material substitution) 10% – 40% Aerodynamics 4% – 10% Other 4% – 8%
CONVENTIONAL POWERTRAIN
Variable Valve Control (VVC) 10% – 12% Other PFI Spark Ignition Refinements 5% – 10% Direct Injection Spark Ignition (DISI) 10% – 20% DI Compression Ignition (DICI/diesel) 20% – 30% Transmission 7% – 14%
ADVANCED POWERTRAIN
Hybrid Drive 30% – 60% Fuel Cell 50% – 70%
*Relative to an average mid-1990s U.S. light duty vehicle rated at 25 mpg (9.4 L/100km).
Friendlier linked with the environment effect. This term turns into the centre
of the interest in 1960’s and became more urgent in the late 20th century. Attentions
are given to reduction of emissions of hydrocarbon, carbon monoxide and oxides of
nitrogen content in exhaust gas. Studies on the fuel and exhaust technology have also
contributed to improvement of engine performance together with reduction of
emissions level. Reformulated petrol and diesel fuel, implementation of exhaust gas
recirculation (EGR), catalytic converter and exhaust technologies, and last but not
least the alternative fuels, are some areas studied in producing environmental friendly
vehicles.
In fact, the combination of these areas is a common thing practiced in automotive
research. This study combined efforts on improving engine performance and reducing
exhaust gas emissions by employing the advanced intake system for the CNG fuelled
engine.
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2.2 CNG as an Alternative Fuel
The search for alternative fuel is caused by two reasons: estimation on the crude
oil deposits and the emissions problem. At the present consumption of petroleum
energy deposit will last more or less in seventy-five years from year 2000 (Nakamura,
et al., 1991). Therefore, over the past decade, alternative fuel had been studied for the
possibility of lower emission, lower fuel cost, better (more secure) fuel availability
and lower dependence on petroleum.
Not all source or form energy can be categorised as an alternative fuel. Stratton
(1996) has listed some suitability factors that would support alternative fuel to
become a choice over petroleum as shown in Table 2.
Table. 2: Factors Affecting the Suitability of an Alternative Fuel Item Requirements
Fuel Reserves Reserves of the fuel must be plentiful Refuelling infrastructure
A sufficient number of refuelling points must exist.
Component availability
Specialized engines, fuel tanks, etc. must be commercially available
Emission potential
The alternative fuel must offer reduced emissions
Safety The fuel storage system must be capable of being installed into the subject vehicle
Financial requirements
The costs associated with using the alternative fuel must be comparable with existing vehicles
Following these criteria, the Dennis Dart, a United Kingdom bus manufacturer,
has already evaluated eight promising alternative fuels as shown in Table 3. The
results showed that natural gas altogether with biomass, electric and hydrogen have an
opportunity to replace gasoline and diesel.
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Table. 3: Dennis Dart Fuel Requirements for Various Alternative Fuels (Stratton, 1996)
Fuel Storage Pressure
(bar)
Fuel Storage Volume (litres)
Fuel Container Weight
(kg)
Fuel Storage Temperature
(Deg C)
Calorific Value NET
(MJ/kg) Diesel 1 135 30 15 42.9 Petrol 1 160 35 15 43 CNG 200 540 460 15 47.2 LPG 8 230 70 15 46.1 LNG 6 260 80 -161 47.2 Methanol 1 300 70 15 19.7 Electric 1 - 5000+ 15 - Hydrogen 300 270 950 15 119.8
There are three forms of natural gas: liquefied natural gas (LNG), liquefied
petroleum gas (LPG) and compressed natural gas (CNG). Both LNG and CNG are
based on methane. The difference is LNG made by refrigerating natural gas to
condense it into a liquid while CNG still in the gaseous form. LNG is much more
dense than CNG. Therefore, LNG is good for large trucks that need to go a long
distance before they stop for more fuel. LPG is based on propane and other similar
types of hydrocarbon gases. These hydrocarbons are gases at room temperature, but
turn to liquid when they are compressed. Detail fuel characteristics of natural gas can
be seen in Table 4.
2.3 The Potential of CNG
CNG is the most common form on-board storage of natural gas. It is a mixture of
hydrocarbons consisting of approximately 80 to 90 percent methane in gaseous form.
CNG is colourless, odourless, non-toxic but inflammable and lighter than air. This is
due to low energy density and compressed to a pressure of 200 to 250 bar to enhance
the vehicle on-board storage in a cylinder (Aldrich and Chadler, 1997).
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CNG has a low carbon (C) weight per unit of energy, as a result emissions of
CO2, a greenhouse gas, can be reduced by more than 20% compared with gasoline at
equivalent level of work. Moreover, there is a little wall flow fuel in the intake
manifold even at low temperature because of the gaseous state of CNG. Combustion
temperature for CNG fuel also tends to be lower than with gasoline engine.
Table 4. Natural Gas Characteristics Item Liquefied
Natural Gas (LNG)
Liquefied Petroleum Gas (LPG)
Compressed Natural Gas
(CNG)
Chemical Structure
CH4 C3H8 CH4
Primary Components
Methane that is cooled cryogenically
Propane Methane
Main Fuel Source
Underground reserves
A by product of petroleum refining or natural gas processing
Underground reserves
Energy Content per Gallon
73,500 Btu 84,000 Btu 29,000 Btu
Energy Ratio Compared to Gasoline
1.55 to 1 or 65%
1.36 to 1 or 74%
3.84 to 1 or 26% at 3000 psi
Liquid or Gas Liquid Liquid Gas
Source: Alternative Fuel Data Center (AFDC), Office of Transportation Technologies, US Department of Energy
Table. 5: Emissions reduction by CNG
Emissions Reduction against Gasoline Reduction against Diesel Carbon Monoxide
22-24% 10%
Carbon Dioxide
76% Natural gas and diesel both low
Nitrogen Oxides
83% 80%
Non Methane Hydrocarbons
88% 80%
Benzene 99% 97% Lead 100% Not applicable Sulphur Nearly 100% Nearly 100%
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In addition, CNG was expected from HC emission counts because it is harmless
for living things. This was accomplished taking advantage of the HC emission level
counted by non-methane hydrogen carbon (NMHC), a newly stipulated measurement
of HC emission level, and can be reduced by more than 80% compared with gasoline.
Detail comparison between CNG and gasoline can be seen in Table 5 and 6.
Table 6. Methane and Gasoline Characteristics (Guibet and Faure-Birchem, 1999)
Characteristics Methane Conventional Gasoline
Octane Rating Up to 130 95 Mass Heating Value (kJ/kg) 50,009 42,690 Energy content of the carburetted mixture (kJ/dm3)
3.10 3.46
Lower inflammability limit (m/s) 0.50 0.60*
Laminar flame speed (cm/s) at an equivalence ratio of 0.80
30 37.5*
Minimum ignition energy (mJ) 0.33 0.26** Adiabatic flame temperature (K) 2,227 2,266
* Data for isooctane ** Data for butane Benefits of using CNG fuel in vehicles include (Rosli et al, 2001):
a. Higher octane number in the range of 120 to 130, which is considerably higher
than 93 to 99 octanes for gasoline. This made the CNG fuel possible to run at
high compression ratio engine without any knocking phenomena.
b. Higher flammability compared to gasoline that make it appropriate to run on
lean burn technology.
c. Burns cleaner than most fuel. Engine-out emissions of HC and NOx can be
reduced below the corresponding levels for gasoline engines as can be seen in
Table 5.
d. Safer; it is lighter and dissipates quickly. It ignites quickly, it ignites only when
the gas to air ratio is between 5 – 15% by volume.
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Table 7. Fuel Price
Fuel Pump Price/Litre 1) Projected Price per Equivalent Gallon
of gasoline2)
NGV RM 0.56 (US$ 0.15) US$ 0.88 Petrol (Unleaded) RON 97 RM 1.20 (US$ 0.32) US$ 1.21 Petrol (Unleaded) RON 92 RM 1.16 (US$ 0.31) US$ 1.07 Diesel RM 0.70 (US$ 0.18) n.a Autogas (LPG) RM 0.751 (US$ 0.20) n.a Note: 1) Petronas (2000) and 2) Maxwell and Jones (1995)
e. Because it is a clean burning fuel, it reduces the required maintenance of
vehicle; can be half of gasoline—oil changes more than every 15-30,000 km,
spark plug points can be up to 120,000 km.
f. Plenty of reserve; there is an estimated 65-70 year supply of natural gas.
Besides made from fossil, natural gas can also be made from agricultural waste,
human waste and garbage.
g. Cheaper per litre equivalent than gasoline, in Europe 14-17 less than gasoline
and 12-74% less expensive than diesel. In Malaysia, the CNG price is half less
expensive compared to gasoline as shown in Table 7.
However, CNG fuel has some disadvantages that limited its potential to achieve
the optimum engine performance, such as:
a. Since CNG is in gaseous form, it has a low density. CNG in the mixture drawn
into the cylinder displaces approximately 8 to 10% of oxygen. This reduces the
volumetric efficiency due to larger space occupied in the combustion chamber
available for combustion.
b. CNG has a low flame speed. Its burns slower than conventional fuels, such as
gasoline and diesel (Andrew and Bradley, 1975). Values as much as 60%
decrease in lower burning velocity for natural gas has been measured (Duan,
1996). These effects the total combustion duration prolonged compared with
diesel and gasoline. This can cause a further reduction in the engine output of 5
to 10%.
c. Absence of fuel evaporation. When gasoline evaporates (required before
combustion), the energy required for the phase change decrease intake charge
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temperature and air partial pressure. The decrease in temperature offsets the
decrease in air partial pressure and results in a positive increase to volumetric
efficiency of about 2%. CNG does not evaporate before combustion, losing any
potential gain from the heat vaporization
2.4 State of Art of CNG Engine Research
The use of CNG as an alternative fuel in an engine can be divided into three main
types according to their fuel usage as follows:
i. Dual Fuel
This is a development from conventional diesel engine. In this type of engine,
both diesel and natural gas were introduced into the engine cylinders during
compression. As natural gas will not ignite under compression alone, the
diesel is required to act ignite the gas/air mixture. When natural gas refuelling
points are not available, the engine can revert to conventional operation.
ii. Bi-Fuel
This type of engine development is based on the conventional petrol engines
where the fuel system has been modified to operate either petrol or gas. When
natural gas refuelling is not available, normal running on petrol is possible.
iii. Dedicated/Mono Fuel
This is a specialized engine type, which has been designed and optimised to
operate only on natural gas. This enables the characteristics of natural gas to
be fully exploited without the need to compromise in design to enable other
fuel usage (Mardani and Rosli, 2001).
Up to now, most of the CNG engines are simply conversions from either petrol or
diesel, which are far from the optimal design (Duan, 1996). Examples of such
conversion include a Honda Civic GX, which was based on the Civic 1.6-liter
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gasoline while the Ford Crown Victoria Dedicated Vehicle from gasoline base Crown
Victoria. The Honda Civic was modified through the change of compression ratio,
valve train system and exhaust system (Lapetz et al, 1995). The modification carried
on the Ford Crown Victoria consists of four major areas: fuel storage, fuel metering,
power train and the emission control system (Suga, Knight and Arai, 1997).
The CNG engine, either in dual-fuel, bi-fuel or dedicated forms has lower
performance compared to that of gasoline. For the case of Honda 1997 Civic GX
1.6L, the use of natural gas in a conventional gasoline engine led to a 12% reduction
in power and a 13 % reduction in torque at Wide Open Throttle (WOT) (Suga, Knight
and Arai, 1997). In addition, torque and power in Ford 1996 Crown Victoria
decreases approximately 12% (Lapetz et al, 1995). Based on the Maxwell and Jones
(1995) works, the average power and torque loss of CNG compared to gasoline is in
the range of 3 to 19.7% and 1.6 to 21.6%, respectively.
For simple conversion of the carburettor and EFI based engine, the UTM CNG
Engine research centre have already running the performance engine experiment. For
1.5 L carburettor based engine, the results showed that gasoline produced brake power
up to 6 kW at 3500 rpm compared to 4.8 kW for CNG fuelled engine (Rosli and
Mardani, 2001). 1.6 L EFI engine performance data shows the similar trend, up to 33
kW and 29 kW for gasoline and CNG fuelled engine at 3500 rpm at full load,
respectively (Mardani et al, 2002).
This engine lack of performance is cause by two factors: the CNG fuel
characteristics and the improper operating conditions of the CNG engine. Therefore,
most of the researches on CNG engine are directed to accomplish these factors. The
research areas as well as the potential technology development to achieve optimum
operation of CNG engine has already plotted in Figure 1 (Rosli c, 2001).
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Figure 1: CNG Engine Research Map
In this figure, the low emission produced was not discussed since it has
already taken for granted the benefits for CNG fuel. However, the installation of EGR
or 3 Way Catalyst in order to reduce the NOx produced is recommended.
To get the optimum conditions as state in Figure 1, detail strategies are described
in Figure 2.
2.5 Combustion System
In the combustion area, fast burn combustion process that generated complete
combustion duration is among the best conditions that should be fulfilling in optimum
CNG engine. This system face up the low flame speed CNG’s problem. One option to
have this system is by put into practice turbulent condition inside the combustion
CNG Engine Optimum Operation
• Supercharged or turbocharged
• Lean Burn Operation
• New Design of Combustion Chamber
• Advance Intake Valve Close Timing
• High Compression Ratio
• Turbulent Flow• New Design of
Combustion Chamber
• Swirl or Tumble
• Direct Injection• New Design of
Combustion Chamber
• Type of Injector
• Addition / Injection of H2
• A Fast Burn Combustion Process
• Lean Burn Operation
New Setting for: • MBT • Injection and • Intake Closed
Valve Timing
Lighter and Stronger Material such as Composite for CNG tank
High volumetric Efficiency
High thermal
Efficiency
High combustion
Performance
High Speed Peak
Performance
Lighter Storage System
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chamber. Johansson and Olsson (1995) developed ten different geometries of the
combustion chambers. The results showed a high correlation between in cylinder
turbulence and rate of heat release in the combustion process. The turbulent flow
improved the thermal efficiency by providing the homogenous mixture of air and gas.
It’s also increase the flame speed of the combustion process. However, the results also
showed that geometries that gave the fastest combustion would also gave the highest
NOx values. Among the turbulent flow, tumble is simpler as a system compare than
that of swirl (Ando, 1996).
Figure 2: Engine Design Considerations
In their further study, Einwall and Johansson (1997) investigated the effect of
six different combustion chambers on the combustion performance. The results
showed that different geometrical combustion chamber, with the same compression
ratio (12:1), have very different combustion performance. The Quartette type of
combustion chamber reached the highest peak turbulence.
Another way on improving burning rate is generated charge motion combustion
chamber by squishing. High levels of turbulent generated from the squish have an
effect on increasing burning rates, which resulted in improvement of thermal
efficiency. Evan (1996) proved that the faster burning rates led to an average of 1.5%
reduction in BSFC or 1.5% increase in power output under wide open throttle
• Supercharged or turbocharged equipment
• Turbulent device
• Lean burn operation
• Advance Intake Valve Close Timing
• Heat Transfer Process
• Pressurise intake flow
• High Compression Pistons • Higher Temperature Resistance for
Cylinder Materials • Hardened Exhaust valves • Combustion chamber shape and spark
plug location • Fast Burn Combustion Chamber
Mechanism • New Design of Combustion Chamber • Gaseous Injector
• Composite Material
• 3 Way Catalyst • EGR
CNG Engine Design Considerations
Intake System
Combustion Process
Exhaust System
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condition, as compare to the slowest burning cases. However the highest turbulence
level combustion chamber also showed the highest emission levels.
An additional method to improve the burning rate is by adding hydrogen into the
CNG/air mixture. The addition of 20% hydrogen into the natural gas will reduced
equivalent ratio by 15% without increasing ignition delay and combustion duration.
(Swain et al., 1993)
The implementation of higher compression ratio is also recommended in CNG
fuelled vehicle. It does not generate the knocking phenomena since CNG fuel has
high octane number. For this reason, the high compression ratio has been adopted by
Toyota to design a CNG Camry. The Toyota also implemented the gaseous fuel
injector that suitable for the CNG operation (Kato, 1999). Not only compression
ratio, but also modification of setting up MBT and the use of gaseous fuel injection
systems can improve the CNG engine performance (Duan, 1996). Moreover, Ford
introduced the Natural Gas Vehicle (NGV) truck by modifying injector timing, fuel
control and spark advance (Vermiglio et al, 1997).
The simulations areas also utilised to increase the performance of CNG
engine. Oullette et al (1998) had simulated the combustion process and provide better
understanding of the injection and combustion process of the pilot-ignited directly
injected natural gas. The mathematical simulation was expected to optimise the
injection process by looking in particularly at the geometry and the injection delay
between two fuels. The model includes modifications for under expanded natural gas
jets and includes a turbulent combustion model. Yossefi et al (2000) used a large-
scale computer simulation of natural gas engine to examine the long delay from the
time of ignition to the start of significant heat release.
In the exhaust area, since higher compression ratio produce higher NOx, the
function of EGR and 3-Way Catalyst are recommended. In addition, the
implementation of turbulent combustion chamber shape is also producing higher NOx.
In the case of Toyota Camry, in order to reduce exhaust emissions, a multi-port
injection system was chosen with the use of newly developed injectors and pressure
regulator. At the same time, precise A/F ratio control and special catalysts for CNG
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exhaust gas had been utilized. These entire enhancements had to restore its power
output to near that of the gasoline base engine.
2.5 Intake System
Proper design of an engine's intake and exhaust system can offer the benefits
of torque increase, fuel economy, and emission control (Kong and Woods, 1992). A
large amount of attention is given to the flow characteristic and geometrical shapes.
Among the intake system parts, results from Tallio et al (1993) showed that the
primary runner entrances accounted for over half of the total system loss. Therefore,
the primary runner entrance designed is important.
A dual intake system is also being considered as an alternative for improving
volumetric efficiency, hence the engine performance. With the implementation of
dual intake and exhaust system, Saxena (1995) reported 34% reduction in
hydrocarbons mass emissions accompanied with about 28% reduction in fuel
consumption. The reduction in carbon monoxide emissions was substantial whereas
the carbon dioxide emissions reductions were marginal.
Kawashima et al (1998) combined the swirl flow with dual intake system. A
variable swirl intake port system for 4-valves/cylinder direct-injection engines was
developed. This system combines two mutually independent intake ports, one of
which is a helical port for generating an ultra-high swirl ratio and the other is a
tangential port for generating a low swirl ratio. The tangential port incorporates a
swirl control valve that controls the swirl ratio by varying the flow rate. This resulted
in the development of a variable swirl intake port system capable of controlling the
swirl ratio over a wide range from 3.5 to 10.
The pressurised and turbulent intake flow is an ideal for CNG operation.
These conditions will increase the volumetric efficiency and increase the flame speed.
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Many researchers tried to improve the CNG engine by implementing the turbocharger
and supercharge as well as advance timing for intake valve closed basically to
increase the air content in the combustion chamber. For the case of CNG, given that
the fuel has a higher flammability these treatments are actually possible. Kubesh et al
(1995) developed an electronically controlled natural gas-fuelled engine with a
turbocharged-aftercooled engine controlled by an electronic control system. Tilagone
et al.(1996) found that an increase up to 16% of thermal efficiency on a turbocharge
SI CNG fuelled engine with multi point injection and optimised ignition timing with
spark advance 200 higher running on stoichiometric A/F ratio.
The heat transfers process also implemented in increasing the intake system
performance. The intercooler and aftercooler were among the common practice. This
usually employ with the turbo and supercharged system. Hardman (1994) applied the
aftercooler to increase the volumetric efficiency of the two-stroke turbocharged
engine. Two type of inter or aftercooler can be found in the market: air-to-air cooler
or water to air cooler. Kays and London (1998) concluded that the water to air is
better than air to air cooler in term of heat transfer process.
Use of lean-burn strategy tends to be popular due to benefit of higher efficiency
and lower NOx emissions. Because lean burn operation burns fuel in excess air
(usually 60% or more), it reduces in-cylinder peak temperatures and hence the NOx
emissions too. Lean-burn can also achieve higher efficiency since it can use higher
compression ratio due to knock tendency of lean mixtures. Throttling losses in the
lean-burn engine are also lower at a given power level since the mixture containing a
given amount of fuel occupies a larger volume.
Despite those advantages, lean burn operation on gas engine, however, have a
number of negative factors. Lean burn mixture leads to a very slow flame speed thus
further power losses expected. With an ordinary combustion system, lean burn
operation on gas couldn’t achieve a stable and complete combustion, which will result
in a poor performance, lower efficiency and higher emissions. A high-turbulence
combustion chamber designed for short flame travel paths and rapid combustion, and
a high-energy ignition source are desired for lean burn gas engines.
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CHAPTER III
RESEARCH METHODLOGY
3.1 Introduction
A combination of experimental and simulation technique were involved in
producing this advanced intake system. In the experimental procedures, an intake and
engine performance test rig was designed, built and used for investigating the intake
system characteristic and CNG engine performance. The simulation approach was
implemented in design phase, especially in producing appropriate mixer and swirl
device.
The above range of studies required the use of the line of attack, test
apparatus, test sections, procedures and techniques. In this chapter, details of the
methodology, experimental procedures, instrumentations, and limitations are
demonstrated.
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3.2 Methodology
The pressurised and turbulent flow of intake system is essential for CNG fuelled
engine operation (Mardani, 2001). To perform this situation, the line of attack of this
research was based on the philosophy adding small, useful and economical devices
with the combination of flow principle management without major modification of
the intake system. Therefore, the focus in this study was on the introducing a venturi-
burner mixer and a swirled device in the intake system for optimum CNG fuelled
engine. This strategy was chosen due to a number of considerations:
a. The existing design of intake system was already proven to be applied
remarkably to promote a sufficient air into the cylinder in the conventional
fuel system (gasoline and diesel) with a proper setting of wave tuned (Royo
et.al., 1994).
b. In order to perform excellently in the CNG operation, the required operating
condition for the CNG intake system is the mixing quality of air-gas mixture
and turbulent-pressurised condition to support the low volumetric efficiency
and low flame speed’s problem. The implementation of venturi-mixer and
swirled-devise may fulfil this intake system requirement.
c. The implementation of the turbo or super charged devise might also be
employed. However, the utilization of this method means call for adding a
new system. Since the power to weight ratio of CNG fuelled engine is
relatively low, this method will generate it lower.
d. Economical aspect is another rationale. To encourage customer to use the
CNG fuelled vehicle, a smaller amount of transformation will make it
possible to grow up number of vehicles running on CNG fuel. Through the
implementation of venturi-mixer and swirled-device the optimum
performance of CNG fuelled engine can be achieved with less modification
of the existing intake system.
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3.3 Combined Methods
This research combined the experimental method with the simulation tools to
construct an advanced intake system for CNG fuelled engine. Two stages of
experiment were conducted in this study with an addition of simulation process in
between. First stage was to investigate the intake system and engine performance
characteristic of a CNG fuelled engine with its initial condition. Following this stage,
the design phase that includes the simulation process was running to produce a
venturi-burner mixer and a swirled-device. Subsequently, a series of recommended
mixer and swirled-device were tested in a compact flow test rig connected to the
SuperFlow flow bench. The final recommended design was then fabricated and
introduced into the intake system.
The second stage was to investigate the effect of an advanced intake system
(with its venturi-burner mixer and swirled device) on the engine power output of a
CNG fuelled engine. The engine performance test followed the JIS standard. The flow
test is to evaluate the mixing quality in the SuperFlow, which follows the Flowbench
Operator’s Manual. While the simulation process uses Star CD software that
incorporates finite volume method with SIMPLE algorithm. The workflow of this
methodology is shown in Figure 3.1.
The literature review as already explained in Chapter II is a tool to classify the
research areas in CNG engine. Through a clear analysis, it is suggested that the
research on CNG intake system can play an important role to improve the CNG
engine output. The next step was then planning a research design that contains an
attack strategy to achieve the objective. This step then divided into two sections; the
experimental rig design and the simulation design. In the experimental rig design, a
detail element such as type of engine, dynamometer capacity, parameters will be
recorded till the type of measurement system should be identified. Moreover, to
simplify and to improve the accuracy of the measurement system, arrangement of data
acquisition system is also defined. Type of engine testing standard should be selected.
In this study, the Japan Industrial Standard (JIS) is chosen because of its accuracy and
also accepted commonly in engine performance testing.
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In parallel, the simulation process start with the analysis of the parameters that
affected the mixing quality and produced pressurise flow in the mixer. The selection
to employ the venturi-burner type mixer is based on several considerations, such as:
a. The mixer should produce a uniform mixing quality, the burner type with
the nozzles put surrounding diameter is assumed to be fulfil this criteria.
b. The mixer should produce pressurise flow, the venturi type with the length
arrangement and angle of attack is also assumed will promote pressurised
flow before entering the cylinder.
Based on results from simulation, several recommended designs were then fabricated.
The following process was validate the fabricated designs in term of flow
characteristic and mixing quality using the SuperFlow flow bench device. The
selected designs were then installed in the intake system. The last step was testing the
designs in term of intake system and engine performance test.
A
Research Design and Strategy of attack (Step II)
Start
Literature Review and Problem Mapping (Step I)
Design of Mixer and Swirled-device
Design and Fabricate Engine Testing Experimental
Installation of Measurement and Data Acquisition System
Numerical Analysis and Simulation Process
CNG and Gasoline Engine Performance Testing (Part I)
Final Design of Venturi-Burner Mixer and Swirled Device
Build the Intake System Rig with Transparent Hose
Fabricate A Series of Venturi-Burner Mixer and Swirled Device
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3.4 Engine Test Rig
As seen in Figure 3.2, basically the engine test rig consists of four main
components: the engine itself, the CNG conversion kit, dynamometer and the cooling
system device. The cooling system itself contain a water pump, a variable fan speed, a
radiator and a flow meter that connected through a series of pipe with a number of
control valves. The function of cooling device is to adjust the coolant rate either in the
water jacket or along the intake manifold.
The parameters recorded in this section are:
a. Pressure rise inside cylinder that measured by Kistler M8 pressure
transducer. This pressure transducer was attached in the first cylinder head,
Results Analysis
Selected Design Recommendation
Intake System and Engine Performance Testing (Part 2)
Final Recommendations
Finish
Flow Characteristic Testing with SuperFlow bench
Install the Mixer and Swirled Device into the Intake System
Figure 3.1 Overall Methodology Flowchart
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as shown in Figure 3.4. The flash mount type of pressure transducer is
applied in this experiment.
b. Engine speed and crank angle were recorded using crank encoder and
crank angle that coupled into the engine shaft.
c. Power and torque are determined by using hydraulic dynamometer that has
already added by a control load cell that connected to the engine load
display.
d. Gasoline fuel consumption was measured using a fuel meter that has
already calibrated with a special burette which has a stabilize hand in order
to make a steady condition when measurement is taken.
e. Gas consumption was measured by Sierra 820 Series Top-Trak Mass flow
meter that already calibrated from the factory.
f. The air consumption was measured with the U tube pressure gauge that
followed the JIS placed 15 cm before the carburettor or mixer.
g. Temperature of the coolant in the radiator and water jacket were recorded
using K-type thermocouples.
h. The hygrometer was used to measure the humidity of air before the
experiment is running.
Simultaneously with the engine performance test, the emission results were also
recorded. The exhaust gas analyser was installed at the end of exhaust muffler. The
hydrocarbon (HC), carbon monoxide (CO), carbon dioxide (CO2), oxygen and
nitrogen oxide (NOx) are among the gas emissions that normally recorded in the
3.5. Pressure Transducer Hole in the Cylinder Head
Figure 3.4. Space for Pressure Transducer Sleeve Figure
Hole for PTPT sleeve
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emission test. Due to device limitation, in this study the Horiba exhaust gas analyser
only measured HC, O2, CO and CO2. All the data were taken for CNG and gasoline
fuelled engine operations.
1 Engine Tested 2 Crank Angle 3 Dynamometer 4 Crank Encoder 5 Exhaust Analyser 6 Dyno controller 7 CNG Tank 8 CNG Kit
9 Mixer 10 Fuel Tank 11 Air Tank 12 Signal
Conditioning 13 Thermocouple
Scanner 14 Oscilloscope
15 Computer 16 Radiator Fan 17 Flowmeter 18 Radiator 19 Valve 20 Water Pump 21 Heater 22 Water Tank
Figure 3.2. Schematic diagram of the test rig facility
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Figure 3.3. Experimental set-up photograph A computer based data acquisition (DAQ) system were supported the
measurement process. This DAQ consists of a National Instrument DAQ plug in card
that converted analog to digital signal. The charge module was also used to amplifie
and converts the charge signal from pressure transducer to voltage. The voltage
module conditions signals from the encoder. All these components were
3.5 Intake System Testing Rig and Procedures
In the intake system measurement, the pressure and velocity along the intake
manifold were observed for various engine speed and operating load. A series of U-
tube were tapped along the intake manifold; one in the plenum, two in the runner.
While the air-meter is used to determine velocities and air temperatures after the
mixer. The intake system attach to the CNG fuelled engine experimental rig is shown
in Figure 2.
Cooling System Control Unit Device
CNG Tank DAQ System
Load Controller
Exhaust Analyser
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Pressure and Velocity Measurement Mixer and Intake Manifold in
EFI CNG Engine Figure 2. Intake System Rig
Intake Manifold DAS and CNG Conversion kit
Figure 3. Intake Manifold and Data Acquisition System for CNG Operation
The engine was run to get the steady state condition for half an hour. The
engine was started with 1000 revolution per minute (rpm), at which wide open throttle
(WOT) condition the items below were measured:
a. torque from dynamometer was recorded through a load cell display
b. fuel consumption, either petrol and gasoline
c. pressure rise inside cylinder through the pressure transducer
d. intake profiles such as temperature, pressure and velocity
Table 1. Engine Specification
Name of Parts Size/type Type 4G92 EFI Valve/No. Of Cylinder 16V-DOCH/4 Bore x Stroke (mm) 81 x 77.5 Capacity (cc) 1597
Vacuum Gauge
Air Meter U- tubes
Mixer Intake System
Tapped Location
CNG tank
DAS display
Exhaust Analyser
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Compression Ratio 11 Horsepower (kW/rpm) 131/7700* (premium fuel) Torque (Nm/rpm) 167/7500
The same procedures were repeated for different speeds in the range of 1500
to 3500 rpm. The engine used is specified in Table 1.
Cooler Intake System
The other strategy to improve the CNG performance that already implemented
in this study was to use the cooler intake system. A new cooling system device was
constructed to vary the cooling capacity. It contains a variable fan speed and a water
pump, which combined with a controlled heater and a series of pipe-valve
combination.
1. Water Tank 2. Valve 3. Radiator 4. Fan
5. Heater 6. Water Pump 7. Flow meter
Figure 1. Schematic diagram of the cooling system
This cooling system is powered with three phase electrical source. The data
acquisition system is installed to measure and record the cylinder pressure during the
strokes altogether with engine speed and temperatures. The schematic diagram and an
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engine photograph were shown in Figure 1 and 2. The engine was run until it reaches
the steady state condition. The engine was started with 1000 revolution per minute
(rpm), at which stage the torque, fuel consumption and pressure were measured. The
test was held at full load for three different fuel temperature conditions, 25, 30 and
350 C. The same procedures were repeated for different speeds in the range of 1500 to
3500 rpm.
3.7 Mixer Design
The mixer being studied was developed by the Universiti Teknologi Malaysia
(UTM) CNG Research Group for the use of mixing air and CNG before flowing into
the cylinder of a converted gasoline engine as shown in Figure 1. Further
development was done by varying the angle of the inlet port. The various angles
functioned to give smooth flowing of mixture and avoid back flow.
The mixer was modeled in commercial Computational Fluid Dynamics (CFD)
code STAR-CD and simulations were done on various angles of the inlet; 30°, 40°,
50° and 60° to see the best mixture flow effect judging from its velocity vectors,
pressure and turbulent kinetic energy. The mixer computational domain was divided
into 5 logical blocks; the inlet adaptor, inlet, venturi, outlet and outlet adaptor. Grid
generation were done on all these blocks with coarse meshes in the inlet adaptor, inlet
and outlet adaptor blocks, and finer meshes at the outlet and venturi blocks where the
mixture flow effect can be seen. Figure 2 shows the complete mesh of the mixer
model with the yellow arrows indicating the inlet passage of air at the left side and
CNG fuel at the 8 small passages encircling the inlet part.
In the original mixer, the tunnel for the in-flow of CNG is located at the angle
in between the inlet and venturi before the air/fuel mixing flow through the venturi. In
the computational model, the CNG inlet is modeled as 8 small holes circling around
the inlet wall just before the venturi.
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From the experimental data obtained in this research project, the air velocity
flowing into the mixer is 7 m/s, 10 m/s, 13 m/s and 16 m/s when the engine is running
at 2000 rpm, 2500 rpm, 3000 rpm and 3500 rpm respectively. However in the analysis
here only the 3500-rpm is taken for experiment, thus the air and CNG are modeled to
flow into the mixer at 16 m/s. The air was modeled as high turbulence model flowing
into the mixer at temperature 293 K and 1 atmospheric pressure.
The boundary condition comprised of inlet, outlet, and wall boundary. The
inlet and outlet boundaries are located at the front and end of the mixer respectively,
with the other surfaces being assigned as no-slip wall boundary automatically.
Solutions were obtained using SIMPLE algorithm for steady state calculations.
The mass and momentum conservation equations solved by STAR-CD for
general incompressible and compressible fluid flows and a moving coordinate frame
(the Navier Stokes equations), in Cartesian tensor notation [18]:
( ) ( ) mjj
sux
gtg
=∂∂
+∂∂ ~1 ρρ (1)
( ) ( ) ii
ijijj
i sxpuu
xug
tg+
∂∂
−=−∂∂
+∂∂ τρρ ~1 (2)
Where
t : time
xi : Cartesian coordinate ( i = 1,2,3 )
ui : absolute fluid velocity component in direction xi
ju~ : uj – ucj , relative velocity between fluid and local (moving) coordinate
frame that moves with velocity ucj
p : piezometric pressure = ps - ρ0 gm xm where ps is static pressure, ρ0 is
reference density, the gm are gravitational field components and the xm
are coordinates from a datum, where ρ0 is defined
0
ρ : density
τij : stress tensor components
sm : mass source
si : momentum source components
g : determinant of metric tensor
inlet adaptorinlet
various angle
outlet
venturioutlet adaptor
I. FIGURE 1: Side View of Mixer FIGURE 2: Meshing of the Mixer
The fabrication process is being done based on simulation results. The mixer
design is consists of three principles: venturi, fan and burner. All of these principles
are to perform pressurised and turbulent flow. In the venturi mixer design three
parameters were chosen; length, angle and diameter. Whilst in the burner model the
parameters consist of: number of hole surrounding the mixing area, hole diameter and
type of hole (nozzle or common type). Meanwhile, the fan model consists of three
parameters also: angle of attack, number of blades and diameter. This paper presented
three type of mixer, one for each models.
Venturi Fan Burner
Figure 1. Type of Mixers
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3.7 Swirl-Device Design
The UTM CNG Research team had developed a swirl device capable to
generate swirling flow in CNG engine cylinder. This device is fixed at the intake port
and the air/fuel mixture will become swirling flow after it goes through the device.
The device together with engine cylinder and intake port were modeled in
commercial Computational Fluid Dynamics (CFD) code STAR-CD and simulations
were done on two locations of the device in the intake port in order to see the
maximum effect of swirling flow; the first one before the intake valve and the second
around the intake valve as shown in Figure 1 and Figure 2 respectively. Figure 3
shows the complete mesh of the model.
In the analysis, the mixture is modeled as air to save cost of calculations. The
air was modeled as high turbulence model flowing into the cylinder through the intake
port at 1 atmospheric pressure and temperature of 293 K.
The boundary condition comprised of pressure and wall boundary. The
pressure boundaries are located at the start of intake port and the bottom of the
cylinder (at 0 pressure), with the other surfaces being assigned as no-slip wall
boundary automatically. Solutions were obtained using SIMPLE algorithm for steady
state calculations.
The mass and momentum conservation equations solved by STAR-CD for
general incompressible and compressible fluid flows and a moving coordinate frame
(the Navier Stokes equations), in Cartesian tensor notation [18]:
( ) ( ) mjj
sux
gtg
=∂∂
+∂∂ ~1 ρρ (1)
( ) ( ) ii
ijijj
i sxpuu
xug
tg+
∂∂
−=−∂∂
+∂∂ τρρ ~1 (2)
0
Figure 1. Swirl device before intake
valves
Figure 2. Swirl device around the intake valves
Figure 3. Meshing of intake ports and cylinder model Where
t : time
xi : Cartesian coordinate ( i = 1,2,3 )
ui : absolute fluid velocity component in direction xi
ju~ : uj – ucj , relative velocity between fluid and local (moving) coordinate
frame that moves with velocity ucj
p : piezometric pressure = ps - ρ0 gm xm where ps is static pressure, ρ0 is
0
reference density, the gm are gravitational field components and the xm
are coordinates from a datum, where ρ0 is defined
ρ : density
τij : stress tensor components sm : mass source si : momentum source components
g : determinant of metric tensor
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CHAPTER IV
RESULTS AND DISCUSSIONS
4.1 Introduction
The overall findings show a clear message that the advanced CNG engine was
being produced. In short, this chapter will describe the following criteria that make
this advanced system is significance: mixer and swirl-device results, intake system
and engine performance results.
4.2 Mixer Results
4.2.1 Simulation Results
4.2.2 Inlet and Outlet Angle Parameters
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The visualization of the mixture flow with its velocity, pressure and turbulent
kinetic energy value are shown at mid plane of the mixer. The differences can be
clearly seen between all the four mixers’ dimension as shown in Figure 3, 4 and 5
below.
The maximum velocity is recorded at the CNG fuel inlet holes for all the four
mixer dimensions. Velocity starts to slow down as the mixture flow through the
venturi to the mixer outlet with the maximum value of 160.6 m/s in the venturi for the
30° angle inlet as shown in Figure 3.
Figure 4 shows that pressure at the mixer inlet is higher than the outlet for all the
four mixers. Differences of pressure at the beginning and the end of the venturi is
recorded as 3300 Pa for 30° angle, 2350 Pa for 40° angle, 6050 Pa for 50° angle and
5260 Pa for 60° angle of inlet.
As for turbulent kinetic energy, it is at its lowest value at the center of the venturi.
Turbulent effect occurs at the venturi wall with the 60° angle mixer has a relatively
higher turbulent kinetic energy compare to the other mixers as shown in Figure 5.
Figure 6, 7 and 8 show the summary of the simulation results obtained.
II. Velocity
(a)
(b)
0
(c) (d)
FIGURE 3: Effects of Velocity Magnitude in Mixer with Inlet Angle (a) 30°, (b) 40°, (c) 50° and (d) 60°
III. Pressure
(a)
(b)
(c)
(d)
FIGURE 4: Effects of Pressure in Mixer With Inlet Angle (a) 30°, (b) 40°, (c) 50°
and (d) 60°
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IV. Turbulent Kinetic Energy
(a)
(b)
(c)
(d)
FIGURE 5: Effects of Turbulent Kinetic Energy for Mixer with Inlet Angle (a) 30°, (b) 40°, (c) 50° and (d) 60°
0
20
40
60
80
100
120
140
160
180
0 10 20 30 40 50 60 70
inlet angle (degree)
velo
city
(m/s
)
FIGURE 6: Maximum Velocity in Venturi vs. Inlet Angle
0
1000
2000
3000
4000
5000
6000
7000
0 10 20 30 40 50 60 70
inlet angle (degree)
pres
sure
diff
eren
ce (P
a)
FIGURE 7: Pressure Difference in Venturi vs. Inlet Angle
0
0
100
200
300
400
500
600
0 10 20 30 40 50 60 70
inlet angle (degree)
turb
ulen
t kin
etic
ene
rgy
(m2/
s2)
FIGURE 8: Turbulent Kinetic Energy vs. Inlet Angle
A lower velocity of mixture, higher pressure difference and higher turbulent
effect in the venturi could make a better mixer. Low velocity provides more time for
mixture to complete mixing process, a higher pressure difference could draw higher
total mass flow and high turbulent effect provides better quality of mixing.
Judging from here, a conclusion can be drawn that the mixer with 60° inlet angle will
give the optimum results for mixture mixing, thus increasing engine performance.
Further development will be done with this 60° inlet angle mixer to see the effects on
various quantity of gaseous fuel inlet. However, this conclusion is made based only
on simulation results and further experimental works will be conducted with these
mixers to verify these results.
4.2.3 Hole Dimension Parameters
Further development was done on the mixer first developed by the UTM CNG
Research team. After getting the optimum dimension of the mixer that will gives
optimum results in performance for engine, it is further improved by determining the
number of CNG fuel inlet holes needed to give optimum mixing quality of fuel and
air. The CNG fuel inlet holes are located just before the venturi of the mixer.
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The methods of investigation are the same as in the research of effects of mixer
dimension, and it can be referred in the previous paper. Figure 1 and 2 below show
the new mixer dimension with a 60° inlet angle from previous research.
Figure 3, 4 and 5 below show the vector of mixture flow in the mid-plane of the
mixer with its velocity, pressure and turbulent kinetic energy values. Differences in
quantity of CNG fuel inlet holes for each mixer resulted in different mixture flow
characteristics.
For all the four mixers, the highest flow velocity occurs at the fuel inlet holes.
Velocity starts to slow down as the mixture flow through the venturi to the mixer
outlet with one-CNG inlet hole mixer recorded the highest velocity in the venturi with
the value of 132.9 m/s as shown in Figure 3. Quantity of backflow of mixture is the
highest for the one-CNG inlet hole, and it get lesser as more CNG inlet holes are
added. Backflow is almost the same for the eight and sixteen-CNG inlet hole mixers.
Figure 4 shows that pressure at the mixer inlet is higher than the outlet for all the
four mixers. Differences of pressure at the beginning and the end of the venturi is
recorded as 7690 Pa for one-CNG inlet hole, 7738 Pa for four-CNG inlet hole, 7885
Pa for eight-CNG inlet hole and 7494 Pa for sixteen-CNG inlet hole mixer.
Turbulent kinetic energy is at its lowest value at the center of the venturi.
Turbulent effect occurs at the venturi wall with the eight-CNG inlet hole mixer has a
relatively higher turbulent kinetic energy compare to the other mixers as shown in
Figure 5. Figure 6 and 7 show the summary of results obtained.
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V. Velocity
(a) (b)
(c) (d) FIGURE 3: Effects of Velocity Magnitude in Mixer with (a) one, (b) four, (c) eight and (d) sixteen CNG Inlet Holes VI. Pressure
(a) (b)
0
(c) (d) FIGURE 4: Effects of Pressure in Mixer with (a) one, (b) four, (c) eight and (d)
sixteen CNG Inlet Holes
VII. Turbulent Kinetic Energy
(a) (b)
(c) (d) FIGURE 5: Effects of Turbulent Kinetic Energy in Mixer with (a) one, (b) four, (c)
eight and (d) Sixteen CNG Inlet Holes
0
0
50
100
150
200
250
300
0 2 4 6 8 10 12 14 16
no. of CNG inlet hole
velocity (m/s)
turbulent kineticenergy (m2/s2)
FIGURE 6: Velocity and Turbulent Kinetic Energy versus No. of CNG inlet hole
7450
7500
7550
7600
7650
7700
7750
7800
7850
7900
7950
0 2 4 6 8 10 12 14 16
No. of CNG inlet hole
Diff
eren
ce o
f pre
ssur
e (P
a)
FIGURE 7: Pressure difference versus No. of CNG inlet holes
The effectiveness of a mixer to provide quality mixing of air and fuel can be
determined by observing the mixture flow direction in the mixer with its velocity,
pressure and turbulent kinetic values. Mixture will have more time to have a complete
mixing when its velocity is slow in the venturi. A higher pressure difference between
the beginning and end of the venturi; and lesser backflow at the outlet could draw
higher total mass flow into the cylinder while high turbulent effect provides better
quality of mixing.
Judging from here, a conclusion can be drawn that the mixer with eight CNG
inlet holes will give the optimum results for mixture mixing, thus increasing engine
performance. Though the velocity of mixture in that mixer is high, its other
advantages in pressure difference, backflow and turbulent kinetic energy can
compensate the inferior area. From these researches, a new mixer with 60° inlet angle
and 8 CNG fuel inlets can be developed and experimental works can be done in the
near further after this mixer is fabricated.
0
4.3 Swirl-device Simulation Results
Figure 4, 5 and 6 show the velocity vectors of air flow in the cylinder from top
view. The velocity of air for the intake port without swirl device is mostly in the range
of 6.866 m/s to 57.74 m/s, while the intake port with swirl device at location before
the intake valve has velocity mostly ranging from 47.26 m/s to 207.3 m/s. Lastly, for
the intake port with swirl device at location around the intake valve, the velocity
recorded was mostly in the range of 16.28 m/s to 79.08 m/s.
The swirl device is capable of increasing mixture velocity flowing into the
cylinder. Though when it is being put at the location before the intake valve the
velocity will be much higher, but from the visual results one can see that there is very
little swirling flow. The flow is very much in a chaotic way and this shows that the
effect of swirl couldn’t be created when the device is far from the intake hole of the
cylinder. As a matter of facts, the swirling effects is much better for the intake port
without any swirl device than the one with the device being located before the intake
valve. This phenomena happens because the swirl has already lost much of its energy
when it flows into the cylinder through the long distance between the device and the
cylinder.
The best swirling flow effects can be seen in Figure 6 when the swirl device is
located around the intake valve. Since the device is just near the intake hole of the
cylinder, the swirl effects can be preserved and its velocity is higher too compare to
the intake port without swirl device. The flow velocity increases as it flows further
from the center of the cylinder. Figure 7 shows the air flow from side view of the
cylinder when the swirl device is located around the intake valve.
Swirling flow can be created by implementing a swirl device in the intake port.
The effectiveness of this device is in dependence of its location; the nearer it is to the
intake hole of engine cylinder, the better the effects will be. In this research, when the
device is in the location around the intake valve, the best results of swirl effect can be
obtained. When the swirl effect is increased, the CNG engine power output will be
increased too.
0
After these simulation works, further research will be done by the UTM CNG
Research team to fabricate a few of these devices with different parameters and
engine testing will be done to validate the effects of these swirl devices by the results
of increased engine power output.
Figure 4. Intake port without swirl device
Figure 5. Intake port with swirl device
before the intake valve
Figure 6. Intake port with swirl device around the intake valve
Figure 7. Side view of intake port with
swirl device around the intake valve
4.4 Performance Test Results
4.4.1 Engine Performance Comparisons
0
At first step on the experimental stage, the results showed that the CNG produced
lower cylinder pressure compared to that of gasoline as shown in Figure 4. The
cylinder pressure of gasoline can reach nearly 46.27 bars as the CNG approximately
38.56 bars at 2500 rpm. This 16% is mainly because of low volumetric efficiency and
advanced ignition timing (Mardani, 2001).
Consequently, the torque and power produced by CNG fuelled engine is lesser
compare to that of gasoline. Figure 3 showed that at 3500 rpm the gasoline-fuelled
engine produced up to 91 Nm compared to 75 Nm from the CNG fuelled engine. The
gasoline also produced higher power compared to CNG fuelled engine in the value of
33 kW to 27.5 kW.
1500 2000 2500 3000 350030
40
50
60
70
80
90
100
5
10
15
20
25
30
35
Pow
er (k
W)
Torq
ue (N
m)
Engine Speed (rpm)
Gasoline CNG
Figure 3. Performance Test Results
As a result, the CNG fuelled engine produce less work compared to that of
gasoline. Figure 6 showed the P-V diagram for CNG and gasoline operation.
0
-100 0 100 200 300 400 500 600 700 800-10
0
10
20
30
40
50
Cyl
inde
r Pre
ssur
e (b
ar)
Crank Angle (deg.)
Gasoline CNG
at 2500 rpm
Figure 4. Cylinder Pressure for CNG and Gasoline
0.0000 0.0001 0.0002 0.0003 0.0004 0.0005-1000000
0
1000000
2000000
3000000
4000000
5000000
Cyl
inde
r Pre
ssur
e (P
a)
Volume (m3)
Gasoline CNG
Figure 5. P-V Diagram for CNG and Gasoline Operation
0
4.4.2 Effect of Mixer Types on the Engine Performance Test
The CNG engine performance was improved as the new mixer installed in the test
rig. Slightly lower CNG performance has been achieved in this test. The experimental
results showed that the burner type in CNG mode produced the highest cylinder
pressure compared to that of fan and venturi mixers as shown in Figure 4. The
burner’s cylinder pressure may reach nearly 41.5 bars as the fan and venturi’s showed
the value of 37.5 and 39, respectively. All data is taken at operating condition of
WOT at 3000 rpm. However, all of the CNG mode data on cylinder pressure were
lower compared to gasoline operation where at same condition produced up to 45.8
bars This approximately 10% dropped is mainly because of low volumetric efficiency
and advanced ignition timing (Mardani and Rosli, 2001). An interesting result came
from fan’s mode. As seen in Figure 4, the pressure rise profile for fan mixer is a little
bit earlier compared to the rest, even for gasoline mode. From the data, the peak
pressure for gasoline and burner or venturi types were around 374 to 376 deg. of
crank angle, while the fan’s type its occurred at 368 deg. This result may represent
that due to turbulent flow conditions, for the same ignition timing, a faster combustion
process occurred.
Figure 4. Pressure Rise Profile
-100 0 100 200 300 400 500 600 700 800
0
10
20
30
40
50
Pre
ssur
e (b
ar)
Crank Angle (deg.)
Gasoline Fan Venturi Burner
0
Similar trend also occurred in the torque and power produced. Figure 5 shows
that at 3500 rpm the burner operation produced up to 98 Nm compared to 84.6 and
85.3 for fan and venturi mode, respectively. The gasoline produced higher torque
compared to all CNG produced at around 91 Nm. Figure 6 also shows the parallel
tendency with gasoline come first followed by burner and venturi with fan still the
last.
1500 2000 2500 3000 350040
45
50
55
60
65
70
75
80
85
90
95To
rque
(Nm
)
Engine Speed (rpm)
Gasoline CNG Fan CNG Venturi CNG Burner
Figure 5. Torque Test Results
0
1500 2000 2500 3000 3500
15
20
25
30
35
40
45
50
55
60
Pow
er (k
W)
Engine Speed (rpm)
Gasoline CNG Fan CNG Venturi CNG Burner
Figure 6. Power Test Results
4.4.2 The Effect of Fuel Temperature on Engine Performance
The experiment also showed that the CNG temperature affected the out put power
produced. Three different temperatures produced different values of cylinder
pressures. The lower the temperature, the higher the pressure produced in the
cylinder. At 250 C CNG temperature, the pressure produced nearly 40.5 bars, while at
350 C it dropped to 34.7 bars, as shown in Figure 5. This phenomena happens due to
increased of fuel density with the decreased of fuel temperature.
0
0 100 200 300 400 500 600 700 800
0
10
20
30
40
CYl
inde
r Pre
ssur
e (b
ar)
Crank Angle (deg.)
300C 350C 250C
at 2500 rpm
FIGURE 5. Cylinder Pressure for Different CNG Temperatures
4.4.4 The Effect of Compression Rations of Engine Performance
The experimental results showed that the CNG produced lower cylinder pressure
compared to that of gasoline for all compression ratios level as shown in Figure 3.
The cylinder pressure of gasoline can reach nearly 18.3 bars as the CNG
approximately 13.8 bars at compression ratio 9 to 1 and up to 16.7 bars at
compression ratio 12 to 1 at 2000 rpm. This lower of pressure rise is mainly because
of low volumetric efficiency and advanced ignition timing (Mardani, 2001).
0
0 100 200 300 400 500 600 700 800
-2
0
2
4
6
8
10
12
14
16
18
20
Pres
sure
Ris
e (b
ar)
Crank Angle (deg.)
CNG CR 9 CNG CR 10 CNG CR 11 CNG CR 12 Gasoline CR 10
Fig. 3 Pressure Rise Profile
Consequently, the torque and power produced by CNG fuelled engine is lesser
compare to that of gasoline. Figure 4 showed that at 3500 rpm the gasoline fuelled
engine produced up to 39 Nm compared to 34 Nm at compression ratio 9 to 1 and
38.4 Nm at compression ratio 12 to 1 from the CNG fuelled engine. The gasoline also
produced higher power compared to CNG fuelled engine in the value of 24.7 kW to
21.5 kW at compression ratio 9 to 1 and 24.3 at compression ratio 12 to 1.
The results also showed than higher compression ratio increased the pressure rise
and hence the torque and power output for the range of 9:1 to 12:1 ratios. These
phenomena occurred mainly due to increased of thermal efficiency with the
implementation of higher compression ratio (Heywood, 1988).
0
1500 2000 2500 3000 350012
14
16
18
20
22
24
26
28
30
32
34
36
38
40
Torq
ue (N
m)
Engine Speed (rpm)
Gasoline 10 CR CNG 9 CR CNG 10 CR CNG 11 CR CNG 12 CR
Fig. 4 Engine Torque against Engine Speed
1500 2000 2500 3000 35000
2
4
6
8
10
12
14
16
18
20
22
24
26
Pow
er (k
W)
Engine Speed (rpm)
Gasoline CR 10 CNG CR 9 CNG CR 10 CNG CR 11 CNG CR 12
Fig. 5 Engine Power against Engine Speed
4.4.5 Heat Rejection for CNG and Gasoline Operation
The experiment also showed that the CNG produced higher heat rejection to
coolant compared to gasoline operation for all engine speeds except at 3500 rpm as
0
shown in Figure 6. This may happens due to the un-optimum combustion process
occurred in CNG engine operation. Table 2 showed that the CNG generated higher
temperature on engine block compared to that of gasoline.
The results have a similar correlation with the heat dissipation profile. At the
three position where the thermocouple were placed, the CNG fuelled engine
dissipated more heat as shown in figure 7. This mean that the CNG fuelled engine
operation dissipated more heat to the cooling system compared to the gasoline engine
operation.
1500 2000 2500 3000 35008.0
8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
12.5
Hea
t Rej
ectio
n to
Coo
lant
(kW
)
Engine Speed (rpm)
Gasoline CNG
Figure 6. Heat Rejection for CNG and Gasoline Operation
Table 2. Coolant and Water Jacket Wall Temperature profile at Full Load
Inlet Wall
Temperature (0C) Coolant Temperature
(0C) Outlet Wall
Temperature (0C) Speed (rpm)
CNG Gasoline CNG Gasoline CNG Gasoline 1500 84.2 89.1 84.1 86.5 81.3 81.5 2000 84.3 86.1 82.8 84.6 79.9 82.8 2500 86.8 88.5 82.4 85.6 74.3 82.8 3000 85.3 88.4 82.8 86.6 76.3 83.4 3500 88.1 85.3 87.6 84.9 81.7 80.6
0
4.4.6 Intake System Test Results
In the velocity profile, the venturi produced the highest velocities along the
intake manifold, followed by burner’s and fan’s. Figure 7 and 8, illustrates the data
taken at 3000 rpm.
1 2 3 424
26
28
30
32
34
36Ve
loci
ty (m
/s)
Point
Fan Venturi Burner
Figure 7. Velocity profile at Intake System
At point 2 venturi mixer produced up to 35.7 m/s, followed by burner and fan remains
the last by 35.1 and 34.3 m/s, respectively. This may occur due to venturi shape push
the mixture air gas to speed up the velocity.
0
1 2 3 4-230
-220
-210
-200
-190
-180
Pre
ssur
e (P
a)
Point
Fan Venturi Burner
Figure 8. Pressure profile at the Intake System As shows in Figure 7, at point 1 (plenum) the velocity is low due to geometrical shape
and then increased at point 2 (see Figure 2) because it is a straight tube and then
followed by drop in point 3 and 4. Dropped in points 3 and 4 mostly because of the
flows have to slow down when changing direction at the curvature tube.
The similar tens also occurred in pressure profile as shown in Figure 8. The
venturi mixer produced the highest vacuum pressure at point 2 with 218 (Pa) followed
by burner and fan’s type with 215 and 216 (Pa), respectively.
4.4.7 Emission Results
Emission of carbon monoxide, carbon dioxide and unburnt hydrocarbons from a
CNG fuelled engine against the engine speed follow similar pattern of gasoline
engines. It can be seen on Figure 6 and 7, the carbon monoxide (CO) and dioxide
0
(CO2) were lower than that of gasoline engine for all engine speed, due to low carbon
content.
The unburnt hydrocarbon (HC) emissions from CNG fuelled engines are also less
than that of gasoline engines. Theoretically, the HC emissions from CNG fuelled
engines should be lower due to the gaseous from which gives an excellent mixing.
The CNG fuel also produced lower carbon dioxide compared to that of gasoline.
However, the CNG fuelled engine produced higher O2.
1000 1500 2000 2500 3000 35000.000.020.040.060.08
45678
% v
ol. C
O
Engine Speed (rpm)
Gasoline CNG
1000 1500 2000 2500 3000 35003040506070
180200220240260
HC
(ppm
)
Engine Speed (rpm)
Gasoline CNG
FIGURE 6. Emission of Carbon Monoxide Against
Engine Speed
FIGURE 7.
Emission of Hydro Carbon Against Engine Speed
0
1000 1500 2000 2500 3000 35000.51.01.52.02.53.03.54.04.55.05.5
% v
ol. O
2
Engine Speed (rpm)
Gasoline CNG
1000 1500 2000 2500 3000 35009.0
9.5
10.0
10.5
11.0
11.5
12.0
12.5
% v
ol. C
O2
Engine Speed (rpm)
Gasoline CNG
FIGURE 8.
Emission of Oxygen Dioxide Against Engine Speed
FIGURE 9.
Emission of Carbon Dioxide Against Engine Speed
4.4.8 Effect of Compression Ratios on Exhaust Emissions
Emission of carbon monoxide, carbon dioxide and unburnt hydrocarbons from a
CNG fuelled engine against the engine speed follow similar pattern of gasoline
engines. It can be seen on Figure 6 and 7, the carbon monoxide (CO) and dioxide
(CO2) were lower than that of gasoline engine for all engine speed, due to low carbon
content. However, increased of compression ratio affected on increased of the CO and
CO2 products. The similar trend also occurred in the unburnt hydrocarbon (HC)
emissions from CNG fuelled engines. Less HC was produced by CNG fuelled engine
than that of gasoline engines as shown in Figure 8. Theoretically, the HC emissions
from CNG fuelled engines should be lower due to the gaseous from which gives an
excellent mixing. Increased in compression ratio affected on increased of the HC
products also.
0
1000 1500 2000 2500 3000 35000.0
0.5
1.0
1.5
2.0
2.5
3
4
5
6
7
8
% v
ol. C
O
Engine Speed (rpm)
Gasoline CR 10 CNG CR 9 CNG CR 10 CNG CR 11 CNG CR 12
Fig. 6 Emissions of Carbon monoxide
1000 1500 2000 2500 3000 35008
10
12
14
16
18
20
22
24
% v
ol. C
O2
Engine Speed (rpm)
Gasoline CR 10 CNG CR 9 CNG CR 10 CNG CR 11 CNG CR 12
Fig. 7 Emissions of Carbon dioxides
0
1000 1500 2000 2500 3000 350050
60
70
80
90
240
260
280
300
320
HC
(ppm
)
Engine Speed (rpm)
Gasoline CR 10 CNG CR 9 CNG CR 10 CNG CR 11 CNG CR 12
Fig. 8 Emissions of Hydrocarbon
0
CHAPTER V
CONLUSIONS AND RECOMMENDATIONS
5.1 Introduction
The CNG fuel operation has already proven to be workable. The implementation
of advanced intake system is demonstrated to improve the CNG fuelled engine
performance.
5.2 Mixer
The venturi-burner mixer is approved to increase the intake pressure hence
improve the combustion performance resulted in advanced the engine power. The
combination of 600 of inlet angle and 300 of outlet angle with 8 holes is proven to
increase the engine performance to up to 5% that made it closer to the gasoline
standard engine performance.
0
5.3 Swirl-Device
The swirl-device located at the intake port is verified to generate the swirl flow
that improve the combustion performance and hence the engine performance.
5.4 Intake System
In the overall, the advanced intake system is proven to bring the CNG fuelled
engine performance to come up to that of gasoline. This is done through improved
the intake pressure flow and enlarged the combustion flame speed.
5.5 Engine Performance
This CNG fuelled engine with the advanced intake system is completely
improve the engine performance. There is an increased of 8% of power output due to
the used of this advanced intake system.
5.6 Exhaust Emission
The CNG fuelled engine is totally produced lesser emissions of CO, CO2 and
hydrocarbon (HC) compared to that of gasoline.
0
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0
Published Papers
1. Rosli Abu Bakar, Mardani Ali Sera and Wong Hung Mun, Heat Transfer
Analysis In Cooling System Of A CNG Fuelled SI Engine, Brunei
International Conference on Engineering Technology, Brunei, October 2001.
2. Rosli Abu Bakar and Mardani Ali Sera, The Realization of Optimum CNG
Engine: It’s Implication On Engine Design, Advances in Malaysian Energy
Research 2001,Kuala Lumpur, pp 212 –218, October 2001
3. Mardani Ali Sera and Rosli Abu Bakar, The Comparison Study on 1.5 L
Engine Performance And Emission Using Gasoline And Natural Gas Fuel,
Malaysian Science and Technology Congress (MSTC) 2001, Melaka, October
2001.
4. Rosli Abu Bakar, Mardani Ali Sera and Wong Hong Mun, Towards The
Implementation Of CNG Engine: A Literature Review Approach To Problems
and Solutions, BSME-ASME International Conference on Thermal
Engineering, 31 December 2001 – 2 January 2002, Dhaka
5. Rosli Abu Bakar, Teoh Ka Jin, & Mardani Ali Sera, “Improvement of New
Fin Design for Automotive Water Cooling System”, BSME-ASME
International Conference on Thermal Engineering, Dhaka, 2002.
6. Mardani Ali Sera, Rosli Abu Bakar and Sin Kwan Leong, Effect of Fuel
Density on the Performance of a CNG Fuelled Engine, 4th Asian Science and
Technological Congress 2002, Kuala Lumpur, April 2002
7. Rosli Abu Bakar, Sin Kwan Leong, Mardani Ali Sera, The Effects of
Turbulent Flow In CNG Engine Mixer Using Computational Fluid Dynamics,
4th Asian Science and Technological Congress 2002, Kuala Lumpur, April
2002
0
8. Rosli Abu Bakar, Mardani Ali Sera, Srithar a/l Rajoo and Sin Kwan Leong,
Study On Engine and Heat Transfer Characteristics of a CNG And Gasoline
Fuelled EFI Engine, 6th Asia Pacific International Symposium on Combustion
and Energy Utilization, Kuala Lumpur, May, 2002
9. Rosli Abu Bakar, Azhar Abdul Aziz and Mardani Ali Sera, Effect of Air Fuel
Mixer Design on Engine Performance and Exhaust Emission of A CNG
Fuelled Vehicles, 2nd World Engineering Conference (WEC), Serawak, July
2002.
10. Rosli Abu Bakar And Mardani Ali Sera, Effect of Compression Ratios On
Engine Performance And Emissions Of A CNG Fuelled Engine, 3rd Pacific-
Asia Conference on Mechanical Engineering, August 29-31, 2002, Manila,
Philippines.
11. Mardani Ali Sera and Rosli Abu Bakar, Intake System for CNG Fuelled
Engine, Malaysian Science and Technology Congress (MSTC) 2002, Johor
Bahru , September, 2002.
12. Rosli Abu Bakar, Sin Kwan Leong, Mardani Ali Sera, Effects of New Mixer
Dimension And Quantity Of Gaseous Fuel Inlet in a Compressed Natural Gas
(CNG) Engine (Part 1), Malaysian Science and Technology Congress (MSTC)
2002, Johor Bahru , September, 2002.
13. Rosli Abu Bakar, Sin Kwan Leong, Mardani Ali Sera, Effects of New Mixer
Dimension And Quantity Of Gaseous Fuel Inlet in a Compressed Natural Gas
(CNG) Engine (Part 2), Malaysian Science and Technology Congress (MSTC)
2002, Johor Bahru , September, 2002.
14. Rosli Abu Bakar, Sin Kwan Leong, Mardani Ali Sera, Effects of Swirl Device
in a Compressed Natural Gas (CNG), 3rd International RAMM Conference.
0
15. Rosli Abu Bakar, Mardani Ali Sera and Sin Kwan Leong, CNG Engine
Performance Improvement Strategy Through Advanced Intake System, 2003
JSAE/SAE Spring Fuels & Lubricants, May 19 - 22, 2003.
16. Rosli Abu bakar, Mardani Ali Sera and Sin Kwan Leong, Engine Mapping
Comparisons on the CNG and Gasoline Fuelled Engine, APCSEET 2003.
0
Published Thesis
1. “Design and Develop New Mixer for Compressed Natural Gas Engine”,
Phuah Cheng Pheng, 2001.
2. “Design of an Electronic Control System for CNG Fuelled SI Engine”, Sew
Wey Ping,2001.
3. “New Design of Compressed Natural Gas Mixer”, Ngo Jian Yee, 2001.
4. “Electronic Control System For CNG Engine”, Surenthan Ramasamy, 2002.