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American Journal of Applied Sciences 6 (5): 929-936, 2009
ISSN 1546-9239
© 2009 Science Publications
Development of Dual Fuel Single Cylinder Natural Gas Engine an Analysis and
Experimental Investigation for Performance and Emission
Syed Kaleemuddin and G. Amba Prasad Rao
Department of Mechanical Engineering, National Institute of Technology Warangal, India
Abstract: The present study reports the experimental investigations carried and upgradation of 395 cc
air cooled engine to dual fuel (CNG/Gasoline) application. The original 395 cc direct injection
naturally aspirated, air cooled diesel engine was first converted to run on Gasoline by addition of
electronic ignition system and reduction in compression ratio to suit both gasoline and CNG
application. CFX software has been employed to calculate and improve the cooling capacity of engine
with the use of CNG. Materials of major engine components were reviewed to suit CNG application.
The engine was subsequently tuned with dual multi-mapped ignition timing for bi-fuel stoichiometric
operation on engine dynamometer and then fitted on a 3-Wheeler vehicle. The vehicle was optimized
on a chassis dynamometer to meet the proposed Bharat Stage-III norms. The engine has passed current
BS-II emission norms with 48% margin in CO emission and 76% margin in NMHC (Non-Methane
Hydrocarbons) and Extensive trials were conducted on engine and vehicle to optimize with CNG kit
and minimum loaded three way cat-con to finally to met proposed BS-III norms.
Key words: Dual fuel CNG, performance, emission
o
INTRODUCTION in a liquid (LNG) form at -160 C, has an research
octane number (RON) of about 127, is good suited for
Extensive Research has given a way for a number SI engines, can be run on without knocking on high
of alternate fuels to mitigate the problems of fuel crisis compression ratios. Due its high auto ignition
and associated environmental degradation. It is not an temperature it is readily suited for SI engines. Table 1
exaggeration that automotive population has given rise depicts the important properties of CNG, gasoline and
to severe air pollution. The liquid dominated prime diesel fuel.
movers have driven the vehicles for many years and Natural gas is pressurized to 22MPa in vehicular
leaving the danger of its existence. Use of gaseous fuels storage tanks, so that it has about 1/3 of the volumetric
in for fueling the Engines reduces reactive energy density of gasoline. The storage pressure is
hydrocarbons and do not pose the problem of about 20 times that of propane. Combustion of methane
vaporization as with the liquid fuels. Two gaseous fuels is different from that of liquid hydrocarbon combustion
viz. LPG (Liquid Petroleum Gas) and CNG since only carbon-hydrogen bonds are involved and no
(Compressed Natural Gas) have attracted the attention carbon-carbon bonds, so the combustion process is
[1]
of both industry and transportation sectors . As more likely to be complete, producing less non-methane
domestic sector is dominated by the use of LPG for hydrocarbons. Natural gas has a lower adiabatic flame
meting cooking and other allied applications, attention temperature (~2240K) than gasoline (~2310K), due to
is being diverted towards the use of natural gas on a its higher product water content. Operation under lean
large scale. Natural gas, a naturally occurring fuel conditions will also lower the peak combustion
[2]
found in oil fields (one of the worlds most abundant temperatures . The lower combustion temperatures
fossil fuel). It is primarily composed of about 90-95% lower the NO formation rate and produce less engine-
methane (CH4), with small traces of additional out NO . Natural gas can replace diesel fuel in heavy
x
compounds such as 0-4% Nitrogen, 4% ethane and 1- duty engines with the addition of a spark ignition
2% propane Methane has a lower carbon to hydrogen system. A number of heavy duty diesel engine
ratio relative to gasoline, so its CO emissions are about manufacturers are also producing a dedicated natural
2
22-25% lower than gasoline. Natural gas is stored in a gas heavy duty engines. The natural gas fueled engines
compressed (CNG) state at room temperatures and also are operated lean with an equivalence ratio as low as
Corresponding Author: Syed Kaleemuddin, Department of Mechanical Engineering,
National Institute of Technology Warangal, India Tel: +91- 0240-2479340 Fax: +91 -0240 -2479334
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Am. J. Applied Sci., 6 (5): 929-936, 2009
Table 1: Fuel properties Table 2: Diesel engine specification and vehicle details
Property Gasoline Diesel CNG Parameter Specification
Chemical formula CH C H CH Engine type DI, Naturally aspirated, Air cooled
8 16 12 26 4
State Liquid Liquid Gas Bore×Stroke, mm 86×68
Energy content 100% 110% 25% Number of cylinders 1
Octane rating 87∼93 120∼130 Displacement, cc 395
Auto ignition temp. 225°C 220°C 450°C Compression ratio 18:1
Stoichiometric ratio 14.7 15 17.3 Fuel pump PFE 1Q
Injector nozzle type P type DSLA
0.7. The resulting lower in-cylinder temperatures Vehicles Load carrier
reduce the NO levels. In the literature, it is observed Unladen mass, kg 384
x Reference mass, kg 534
most of the work on the use of CNG has been carried Gross Vehicle Weight, kg 995
out on the multi-cylinder water cooled engines or single Gear box Four speed
cylinder water cooled engines experimentally Differential ratio 2.385
Tyre size 4.5×10” 8PR
investigated the effect of advanced injection timing on
emission characteristics of a diesel engine running on Spark ignition engine design was done by
natural gas. The test results showed that alternative modifying existing cylinder head, Piston assembly,
fuels exhibit longer ignition delay, with slow burning Flywheel and replacing fuel injection system with
[3]
rates . The ignition delay was reduced through electronic ignition system on engine. Valve timing of
advanced injection timing but tended to incur a slight existing diesel was found suitable for spark ignition
increase in fuel consumption. The CO and CO2 engine and was unaltered.
emissions were reduced through advanced injection
timing. Cylinder head: Diesel engine intake and exhaust port
Due to the threat posed by the automotive with average flow coefficient of 0.274 for intake port
population, different nations have gone in for setting and 0.308 for exhaust port was retained in order to
different stringent emission norms. Thus the engine build a gasoline engine with typical swirl cylinder head.
manufacturing is put under enormous pressure to The flow coefficients were measure in accordance with
comply with stringent emission norms. procedure laid down by Ricardo[4,5], The decision of
Present research reports the experimental same cylinder head adopting was taken in order to
investigations carried out on light duty automotive commonise machining of cylinder head for both
engine to employ CNG and to comply with the production running diesel engine and newly developed
proposed new emissions standards. The investigations spark-ignition engine also it reduces tooling cost. Spark
o
include: plug thread tapping was made at 20 inclination in the
cylinder head was in place of diesel injector, so that
• Conversion of 395cc high speed diesel engine into spark plug is located centrally with required spark plug
spark-ignition engine protrusion in order to produce short flame travel which
• Design modification was carried for CNG reflect in rapid and relatively complete combustion.
compatible solution
• CFD analysis to improve the cooling system Flywheel weight reduction: Since gasoline engine is
• Spark ignition engine was tuned for bi-fuel quantity governed lightweight flywheel is preferred
stoichiometric operation on CNG as fuel hence additional base diesel engine flywheel was
• Performance and emission tests were carried out machined to reduce its weight to 6.25kg from existing
14 kg.
engine dynamometer and chassis dynamometer and
• Finally, CNG fueled engine was optimized for Compression ratio: Diesel engine compression ratio of
emission on reference 3-wheeler vehicle to achieve 18:1 was changed to optimum working compression
equivalent mileage as diesel ratio of 9:1 for spark ignition engine. Piston toping
clearance was increased from 0.75-7.4 mm to achieve
MATERIAL AND METHODS spark ignition compression ratio as illustrated in Fig. 1.
Spark ignition engine working compression ratio of 9:1
The diesel engine complying with BS-II emission was kept on higher side in order to adopt it for CNG as
norms was adopted to convert it into spark-ignition a fuel, which demands for higher compression ratio due
engine whose specification along with test vehicle to its high auto ignition temperature and low calorific
details is illustrated in below Table 2. value[6]. 9:1 compression ratio was achieved by
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Am. J. Applied Sci., 6 (5): 929-936, 2009
compactable for electromagnetic interference. The
spark plug temperature was recorded on engine and as
well on the vehicle by running the vehicle at different
speeds. The temperature was found 200°C higher but
within acceptable range for CNG application. This is
because of more heat losses compared to diesel engine
even after increasing cooling surface area.
Cooling system improvement-CFD analysis:
Gasoline engines mostly run hotter as compared to
diesel engine due its homogeneous combustion process
Fig. 1: Pan cake combustion chamber as compared to lean burn heterogeneous nature of diesel
combustion process. Further, CNG engine will run
modifying existing reentrant piston crown to pan cake hotter than gasoline engine due to delay in combustion
combustion chamber. Pan cake combustion chamber process because of its higher auto ignition temperature
piston was adopted to avoid hot spot during spark and lower specific weight. To make CNG compatible
ignition combustion as cylinder was having intake swirl analysis was done on existing diesel engine cooling
port. system through CFX (Computational Fluid Dynamic)
software. From the CFD analysis it was concluded that
Carburetor selection: Mechanical controlled variable existing surface area was adequate for diesel
depression carburetor with piston type throttle was application only. Specially for CNG application
selected. Were the throttle is situated in the venture additional surface area of 15% was required for
zone itself, area of venturi was varied by throttling adequate cooling. To achieve increase in surface area
carburetor piston up and down to provide the right for effective cooling, the number of fins on the cylinder
quantity of mixture to meet the engine operating head and cylinder barrel was increased without major
[7]
conditions . The quantity of fuel delivered was decrease in space between the fins hence the thermal
controlled by various jets and passages and metering balancing of the cylinder head and block were retained.
needle moving inside the calibrated orifices. The The flow rate of fan is increased by 10-15%, by
metering needle is attached to throttle itself. Carburetor modifying the blade design. The changes are made in
piston was anodized in order to take care of wear and the air-shroud and back-plate for accommodating the
abrasion during dry run of CNG. fan design as shown in Fig. 2.
Turbulent Kinetic Energy profile of CFD analysis
Electronic ignition system: From the base diesel of existing system is shown in Fig. 3 where poor air
engine, fuel injection system and governing mechanism velocity is causing excess heat energy loss leading to
were removed and spark ignition system was over heating of engine and drop in performance. Figure
introduced with electronic multi mapped DC Igniter 4 shows for improved system where air velocity has
[7,8]
with pulsar pickup . High tension coil with high improved engine cooling reducing hot spot from
energy capacity was used in order to care delay turbulent kinetic energy profile. The analysis has given
combustion due to high auto ignition temperature of 10-12% improvement in engine cooling on actual
CNG fuel. In order to take care valve train mechanical engine.
safety higher engine speed cut off was introduce in DC
igniter which cut off spark from spark plug as soon as CNG compactable material: As CNG operated engine
engine reaches 4100 rpm. was running hotter by hundred degree centigrade in
CNG as compared to gasoline. Engine material of
Spark plug selection: On assessment twin electrode cylinder head, valve and valve seat insert were
resistive spark plug was adopted on engine in case of [9,10]
reviewed for CNG compatibility . Cylinder head
twin electrode plugs ignition spark selects the best route material was upgraded with silicon copper high alloy
to take from the centre electrode to the ground material to retain hardness at elevated temperature,
electrode[7,8]. The possible spark path are four as against valves material was reviewed from mono metal with bi-
one in single electrode spark plug. This increase the metal valve with satellite coating on valve head in order
probability of ignition and improve the acceleration to avoid premature wear due dryness of CNG fuel.
startability even for delayed fuel characteristic of CNG. Cobalt base alloy was used in valve seat inserts which
On assessment, resistive spark plug has shown remain intact even at elevated temperatures.
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Am. J. Applied Sci., 6 (5): 929-936, 2009
Air shroud
Back plate
Flywheel
Fig. 2: Cooling system of engine
Fig. 4: Improved system turbulent kinetic energy profile
Air filter Pressure guage
Carburetor
CNG regulator
Petrol tank
Engine CNG bottle
Ignition switch
Fuse
Vacuum pipe CNG solenoid Relay
Petrol solenoid valve Controller
Selector switch Battery
Fig. 5: Schematic layout of engine with CNG system
system was becoming more sensitive especially in part
Fig. 3: Existing system turbulent kinetic energy profile load condition where effective compression ratio
decrease due to homogenous combustion process. To
Experimental method study on stoichiometric air to fuel ratio in gasoline and
Ignition timing optimization: Ignition timing was CNG intake system was optimized[11]. During initial
mapped for each engine speed and load for better engine performance there was drop in volumetric
engine performance and fuel economy. Figure 5 shows efficiency observed, drop in volumetric efficiency was
schematic layout of engine setup use for experimental mostly due to poor CNG fuel and pulsation effect at
research. higher engine speed. Many trials was done by adding
To compensate for dual Gasoline and CNG volume in intake system to reduce pulsation effect
application, dual ignition timing curve was mapped to which results in increasing volumetric efficiency.
achieve better power, torque and over all performance Resonator optimum volume of 5 L could achieve nearly
and also to meet the engineering target for mass equivalent volumetric efficiency as of diesel. Figure 7
emission test on chassis dynamometer. Variable ignition shows the trends of volumetric efficiency with different
timing of 15° btdc at low idling engine speed to 25° volume in intake system.
btdc at rated engine speed was optimized for gasoline
mode and 29° btdc at rated speed was optimized for Combustion pressure measurement: Combustion
CNG mode as shown in Fig. 6. Selection of respective pressure measurement was done by AVL endoscope.
curve is sensed through change over switch of CNG kit. With CNG as fuel there was drop in combustion
pressure to 36 bar as against 55 bar of diesel as show in
Engine optimization on engine dynamometer: Fig. 8.This drop in combustion pressure is significance
During engine optimization in CNG mode intake as compression ratio for CNG is lesser then diesel
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