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Experimental Combustion Emission
Characteristics of Premixed Charged
Compression Ignition Engine 1V. Pugalendhi,
2K. Annamalai,
3S. Lingesan and
4Krishnan
1Department of Mechanical Engineering,
Tagore Engineering College,
Chennai.
pugalmit@gmail.com 2Department of Automobile Engineering,
MIT Campus,
Chennai.
kannamalai70@gmail.com 3Department of Automobile Engineering,
MIT Campus, Chennai.
s.lingesan@gmail.com 4Department of Automobile Engineering,
MIT Campus, Chennai.
Abstract Premixed Charge Compression Ignition (PCCI) is the solution for
efficient diesel combustion. Ethanol blended fuel is premixed with the air,
vaporized using the exhaust gas to increase its temperature before entry
into the combustion chamber . Therefore the reduction of temperature
sensitive oxide emission, increased mechanical energy conversion, reduced
specific energy consumption resulted from preheated ethanol. Also there
will be reduction in exhaust temperature because of preheating using
exhaust gas.Thus the performance and emission characteristics of the
preheated ethanol blend fuel PCCI direct injection diesel engine has been
compared with the conventional diesel engine and found that this as
perfect alternative.
International Journal of Pure and Applied MathematicsVolume 119 No. 12 2018, 2961-2973ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu
2961
Key Words: PCCI Engine; Ethanol fuel; Preheat; Vapourizing.
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1. Introduction
In this century, it is believed that crude oil and petroleum will become very
scarce and costly in the near future. Day to day, fuel economy of engines is
getting improved and will continue to improve. However, enormous increase in
number of vehicles has dictating the demand for fuel. With increased use and
the depletion of fossil fuel, alternative fuel technology will become very
common is the coming decades.
All these years there have always been some IC engines filled with non-gasoline
or diesel oil fuels. Because of the high cost of petroleum products, some
developing countries are trying to use alternate fuels for their vehicles.
However, their numbers have been relatively very small.
Another reason motivating the development of alternate fuels for the IC engine
is the concern over the emission problems of gasoline and diesel engines
combined with other air polluting systems, the large number of automobiles is a
major contributor to the air quality problem of the world. Quite a lot of
improvements have been made in reducing emissions from automobile engines.
Government bodies aremaking stringent mandates to reducing the polluting
emissions and they are constantly constricting the polluting emission level.
Further, it also closely scrutinizes the engine makers to follow up the emission
standards. But, if a 35% improvement made over period of years, it is to be
noted that during the same time the number of automobiles in the world
increases by 40% thereby nullifying the improvement. Lot of efforts has gone
into for achieving the net improvement in cleaning up automobile exhaust.
However, more improvements are needed to bring down the ever increasing air
pollution due to automobile population.
A Third reason for alternate fuel development is the fact that a large percentage
crude oil must be imported from other countries which control the larger oil
fields. Notably, India ranks top in the highest crude oil importing nations. As of
now many alternate fuels have been used in limited quantities in automobiles.
The above reasons paves way for the compulsion in development of in alternate
for the gasoline and diesel fuels.
The engines used for alternate fuels are modified engines which were originally
designed for gasoline or diesel fuelling. They are, therefore, not the optimum
design for the other fuels. Only when extensive research and development is
done over a period of years, maximum performance and efficiency can be
realized from those engines. However, the research and development is difficult
to justify until the fuels are accepted as variable for large number of engines.
On the other hand, the gasoline and diesel fuelled engines in use have crossed
huge numbers where if an perfect alternate fuel has been placed, a large amount
of money has to be spent to fine tune the exiting diesel engine tom work with
new alternative.Else, the old engine has to be replaced with a new one.Both the
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options will cost much where this too makes an obstacle for taking an alternate
fuel. So a perfect solution for the above problem is reduce the diesel fuel
consumption without making any modifications in the engine.
Duel fuel engine, HCCI, PCCI, RCCI engines are some best of the modified
engines using alternate fuel with the conventional fuel. On the abovementioned
engines PCCI engine serves good with less modifications it has its own
disadvantages.
Similarly in the alternate fuels ethanol, methanol, CNG, LPG, Bio-diesel and
vegetable oils are some good and extensively using alternate fuels. Out of them
ethanol, methanol and CNG has the highest availability and can be made as on
alternative for the conventional fuels.
Our objective is to reduce the diesel fuel consumption without compromising its
performance characteristics and reduced and polluting emissions by adding an
alternate fuel with the conventional fuel without any engine modification we
studied many textbooks and done through a large number of literature studies on
alternate fuels and engine modifications at lastwe found ethanol to be best
alternative and in PCCI engine.
But the problem of using ethanol in diesel engine is the auto ignition
temperature which is higher for ethanol then diesel so, ethanol is heated to
vapour state before mixing it with air by using the exhaust gas. Since the heat in
the exhaust gas is usually wasted, we use the waste heat in exhaust gas to
vaporise ethanol. Various ratios of ethanol and diesel is used in the PCCI DI
diesel engine and its performance and emission characteristics are compared
with the conventional diesel engine.
2. Literature Survey
1. Valentina Fraioli et al
IstitutoMotori – CNR, Napoli, Italy
ETHANOL EFFECT AS PREMIXED FUEL IN DUAL-FUEL CI
ENGINES: EXPERIMENTAL AND NUMERICAL INVESTIGATIONS
The results of two research activities are reported and compared: tests on an
optical single cylinder research engine and numerical simulations, so achieving
a combined approach to the study of dual-fuel configuration. Optical
diagnostics has been applied in a transparent direct injection diesel engine
equipped with the head of a Euro5 commercial engine and the latest generation
common rail injection system. Pure ethanol is injected in the intake manifold,
while n-heptane is directly injected in the cylinder. UV digital imaging is
applied to the optical engine allowing to detect crucial chemical intermediates,
like OH, HCO, and CO, in terms of their spatial distribution and temporal
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evolution. This analysis allows to identify in-cylinder zones with high reactivity
of mixed fuels and to investigate the effect of the presence of ethanol on the
burning dynamics of the directly injected fuel.
2. Abhishek Paul et al
Department of Mechanical Engineering, National Institute of Technology,
Agartala 799055, India
AN EXPERIMENTAL INVESTIGATION OF PERFORMANCE-
EMISSION TRADE OFF OF A CI ENGINE FUELED BY DIESEL-
COMPRESSED NATURAL GAS (CNG) COMBINATION AND DIESEL
ETHANOL BLENDS WITH CNG ENRICHMENT
The potential of diesel ethanol blending and subsequent CNG (compressed
natural gas) enrichment have been investigated. The study starts with a
miscibility test of ethanol in diesel, which paves the way for an experimental
comparison between performance and emission characteristics of Diesel-
Ethanol blends, Diesel-CNG combinations and Diesel-Ethanol blends with
CNG enrichment. The results indicates that diesel ethanol blend D95E5 (95%
diesel 5% ethanol) with low CNG enrichment produces a better performance-
emission characteristics as compared to base diesel operation as well as diesel-
ethanol blend operation. Results also portrayed ethanol’s potential in reducing
NOx emission, BSEC and smoke opacity.
3. Methodology
The research was based on a single cylinder, fourstroke, air cooled, constant
speed direct injection diesel engine developing 4.4 Kw t aconstant speed of
1500 rpm. This experiment consists of two fuel tanks. One contains diesel fuel
and the another one is for secondary fuel.Before mixing the ethanol with air it is
preheated to vapor state using the exhaust gas. Then the vaporized ethanol flows
through a flow controller which regulates the amount of ethanol into the engine.
The vaporized ethanol is mixed with the use of carburetor. It reduces the
consumption of diesel fuel and makes complete combustion. An AVL 365c
angle decoder test rig is mounted on the cam shaft of the engine for obtaining
various results during engine operation. AVL 415 smoke meter is used to
measure the smoke opacity. A gas analyzer is used to determine the gas
composition. A counter flow heat exchanger is used to exchange heat from
exhaust gas to ethanol fuel. Fig 1 shows the construction of the experimental
setup. Table 1 contains the specifications of the test engine and table 2 shows
the properties of diesel and ethanol fuel.
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Figure 1 Block Diagram of experimental setup
Table 1 Technical specifications of the test engine
Engine type Four stroke diesel engine
Fuel used Diesel
Bore 87.5 mm
Stroke 110 mm
Swept volume 661.5 cc
Injection timing 230bTDC
Nozzle opening pressure 220 bar
Rated output 4.4 kW
Rated speed 1500 rpm
Compression ratio 17.5 : 1
Cooling system Air
Table 2 Properties of Diesel and Ethanol fuel
Fuel properties Diesel Ethanol
Density (g/cm3) 0.82 0.7863
Boiling point( oc) 240-360 79
L.H. of vaporization (MJ/kg) 0.256 0.839
Auto ignition temperature ( oc) 260 423
Calorific value (MJ/kg) 44.9 29.8
Cetane number 40-60 8
Stoichiometric air fuel ratio 14.5 8.97
4. Result
In this work, the combustion characteristic such as Pressure with respect to
crank angle of preheatedethanol fuel is compared with the baseline
directinjection diesel combustion. Similarly the performance characteristicssuch
as brake thermal efficiency and brake specificenergy consumption and emission
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characteristics such as oxides of nitrogen and smoke emissions were
comparedwith baseline diesel fuel. The result of this exhaustive researchhas
brought out the significance of dual fuel to the emergingneeds of complete
combustion.
COMBUSTION CHARACTERISTICS Pressure vs. crank angle
The variation of cylinder pressure with the crank angle diagramis shown in Fig.
2. It is observed that the preheatedethanol fuel exhibits a higher cylinder
pressure compared to that of baseline diesel fuel. The maximum peak pressure
of 68.85bar and68.2 bar occurs at 70and 8
0aTDC for preheated ethanol and neat
diesel fuel. The cylinder peak pressure andmaximum rate of pressure rise for
preheated ethanol werefound as higher due to improvement in premixed
combustiondue to increased flame rapidity that leads to a complete combustion.
Another reason might be higher energy releaserate, so the peak cylinder
pressure shifted 20CAbTDC and it is slightly away from the diesel peak
pressureregime for preheated ethanol fuel. The increasedignition delay would
increase the amount of fuel burnt duringthe premixed combustion phase. Hence
there is an increase inpeak pressure that would have only been to shift in the
heatrelease pattern on premixed combustion region.
Figure 2Variation of pressure with crank angle.
PERFORMANCE CHARACTERISTICS Brake thermal efficiency
The variation of brake thermal efficiency with brake meaneffective pressure is
shown in Fig. 3. It is evident from thegraph that brake thermal efficiency
increases in dual fuelmode. The increase in brake thermal efficiency from no
loadto full load condition indicates the capability of the combustionsystem to
convert the fuel energy into mechanical work.Generally, the highest thermal
efficiency occurs at the full load,where only the combustion efficiency is
maximized. The brakethermal efficiency at full load is 31.86% preheated
ethanol fueled diesel, which is 3.69% higher as compared to diesel. The BTE
increases dueto an enhanced combustion rate of premixed fuel. The
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combinedeffect of lower density and lower fire point of the preheatedethanol
increases the combustion rate.
Figure 3Variation of brake thermal efficiency with respect tobrake mean
effective pressure.
Brake specific energy consumption
The mass of fuel consumption is shown in Fig. 4. If two differentfuels of
varying density are blended, then the brake specificenergy consumption is
measured as a replacement for BrakeSpecific Fuel Consumption (BSFC).
BSEC =BSFC * CV
where CV is the calorific value of the fuel, the brake specificenergy
consumption is represented in terms of MJ/kW h. Itis clear that BSEC is lower
for ethanolfuel compared to the normal diesel mode. Generally BSECdecreases
with an increase in the brake power. This may be due to the decrease of the
calorific value by adding the premixedethanol fuel. The brake specific energy
consumptionfor preheated ethanol fuel at 20% load is21.69 MJ/kW h, and at
fullload is 11.29 MJ/kW h. Fordiesel it is 27.19 MJ/kW h at 20% load and 13.59
MJ/kWhat full load. The above trend agrees with the result ofHansah et al. [6].
Figure 4Variation of brake specific energy consumption with respect to
brake mean effective pressure.
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EMISSION CHARACTERISTICS Brake specific nitrogen oxides
The variation of brake specific nitrogen oxide given in terms ofg/kW h with
respect to diesel is shown in Fig. 5. It is observedfrom the graph that oxides of
nitrogen emissions are reduced to 24% on average for preheated ethanolfuel
than the neat diesel fuel operation. The reason might bethe formation of
partially lean air fuel mixture inside the combustion chamber compared to
diesel combustion due tolower combustion temperatures, since oxides of
nitrogen formationare very sensitive to the temperature of the cycle. Inparticular
premixed ethanol shows 9.5% lesser NOx emissionat the full load than the
diesel due to lower combustion temperaturecaused by the lower heating value of
the ethanol.Another reason may be due to high latent heat of vaporizationwhich
increases the specific heat of the premixed fuel mixture.The increase in specific
heat reduced the peak combustion temperature.But at the fully loaded condition
oxides of nitrogenemission increases slightly for the preheated ethanol fuel. The
cause may be due to the increased fuel octanenumber of the premixed fuel,
since a higher temperature isrequired to get auto ignition. Another reason might
be due to the strength of air fuel mixture which is rich that increasesthe
combustion rate and higher rates of pressure rise. It isdue to the reason that at
the richest zones, sudden auto ignitionof the mixture takes place and
combustion temperaturewill also locally be higher. At the instance of higher
combustiontemperature few diatomic nitrogen breakdown of
monatomicnitrogen forms more oxides of nitrogen.
Figure 5Variation of oxides of nitrogen with brake mean effective pressure.
Smoke Opacity
The variation of smoke emission with respect to brake meaneffective pressure is
shown in Fig. 6. The smoke emissiondecreased significantly for preheated
ethanol fuelthan with conventional mode of diesel operation owing tomore
oxygen and less carbon in the premixed fuel. The reasonmight be that premixed
combustion will be more as comparedto conventional engines, during which the
fixed oxygen atomin the premixed ethanol can improve combustionin fuel rich
regions, which reduces the smoke formation. Thesmoke emissions are
significantly reduced to 67%for preheated ethanol fuel as compared to
normalmode of operation. The other reason for the reduction insmoke emission
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at the part loads is due to the disappearanceof rich regions of mixture around the
fuel spray in diesel combustionand air fuel mixture becomes partially
homogeneous.This may also due to the high latent heat of premixed fuelwhich
increases ignition delay period. Smoke emission isdecreased due to reduced
quantity of diesel that was injectedfor premixed combustion and the absence of
localized fuel–air mixture is also the one of the reasons for the reduction
insmoke emission.
5. Conclusion
`This research work has been done with concerning about the current and future
needs of PCCI engine. Various parameters such as brake thermal efficiency,
brake specific energy consumption, Oxides of nitrogen ,smoke are measured
and analyzed. It is observed that
1. There is an increase in the brake thermal efficiency by 3.69% higher as
compared to conventional diesel engine.
2. There is reduction in the emission of oxides of nitrogen and smoke by
9.5% and 67% respectively as compared to conventional diesel engine.
3. Since preheating is done using exhaust gas, exhaust temperature gets
reduced.
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