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HOMOGINEOUS CHARGED

COMPRESSION IGNITION

ENGINE

Mahajan Vinayak S.1, Lad Vijay V.2

1Third year Mechanical Engineering

student, S.N.D.College o Engineering

!"esearch Center, #eola $Nashik%.

2Third year Mechanical Engineering

student, S.N.D.College o Engineering

!"esearch Center, #eola $Nashik%.

Abstract

Concerns about energy security, greenhouse gasemissions, and toxic emissions are driving

engine manufacturers to develop new engines

that have both high efficiency and very low

emissions of nitric oxides (NOX)and particulates.

he homogeneous charge compression ignition

(!CC") engine is of wide interest because it

could be a third type of combustion process

!omogeneous charge compression ignitionengines are being considered as an alternative to

diesel engines. he !omogeneous Charge

Compression "gnition #ngine has the potential to

combine the best of the $par% "gnition and

Compression "gnition #ngines.

&ith high octane number fuel the engine

operates with high compression 'atio and lean

mixtures giving C" engine euivalent fuel

consumption or better. ue to premixed charge

without rich or $tichomythic *ones, very lowNox emissions (+-ppm) !igh thermal

efficiency (over /-0) can be achieved. 1uel

efficiency of !CC" as compared to normal $"

engine is noted to be increased from /0 to

2-0. his is an improvement of --0

euivalent to a reduction of fuel consumption

with /-0. he ma3or benefit of !CC" compared

to C" is the low emission of Nox and 45.

his paper presents some results from advanced6aser diagnostics showing the fundamental

behavior of the process from a close to

homogeneous combustion onset towards a very

stratified process at around 7-8/-0 heat

released. he need for active combustion control

is shown and possible means of control are

discussed. 'esults with multi8cylinder enginesusing negative valve overlap, variable

compression ratio, and fast inlet temperature

control as well as dual fuel are given.

INTRODUCTION:-

he internal combustion engine is the %ey to the

modern society. &ithout the transportation

performed by the millions of vehicles on road

and at sea we would not have reached the living

standard of today.

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HCCI FUNDAMENTALS: - !# !CC"

4'"NC"46# 9 !CC" means that the fuel and

air should be mixed before combustion starts and

that the mixture is auto ignited due to the

increase in temperature from the compression

stro%e. hus !CC" is similar to $" in the sensethat both engines use a premixed charge and

!CC" is similar to C" as both rely on auto

ignition for combustion initiation. !owever, the

combustion process is totally different for the

three types. 1igure shows the difference

between (a) $" combustion and (b) !CC".

"n the $" engine we have three *ones, a burnt

*one, an unburned *one and between them a thin

reaction *one where the chemistry ta%es place.his reaction *one propagates through the

combustion chamber and thus we have flame

propagation. #ven though the reactions are fastin the reaction *one, the combustion process will

ta%e some time as the *one must propagate from

spar% plug (*ero mass) to the far liner wall (mass

wt). &ith the !CC" process the entire mass in

the cylinder will react at once.he right part of 1igure shows !CC", called it

:ctive hermo8atmosphere Combustion, ::C.&e see that the entire mass is active but the

reaction rate is low both locally and globally.

his means that the combustion process will ta%e

some time even if all the charge is active. he

total :mount of heat released, ;, will be the

same for both processes. "t could be noted thatthe combustion process can have the same

duration even though !CC" normally has a fasterburn rate. "nitial tests in 6und on a two8stro%e

engine revealed the fundamental difference

between these two types of engines.

1igure 7 shows Normal flame propagation from

two spar% plugs at the rated speed of

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OPERATIONAL METHOD FOR

HCCI ENGINE:-

: mixture of hot and air will ignite when the

concentration and temperature of reactant is

sufficient high. he concentration and

temperature can be increased several different

ways?

88!igh compression ratio.

88 4re8heat induction gases.

881orced induction.

88 retain or reinduct exhaust.

REQUIRMENTS FOR HCCI:-

he !CC" combustion process puts two ma3or

reuirements on the conditions in the cylinder?

(a) he temperature after compression stro%e

should eual the auto ignition temperature of the

fuel@air mixture.

(b) he mixture should be diluted enough to

give reasonable burn rate.

1igure A shows the auto ignition temperature for

a few fuels as a function of. he auto ignition

temperature has some correlation with the fuels>

resistance of %noc% in $" engines and thus the

octane number. 1or iso8octane, the auto ignition

temperature is roughly ---B. his means that

the temperature in the Cylinder should be ---

B at the end of the compression stro%e where the

reactions should start. his temperature can be

reached in two ways, either the temperature in

the cylinder at the start of compression is

controlled or the increase in temperature due to

compression i.e. compression ratio is controlled.

"t could be interesting to note that the auto

ignition temperature is a very wea% function of

air@fuel ratio. he change in auto ignition

temperature for "so8octane is only /-B with a

factor 7 change in 1igure A also shows the

normal rich and lean limits found with !CC"

&ith a too rich mixture the reactivity of the

charge is too high. his means that the burn rate

becomes extremely high with richer mixtures. "f

an !CC" engine is run too rich the entire charge

can be consumed within a fraction of a cran%

angle. his gives rise to extreme pressure rise

rates and hence mechanical stress and noise.

&ith a high auto ignition temperature li%e that of

natural gas, it is also possible that formation of

Nox can be the load8limiting factor.

1igure / shows the NO formation as a function

of maximum temperature. ery low emission

levels are measured with ethanol. "f the

combustion starts at a higher temperature li%e

with natural gas, the temperature after

combustion will also be higher for a given

amount of heat released. On the lean side, the

temperature increase from the combustion is too

low to have complete combustion. 4artial

oxidation of fuel to CO can occur at extremely

lean mixturesD EFabove A has been tested.

!owever, the oxidation of CO to CO7 reuires a

emperature of A--8/-- B. :s a summary,!CC" is governed by three temperatures. &e

need to reach the auto ignition temperature to get

things startedD the combustion should then

increase the temperature to at least A-- B to

have good combustion efficiency but it should

not be increased to more that G-- B to prevent

NOx formation.

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HCCI COMBUSTION PROCESS IN

DETAIL:-

he above description of !CC" gives 3ust a

rough idea about the reuirements and conditions

of the combustion process. "t is also of greatest

interest to acuire detailed %nowledge of the

process. "n order to get such information, laser

based diagnostics is of crucial importance. $ome

of the activities in this field from 6und

Hniversity will thus be presented.

INHOMOGENEOUS

COMBUSTION:-

he first #xperiments with laser8based

diagnostics were performed to analy*e the

difference in combustion between a perfectlyhomogeneous fuel@air mixture and one with

small gradients. 6aser induced fluorescence of

fuel tracer or O! was used to mar% the

combustion process. 1igure I shows the system

setup with a laser generating a vertical laser

sheet. 1igure = shows the fuel distribution for the

two cases with an "n homogeneity of

approximately /0 in the case of port fuel

in3ection and homogeneity within the detection

limit for the case with a mixing tan% and fuel

in3ection far upstream. 1igure G and 1igure