M40_HCCI_ENGINE1
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Transcript of M40_HCCI_ENGINE1
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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