The shortcomings of traditional combustion techniques are being continually evaluated
and alternate combustion modes are being sought. One such combustion mode that is
receiving a lot of attention is Homogenous Charge Compression Ignition (HCCI). HCCI
is a combustion process that has the potential to be highly efficient and produces low
emissions. It can provide high, diesel-like efficiencies using gasoline, diesel, and most
alternative fuels. The major drawback with HCCI is controlling the ignition timing over a
wide range of load and speed. The local chemical and thermal conditions of the charge
mixture, towards the end of the compression stroke, have significant influences on the
set-off auto-ignition. In this paper, numerical study has been carried out to examine the
effects of mixture quality on the occurrence of auto-ignition at the end of the compression
stroke inside a pentroof combustion chamber. The effect of different Internal Exhaust
Gas Re-circulation (IEGR) are investigated. The use of IEGR acts as an indirect control
method, the rate of combustion can be slowed down; however the percentage of IEGR
retained in the cylinder affects the onset of auto-ignition. The calculated results have been
validated against published experimental data, so that the correlation between the two can
be discussed. It is found that the inhomogeneity of the air, fuel and the IEGR mixing,
presented here in terms of temperature distribution, plays an important role in initiating,
and potentially further controlling the HCCI combustion. During the compression
process, certain parts of the engine charge are found to reach a higher temperature which
auto-ignited depending on the percentages of IEGR used
