A numerical study of the effects of IEGR on the set-off auto-ignition in an HCCI engine
2011-08-15T11:38:01Z (GMT) by
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.