Mixture homogeneity plays a crucial role in HCCI engine. In the present study, the mixture homogeneity was analysed by three-dimensional engine model. Combustion was studied by zero-dimensional single zone model. The engine parameters studied include speed, injector location, valve lift, and mass of fuel injected. Valve lift and injector location had less impact on mixture formation and combustion phasing compared to other parameters. Engine speed had a noticeable effect on mixture homogeneity and combustion characteristics. 1. Introduction Over the last decade, we have seen an exponential growth in the consumption of diesel and petrol by automobiles. This has contributed a great deal in air pollution. Hence, it is important to use the right technology to harness maximum output from the fuel and at the same time, reduce pollutions. Homogenous charged compression ignition (HCCI) engine is a mix of both conventional spark-ignition and diesel compression ignition technology. The combination of these two designs offers diesel-like high efficiency and at the same time, reduces and particulate matter emissions. HCCI simply means that the fuel is homogeneously mixed with air in the combustion chamber (very similar to a regular spark-ignited gasoline engine), but with a very high proportion of air to fuel (lean mixture). Currently, lots of researches are being done on challenges faced to operate an engine in HCCI mode; some of them are mixture homogeneity, combustion phasing, and limited operating range. Among these, mixture homogeneity at the end of compression stroke plays a crucial role in implementing HCCI successfully [1]. Various modeling strategies have been used to study combustion in HCCI gasoline engines, which include zero-dimensional single zone [2, 3], quasidimensional multizone [4], one-dimensional cycle simulation coupled with chemical kinetics model [5–7], multidimensional multizone [8–11], and multi-dimensional with detailed chemistry [12–16]. Multi-dimensional modeling provides high levels of accuracy but at the cost of computational time. Xu et al. [3] developed a single zone combustion model based on detailed chemical kinetics combined with a thermodynamic engine simulation program. It was found that the main combustion, marked by the rapid increase of temperature, starts in the temperature range of 1000–1050？K. Roy and Valeri [11] devised a multi zone model with a detailed chemistry approach. The results demonstrated that the separate combustion zones predict well the cylinder pressure history and the rate of heat release, as well as the
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