The automotive engine has been improved significantly over the last decade to achieve the stringent emission norms and this has helped to improve the performance and fuel efficiency. However, to meet future exhaust emission norms, there is a need to develop an alternative combustion system which will further reduce engine emissions. Homogeneous Charge Compression Ignition (HCCI) is an alternate combustion technology with high efficiency as well as low NO_x and PM emissions. This paper gives an overview of the various numerical modeling methods used for the HCCI combustion analysis. This will be useful for understanding the numerical approach to study engine parameters like inlet air temperature, Exhaust Gas Recirculation (EGR), compression ratio, valve timing and injection strategy on the HCCI combustion and exhaust emission.

Homogeneous Charge Compression Ignition (HCCI) combustion is a technique of auto-igniting super lean mixture through compression using the piston without any external ignition source. In HCCI, a (more or less) homogeneous mixture of air and fuel (together with optional combustion product) is compressed and ignited by the heat of compression. HCCI combustion can be considered as a combination of the diesel and Otto cycle combustion processes as it combines the homogeneous mixture preparation of an Otto engine cycle with the compression ignition of a diesel engine. However, the combustion process involved is often different due to differences in the nature of the fuels; diesel fuel has a higher evaporation temperature at atmospheric pressure than gasoline and it is less resistant to auto-ignition; when temperature and pressure of the mixture is high enough, the compressed homogeneous charge ignites simultaneously at multiple spots in the combustion chamber so there is neither a diffusion flame (as in compression ignition engine) nor a flame front traveling through a premixed charge (as in spark ignition engine). The air-fuel mixture is often diluted with Exhaust Gas Recirculation (EGR) in order to limit the rate of combustion or to delay the start of ignition.

In the field of Internal Combustion (IC) engines' research, HCCI combustion process has gained considerable interest in the last decade because of large reduction in NO_x emissions. Since the mixture is lean, diluted and homogeneous, theoretically there are no high-temperature stoichiometric combustion zones that are essential for NO_x formation and no fuel-rich soot-forming zones. Actually NO_x and soot-forming zones depend on the actual homogeneity of the air-fuel mixture. Numerous experiments have shown that NO_x and soot emissions are drastically reduced and in some cases approach zero.

Mechanical Engineering Journal, Future Engine Application, HCCI Combustion Process, Homogeneous Charge Compression Ignition, HCCI, Computer Modeling, Zero-Dimensional Models, Gasoline Direct Injection Engine, Single Zone Models, Visualization Techniques, Fuel Injection Strategy, Conventional IC Engines.