Computational studies on HCCI engines.

Emission legislation is changing in an effort to reduce exhaust emissions from the IC engines. Research and development has been focused on improving both spark-ignition and compression ignition engines to make them more efficient. Over the last decade, research has been increasing in Homogeneous Charge Compression Ignition (HCCI) engines. This alternative combustion process has the potential to combine the best of spark-ignition engines, namely the cleaner combustion with virtual no emission of NOx and soot, with the best of compression ignition, the increased engine efficiency with low fuel consumption and consequently lower carbon dioxide emissions. In this thesis, the effect upon HCCI combustion of different additives has been investigated. These additives can be used, to control the start of auto-ignition and/or to extend the load limits in which HCCI operation is possible. As part of this work, the HCCI combustion capability of running with different fuels was investigated. In order to study these effects on HCCI combustion, a detailed chemistry fuel oxidation mechanism was used together with a powerful chemical kinetic modelling tool, CHEMKIN. Simulations of the HCCI combustion were performed using a single-zone zero dimensional model and later a simpler multi-zone model comprising three different zones. Using the single-zone CHEMKIN model, additives influence on combustion was studied. From this study more complex mixtures were defined and more simulations were done, this time including different fuels such as ethanol, iso-octane and mixtures of both. A more complex model other than the single-zone tool available at CHEMKIN was developed and comparisons between the two simulation methods were performed. The results obtained from the simulations performed confirmed the fuel tolerance of HCCI combustion and the capability of running water diluted mixtures.