Abstract:
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.