A Numerical Analysis Of The Hcci Engine Auto-ignition Characteristic Of Different Fuels

The homogeneous charge compression ignition combustion process offers good fuel economy and very low nitrogen-oxide and particulate emissions. Therefore, HCCI combustion is considered as one option to improve the efficiency of the spark-ignited gasoline engine, and also to reduce NOx after treatment requirement for the latest generations of compression-ignited diesel engines. However, several technical difficulties need to be resolved before HCCI can be widely implemented in production engines. One of the keys problems of an HCCI engine is to control ignition timing. There are few regular methods to control the mixture auto-ignition phasing: the use of variable intake charge temperature or exhaust gas recirculation.This paper describes a numerical study of the ignition time on HCCI combustion parametric calculations were performed over wide ranges by changing equivalence ratio, inlet temperature, inlet pressure, engine speed, compression ratio, EGR and NO under the assumption of ideal homogeneous charge. Engine performance were evaluated at low-loads, with the full chemistry mechanisms for iso-octane, to determine the expected behavior of the bulk-gases for the limiting case of no heat transfer, crevices, or change in homogeneities.Simulation results show that the equivalence ratio has shown a clear prompting effect in the ignition times. With the same equivalence ratio, a higher compression ratio causes a smaller end-volume in the cylinder before ignition at a higher pressure and temperature, resulting in an overall higher concentration of all the species, and the ignition time to reduce. A higher inlet temperature decreases the ignition delay. A higher inlet pressure decreases the ignition delay. A higher engine speed increases the ignition delay, the reason is that the reaction ratio is lower than the engine speed. A higher equivalence ratio, without ignition, increasing the heat capacity, results into a lower gas temperature. With ignition, a higher equivalence ratio decrease the ignition delay. The effect of EGR on ignition is no liner. Generally speaking, a higher EGR decrease the ignition delay.