Effect of Nitrogen Dilution on the characteristics of HCCI Combustion

摘要

Ignition delay times and combustion times of iso-octane/air mixture and nitrogen-diluted/non-diluted gasoline/air mixture were measured by using a rapid compression machine under the conditions equivalent to practical engines. The dilution ratios were 0, 20 and 50% by external percentage. For the case of iso-octane, the pressure range is 1.77 to 2.37 MPa, and temperature range is 732 to 1046 K. For the case of gasoline, the pressure range is 2.14 to 2.45 MPa, and temperature range is 659 to 1108 K. The results show the existence of two ignition regimes. In one regime, mixture spontaneously ignites at multiple points sequentially in the combustion chamber. Another regime yields reaction front formation and propagation inside the combustion chamber prior to multiple points ignition. Being diluted with nitrogen, HCCI combustion becomes slow and ignition delay times become long in the entire temperature range, especially in NTC. For all the nitrogen dilution ratios, the combustion time increased in proportion to the ignition delay time. Combustion time can be related to the difference of local ignition delay time which is caused by local inhomogeneity of temperature.