Experimental study on the cycle-by-cycle variations of homogeneous charge compression ignition combustion using primary reference fuels and their mixtures

In this paper, the combustion stabilities and cycle-by-cycle variations of homogeneous charge compression ignition (HCCI) combustion using neat n-heptane, PRF20, PRF40, PRF50, and PRF60 were investigated. In-cylinder pressures of 100 combustion cycles for each test fuel on a single-cylinder engine were recorded. Consequently, cycle-to-cycle variations of the main combustion parameters and performance parameters were analysed, and the interdependency between the combustion parameter and performance parameters were also evaluated. The results reveal that the cycle-by-cycle variations deteriorate with the increase of the research octane number (RON). Especially, the coefficient of variations (COVs) of all parameters increase substantially when the RON of test fuels exceeds 40. For a certain test fuel, the COVs of combustion parameters that were used to depict the combustion characteristics during the early stage of combustion are very small, the COVs of combustion parameters that were used to describe the combustion characteristics of the post stage of the combustion are the largest, and the COVs of the i.m.e.p. and Pm maintain at a middle level. Furthermore, a better interdependency also exists between the ignition timing of the low temperature reaction (LTR) and high temperature reaction (HTR), between the maximum pressure rise rate and its corresponding crank angle, between the peak values of the heat release and its corresponding crank angle.