The Relevance of Different Fuel Indices to Describe Autoignition Behaviour of Gasoline in Light Duty DICI Engine under PPC Mode 2019-01-1147

Partially premixed combustion (PPC) with gasoline fuels is a promising new combustion concept for future IC engines. However, many researchers have argued the capabilities of RON and MON to describe autoignition behavior of gasoline fuels in advanced combustion concepts such as PPC. The objective of this study is to develop a novel method called PPC Number to characterize the auto ignition quality of gasoline fuels in light-duty DICI engine under PPC conditions. The experimental investigations were performed on a 4-cylinder Volvo D4 2 liter engine. The ignition delay which defined as the crank angle degrees between the start of injection and start of combustion was used to represent the auto ignition quality of a fuel. The ignition delays of primary reference fuels, PRF (blends of n-heptane and iso-octane) were used to develop a reference curve on which a PPC metric for gasoline can be based. The PPC Number of a specific gasoline is defined as the octane number of the PRF which has the same ignition delay as the gasoline under the same operating condition. Twelve different gasolines having RON values between 55 and 95 were tested at two different operating conditions of 0% EGR and 40% EGR level namely Case0 and Case40 respectively. The intake pressure of Case0 and Case40 were 1.5 bar and 1.8 bar respectively with constant inlet temperature at 110oC. The PPC Numbers of all gasolines were measured and the applicability of the Octane Index from Kalghatgi was assessed. The results reveal that the spray target and piston geometry give big impact to the autoignition quality of fuels. When comparing between indices, PPC Number shows consistence correlations with ignition delay at both conditions.