Combustion characteristics of gasoline and n-butane under lean stratified mixture conditions in a spray-guided direct injection spark ignition engine

Abstract In the present research, macroscopic spray visualization tests were carried out in a constant-volume combustion chamber (CVCC) under replicated ambient conditions of a stratified combustion mode, in order to achieve stable stratified combustion with gasoline and n -butane. With the spray visualization tests, n -butane spray was immediately evaporated after the end of injection, unlike gasoline. Compared to gasoline, the spray structure of n -butane was collapsed toward the injector tip axis, and the collapse became severe as injection pressure was increased. Based on those results, a single-cylinder metal engine experiment was conducted to investigate combustion and emission characteristics of gasoline and n -butane. Due to the different spray characteristics between gasoline and n -butane, operational parameters including injection pressure and injection as well as ignition timings were set to be different for each fuel, for stable stratified combustion. n -Butane required shorter mixture formation time, but the range of suitable mixture formation times was narrower than that of gasoline. However, the combustion efficiency of n -butane was higher than that of gasoline under stable stratified combustion conditions. In addition, unlike gasoline, n -butane showed a similar heat release rate (HRR) trend regardless of injection and ignition timings. Particulate matter emission of n -butane was nearly zero while nitrogen oxides (NOx) emissions were similar to those of gasoline when the combustion phase of each fuel was similar.