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

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. (C) 2016 Elsevier Ltd. All rights reserved.