Combustion characteristics of naphtha and n-heptane fuels in an auto-ignited HCCI engine at different lambda values and engine loads

Abstract

In this study, it was aimed to control the HCCI combustion phase. For this purpose, low and high reactivity pure fuels and their mixtures in various ratios were tested. Reference n-heptane was chosen as the high reactivity fuel, while heavy naphtha was used as the low reactivity fuel. Detailed combustion analysis was performed using in-cylinder pressure data. IMEP, the start of combustion, combustion duration, indicated thermal efficiency, MPRR and COVimep maps were examined at different engine speeds and lambda values. Almost zero NOx and soot emissions were observed under all test conditions. On the other hand, CO and HC emissions were analyzed comparatively. It has been determined that HN75 fuel provides optimum operating conditions for HCCI combustion and also causes low CO and HC emissions. Indicated thermal efficiency was obtained at about 36% and in a wide operating range in the use of HN75 and HN100 fuels. This study shows that heavy naphtha fuel significantly improved combustion phase control in HCCI engines. Particularly remarkable results were obtained in terms of performance and emission values at 50% and 75% mixing ratios with n-heptane.