A Study on the Compression Ignition Characteristics of FAME for Low Compression Ratio Diesel Engine 2012-32-0010

The purpose of this study is to clarify ignition characteristics and engine performance of FAME for 4-stroke diesel engine in low compression ratios. Diesel fuel and coconut oil methyl ester (CME) were selected as test fuels, because CME consisted of saturate FAMEs which were good ignition characteristics. To reduce the compression ratio, thin copperplates were inserted between cylinder head and cylinder block and the compression ratio was reduced from 20.6 that was standard to 15. The engine starting test and an ordinary engine performance test were made at 3600 min.^-₁. In engine starting test, the engine was soaked at room temperature and the ignition timing of diesel fuel was remarkably delayed compared with CME. When the compression ratio was 16, for diesel fuel, the misfiring cycles were included during engine warming up. In case of 15 of compression ratio, the engine could not be started by diesel fuel; however the engine could be run by CME. In an ordinary engine performance test, for any compression ratios, the ignition timing of CME was always earlier than that of diesel fuel, so that CME had good ignitability in case of low compression ratio. The brake thermal efficiency of CME was almost equal to that of diesel fuel in low compression ratio. When the compression ratio was reduced, NO_x was decreased for both fuels. However, in case of high load, NO_x emission of diesel fuel was slightly higher than that of CME because the high rate of heat release was shown due to ignition delay. For both fuels, the smoke emission increased as the compression ratio decreased. The smoke concentration of CME is lower than that of diesel fuel in the low compression ratio; however the smoke concentration is higher than that of high compression ratio.