Abstract
This paper investigates the performance, exhaust emissions, and combustion characteristics of a dual fuel diesel engine fueled by compressed natural gas (CNG) supplied in an intake-pipe as the main fuel. The experiments used standard ignition fuels prepared by n-hexadecane and heptamethylnonane which are used to define the ignitability of diesel combustion, and focused on the influence of fuels with similar or poorer ignitability than ordinary gas oil such as fuels with cetane numbers (C.N.), 55, 50, 45, 40, 35, and 30. Compared with gas oil ignition, standard ignition fuels with C.N. below 40 showed significantly delayed ignition timings, higher exhaust gas temperatures, and extremely lower brake thermal efficiencies with increasing CNG supply ratios. Therefore, it is concluded that the lower practical C.N. limit for this engine is about 45 for dual fuel operation.
