For an effective utilization of various gaseous fuels, the general-purpose diesel engine with a conventional jerk-pump system have been used to efficiently convert to the power in many cases through the diesel dual fuel (DDF) operation. In this study, natural-gas fuel is supplied into the intake air-flow of a single-cylinder test engine to prepare the gas mixture, and a small amount of fuel is injected directly into the cylinder to ignite the gas-mixture in the condition of a constant engine-speed and a wide open throttle. Also, nitrogen is introduced to the intake air-flow to reduce the oxygen concentration. In particular, effects of oxygen concentration of intake air on combustion process and engine performance are investigated at a wide range of equivalence ratios in various injection timings to clarify the feasibility of EGR. Based on the experimental results, it is shown that EGR enables to exhibit the improvement in brake thermal efficiency and the much decrease in exhaust NOx concentration in the case of earlier injection.
