Experimental Investigation of Cycle-by-Cycle Variations in a Natural Gas/Diesel Dual Fuel Engine with EGR

This study presents a detailed experimental investigation on the cycle-by-cycle variations in a natural gas/diesel dual fuel engine with EGR. The experiment used a single-cylinder, four-stroke, water-cooled, DI diesel engine. The EGR ratio, diesel injection timing and pilot diesel quantity were varied respectively while all the other parameters were held constant. The parameters of cylinder pressure are used to investigate the cyclic variations. The results show that the cylinder peak pressure, the maximum rate of pressure rise and the indicated mean effective pressure decrease. COV_imep increases to 18.9% with 25% EGR ratio. The interdependency between the pressure parameters and their corresponding crank angles become weak with the increasing EGR ratio. The increasing EGR ratio increases the ignition delay. The cylinder peak pressure and the maximum rate of pressure rise increase dramatically with the advance of the pilot diesel injection timing. However, the indicated mean effective pressure changes slightly. The cyclic variations of the cylinder peak pressure and the indicated mean effective decrease with the advance of pilot injection timing. However, the cyclic variations of the maximum rate of pressure rise increase. Different relationships between the pilot quantity and the cycle-by-cycle variations are presented at different loads. At the low load, overhigh and overlow pilot diesel quantities lead to high cycle-by-cycle variations. The effect of the pilot quantity is not distinct with the increasing load. The values of COV are all under 10%. The cylinder peak pressure and the maximum rate of pressure rise increase with the increasing pilot diesel quantity at all the loads, and the independence of the cylinder peak pressure and the maximum rate of pressure rise to their corresponding crank angles become strong.