EFFECTS OF PISTON COATING ON COMBUSTION STABILITY IN A CRDI DIESEL ENGINE RUN UNDER DUAL-FUEL MODE

Combustion stability in diesel engines is defined by cycle-to-cycle variations. In this study, effects of piston coating and engine load on cycle-to-cycle combustion behavior were investigated in a diesel engine operated on gaseous fuel mixture at different loads. Coated and uncoated piston tests under dual-fuel and single diesel modes were performed at three different loads including 50 Nm, 75 Nm, and 100 Nm at a constant speed of 1750 rpm. The piston bowls were coated by %8 yttria stabilized zirconia with the thickness of 0.4 mm. Dual-fuel mode is consisted of mixture of hydrogen enriched synthetic biogas, with the percentage of 80% CH4, 10% CO2, and 10% H2. Main combustion parameters (cylinder pressure with crank angle, peak cylinder pressure (CPmax), peak pressure rise rate (PRRmax), indicated mean effective pressure (IMEP), CA10, CA50, CA90, and CA10-90 duration) were addressed in view of cyclic aspects. The results showed that the piston coating was comparatively more effective in reducing the coefficient of variation (COV) and standard deviation (SD) values of main combustion parameters, especially at low and medium loads. SD, frequency distribution, and COVs of CP max and IMEP were quite better at a medium test load of 75 Nm. The piston coating also reduced COV of CP with crank angle under all tests. As increasing the engine load, cyclic samples of CP max and PRRmax enhanced and advanced for both diesel and dual-fuel modes. By the piston coating and engine loads, Cyclic CA10 and CA50 variations were slightly affected whereas cyclic CA90 were tremendously changed. Therefore, CA10-90 period was importantly affected by piston coating and load. The highest relationship among the main combustion parameters was between CP max and PRRmax for both piston cases. In dual-fuel mode, a strong relationship emerged between IMEP and CPmaxat low load.