Cyclic Combustion Variability of Dimethyl-Ether-Fueled Agricultural Tractor Engine

Abstract Combustion in dimethyl-ether (DME)-fueled engines needs to be assessed carefully for its widespread acceptability from a drivability viewpoint. Since the test engine used in an off-highway segment, it was tested in a steady-state cycle for engine performance, combustion, emissions, and their cyclic variations, which were the only parameters to assess the drivability. This study investigated and analyzed the cyclic variations of a 100% DME-fueled engine equipped with modified mechanical fuel injection equipment. It was compared with baseline diesel to understand its positive and negative aspects. Experiments were conducted at different engine speeds (1200,1600, and 2000 rpm) and loads (No Load, 1.29, 2.59, 3.88, 5.18, and 6.47 bar brake mean effective pressure (BMEP)) . In-cylinder pressure was recorded for 250 consecutive engine cycles, and many combustion parameters were comparatively analyzed for diesel and DME fuelings. The coefficient of variation (COV) of maximum in-cylinder pressure (Pmax) was lower for DME than diesel at 1600 rpm and comparable at the other remaining engine speeds (1200 and 2000 rpm). Variations in COV of Pmax were higher at low loads and negligible at high loads for both test fuels. At 2000 rpm, the crank angle positions at which Pmax occurred were distributed in a narrow range for DME, representing higher combustion stability than baseline diesel. Variations in the maximum rate of pressure rise (RoPRmax) were lower for DME at 3.88 and 6.47 bar BMEP, while these were higher at 1.29 bar BMEP than baseline diesel. COV of indicated mean effective pressure (COVIMEP) decreased from lower to higher loads for diesel and DME fueling at 1600 and 2000 rpm engine speeds. The differences in COVIMEP between diesel and DME were negligible at higher loads, representing engine stability similar to baseline diesel. Combustion parameters assessed indicated that DME fueling led to lower cyclic variations than baseline diesel as the engine operated from lower to higher loads. At lower loads, DME fueling showed higher cyclic variations than baseline diesel.