Experimental Investigation of Combustion Characteristics of a Single Cylinder Diesel Engine at Altitude
Abstract Concern over the change of atmospheric conditions at high altitudes prompted interests in the deteriorated efficiency and emissions from heavy-duty diesel engines. This study utilized a single-cylinder, four stroke, direct injected diesel engine to experimentally investigate the altitude effects on combustion characteristics. High altitude operations were simulated via reducing the intake pressure but maintaining constant engine speed and torque. The results suggested reduced in-cylinder pressure but increased temperature as altitude rose. The combustion analysis indicated a slight longer ignition delay, raising and retarding the pressure rise rate and energy release rate in the premixed combustion process. A smaller excess air ratio contributed to combustion deterioration, reflected from a retarded end of combustion, a longer combustion duration, a reduced thermal efficiency, and an increased level of incomplete combustion. However, the phasing and combustion profile were not significantly impacted, when the altitude was elevated from sea level to 2000m, at least for the engine and conditions investigated in this study. Consequently, it is not necessary to adjust the engine ECU when operated in the U.S., considering that the mean elevations of most states are lower than 2000m.