Effects of the Fuel Injection Strategy on Low Compression Ratio Diesel Engine During Cold Start at Different Altitudes

Abstract:

An experimental study on the fuel injection strategy for low compression ratio diesel engine at different altitudes was conducted. Tests were conducted on a midspeed heavyduty intercooledturbocharged diesel 14.25∶1 CR (compression ratio) engine whose intake and exhaust pressure was controlled by the Plateau simulation test system to stimulate the altitude conditions including 0, 1 000, 2 000, 3 000， 3 750 and 4 500 m. The results indicate that the time of cranking period is increased with the altitude, the rising ratio of speed of startup period is reduced, the time and undershoot speed of after start period is increased, and the starting performance is deteriorated. Besides, under the conditions of high altitude, the starting performance is more significantly effected by altitude, at an altitude of 2 000 m and below, the time of startup period and after start period is reduced by an average of 1.10 and 1.47 s for every increase in altitude of 1 000 m. At an altitude of 3 000 m and above, the time of startup period and after start period is reduced by an average of 18.48 s, 2.75 s for every increase in altitude of 1 000 m. On the plain, the increase of fuel advance angle, the starting performance is deteriorated, the time of cranking period is increased and the rising ratio of the speed of startup period is reduced, and the time of startup period and after start period is increased. Different total fuel mass injection strategies has little influence on the cold start process on the plain. At an altitude of 4 500 m, the appropriate increase of the fuel supply advance angle and the appropriate reduction of the total fuel mass injection could improve the starting performance. Too large an amount of total fuel mass may lead to the fluctuation in startup period, and the starting stability is deteriorated, however, too small amount of total fuel mass may prolong the time of cranking period and startup period.

Key words:diesel engine; low compression ratio; variable altitude; start; advance angle of fuel supply; total fuel mass