Effect of the altitude on the combustion characteristics of a low-compression-ratio diesel engine during the start-up process

Abstract

One of the ways to meet future emission standards for cars and to limit the peak pressure of a heavy-duty, highly supercharged diesel engine is to reduce the compression ratio. Nevertheless, complications appear because stringent limitations to a reduction in the diesel compression ratio are the start-up requirements, in particular at high altitudes. An experimental study was conducted on the effect of the altitude on the combustion characteristics during the start-up process of a direct-injection midspeed intercooled turbocharged diesel engine with a compression ratio of 14.25:1. Specialized testing was conducted on the low-compression-ratio diesel engine, the intake pressure and the exhaust pressure of which were controlled by a plateau simulation test system to simulate the conditions at altitudes of 0 m, 1000 m, 2000 m, 3000 m, 3750 m and 4500 m. The results indicated that the pressure in the cylinder was lower during the cranking period as the altitude increased and that this caused the ignition operation to become difficult at altitudes above 3000 m. The combustion characteristics are significantly impacted by altitudes above 2000 m. At an altitude of 0–1000 m, the curve pattern of the cycle cylinder pressure had mainly a single peak during the start-up period. When the altitude increased to 2000 m, twin peaks and afterburn appeared in the cycles. Misfire appeared during the start-up period when the altitude increased to 3000 m, the combustion instability increased and the average indicated mean effective pressure decreased rapidly. When the altitude increases, the cycle-to-cycle variations in the peak pressure increased during idle, the ignition and the crank angle position at 50% of the cumulative heat release rate were delayed and the combustion duration was extended.

The Emission Characteristics of a Diesel Engine During Start-Up Process at Different Altitudes

“…Oxygen content and inlet air pressure were relatively low when the altitude increased, which would cause a lower in-cylinder pressure and temperature at TDC. The single peak pattern turned into other minority and the misfire pattern grew more obvious because of the longer ignition delay at increasing altitudes, which produced more misfire patterns and other incomplete and inefficient combustion conditions [27].…”

A novel method to improve the cold starting ability of a low compression ratio diesel engine through recompression of the charge

“…Misfire and combustion instabilities were detected at ambient pressures prevalent at 3000 m altitude. 10 This is mainly due to the drop in cylinder pressure during compression which needs to be compensated by further increasing the temperature of air during compression in such cases. To mitigate this, starting aid like glow plugs are being used for achieving reasonable starting ability at these conditions, but it is not sufficient to achieve desirable combustion stability and hydrocarbon (HC) emissions during warm-up in low CR diesel engines.…”