Abstract
A four-cylinder, direct-injection (DI) diesel engine was used to study the effects of altitude on the variations of the exhaust soot emission and engine performance. The experiments were conducted in Mashhad, Iran, at an altitude of 975 m above sea level. A three-lobe rotary blower of Roots type was employed in order to simulate the altitudes down to 350 m by increasing the inlet manifold pressure of the engine. The tests were performed based on the ECE-R49 test cycle, and for each testing point, the experiments were repeated for five boosting pressures which correspond to five different altitudes. Results indicate that with increasing the altitude from 350 m to 975 m, the soot emission increases about 40%. This increase is due to the relatively lower the air density introduced into the cylinders in higher altitudes that leads to the increase of autoignition delay time which could shorten the late combustion phase; hence, the soot burnout process deteriorates. Also it was found that at low engine loads, the Brake-Specific Fuel Consumption (BSFC) increases about 20% with raising the altitude from 350 m to 975 m. At higher loads, the raising rate of fuel consumption is insignificant. The effects of altitude on the other engine parameters such as induced air mass flow rate, volumetric efficiency, equivalence ratio, and exhaust temperature were investigated as well. In addition, a sensitivity analysis was conducted and the results revealed that among the engine parameters, the soot emission alteration has the most sensitivity to the change of the altitude. First Published Online: 16 Jul 2013
Highlights
The enormous magnitude of emissions produced by automotive engines consist the major portion of the environmental pollutions (Abdel-Rahman 1998)
It declares that the mass flow rate of inlet air decreases with the increase of altitude due to reduction of the pressure and, the density of the inlet air at high altitudes
When the engine speed is low (1750 rpm), the inlet air mass flow reduces by 20% with the increase of the altitude from 350 to 975 m
Summary
The enormous magnitude of emissions produced by automotive engines consist the major portion of the environmental pollutions (Abdel-Rahman 1998). Reduction of soot and NOx emissions from diesel engines was extensively pursued by the researchers and new stricter emission control policies like EURO-V highlight the importance of NOx and soot emission reduction because of their hazardous effects on human health and the environment (Zannis et al 2007). The effects of pollution emissions from diesel engines on the environment include visibility reduction, water and soil pollution, global climate change, etc. In addition to human health and the environment problems, it should be noted that the emissions may have injurious consequences on the maintenance and lifetime of diesel engine. The contamination of lubricating oil by diesel soot is an important factor leading to the increased engine wear (George et al 2007)
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