Effects of Enriched Oxygen and Nitrogen Intake on Combustion Process and Emission Features in a Diesel Engine

A single-cylinder, naturally aspirated, air-cooled diesel engine is used to study the effects of variable oxygen-enriched and nitrogen-enriched intake charge on engine combustion features and emission characteristics. The results show that with the increase in intake oxygen concentration from nitrogen-enriched modes, the ignition delay is decreased, and the maximum pressure rise rate and peak pressure are increased. The effect of enriched nitrogen on prolonging ignition delay appears to be more evident than that of enriched oxygen on shortening the ignition delay. As a whole, the increase rate of four types of pollutants show a quadratic polynomial relationship with the increase rate of intake oxygen. In oxygen-enriched modes, the effects of increased oxygen on the reduction of hydrocarbons (HC) and carbon monoxide (CO) emissions and smoke become weak, whereas in nitrogen-enriched modes, the CO and HC emissions and smoke deteriorate rapidly. Nitrogen oxide (NOx) emissions are steeply increased in oxygen-enriched modes, but slowly decline in nitrogen-enriched modes. At high loads, the oxygen supply is restricted, so the effect of the intake oxygen variation on CO emissions and smoke is enhanced. However, at low loads, the intake oxygen significantly affects the bulk gas temperature in cylinder, resulting in a more sensitive variation in HC and NOx emissions. (C) 2016 American Society of Civil Engineers.