Research On Oxygen-enriched Combustion Mechanism And Combustion Paths Of Diesel Engine

Currently, the main theme of the development of the internal combustion engine industry is energy-saving and environmental protection. In order to achieve this goal, researchers developed lots of very valuable technologies. The technology of oxygen-enriched combustion technology is concerned by both domestic and foreign researchers. Based on the mixed research methods of experimental study and numerical calculation, this paper analyzed the reaction mechanism and combustion paths of the oxygen-enriched combustion in diesel engine. The result can provide certain theoretical guidance for clean combustion of diesel engine.A 4100QBZL-2 diesel engine’s intak and exhaust system were transformed to realize suppling different oxygen concentration intake, different rate of EGR and different proportion of emulsified diesel. The experimental researchs of different concentration oxygen-enriched combustion, oxygen-enriched combustion with different rate of EGR and different proportion of water emulsified fuel were developed on the diesel engine. At the same time, the corresponding numerical calculation was conducted by the method of 3D CFD code coupling to n-heptane oxidation reaction mechanism. Results show that: oxygen-enriched combustion can improve diesel engine’s power, and reduce smoke, CO and HC emissions. However, it makes NOx emissions worse. The technology of oxygen-enriched combustion with EGR and water emulsified fuel can reduce NOx emissions. There is a best optimical rate to reduce both smoke and NOx in the premise of not significant influence on the power output.Based on the chemical reaction kinetics of diesel engine combustion, the low-temperature, middle -temperature and high-temperature reaction mechanism of oxygen-enriched combustion were analyzed by using CHEMKIN and CFD three-dimensional combustion model coupled simplified N-heptane oxidation kinetic model. The result indicates that: oxygen-enriched combustion can promote the low-temperature, middle-temperature and high-temperature reaction mechanism of n-heptane oxidation, which result in changes of diesel engine’s combustion and emission. The combustion path was researched by a detailed n-heptane oxidation reaction combined model which was constructed in this paper including PAH and NOx reaction mechanism. The result indicates that: the combined model can be used to predict diesel engine’s PAH, Soot and NOx emissions, and the predicted results are reliable. PAH, Soot and NOx emissions from oxygen-enriched diesel engine can be determined by combustion temperature and oxygen-fuel ratio of the mixture. The technology of oxygen-enriched combustion with EGR and water emulsified fuel is proved a very promising technology to reduce diesel engine’s emissions. In addition, this paper put forward two kinds of oxygen-enriched combustion path control strategy and corresponding technical measures to resolve the NOx deterioration problem, which will provide certain theoretical guidance for the clean combustion of diesel engine.