| The application of oxygen-enriched intake air technology in the diesel engines can not only reduce soot emission significantly, but also improve the thermal efficiency of combustion and increase engine power density. Active exploration is conducted on oxygen-enriched combustion theory and technology in diesel engines by both domestic and foreign researchers. The method of the combination of experiments and simulations to research joint application of oxygen-enriched intake air technology, EGR and water emulsions technology was adopted in this paper. And the influence of oxygen concentration, EGR rate and emulsification rates on combustion and emission in turbocharged diesel engine was studied. It is very important for the development and improvement of the oxygen-enriched intake air technology.Self-designed oxygen supply system was used to carry out the oxygen-enriched combustion experiments in turbocharged inter-cooler diesel engine, the volume fraction of EGR gas in the intake air is 0% (no mixing EGR gas), 32%, 48% and 50%. With the different EGR rate, the oxygen concentration is 21% (atmosphere), 22%, 23% and 24% by volume. Base on the result of research: with the increase of intake oxygen concentration, NOx emissions increases dramatically without mixing the EGR gas in intake air.Using the mixture, which blended oxygen-enriched air with Ultra-High rate cold EGR gas, Smoke was reduced and excessive growth of NOx was inhibited, engine's thermal efficiency and power should not be affected simultaneously. With right fraction of oxygen and EGR gas in intake air, the NOx-Smoke can be reduced simultaneously in-engine. Under the engine's different working condition, the NOx-Smoke lower emission zone's shape and dimension is different.The combustion characteristic and cycle-to-cycle variations of using oxygen-enriched intake air (in the inlet air the volume fraction of Oxygen as follows: 21%, 23%, 25% and 30%) and water-diesel fuel emulsions (the amount of water are 0%, 10%, 20%and 30% by volume) in a DI engine were investigated. In-cylinder pressures of 20 combustion cycles and maximum pressures under economic speed and medium load operation (1600r/m 100Nm) condition were recorded. Consequently, cycle-to-cycle variations of maximum pressures and combustion characteristic were analyzed. The results reveal that, under the conditions of pure diesel, with the increase of oxygen concentration, the maximum cylinder pressures increase; the cyclic variability of the maximum cylinder pressures and the ignition timing decrease. Using water emulsion diesel, with the increase of volume fraction of water, the ignition timing is increased, but it's still follow the oxygen concentration increase law. The ignition delay increased dramatic, the in-cylinder burning deteriorated and the variations of maximum pressure grew, when the fraction of water is over 30%.The combustion process of oxygen-enriched air intake in turbocharged diesel engine was calculated by using the coupling of FIRE & CHEMKIN. The information of cylinder pressure, mean temperature of cylinder gas, mass fraction of reaction component was obtained. Base on the result: within the limit of 21%~24% of volume percentage of oxygen, with the increase of intake oxygen concentration, maximum cylinder pressure and maximum combustion temperature increase, NOx emission increases significantly. Separately mixing oxygen and carbon dioxide to 24% and 10% in intake air, to achieve the oxygen enriched combustion under high percentage EGR rate in cylinder, the maximum cylinder pressure and maximum combustion temperature is decreased significantly and the ignition delay has been extended obviously. The simulation results are correspond with the experimental results, which show using the existing mathematical model to describe oxygen enriched combustion in disele engine's cylinder is appropriate.
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