| Under the pressure of global energy crisis and environmental pollution problems, fuel-efficient and eco-friendly vehicle power system is becoming the mainstream of the international automobile industry development direction. Increasing the amount of oxygen intake into the engine combustion chamber is the key to strengthen the engine combustion and improve the engine dynamic and economic performance. At present turbo-charging and oxygen-enriched inlet are the two main methods to increase the quantity of oxygen intake into the engine cylinder. Compared with the method of turbo-charging, oxygen-enriched combustion can improve the engine dynamic response performance with lower application cost and a small change of the engine total air intake.As the new automobile technology(engine exhaust gas waste heat power generation, on-board solar cells and brake/deceleration energy recovery etc.) development and improvement, the car will produce a large number of surplus energy in the future. Based on the fuel cell reverse reaction, using the surplus energy can obtain hydrogen and oxygen. Supplying the engine air intake system with these gases, oxygen and/or hydrogen enriched combustion can be realized.In this paper, with the object to improve the engine combustion process and decrease its emissions, using numerical simulation as the main method,in the view of the combustion and emission characteristic of the gasoline engine intake into oxygenenriched air or with EGR or with H2 and EGR, and the best proportion of O2/EGR and O2/ H2 /EGR in intake air, etc., the following researches are conducted:Fist, with Catia a three-dimensional geometric model of the engine is established based on the disassemble, measurement and raster scan of the engine. Based on the engine geometric model, the engine CFD model is established with Converge.Second, under the condition of 2000r/min and full load, the effect of inlet oxygen enrichment on the combustion and emission characteristic of the gasoline engine is studied, and the spark ignition moment after oxygen enrichment is optimized. From the research, oxygen-enriched combustion can increase the engine dynamic performance and reduce the emissions of HC and CO, while the thermal load and mechanical load of the engine are enhanced, and the NOX emission is increased; After optimizing the spark ignition moment, the engine combustion and emission characteristics are improved, and the inlet oxygen content increases 1%, the best ignition time delays 1.5 ° CA;Third, under the condition of 2000r/min and full load, the effect of inlet oxygen enrichment with EGR on the combustion and emission characteristic of the gasoline engine is studied, the optimum proportioning of O2 and EGR is determined, and the spark ignition moment is optimized under the optimal proportion. The results show that using EGR can reduce the thermal load and mechanical load of the engine, decrease the engine NOX emission, whereas the emissions of HC and CO is increased and the engine dynamic performance is reduced; Excess EGR will deteriorate the engine combustion; 27.3% of O2 and 20% of the EGR ratio is the best proportion; Under this proportion the optimal spark ignition moment is 23.4°CA BTDC.Forth, under the condition of 2000r/min and full load, with the optimum proportioning of O2 and EGR, the effect of hydrogen enrichment on the combustion and emission characteristic of the gasoline engine is investigated, the optimal amount of hydrogen is determined, and then the spark ignition moment is optimized. From the research, compared with no hydrogen enrichment, hydrogen enriched combustion with oxygen enrichment and EGR simultaneously can improve the engine combustion, reduce the emissions of HC and CO, and increase the engine NOX emission. It also to cause a decline in engine indicated power and indicated thermal efficiency. After hydrogenation, the engine indicated power and indicated thermal efficiency will reach their maximum value respectively with 0.4%(by mass) hydrogen content. The proportioning of 27.3%/O2, 20%/EGR and 0.4%/H2 is optimum. Under this proportion the optimal spark ignition moment is 23.4°CA BTDC.In this paper, an accurate engine CFD model is established by the optical method. Based on the CFD model, the characteristics of oxygen enriched combustion, oxygen enriched combustion with EGR and oxgen-hydrogen enriched combustion with EGR of a PFI engine are studied. According to the above researches, several driving strategies are proposed for the car using oxygen-enriched and/or hydrogen-enriched combustion technology. When overtaking occurs, the driver can take a large oxygen enrichment percentage for a short period to improve the engine transient dynamic performance; When driving a long time with no loads change, the driver can take oxygen-enriched with EGR or oxygen-hydrogen enriched with EGR to obtain a better economic and emission characteristics with a little penalty on engine dynamic performance. |
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