| As China's socialist modernization and sustainable development required, further enhance performance, reducing energy consumption and reducing environmental pollution are required for the engine. The quality of the engine combustion properties are a direct impact on the engine energy consumption, performance and emissions. We need to break through the limitations of the traditional internal combustion engine, looking for efficient, clean combustion mode, and develop the new type of engine research and various alternative fuels.A lot of innovations and variety of technologies such as pressurization, three-way catalytic treatment, EGR, lean burn, HCCI etc. have been taken; under the normal conditions engine technology has reached an alarmingly high level. However, in exceptional circumstances the power of the engine decrease, the combustion deteriorate, emissions increase, engine overheating, deflagration or even happene, working stability deteriorate. Especially at cold start, warm-up, rapid changing conditions, engine performance and working conditions even worse. In the trenches, local space, military security condition, and other special environmental conditions, vehicle and engine power are facing not conventional working conditions.This paper is supported by the National Natural Science Fund Project (NO.50676039). The optimal control of combustion and emissions is researched. The combustion and emissions of engine are controlled by oxygen and nitrogen components of inlet air. Accelerant oxygen, flame-retardant nitrogen, forms the dual constraints of combustion. Theoretically, intake of oxygen and nitrogen composition has active and passive role on combustion. The meaning of the initiative is the use of oxygen and nitrogen components to control combustion, similar to the concept of EGR control technology. The meaning of the passiveness is getting the best burning program and making up for the deterioration of combustion.With sufficient oxygen, fire burns rapidly, the fire duration gets short, the low-temperature ignition and combustion speed up, burn-off character enhances, combustion temperature increases, it's in favor of low-quality fuel combustion and cold-start combustion, power, economy and emissions performance increase, especially for low temperature cold-start, warm-up and some sudden changing working conditions, HC, CO and particulate emissions decrease obviously. However, with the oxygen content increased, the combustion speed up, combustion stability deteriorate, and higher flame temperature will also cause an increase of NOx emissions in cylinder.In contrast, nitrogen as a diluent retardant, oxygen concentration has been reduced by rich nitrogen intake air, combustion temperature decreased, NOx emissions decrease from combustion. At the same intake charge, the increase in specific heat is not conducive to cold-start and engine operating conditions of rapid change. Therefore, based on the above-mentioned air components adjustment, the control of engine combustion and emission has been in the international attention.From basic research point of view, the combustion, power, economy and emission performance of engine have been researched with variable air components, such as two different components (oxygen– nitrogen share, oxygen - carbon dioxide share), three-component (oxygen - nitrogen - carbon dioxide share) and multicomponent (oxygen - nitrogen - carbon dioxide - vapor share). No matter how the multiple components are, the key question is how the combustion and retardant share impact combustion and emissions.With the application of oxygen-enriched air, these phenomena can be improved, such as the engine power decrease, the deterioration of combustion, emissions increase, engine overheating and the deterioration of working stability. Application of nitrogen-enriched air at the engine can replace the exhaust gas recirculation and reduce NOx emissions.In order to get oxygen or nitrogen enriched air for engines, the variable intake component membrane devices are designed, positive pressure and negative pressure experimental system are set up. The separation characteristics of oxygen-enriched air and nitrogen-enriched air, as well as the separation process performance have been researched in this paper. The ideal separation factor, as well as the oxygen permeability coefficient and the impact of intaking air flow to oxygen-enriched air are analyzed theoretically. The experiment shows that the composition density of both streams is in inverse proportion to the flow mass on the adjustment of pressure mode, but in direct proportion as to the NEA stream and both parameters (composition density and flow mass) of the stream of NEA hardly changed on the adjustment of vacuum mode. Furthermore, it is clear that the pressure mode is fit for the operation of NEA stream and the vacuum mode is fit for the OEA stream.GT-POWER software is used, combined with SI turbulence combustion model. Based on the influence on flame speed affected by different oxygen concentration, the influence on combustion characteristics of gasoline engine affected by oxygen concentration under theoretical air-fuel ratio is analyzed. In order to analyze the total effect by the oxygen concentration and different influencing factor, this paper selected four different oxygen concentrations. Further more, the influence on combustion characteristics of gasoline engine affected by different oxygen concentration with the same fuel-injection is analyzed in this paper with oxygen-enriched combustion. General energy utilizing and energy-quality of gasoline engine are analyzed with thermodynamic theory.When the oxygen concentration increases, the combusting lagging period and the 0-50% fuel burn duration decrease, the 50-75% fuel burn duration decrease, the main burn duration increase, the total combustion duration decreases a little, the brake mean effective pressure increase, the time of the maximum pressure and of the maximum rate of pressure rise are earlier than before, the indicate power and torque increase and have the same maximum increase rate of 21%, the indicate efficiency has a maximum increase rate of 2.4% and the specific fuel consumption decrease. When the oxygen concentration increases, the NOx increases rapidly, but the increase rate is shorter and shorter when the oxygen concentration is higher and higher. When the oxygen concentration goes from 21% to 23%, 25% and 27%, the NOx increase rate goes from 36.2% to 50.7% and 56.2%.When the oxygen concentration increases, the power and the torque increase at the same speed. When the intake pressure increases, the power and the torque increase linearly. When the oxygen concentration increases, the power and torque increase at the same intake pressure and the increase rate is higher when the intake pressure is higher. When the load increases, the power, the torque and the brake efficiency increase, the brake specific fuel consumption decreases. When the compression ratio increases, the power, the torque and the brake efficiency increase, the brake specific fuel consumption decreases.The important pocession production density of H2O2 & CH2O of nitrogen-enriched combustion was investigated with gas reaction chemical kinetics software-CHEMKIN combined with n-heptanes detail reaction mechanism.The effects of intake charge temperature,rotate speed and the nitrogen concentration in the air were studied,which to n-heptane combustion.The effect of the nitrogen concentration in the air and rotate speed were studied and the results show:When the intake charge temperature is certain,along with in nitrogen increases contently,the production district of CH2O becomes wide,the peak rises.As nitrogen concentration in the air raises to 82%,after 30/°TDC,the total amount of the CH2O varies little.That says the CH2O doesnot oxidation consume any longer in the high temperature reaction,which is counteract by the nitrogen.As the nitrogen enriches,the timing of the peak of pocession production H2O2 delays.When the nitrogen concentration is kept constant,as the intake charge temperature rises, the timing of the peak of pocession production H2O2 advances,the peak of pocession production H2O2 reduces,the production district of H2O2 becomes narrow. As the procession production,H2O2 oxidation consumes quickly,which is beneficial to the n-heptane combustion.The investigation on the variable intake-air composition (oxygen concentration 21%-27%) in the start of a spark ignition engine aims to study the dynamic characteristics of combustion and emission to understand the feasibility improving the performance of engine. The oxygen-enriched air improves combustion, promotes the stability and reduces CO and HC obviously, and also results in a little higher NOx. Nevertheless the rise of NOx keeps the lower level in the start process. It is recognized that the oxygen enrichment in the start can bring a potential to control combustion and emission Experiment results show that the function of oxygen-enriched intake air is more important in the lower degree of oxygen enrichment, such as 23%~25%. In fact as the oxygen enrichment arrives in a higher level, the weaker the reducing HC and CO emissions. Therefore the lower oxygen enrichment in engine is much more profitable for a comprehensive better HC, CO and NOx emissions. Through detecting the misfire behavior by optical sensor, it is clear that the misfire rate decreases with oxygen-enrichment and it leads to the higher combustion stability in the mild oxygen-enrichment.To sum up, through the intake of oxygen and nitrogen components share modulation and the combustion optimizing, engine power performence and ultra-low emissions can be reached, larger social and economic benefits are availabile. This technical has application potential.
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