Improvement Of Combustion And Emission Of Natural Gas Engine Based On Double Dilution

The energy deficient and global environmental problem has become the focus which the world pays attention. Along with the technological advance and development of society, quantity of automobile which has taken the massive limited oil resources increases year by year. It has enlarged to the atmospheric pollution level simultaneously. Natural gas engines commended considerable respect, because of its well performance of emission,rich in natural resources,high octane. Facing more and more strict request of emissions regulations, how to realize low emissions of engines and economical efficiency, is a question which urgently waits to be solved. The lean combustion technology may raise thermal efficiency of natural gas engines and improve emissions fully, but only depends on the air dilution; it has lean combustion limit, and can not make emissions of NOx to anticipated target.This research proposed the double dilution way that uses the extra air and the exhaust gas recirculation to dilute to the mixture air, and carry on a research into the combustion stability and rapidity of combustion influence through the combustion limit condition, expands lean combustion limit, and improves the NOx emissions. Design the EGR electrically controlled system. Based on the MCS-51 series monolithic integrated circuit, has designed the driving circuit, the AD/DA switching circuit and the display circuit and so on. And it has compiled the application procedure by the assembly language. It has realized to accuracy control of the EGR valve through deal with the opening,the speed and changes, achieved the goal that has adjusted EGR.This research mainly uses the ESC test loop 13 operating modes to carry on the experiment. Experimental study the effect which double dilutions to combustion process and emissions influence on CA6SE1-21N natural gas engine. The findings indicated that: The double dilutions influenced on combustion process of CNG obviously, it may achieve the goal which expands lean combustion limit, improves the NOx emissions, through reasonable optimize the gas circulation coefficient and excess air coefficient.The research conclusion as follows:1. Along with increase of waste gas circulation coefficient, the effective thermal efficiency of engine reduces slightly; the power of engine does not change basically.2. After using the double dilutions, compares with uses the sole air dilution, the highest combustion pressure in the cylinder drop obviously; compares with the air dilution, the crank angle which corresponds to the highest combustion pressure in the cylinder moves ahead obviously. Along with increase of total dilutes rate, the highest average combustion temperature in the cylinder have declining trend. When the engine load is 75%, the biggest decrease range of highest combustion temperature may reach about equally 1100K, drops approximately 45%. When midi-low load, compares with air dilution, the crank angle which corresponds to the highest combustion temperature of double dilution lag to air dilution condition; When high load, the crank angle which corresponds to the highest combustion temperature are basic impartial under two dilution ways .3. Along with increase of circulates waste gas coefficient, center of gravity of the heat release rate moves backward, and tendency to be getting more and more obvious; Along with increase of excess air coefficient, the center of gravity of heat release rate moves ahead. Along with load enlargement, the beginning point of combustion moves ahead; under the identical load, along with increase of circulates waste gas coefficient, the beginning point of combustion moves backward. Along with increase of excess air coefficient, the beginning point of combustion moves ahead.4. No matter what load operating mode, the double dilutions may cause the mass emission of NOxdrop obviously, and it may improve economical efficiency of engine simultaneously. Adopting the double dilution, the mass emission of HC increases slightly. When low load operating mode, the mass emission of HC have serious fluctuation; Regarding to the high load operating mode, along with increase of circulates waste gas coefficient ,the mass emission of HC increases slightly. Along with load increase, the mass emission of HC has declining trend.5. Lean combustion limit is expanded effectively after using the double dilutions. When 25% load operating mode, compared with the air dilution, lean combustion limit of double dilution enhance approximately 13%.6. Compared with the mass emission of NOx and the efficiency in two dilution ways. The double dilution ways can reduce large numbers of the mass emission of NOx when specific gas consumption increases slightly or maintains in the invariable situation basically. For instance, the decrease range of mass emission of NOx may drops approximately above 45%.7. NOx emission can satisfies the nation 4 emissions regulation when using the FAW electrically controlled system and the cruciform combustion chamber; If using the double dilutions simultaneously, NOx emission can satisfies the nation 5 emissions regulation, but specific gas consumption increases slightly.In summary, double dilution's ways may break through existing lean combustion limit, further reduces the NOx emissions, and realizes stable and rapid combustion. Using the double dilutions, not only maintain the well efficiency of engine, but also solves HC, CO through the oxidation processor, makes NOx emission reach the nation 5 emissions regulation standard.