Experimental Study On Combustion And Emission Conrtol Of Turbocharged Natrural Gas Engine

Due to a new round energy revolution caused by the development of shale gas, natural gas engine have been a hot topic for research. Because of its physical and chemical properties, natural gas engine also has the problems of low thermal efficiency and high NOx emission. Thus, the study of optimization on combustion and emissions of natural gas engine becomes more and more important.In this paper, the experiments were studied on a four-cylinder turbocharged natural gas engine. First of all, the effects of equivalence ratio on combustion and emissions of CNG engine were explored, and reducing the equivalent ratio of CNG engine was conducted to optimize emission and economy performances of CNG engine. Then, EGR technology was adopted to further reduce NOx emission of CNG engine on the basis of lean combustion, and the influences of EGR main components, CO2 and N2, on the performance of natural gas engine were studied. And then, intake manifold multi-point EFI of H2 was conducted to improve the combustion and emission performances of CNG engine with EGR, combined with oxidation after-treatment to optimize emission performance of CNG engine. Thus, the collaborative optimization control strategy was formed by combining lean combustion, EGR, manifold multi-point EFI of H2 and oxidation catalyst.Research on equivalent ratio shows that because of lean combustion, thermal efficiency was improved and NOx emission was greatly reduced, but CO and HC emissions were increased. At the same time, the study found that the particulate emission of CNG engine is releatively lower than the emission standard.Because of the limited effect of lean combustion on NOx emission, EGR was used. The research shows that, a small amount of EGR can reduce NOX emission and maintain thermal efficiency and CO emission unchanged, but HC emission and cyclical variation increased. While a large number of EGR can reduce NOx emission significantly, but thermal efficiency decreased, and HC emission and COV increased.And then, the influences of EGR main components(CO2 and N2) on the performance of natural gas engine were studied, and compared with the influence of the inert diluent gas Ar. The study found that the influence of CO2 is the most obvious, followed by N2, and then Ar. With the decreasing of intake oxygen concentration, all CO2, N2 and Ar can reduce NOX emission greatly with the rise of HC emission, while CO emission decreased firstly and then increased slightly. CO2 and N2 lowered the thermal efficiency significantly, while Ar can reduce NOX emissions at the same time of maintaining thermal efficiency.Further, intake manifold multi-point EFI of H2 was used to improve the problems of combustion stability and HC emission of CNG engine with EGR. The study shows that, intake manifold multi-point EFI of H2 can improve the combustion characteristic of CNG engine with EGR, leading to increase maximum pressure, maximum combustion temperature, maximum rate of pressure rise, peak of heat release rate and thermal efficiency, shorten the ignition delay and combustion duration, and decrease COV and HC emission, but NOx emission increased slightly. And oxidation after-treatment device was used to control CO emission and part of HC emission of non methane.