Study On The Conversion Efficiency Evaluation Of Catalytic Converters And Combustion And Emission Characteristics Of A Nature Gas Engine At Low Loads

The development of high efficient catalytic converters for nature gas engines and their optimal match to nature gas engines are an important solution to reduce emissions from motor vehicles. Since the combustion and emission characteristics of a nature gas engine has a direct influence on the efficiency of a exhaust-gas aftertreatment, it is worthing investigating the conversion efficiency of catalytic converters and the combustion and emission characteristics of nature gas engine at low loads.A multi-cylinder sequential injection natural gas engine was retrofitted from a gasoline engine by modifying its gas supply system and developing an electronic control unit. A data acquisition system for throttle opening positions and the vacuum in the intake manifold was also established for the test platform.After the developed catalytic converters were evaluated, the combustion and emission characteristics of a nature gas engine at low loads were investigated to solve the low catalytic converter conversion efficiency in these operating conditions.The results show that when lambda increases, combustion duration lengthens and the coefficient of variation of indicated meant effective pressure (COVimep) increases at low operating conditions. The influence of ignition timings and injection timings on the combustion and emission characteristics of the nature gas engine was different when the lambda was changed. When lambda was less than 1.0, earlier injection timings increase the COVimep, lengthen combustion duration, increase CO and THC emissions; However, when the lambda is more than 1.0, late injection timing cause reduced COVimep, shortened combustion duration, and decreased CO and THC emissions. Matching a catalytic converter to a nature gas engine by adjusting the ignition timing and injection timing can be one way to reduce the emissions from a nature gas engine.