Experimental And Simulation Research On The Light-off Performance Of Methane For TWC Of CNG Engine

With the increasingly prominent problems of the energy crisis and environment pollution in China,the energy saving and emission reduction need to be considered when Chinese government makes policy decisions.And the development of the internal combustion engine industry is also inseparable from the major theme of energy saving and emission reduction.And the use of natural gas as engine fuel is an effective method to change our country's energy structure and reduce exhaust emissions.As the future Chinese sixth emission standard has more stringent requirements for gas engine,the emissions of gas engines under cold-start and hot-start conditions are comprehensively evaluated under the WHTC?World Harmonized Transient Cycle?with more stringent methane emission limitation.To meet the requirements of emission regulation,TWC?Three Way Catalyst?is one of the most efficient equipment.Unlike the hydrocarbon emissions of gasoline engine,the main component of hydrocarbon emissions of CNG?Compressed Natural Gas?engine is methane,and methane is difficult to be oxidized.Therefore,the improvement of methane light-off performance of TWC is necessary to reduce the CH₄ emissions at real operation conditions.In this paper,a model based on the sample test data was built to accurately simulate the light-off process of the TWC.The simulation results were achieved from the analysis of the physical parameters and the parameters of A/F ratio fluctuation.And two character parameters were summarized considering the method of alternative use of aftertreatments.The differences light-off performance of methane of the TWC under different physical parameters were compared and analyzed.In the case of a single variable,the results show that high space velocity would postpone light-off and complete conversion process of methane,but this impact is limited when the space velocity is high enough.The positive effect of the OFA?Open Frontal Area?of substrate on the light-off performance of methane is relatively obvious when the OFA is increased to a certain extent.The larger the cell density of the substrate,the earlier reaching the light-off and complete conversion state,but this influence becomes relatively limited when the cell density is increased to a certain extent.The effect of the thickness of the substrate on the light-off performance of methane is relatively limited.In the light-off process of methane,the TWC with thinner thickness of the substrate would have a relatively similar efficiency under different space velocity.In addition,the effect of A/F ratio fluctuation and the OSC?Oxygen Storage Capacity?of the TWC on the light-off performance of methane were analyzed.In a certain A/F ratio fluctuation range,the results show that increasing of the amplitude of A/F ratio fluctuation would reduce the light-off temperature(T₅₀)and complete conversion temperature(T₉₀)of methane.The longer duty cycle of rich gas composition would cause a smaller T₅₀0 and T₉₀.The fluctuation center under relatively rich gas composition would promote the light-off character of methane.The stronger the OSC,the less the effect of A/F ratio fluctuation.The rich gas composition would contribute to the light-off character of methane of the special TWC.And the OSC and the outlet temperature of TWC are concluded as character parameters of the methane light-off performance of TWC.