Emission characteristics of direct injection natural gas engine using rapid compression machine

Investigation of emission characteristics of a direct injection natural gas engine is carried out using a rapid compression machine. The emissions of three injection modes are measured and compared with that of the homogeneous combustion mode. The experimental results show that the combustion efficiency of the direct injection natural gas combustion is above 0.95 for all fuel supplying modes in the wide range of overall equivalence ratio. Fuel injection can operate within a wide range of equivalence ratio and has low unburned hydrocarbon emission (HC), low CO₂ emission for the same power output, low NO_x emission due to the mixture stratification compared with homogeneous combustion engine, especially in the range near the stoichiometric equivalence ratio where engine power output is needed. Consequently, the direct injection natural gas engine has the advantages of high thermal efficiency like diesel engine and low emission of premixed mixture combustion.