Abstract
Analyses were made of exhaust emission characteristics using four types of natural-gas fuels, which were selected in consideration of the variation in fuel compositions on the market. The results showed that engine-out emissions of NOx and CO2 decreased with an increasing content of methane in the test fuels, whereas the total hydrocarbon (THC) level tended to increase. Engine-out THC emissions contained small quantities of ethylene, acetylene and other species not present in the fuels. The concentrations of methane and other HC species measured in engine-out THC emissions correlated closely with the respective content of these species in the test fuels.