Exhaust Emission and Energy Consumption Effects from Hydrogen Supplementation of Natural Gas

Abstract

An experiment was conducted to evaluate the efficiency and emissions of an engine fueled with a mixture of natural gas and approximately 15% hydrogen by volume. This mixture, called Hythane{trademark}, was compared with natural gas fuel using engine efficiency and engine-out emissions at various engine operating conditions as the basis of comparison. It was found that at low engine loads, using the same spark timing, engine efficiency increased under Hythane fueling but at higher engine loads, natural gas and Hythane had the same efficiency. At low engine speed and load conditions with the same spark timing, engine-out total hydrocarbon (THC) emissions were lower for Hythane fueling. When compared on a carbon specific basis, however, natural gas hydrocarbon emissions were lower. At some test conditions, engine-out emissions were lower under Hythane. Engine-out oxides of nitrogen were higher under Hythane fueling for all test conditions when compared with natural gas at the same spark timing. Advancing spark timing (ST) from 20 degrees before top dead center to 28 degrees before top dead center increases engine efficiency slightly for both fuels. Engine-out NO{sub x} increased with advanced spark timing at a greater rate under Hythane fueling. An increase in THC emissions also occurredmore » as spark timing was advanced with a similar rate of increase for both fuels. Finally, CO emissions were almost completely independent of changes in spark timing. Hydrocarbon speciation resulted in an exhaust gas hydrocarbon breakdown of 92% methane, 3% ethane, 3% ethylene, 1.5% acetylene and trace quantities of other species. This result was consistent regardless of fuel type, engine speed or engine load.« less