Speciated hydrocarbon emissions from a gas-fuelled spark-ignition engine with various operating parameters

Abstract

For natural gas and liquefied petroleum gas (LPG), measurements of the concentrations of individual exhaust hydrocarbon (HC) species have been made under various engine operating conditions in a 2 litre four-cylinder engine using gas chromatography. Non-methane hydrocarbon (NMHC) in addition to the species of HC and other emissions such as CO2, CO and NOx were examined for natural gas and LPG at 1800 r/min for two compression ratios (8.6 and 10.6), various brake mean effective pressure (b.m.e.p.) values (250-800 kPa), spark timings (before top dead centre 10°-55°) and exhaust gas recirculation ratios up to 7 per cent. Fuel conversion efficiencies were also investigated together with emissions to study the effect of engine parameters on the combustion performance in gas engines, especially under the lean burn conditions. It was found that CO2 emission decreased with smaller C value of fuel, leaner mixture strength, higher compression ratio, higher b.m.e.p. and the ignition near the maximum brake torque spark timing. HC emissions from the LPG engine consisted primarily of propane (C3 H8) (more than 60 per cent), ethylene and propylene (C3 H6), while the main emissions from natural gas were methane (more than 60 per cent), ethane, ethylene and propane. Natural gas was shown to have less of a tendency to form ozone than LPG. This was accomplished by reducing the emissions of propylene, which has a relatively high maximum incremental reactivity factor, and propane, which forms a large portion of LPG. In addition, natural gas shows a benefit in the other emissions (i.e. NMHC, NOx and CO2), specific reactivity and brake specific reactivity values except fuel conversion efficiency.