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.

High Ethylene and Propylene in an Area Dominated by Oil Production

“…At an oxygen/fuel ratio 1.1 times the stoichiometric value ("rich-burn" conditions), the ethylene:acetylene ratio was only 4.8, while at 1.55 times the stoichiometric value ("lean-burn" conditions), the ratio was 12.94. Kim and Bae [72] found a similar trend for both the ethylene:acetylene Ethylene and propylene in this study were correlated with acetylene (Spearman r of 0.64 and 0.48, respectively), and the average ethylene:acetylene and propylene:acetylene ratios for measurements in this study were 6.05 (3.53, 11.45) and 10.64 (3.95, 37.94). Median ethylene:acetylene and propylene:acetylene ratios were 1.33 and 0.85, respectively.…”

“…Hesterberg, et al [70] showed that, compared to uncontrolled diesel-fueled engines, uncontrolled natural gas-fueled engines have higher propylene:ethylene ratios (0.07 versus 0.28). The propylene:ethylene ratio in our measurements, however, was more than three times higher than that reported for natural gas engines by Hesterberg et al Ethylene and propylene can be generated from the combustion of methane or from combustion of NMHC [71], and Kim and Bae [72] showed that propylene emissions (but not ethylene emissions) increased with the NMHC content of fuel (also see Drobot, et al [73]). The raw gas available at Uinta Basin oil wells is richer in propane and other NMHC [26] than the purified natural gas used by Hesterberg et al, possibly explaining the difference between the two studies.…”

“…At an oxygen/fuel ratio 1.1 times the stoichiometric value ("rich-burn" conditions), the ethylene:acetylene ratio was only 4.8, while at 1.55 times the stoichiometric value ("lean-burn" conditions), the ratio was 12.94. Kim and Bae [72] found a similar trend for both the ethylene:acetylene ratio and the propylene:acetylene ratio. Russ, et al [79] also showed that the ethylene:acetylene ratio increases with decreasing engine temperature (which is associated with lean-burn conditions).…”

“…NO x emissions from engines reach a maximum, and total hydrocarbon emissions (as well as the reactivity of hydrocarbon emissions) reach a minimum, at stoichiometric or near-stoichiometric oxygen:fuel ratios (i.e., rich-burn conditions). The converse is true at higher (i.e., lean-burn) oxygen:fuel ratios because of cooler temperatures and incomplete combustion [72,74,79,81]. Whether engines should be operated to minimize NO x emissions or to minimize organics emissions will depend on the chemical properties of the airshed those engines inhabit.…”

An experimental study of combustion and emissions in a spark-ignition engine fueled with coal-bed gas

“…In contrast, a lower concentration of methane in the coal-bed gas is equivalent to a higher EGR rate and results in a reduction of NOx emissions. For all the cases, the emissions are very low, compared with gasoline engines and natural gas engine [13][14][15][16][17].…”