Comparative effects of oxygenates-gasoline blended fuels on the exhaust emissions in gasoline-powered vehicles

Abstract

This study aimed to investigate the comparative effects of oxygenates such as ethanol (EA), methyl tertiary-butyl ether (MTBE), and ethyl tertiary butyl ether (ETBE) by fixing the oxygen contents as 0.82 wt% 1.65 wt%, and 2.74 wt% of the fuels on the regulated (CO, NMHC and NOx) and unregulated (formaldehyde, acetaldehyde and BTEX) exhaust emissions in gasoline-powered vehicles. The most widely used type of vehicles (light-duty, medium-duty, heavy-duty) in Korea were tested on a chassis dynamometer under the CVS-75 Cycle. When EA, MTBE and ETBE percentage increased, the CO and NMHC concentration decreased. The NOx emission decreased at 1.65 wt% and 2.74 wt% oxygen content of MTBE and ETBE. The emissions of CO decreased by 0.363 g/km, 0.266 g/km and 0.356 g/km for light-duty vehicle when EA, MTBE and ETBE oxygenates blending ratio increased. Increased EA, MTBE and ETBE oxygenates blending ratio demonstrated no specific reducing effect on CO emissions from low-mileage vehicle, but NMHC emissions decreased by 0.011 g/km (medium-duty), 0.015 g/km (light-duty) and 0.018 g/km (heavy-duty). More CO was emitted from MTBE among three oxygenates at same oxygen content. The emitted concentrations of NMHC from three oxygenates at same oxygen content were almost similar, but reduced NOx emissions from EA (10%) to MTBE (20.4%) and ETBE (23.6%) were observed at 2.74 wt% oxygen content. Reducing effect on CO emissions was order of EA > ETBE > MTBE. Formaldehyde emissions increased up to 54.3% as MTBE ratio increased. When oxygen content of ETBE, EA, and MTBE increased from 0.82 wt% to 2.74 wt%, the acetaldehyde emissions increased up to 177.4%, 39.5% and 31.0%, respectively. There was significant formaldehyde concentration difference between high emission vehicle type (light-duty and medium-duty) and low emission vehicle type (heavy-duty and low-mileage) for three oxygenates. Reduction effect of MTBE and ETBE on BTEX was the order of toluene > benzene > ethylbenzene > xylene, and MTBE showed more reduction effect than ETBE at same oxygen content.