Comparative effects of MTBE and ethanol additions into gasoline on exhaust emissions

The effects of the additives of ethanol (EA) and methyl tert-butyl ether (MTBE) in various blend ratios into the gasoline fuel on the exhaust emissions and the catalytic conversion efficiencies were investigated in an EFI gasoline engine. The regulated exhaust emissions (CO, THC and NOX) and the unregulated exhaust emissions (benzene, formaldehyde, acetaldehyde, unburned EA and MTBE) before and after the three-way catalytic converter were measured. The experimental results showed that EA brought about generally lower regulated engine-out emissions than MTBE did. But, the comparison of the unregulated engine-out emissions between both additives was different. Concretely, the effect of EA on benzene emission was worse than that of MTBE on the whole, which was a contrast with formaldehyde emission. The difference in the acetaldehyde comparison depended much on the engine operating conditions, especially the engine speed. Both EA and MTBE were identified in the engine exhaust gases only when they were added to the fuel, and their volume fraction increased with blend ratios. The catalytic conversion efficiencies of the regulated emissions for the EA blends were in general lower than those for MTBE blends, especially at the low and high engine speeds. There was little difference in the catalytic conversion efficiencies for both benzene and formaldehyde, while distinct difference for acetaldehyde.