Effect of methyl tertiary butyl ether (MTBE) as a gasoline additive on engine performance and exhaust emissions

The effect of blending unleaded gasoline with different proportions of methyl-t-butyl ether MTBE (10, 15 and 20 vol % ) on engine performance was studied using a fixed compression ratio SI engine (Opel 4 - cylinder ). The exhaust gases were analyzed for carbon monoxide, carbon dioxide and the hydrocarbons emitted. The results have shown that MTBE blends gave slightly better engine performance than the unleaded gasoline as evidenced by the power output. Analysis of exhaust gases shows better carbon monoxide and hydrocarbon emissions for all MTBE blends tested than unleaded gasoline. A higher carbon dioxide exhaust emission of the blends than the unleaded gasoline also confirms their better combustion. The 20 vol % MTBE blend gave the lowest carbon monoxide and hydrocarbon emissions of all blends used. A comparison was also made between a commercial leaded gasoline sample and the 20 vol % MTBE blend using the same engine and under the same test conditions. Engine performance was similar for both the MTBE blends and the leaded gasoline. However, hydrocarbons and CO emissions were lower for the MTBE blend. A carbon monoxide and hydrocarbon emission reductions in the order of 13 – 43% and 10 – 30% respectively over the entire speed range are estimated; when the 20% MTBE blend is used compared to leaded gasoline.