Effects Of Oxygenates On EFI Gasoline Engine Performance And Emission Characteristics

Methyl tertiary butyl ether (MTBE), widely used as oxygenate to unleaded gasoline, can increase the octane number and oxygen content of gasoline, and hence reduce exhaust pollutants of gasoline engine. However, due to the side-effect to environment and human health, MTBE will be banned in United States and replaced by other less harmful oxygenates. So, it is necessary to find the substitute of MTBE. Ethanol anhydrous (EA) and dimethyl carbonate (DMC) have good performance as oxygenate to gasoline. Therefore, in order to choose the new generation of oxygenate and spread their future application on gasoline engine, it is very valuable to scientifically evaluate the effects of these three kinds of oxygenates on gasoline engine.In this thesis, the investigation was operated on a HL495IQ EFI engine to research the effects of three kinds of oxygenates on the engine performance and emission characteristic. The standard 90# unleaded gasoline was used as a reference and base fuel for the preparation of oxygenates/gasoline blends. MTBE was blended with base gasoline fuel in four ratios (5, 10, 15, and 20 vol%).Then, EA/gasoline blends and DMC/gasoline blends were concocted according to the oxygen content of MTBE/gasoline blends, respectively (namely E5, E10, E15, E20, D5, D10, D15 and D20).The experimental results show that without any adjustment, the output power of gasoline engine is reduced using oxygenated fuel compared with using 90# unleaded gasoline. There is no significant change on the brake specific fuel consumption (BSFC) among E5, M5, D5 and base gasoline, but the BSFC increases with more additives in the base fuel. On the whole, the engine operated with DMC/gasoline blends has the worst power performance. CO, THC, and NOx emissions of EFI engine were measured. The experimental results indicate that generally THC and NOx emissions decrease, but there are no obvious effects on the CO emission for all blended fuels. Three-way catalysts are so effective to reduce CO and THC emissions that the catalytic conversion rate are over 90%, while the NOx conversion efficiency is lower than that of CO and THC.The gas chromatography was used to determine the contents of unregulated emissions, such as formaldehyde, acetaldehyde, and benzene, and so on. First, the optimal separating condition of these unregulated emissions in the FFAP and HP-5 capillary column was attained. Then, the method was proved on the EFI engine and confirmed its feasibility. The experiment indicates that oxygenated fuels can reduce benzene emissions, which is more obvious when EA/gasoline and MTBE/gasoline blends are used. The benzene emissions are decreased by 40% and 50% with E20 and M20 respectively. Further, EA/gasoline blends can reduce formaldehyde emission, but the opposite trend was found for MTBE/gasoline and DMC/gasoline blends. As for oxygenated fuels, the acetaldehyde emission increases continuously with more additives in gasoline fuel. Moreover, some unburned EA, MTBE and DMC emissions in the exhaust gas can be detected. Three-way catalysts are effective to reduce benzene, formaldehyde and DMC emissions, the catalytic conversion rate of benzene reach about 70%,and the formaldehyde and DMC after catalytic converter can not be detected. The catalytic conversion efficiency to acetaldehyde, ethanol and MTBE are lower.