Experimental comparative study on combustion, performance and emissions characteristics of methanol, ethanol and butanol in a spark ignition engine

The comparative analysis on combustion, performance and emissions characteristics of a PFI SI engine fueled with methanol, ethanol and butanol-gasoline blends under various alcohol ratio, equivalence ratio and engine load was carried out. The combustion phasing was advanced after adding alcohols due to the higher burning velocity, which also resulted in BTE decreasing as the engine was running at gasoline’s MBT. Therefore, the sparking timing should be postponed when fueled with alcohols-gasoline blends. The butanol-gasoline blends showed the lower BSFC for its higher LHV. There was no uniform CO emission trend after adding alcohols based on the competing between the increased oxygen content, reduced combustion temperature and combustion duration, compared to gasoline. However, UHC emission was increased for methanol-gasoline blends as a more injected fuel and a sequent more fuel getting into the crevice volumes or absorbed in oil layers and deposited, while decreased for ethanol and butanol-gasoline blends due to the fuel-borne oxygen improving combustion quality. Meanwhile, based on the reduced combustion temperature resulting from more products generated in terms of heat capacity of combustion products for the alcohols, alcohols-gasoline blends presented the lower NOx emission. Ethanol and methanol-gasoline blends produced the lowest UHC and NOx emissions respectively.