The influence of ethanol content in gasoline on speciated emissions from a direct injection stratified charge (DISC) SI engine is assessed. The engine tested is a commercial DISC one that has a wall guided combustion system. The emissions were analyzed using both Fourier transform infrared (FTIR) spectroscopy and conventional emission measurement equipment.
Seven fuels were compared in the study. The first range of fuels was of alkylate type, designed to have 0, 5, 10 and 15 % ethanol in gasoline without changing the evaporation curve. European emissions certification fuel was tested, with and without 5 % ethanol, and finally a specially blended high volatility gasoline was also tested. The measurements were conducted at part-load, where the combustion is in stratified mode. The engine used a series engine control unit (ECU) that regulated the fuel injection, ignition and exhaust gas recirculation (EGR).
A low concentration of ethanol in a commercial gasoline does not alter significantly the operational characteristics of the DISC engine tested. The engine-out hydrocarbon (HC) emissions are practically unchanged, while the carbon monoxide (CO) emissions decrease when 5 % ethanol is added. The tailpipe HC, CO and nitrogen oxides (NOx) emissions are virtually unchanged for the fuel with 5 % ethanol. However, for the alkylate fuels there was a tendency towards increased engine-out and tailpipe HC emissions with increased ethanol content. Aldehyde emissions, which could be measured only for the alkylate fuels, increased slightly when ethanol was added. Stratified charge aldehyde emissions were 2 - 3 times higher than for homogeneous charge operation.