Organic gas emissions from a stoichiometric direct injection spark ignition engine operating on ethanol/gasoline blends

Abstract

The organic gas emissions from a stoichiometric direct injection spark ignition engine operating on ethanol/gasoline blends have been assessed under warmed-up and cold idle conditions. The speciated emissions show that the total organic gas emissions (in ppm C1) decrease with increase in ethanol content. The mole fraction of ethanol in the exhaust is proportional to the volume fraction of ethanol in the fuel: a 10 per cent increase in the latter would yield a 5.5 per cent increase in the former. The ethanol–acetaldehyde ratio (by mol) in the exhaust is 6. These results hold for both the warmed-up and the cold idle conditions, with the exception of E85 at cold idle because of the difficulty in fuel evaporation. The dependence of the organic gas emissions on injection timing may be divided into three regimes. With early injection, the fuel bounce from the piston results in high emissions. With injection in mid-stroke, the emissions are low and not sensitive to the fuel pressure. With injection close to the bottom of the stroke, the interaction of the fuel deposit on the wall and the piston (which comes up shortly) results in higher emissions. The behaviour is similar for all the ethanol/gasoline blends with the exception of E85 under cold idle condition.