Combustion And Emission Characteristics Of A Direct Injection Spark Ignition Engine With Exhaust Gas Recirculation (EGR) And Alcohols

Gasoline Direct Injection is one of the most potential technologies for powertrain nowadays, but it still faces the problems of poor fuel economy at part loads and serious particle matter emissions. Meanwhile, with the development of fermentation of sugar in biomass, butanol is becoming a promising alternative fuel.An experimental study was conducted on a 1.8 L gasoline direct injection engine to study the influence of control parameters, exhaust gas recirculation(EGR) and alcohols addition(including three butanol isomers, i.e. n-butanol, iso-butanol and sec-butanol) on the combustion and emission characteristics at part loads.The results show that ignition timing, air/fuel ratio and injection timing have significant impact on heat release and combustion temperature. Both ignition timing and air/fuel ratio affect carbon monoxide(CO), total hydrocarbon(THC) and nitrogen oxide(NOx) emissions significantly, but the influence of ignition timing on the particle emission is less remarkable. The emissions of CO and THC increase and NOx emission decreases when the injection timing deviates from 280°CA BTDC. Particulate emissions increase with retard of injection timing. However, the early injection timing at 320°CA BTDC leads to dramatic increase in particle number and particle volume concentration emissions. When injection timing is early than of 320°CA BTDC, the particle number concentration for nucleation mode and accumulation mode increases by 192.8% and 520.7%, respectively, and the total particle volume concentration increase by about 327.1%.At part loads, the benefit in the reduction of fuel consumption varies from 5.75%~8.07% as EGR rate increases from 0% to 20%. Moreover, CO, NOx, accumulation mode particle number concentration and particle volume concentration decrease, while THC and nucleation mode particle number concentration increase with increased EGR rate. Higher EGR rate leads to longer flame developing and rapid burning duration. However, the rapid burning period decreases with the addition of alcohol fuels. The shorter rapid burning period yields greater combustion efficiency, which can offset the disadvantage caused by EGR in some extent. In addition, CO, THC and particle emissions decrease with the addition of alcohol fuels.No remarkable differences in the combustion characteristics and engine performance were observed when the three butanol isomers including n-butanol, iso-butanol and sec-butanol were employed, except that the variations of unburned hydrocarbons and particulate emissions. n-Butanol is more promising as an alternative alcohol fuel due to its lower overall emissions.