The influence of alcohol additives and EGR on the combustion and emission characteristics of diesel engine under high-load condition

Alcohol additive combined with exhaust gas recirculated (EGR) were experimentally investigated on a modified single cylinder diesel engine at high-load condition. The effects of different alcohol contents (15% ethanol, 15% butanol and 40% butanol by volume) and EGR rates on combustion characteristics and particle emissions were evaluated. The results indicate that the premixed combustion phase is deeply influenced by alcohol content and EGR rate. With the increased alcohol contents and EGR rates, the peak rate of heat release in the premixed combustion phase increases and the lower gas temperature at the end of the compression stroke causes later ignition. Moreover, indicated thermal efficiency (ITE) increases with an increase of alcohol content but it decreases with increased EGR rates. In terms of emissions, the particle number concentrations show a unimodal distribution with particle size. The peaks of particle number concentration increase rapidly and the distributions shift toward larger particle size with increased EGR rates. With the increased fuel-bound oxygen contents in the blended fuels, moreover, the total particle number concentration (TPNC) decreases. In summary, adopting higher alcohol content of diesel fuels combined with medium EGR may be a better choice for the internal purification of diesel engines at high-load condition.