Optimization of ethanol injected ratio of a stoichiometric spark-ignited ethanol port-injected plus gasoline direct-injected engine at various throttle openings

Ethanol can effectively reduce particulate emissions of engine owing to the high octane value and oxygen level. The impacts of ratio of ethanol port-injected (REPI) on combustion and emissions of a stoichiometric spark-ignited ethanol port-injected (EPI) plus gasoline direct-injected (GDI) engine at various throttle openings (TO) were investigated by experiment. Results show that the best combustion performances can be obtain at REPI = 35 % and 30 % for TO = 7 % and 10 %, separately. The COVimep (coefficient of variation of indicated mean effective pressure) can be limited within 1.3 % in all operating condition. The REPI had a little impact on COVimep under various TOs. At TO = 7 %, CO and HC emissions decreased with the increase of REPI. At TO = 10 %, CO and HC emissions achieved the lowest at REPI = 40 % and 30 % separately. NOX formation depended on the oxygen concentration and charge cooling effect. NOX emissions achieved the lowest at REPI = 30 % and 35 % for TO = 7 % and 10 % separately. At REPI<30 %, NOX TO = 10 %≫NOX TO = 7 %; at REPI>35 %, NOX TO = 10 %>NOX TO = 7 %. The soot emission decreased with increasing REPI; at a constant REPI, sootTO = 10 %>sootTO = 7 %. By compromising combustion and emissions performances, when TO was 7 % and 10 %, the ideal REPI was 35 % and 30 %, separately. Increasing TO would decrease the ideal REPI.