掺混比例和喷射定时对二甲醚-乙醇发动机燃烧和排放的影响

Effects of mixing ratio and injection timing on combustion and emissions of DME-ethanol engine

在一台电控共轨发动机上,试验研究了乙醇掺混比例和喷射定时对二甲醚-乙醇混合燃料燃烧及排放的影响。结果表明:随乙醇比例的增加,滞燃期延长,燃烧持续期缩短,最大压力升高率上升。随喷射推迟,滞燃期延长,燃烧相位延后,燃烧持续期在纯二甲醚时延长,而在掺混乙醇时则先延长后缩短,最大压力升高率先下降后上升。掺混乙醇和推迟喷射使预混燃烧比例增加。随喷射推迟,混合燃料的排气温度升高,喷射推迟到上止点后,排气温度随乙醇比例的增加而升高,排气温度高,则废气能量高,增压器增压比大,进气流量大,导致缸内压缩压力升高。在上止点前喷射时,掺混乙醇能使HC和CO排放保持在较低范围的同时,一定程度降低NO_x排放,掺混15%的乙醇较纯二甲醚最大降低约11%NO_x排放。随推迟喷射,NO_x排放降低,最大降幅达52%,在过分推迟燃料喷射时,因热效率低,循环喷射量增加,含15%乙醇混合燃料的NO_x排放会高于纯二甲醚。HC和CO排放随喷射推迟而升高,且升高幅度增大。

Effects of ethanol nixing ratio and injection timing on the combustion and emission characteristics of DME （dimethyl ether）-ethanol blend were experimentally investigated on an electronically controlled common rail engine. The results show that increasing ethanol proportion leads to ignition delay extending, combustion duration shortening, and maximum pressure rise rate increasing. With the delay of injection, ignition delay increases and the combustion phase is delayed. The duration of the combustion is prolonged when the pure DME is extended but first extends and then shortens for mixed fuel, along with the maximum pressure rising rate first decreasing and then increasing. Mixing ethanol and retarding injection timing increase the proportion of premixed combustion. With injection timing retarding, exhaust temperature of blended fuel increases. When injection timing beyond top dead center, exhaust temperature increases with ethanol proportion increasing. High exhaust temperature with enormous energy contributes to large pressure ratio of the turbocharger and large intake flow rate, which leads to in-cylinder compression pressure increasing. With injection timingprior to top dead center, mixing ethanol keeps HC and CO emissions at a low level while reducing NOx emissions to a certain extent. NOx emissions are reduced by 11% with 15% ethanol mixing ratio. By retarding fuel injection, NOx emissions decrease up to 52%. However, with fuel injection excessively retarded, NOx emissions of 15 % ethanol blended fuel are higher than those of pure DME due to lower thermal efficiency and higher cyclic injection quantity. HC and CO emissions increase first slowly and then rapidly with the injection timing retarding.