气口喷射预混合燃料对生物柴油发动机排放特性的影响

Improved Emission Characteristics of Biodiesel Fuelled Engines by Port Injection of Various Premixed Fuels

在单缸发动机上研究了气口喷射正庚烷、二甲氧基甲烷(DMM)和乙醇的生物柴油发动机的排放特性.结果表明:气口喷射正庚烷时整个燃烧过程呈现明显的三阶段放热,预混合其他两种燃料时仅仅为单阶段放热;采用预混合燃烧可以同时降低NOx和烟度排放,但是预混合乙醇可以得到最大的降低效果;在预混合燃料当量比一定的条件下,随着总当量比增加预喷正庚烷时NOx增长速率最大,预喷DMM时烟度增长最快,预喷乙醇时HC排放显著高于其他两种预混合燃烧且受负荷影响不大;在总当量比一定下,随着预混合比例增加,HC和CO排放逐渐增加,NOx排放逐渐降低,达到某一临界比例后,CO排放开始降低,NOx排放开始增加,而HC排放基本上不变;烟度总是随着预混合比例增加而降低.

This paper investigated the emission characteristics of biodiesel engine with the premixing of nheptane, dimethoxymethane （DMM）, and ethanol from intake port on a single cylinder diesel engine. The experimental results reveal that the overall heat release curve exhibits three-stage combustion with the addition of n-heptane, but it shows only one stage heat release with other two premixed fuels. A simultaneous reduction of NOx and smoke opacity can be obtained with the premixed fuel, but ethanol premixing shows the most significant effects in the reduction of NOx and smoke opacity, compared to other kinds of premixed fuels. For a fixed partial equivalence ratio of premixed fuel, premixing n-heptane shows the larger NOx increase slope, premixing DMM shows the larger smoke opacity increase slope as the increase of the partial equivalence ratio of biodiesel. While the HC emission is mainly influenced by the premixed fuel properties but not the equivalence ratio, ethanol premixing gives the largest HC levels other than n-heptane and DMM premixed fuels. When keeping the overall equivalence ratio at constant, both of HC and CO emissions ascertain but NOx emissions decrease at first up to a critical oremixed ratio. As the premixed ratio exceeds the critical value, NOx emissions start to increase gradually, CO emissions begin to decrease, but HC emissions almost maintain the same levels. Under the above conditions, smoke opacity always improves with the increase of premixed ratio.