高压缩比稀薄燃烧天然气发动机的燃烧与排放特性

Combustion and emission characteristics of lean-burn natural gas engines with a high compression ratio

在稀薄燃烧技术的基础上,提高压缩比可以深入发掘稀薄燃烧天然气发动机的潜能,进一步改善天然气发动机的热效率。为此,在一台进气道喷射天然气发动机上,研究了过量空气系数以及压缩比对发动机燃烧和排放特性的影响。在压缩比分别为10和12的情况下,调整过量空气系数变化范围为1.0～1.4。试验结果表明:随着过量空气系数的增加,最高燃烧压力、最大压力升高率与缸内最高燃烧温度均先升高后下降,气耗率先下降后升高,平均指示压力的循环变动最高不超过8%,CO排放量大幅降低,HC排放量先降低后升高,NOx排放量先略微升高后大幅降低。提高压缩比后,发动机热负荷增加,气耗率降低,平均指示压力的循环变动系数升高,CO排放量降低,HC排放量升高,NOx排放量变化不明显。

Based on the lean-burn technology, to enhance the compression ratio will explore the potential of lean-burn natural gas en gines and further improve their thermal efficiency. In view of this, an experimental study was made on how the combustion and emission characteristics of a port-fuel-injected natural gas engine were affected by excess air ratios （;t） and compression ratios （e）. The experiment condition was that when the compression ratio increased up to 10 and 12 respectively, the excess air ratios ranged from 1.0 to 1.4. The following results are obtained in this experimental study. On one hand, with the increase of the excess air ratio, the maximum cylinder pressure, the maximum rate of pressure rise and the maximum combustion temperature increased at first but then decreased, on the contrary, the gas consumption rate firstly decreased but then increased; the cyclical fluctuation coefficient of mean indication pressure did not exceed 8%, CO emission sharply declined, HC emission decreased firstly but then increased, and NOx emission increased a little hit but then significantly decreased. On the other hand, with the increase of the compression ratio, the heat load of the engine rose, the gas consumption rate decreased, and the cyclical fluctuation coefficient of mean indication pressure increased, the CO emission decreased, the HC emission increased, but the NOx emission changed little.