不同压缩比下稀释方式对直喷汽油机节油影响

Effects of different dilution methods on Fuel Consumption for Gasoline Direct Injection Engine under Different Compression Ratio

摘要:

基于一台1.0 L涡轮增压发动机，在9.6及12的压缩比下，研究了化学当量比、稀薄燃烧（稀燃）及低压废气再循环（EGR）工况下的燃烧与油耗特性.结果表明：EGR在压缩比12、大负荷工况下，节油效果优于稀燃，其余工况下稀燃的节油效果均更好.通过改变压缩比并结合稀燃或EGR，小、中、大负荷下燃油消耗率（BSFC）相比于压缩比9.6化学当量比工况降低最多为7.5%、10.4%和9.3%.结合一维仿真，分析并对比了大负荷下稀燃与EGR的节油原因及其差异.结果表明：在压缩比12、大负荷、过量空气系数（λ）小于1.4的情况下稀燃不能抑制爆震，节油效果不明显；相同工况下EGR可以有效抑制爆震，降低燃油消耗率达5.5%；大负荷下稀燃和EGR的节油来源主要为传热损失和排气损失减少，二者对节油的贡献程度之和大于90%.

关键词:汽油机; 压缩比; 稀燃; 废气再循环; 节油机理

Abstract:

Based on a 1.0 L turbocharged engine, stoichiometric, lean burn and exhaust gas recirculation (EGR) conditions were tested under the compression ratios (CR) of 9.6 and 12 to study their combustion and fuel consumption characteristics. The results show that the fuelsaving effect of EGR is better than that of lean combustion under heavy loads with higher compression ratio, and the fuelsaving effect of lean combustion is better under other conditions. By changing CR together with lean burn or EGR, brake specific fuel consumption (BSFC) can be reduced by at most 7.5%, 10.4% and 9.3% comparing with CR9.6 stoichiometric conditions under light, medium and heavy loads respectively. Combined with onedimensional simulation, the reasons and different characteristics of fuel saving under lean burn and EGR conditions under heavy loads are analyzed and compared. The results show that lean burn under high compression ratio and heavy load when excess air ratio (λ)<1.4 cannot suppress knocking, and the fuel saving effect is not obvious; under the same working condition EGR can effectively suppress knocking and reduce fuel consumption up to 5.5%. The fuelsaving of lean burn and EGR under heavy loads are mainly due to the reduction of heat transfer loss and exhaust loss. The sum of their contribution to fuel economy is higher than 90%.

Key words:gasoline engine; compression ratio; lean burn; exhaust gas recirculation; fuel saving mechanism