Abstract Spark-assisted compression ignition (SACI) has a promising potential to substantially improve engine's fuel efficiency. To this end, two exothermic stages in SACI combustion, flame propagation and auto-ignition, need to be well organized to increase control authority of bulk ignition timing especially in lean burn. In this study, three gasoline surrogates, namely EPRF, ETPRF and TPRF, formulated through blending ethanol/toluene with primary reference fuel (PRF) and having the same research octane number (RON) and octane sensitivity (S), were used to conduct experiments in a rapid compression machine (RCM) under lean engine-relevant conditions (10–30 bar and 722–862 K). Under different ethanol blending ratios, both ethanol's synergistic effect during auto-ignition and its stronger pressure dependence of flame speed (SFlame) than toluene were observed. The ethanol's synergistic effect is mainly attributed to its more HO2 production and then faster consumption by benzyl which results in more OH radical production. As for the stronger pressure dependence of SFlame of ethanol, at 722 K, it is primarily determined by the stronger pressure dependence of H radical in EPRF's flame structure rather than the promotion effect from critical reactions on SFlame; while at 862 K, these two factors influence the pressure dependence of SFlame simultaneously. Whatever the temperature is, third-body reactions have larger impacts on ethanol's SFlame than on toluene's. In this study, the relative magnitude of SFlame’s pressure dependence between ethanol and toluene shows rationality at lower φ and higher T, which is in line with the pressure exponents extracted from the existing high-p laminar burning velocities of ethanol and toluene. Further verification was made in a spark-ignition engine, which showed that low-carbon alcohols, exhibited stronger pressure dependence of SFlame than monophenyl aromatics in commercial gasoline, represented by toluene. The aforementioned characteristics of ethanol can be utilized under different engine loads and provide a reference in fuel design for lean SACI combustion.

中文翻译：

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乙醇和甲苯对自燃的协同效应和汽油替代品火焰速度的压力依赖性研究

摘要 火花辅助压缩点火（SACI）技术在大幅提高发动机燃油效率方面具有广阔的应用前景。为此，需要很好地组织 SACI 燃烧中的两个放热阶段，火焰传播和自燃，以增加对整体点火正时尤其是稀薄燃烧的控制权限。在本研究中，三种汽油替代品，即 EPRF、ETPRF 和 TPRF，通过乙醇/甲苯与主要参考燃料 (PRF) 混合配制而成，并具有相同的研究辛烷值 (RON) 和辛烷灵敏度 (S)，用于进行实验在稀薄发动机相关条件（10-30 bar 和 722-862 K）下的快速压缩机 (RCM) 中。在不同的乙醇混合比例下，乙醇' 观察到自燃过程中的协同效应及其对火焰速度 (SFlame) 的更强压力依赖性比甲苯。乙醇的协同效应主要归因于其产生更多的 HO2，然后苄基消耗更快，从而导致更多的 OH 自由基产生。至于乙醇的SFlame压力依赖性较强，在722K，主要是EPRF火焰结构中H自由基对压力依赖性较强，而不是临界反应对SFlame的促进作用；而在 862 K 时，这两个因素同时影响 SFlame 的压力依赖性。无论温度如何，第三体反应对乙醇 SFlame 的影响大于对甲苯的影响。在这项研究中，SFlame 对乙醇和甲苯的压力依赖性的相对大小在较低的 φ 和较高的 T 下显示出合理性，这与从现有的乙醇和甲苯的高压层流燃烧速度中提取的压力指数一致。在火花点火发动机中进行了进一步验证，结果表明，与以甲苯为代表的商业汽油中的单苯基芳烃相比，低碳醇表现出更强的 SFlame 压力依赖性。乙醇的上述特性可以在不同的发动机负荷下得到利用，为稀SACI燃烧的燃料设计提供参考。这表明低碳醇类比以甲苯为代表的商用汽油中的单苯基芳烃表现出更强的 SFlame 压力依赖性。乙醇的上述特性可以在不同的发动机负荷下得到利用，为稀SACI燃烧的燃料设计提供参考。这表明低碳醇类比以甲苯为代表的商用汽油中的单苯基芳烃表现出更强的 SFlame 压力依赖性。乙醇的上述特性可以在不同的发动机负荷下得到利用，为稀SACI燃烧的燃料设计提供参考。