Effects of Pre-spark Heat Release of Ethanol-Blended Gasoline Surrogate Fuels on Engine Combustion Behavior

IF 16.4 1区化学 Q1 CHEMISTRY, MULTIDISCIPLINARY

Accounts of Chemical Research Pub Date : 2023-05-02 DOI:10.4271/04-17-01-0003

K. Yoshimura, K. Isobe, Mitsutaka Kawashima, Kyohei Yamaguchi, R. Sok, S. Tokuhara, Jin Kusaka

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Abstract

Regulations limiting greenhouse gas (GHG) emissions in the transport sector have become more restrictive in recent years, drawing interest to synthetic fuels such as e-fuels and biofuels that could “decarbonize” existing vehicles. This study focuses on the potential to increase the thermal efficiency of spark-ignition (SI) engines using ethanol as a renewable fuel, which requires a deep understanding of the effects of ethanol on combustion behavior with high compression ratios (CRs). An important phenomenon in this condition is pre-spark heat release (PSHR), which occurs in engines with high CRs in boosted conditions and changes the fuel reactivity, leading to changes in the burning velocity. Fuel blends containing ethanol display high octane sensitivity (OS) and limited low-temperature heat release (LTHR). Consequently, their burning velocities with PSHR may differ from that of gasoline. This study therefore aimed to clarify the effects of ethanol on SI combustion behavior under PSHR conditions. Combustion behavior was studied by performing single-cylinder engine experiments and chemical kinetics simulations. The experimental measurements were performed to characterize the relationship between the occurrence of PSHR and the main combustion duration. Analysis of this relationship showed that the ethanol-blended fuel has a lesser PSHR and a longer combustion duration than the non-ethanol fuel by approximately 5% in high engine load conditions. Simulations using input data from the experiments revealed that the ethanol-blended fuel has a lower laminar burning velocity due to the lower temperature in the unburned mixture caused by its PSHR. Additional simulations examining the chemical effect of partially oxidized reactants caused by PSHR on the laminar burning velocity showed that partially oxidized reactants increase the laminar burning velocity of the ethanol-blended fuel but decrease that of a reference fuel without ethanol. A large number of fuel radicals and oxides of the ethanol-blended fuel enhances chain-branching reactions in the pre-flame zone and possibly increases its laminar burning velocity. However, the thermodynamic effect of PSHR on laminar burning velocity exceeds the chemical effect, and thus the ethanol-blended fuel has a lower turbulent burning velocity in the PSHR conditions.

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乙醇混合汽油替代燃料火花前放热对发动机燃烧性能的影响

近年来，限制交通运输部门温室气体(GHG)排放的法规变得更加严格，这引起了人们对电子燃料和生物燃料等合成燃料的兴趣，这些燃料可以使现有车辆“脱碳”。本研究的重点是提高使用乙醇作为可再生燃料的火花点火(SI)发动机热效率的潜力，这需要深入了解乙醇对高压缩比(CRs)燃烧行为的影响。在这种情况下，一个重要的现象是火花前热释放(PSHR)，它发生在增压条件下的高CRs发动机中，改变了燃料的反应性，导致燃烧速度的变化。混合燃料含有乙醇显示高辛烷值敏感性(OS)和有限的低温热释放(LTHR)。因此，它们在PSHR中的燃烧速度可能与汽油的燃烧速度不同。因此，本研究旨在阐明乙醇在PSHR条件下对SI燃烧行为的影响。通过单缸发动机实验和化学动力学模拟研究了燃烧行为。实验测量了PSHR的发生与主燃烧时间之间的关系。对两者关系的分析表明，在发动机高负荷工况下，与非乙醇燃料相比，乙醇混合燃料的PSHR更小，燃烧持续时间更长约5%。利用实验输入数据进行的模拟表明，由于其PSHR导致未燃烧混合物的温度较低，乙醇混合燃料具有较低的层流燃烧速度。另外，模拟研究了PSHR引起的部分氧化反应物对层流燃烧速度的化学效应，结果表明，部分氧化反应物增加了乙醇混合燃料的层流燃烧速度，但降低了不含乙醇的参考燃料的层流燃烧速度。乙醇混合燃料中大量的燃料自由基和氧化物增强了火焰前区的链支反应，可能增加了层流燃烧速度。然而，PSHR对层流燃烧速度的热力学效应超过了化学效应，因此在PSHR条件下乙醇混合燃料具有较低的湍流燃烧速度。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Accounts of Chemical Research 化学-化学综合

CiteScore

31.40

自引率

1.10%

发文量

312

审稿时长

2 months

期刊介绍： Accounts of Chemical Research presents short, concise and critical articles offering easy-to-read overviews of basic research and applications in all areas of chemistry and biochemistry. These short reviews focus on research from the author’s own laboratory and are designed to teach the reader about a research project. In addition, Accounts of Chemical Research publishes commentaries that give an informed opinion on a current research problem. Special Issues online are devoted to a single topic of unusual activity and significance. Accounts of Chemical Research replaces the traditional article abstract with an article "Conspectus." These entries synopsize the research affording the reader a closer look at the content and significance of an article. Through this provision of a more detailed description of the article contents, the Conspectus enhances the article's discoverability by search engines and the exposure for the research.