Effect of Ethanol and Iso-Octane Blends on Isolated Low-Temperature Heat Release in a Spark Ignition Engine

IF 1 Q4 TRANSPORTATION SCIENCE & TECHNOLOGY
Samuel Philip White, A. Bajwa, Felix Leach
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引用次数: 0

Abstract

Low-temperature heat release (LTHR) is of interest for its potential to help control autoignition in advanced compression ignition (ACI) engines and mitigate knock in spark ignition (SI) engines. Previous studies have identified and investigated LTHR in both ACI and SI engines before the main high-temperature heat release (HTHR) event and, more recently, LTHR in isolation has been demonstrated in SI engines by appropriately curating the in-cylinder thermal state during compression and disabling the spark discharge. Ethanol is an increasingly common component of market fuel blends, owing to its renewable sources. In this work, the effect of adding ethanol to iso-octane (2,2,4-trimethylpentane) blends on their LTHR behavior is demonstrated. Tests were run on a motored single-cylinder engine elevated inlet air temperatures and pressures were adjusted to realize LTHR from blends of iso-octane and ethanol without entering the HTHR regime. The blends were tested with inlet temperatures of 40°C–140°C at equivalence ratios of 0.5, 0.67, and 1.0 with boosted (1.5 barA) conditions. The measured LTHR decreased with increasing ethanol content for all conditions tested; iso-octane–ethanol blends with above 20% ethanol content (by volume) showed minimal LTHR under engine conditions. These net effects resulted from the combination of thermal effects (charge cooling) and chemical effects (reactivity changes at low temperatures). The effect of temperature, pressure, fuel composition, and equivalence ratio on ignition delay times calculated from chemical kinetic modeling are presented alongside pressure–temperature trajectories of the in-cylinder gases to explain the trends. The underlying cause of the trends is explained by using a sensitivity analysis to determine the contribution of each reaction within the chemical kinetic mechanism to first-stage ignition, revealing the effect of introducing ethanol on the OH radical pool and resulting LTHR intensity.
乙醇和异辛烷混合物对火花点火发动机隔离低温放热的影响
低温放热(LTHR)有助于控制先进压燃(ACI)发动机中的自燃,并减轻火花点火(SI)发动机中的爆震,因此备受关注。以前的研究已经确定并调查了 ACI 和 SI 发动机中主要高温放热 (HTHR) 事件之前的 LTHR,最近,通过在压缩过程中适当固化缸内热状态并禁用火花放电,在 SI 发动机中单独展示了 LTHR。由于乙醇的来源可再生,乙醇在市场混合燃料中越来越常见。在这项研究中,我们展示了在异辛烷(2,2,4-三甲基戊烷)混合物中添加乙醇对其低温热稳定性的影响。在一台单缸发动机上进行了测试,对进气温度和压力进行了调整,以实现异辛烷和乙醇混合物的低硫化氢反应,而不进入高硫化氢反应状态。在等效比为 0.5、0.67 和 1.0、增压(1.5 巴 A)条件下,在 40°C-140°C、进气温度为 40°C-140°C、等效比为 0.5、0.67 和 1.0 的条件下对混合气进行了测试。在所有测试条件下,随着乙醇含量的增加,测得的长径比都有所下降;在发动机条件下,乙醇含量超过 20% 的异辛烷-乙醇混合物的长径比最小。这些净效应是热效应(加料冷却)和化学效应(低温下的反应性变化)共同作用的结果。通过化学动力学建模计算出的温度、压力、燃料成分和当量比对点火延迟时间的影响,与气缸内气体的压力-温度轨迹一起呈现,以解释这些趋势。通过使用敏感性分析确定化学动力学机制中每个反应对第一阶段点火的贡献,揭示了引入乙醇对羟基自由基池和由此产生的 LTHR 强度的影响,从而解释了这些趋势的根本原因。
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来源期刊
SAE International Journal of Fuels and Lubricants
SAE International Journal of Fuels and Lubricants TRANSPORTATION SCIENCE & TECHNOLOGY-
CiteScore
2.20
自引率
10.00%
发文量
16
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