Evaluating temperature and fuel stratification for heat-release rate control in a reactivity-controlled compression-ignition engine using optical diagnostics and chemical kinetics modeling
Evaluating temperature and fuel stratification for heat-release rate control in a reactivity-controlled compression-ignition engine using optical diagnostics and chemical kinetics modeling
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DOI：
10.1016/j.combustflame.2015.04.009
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发表时间：
2015-06
影响因子：
4.4
通讯作者：
S. Kokjohn;M. Musculus;R. Reitz
中科院分区：
文献类型：
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作者：
S. Kokjohn;M. Musculus;R. Reitz
在双燃料，反应性控制的压燃（RCCI）发动机的燃烧过程中进行了研究，使用光学诊断和化学动力学建模的组合来解释的当量比，温度和燃料反应性分层的作用，热释放率控制。光学可接近的发动机使用汽油初级参考燃料（PRF）在RCCI燃烧模式下操作。异辛烷（PRF = 100）的良好混合的电荷是通过使用汽油型直接喷射器在进气冲程期间将燃料喷射到发动机气缸中来产生的。在循环后期，正庚烷（PRF = 0）通过安装在中央的柴油型共轨喷射器输送。这种喷射策略在当量比、燃料混合物和温度方面产生分层。本研究的第一部分是利用高速摄影机拍摄喷射事件，并记录高温燃烧化学发光。化学发光成像表明，在目前的工作研究的操作条件下，在挤气区的混合物点燃第一，和反应区的收益向内向燃烧室的中心。本研究的第二部分调查的RCCI战略的电荷准备，使用平面激光诱导荧光（PLIF）的燃料示踪剂在非反应条件下，以量化燃料浓度分布点火前。燃料示踪剂PLIF数据表明，燃烧事件的正庚烷分布的梯度。研究的第三部分使用化学动力学建模的范围内的混合物跨越从燃料示踪剂荧光成像观察到的分布隔离的温度，当量比，和PRF数分层的作用。模拟结果表明，脉冲重复频率数分层是控制点火位置和反应区增长速率的主要因素。等值比的影响较小，但仍然很重要。由于PRF混合物的NTC行为，温度分层的影响可以忽略不计。
The combustion process in a dual-fuel, reactivity-controlled compression-ignition (RCCI) engine is investigated using a combination of optical diagnostics and chemical kinetics modeling to explain the role of equivalence ratio, temperature, and fuel reactivity stratification for heat-release rate control. An optically accessible engine is operated in the RCCI combustion mode using gasoline primary reference fuels (PRF). A well-mixed charge of iso-octane (PRF = 100) is created by injecting fuel into the engine cylinder during the intake stroke using a gasoline-type direct injector. Later in the cycle, n-heptane (PRF = 0) is delivered through a centrally mounted diesel-type common-rail injector. This injection strategy generates stratification in equivalence ratio, fuel blend, and temperature. The first part of this study uses a high-speed camera to image the injection events and record high-temperature combustion chemiluminescence. The chemiluminescence imaging showed that, at the operating condition studied in the present work, mixtures in the squish region ignite first, and the reaction zone proceeds inward toward the center of the combustion chamber. The second part of this study investigates the charge preparation of the RCCI strategy using planar laser-induced fluorescence (PLIF) of a fuel tracer under non-reacting conditions to quantify fuel concentration distributions prior to ignition. The fuel-tracer PLIF data show that the combustion event proceeds down gradients in the n-heptane distribution. The third part of the study uses chemical kinetics modeling over a range of mixtures spanning the distributions observed from the fuel-tracer fluorescence imaging to isolate the roles of temperature, equivalence ratio, and PRF number stratification. The simulations predict that PRF number stratification is the dominant factor controlling the ignition location and growth rate of the reaction zone. Equivalence ratio has a smaller, but still significant, influence. Temperature stratification had a negligible influence due to the NTC behavior of the PRF mixtures.