Data_Sheet_1_A Methodology for Studying the Relationship Between Heat Release Profile and Fuel Stratification in Advanced Compression Ignition Engines.PDF

Low temperature combustion strategies have demonstrated high thermal efficiency with low pollutant emissions (e. g., oxides of nitrogen and particulate matter), resulting from reduced heat transfer losses and lean air-fuel mixtures. One such advanced compression ignition combustion strategy, Reactivity Controlled Compression Ignition (RCCI), has demonstrated improved control over the heat release event due to the introduction of in-cylinder stratification of equivalence ratio and chemical reactivity via direct injection of a high-reactivity fuel into a premixed low-reactivity fuel/air mixture. The nature of the RCCI strategy provides inherent fuel flexibility, however, the direct injection strategy must be tailored to the combination of premixed and direct injected fuel chemistry and engine operating conditions to optimize efficiency and emissions. In this work, a 0-D methodology for predicting the required fuel stratification for a desired heat release rate profile for kinetically controlled stratified-charge combustion strategies is proposed. The methodology, referred to as Fuel Stratification Analysis (FSA), was inspired by a similar approach which utilized ignition predictions calculated via a Livengood-Wu integral approach correlated with experimental heat release profiles to determine in-cylinder temperature stratification in homogeneous charge compression ignition (HCCI) combustion. The methodology proposed in this work expands upon this method to include strategies involving fuel stratification (such as RCCI). Reacting and non-reacting CFD simulations were performed with the KIVA3V release 2 code to validate the CFD. Reacting simulations were validated against published experimental HCCI and RCCI data, and non-reacting simulations were used to generate fuel distribution profiles to compare to the FSA results. The results of this validation showed that the FSA method was able to provide good overall agreement in the predicted fuel distribution compared to the actual fuel distributions from CFD simulations within the range of injection timings of interest in RCCI combustion (−140° to about −35° after top-dead-center). For later injection timings, FSA predictions are not able to capture the actual fuel distributions present at the start of combustion, likely due to a transition into a mixing dominated, as opposed to a kinetically dominated, combustion regime, thereby violating one or more inherent method assumptions.

低温燃烧策略已显示出高热效率与低污染物排放（例如，氮氧化物和颗粒物）的显著优势，这得益于减少的热传递损失和贫燃空气-燃料混合物的使用。其中一种先进的压燃式燃烧策略，即反应性控制压燃（RCCI），通过向预混合的低反应性燃料/空气混合物中直接喷射高反应性燃料，实现了对热释放事件的改进控制，这是因为引入了气缸内当量比和化学活性的分层。RCCI策略的本质提供了固有的燃料灵活性，然而，直接喷射策略必须针对预混合和直接喷射燃料化学成分以及发动机运行条件进行定制，以优化效率和排放。在本研究中，提出了一种预测动力学控制分层充量燃烧策略所需燃料分层的方法，以实现期望的热释放率分布。该方法被称为燃料分层分析（FSA），其灵感来源于一种类似的方法，该方法利用通过Livengood-Wu积分方法计算的点火预测，与实验热释放分布相关联，以确定同质充量压燃（HCCI）燃烧中的气缸温度分层。本研究中提出的方法在此方法的基础上进行了扩展，以包括涉及燃料分层（如RCCI）的策略。使用KIVA3V发布2代码进行了反应和非反应计算流体动力学（CFD）模拟，以验证CFD。反应模拟通过与已发表的实验HCCI和RCCI数据进行了验证，非反应模拟用于生成燃料分布轮廓，以与FSA结果进行比较。验证结果证实，FSA方法能够在预测燃料分布方面与CFD模拟的实际燃料分布实现良好的总体一致性，尤其是在RCCI燃烧中感兴趣的喷射时间范围内（上止点后约−140°至约−35°）。对于更晚的喷射时间，FSA预测无法捕捉到燃烧开始时存在的实际燃料分布，这可能是由于进入了一种以混合为主，而非动力学为主的燃烧状态，从而违反了一个或多个固有的方法假设。