Abstract An optimization methodology based on a genetic algorithm coupled with the KIVA computational fluid dynamics (CFD) code is applied to the design of a combustion system of a heavy-duty diesel engine fueled with dimethyl ether (DME) and working with stoichiometric combustion in order to equip the system with a three way catalyst (TWC) to control the NOx emissions. The target of the optimization is to improve net indicated efficiency (NIE) while keeping NOx emissions, peak pressure and pressure rise rate under the reference engine levels. The results of the study provide an optimum configuration that offers a 0.6% NIE improvement while satisfying the restrictions and offering NOx values lower than 1% of the original emissions. Due to the methodology, not only the optimum combustion system configuration is presented, but also the cause-effect relation of the most relevant inputs with the optimization outputs are identified and analyzed. The new geometry shape reduced heat transfer losses by minimizing the surface area. Injection pressure and swirl proved to be key parameters necessary to overcome the increased mixing requirements of stoichiometric operation. EGR was found to simultaneously increase NIE while controlling NOx emissions. The results show the potential of stoichiometric compression ignition operation using DME as a promising pathway to maintain diesel-like efficiency, while achieving near zero NOx and soot emissions.

中文翻译：

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化学计量二甲醚压燃式发动机燃烧系统的计算优化

摘要 将基于遗传算法结合 KIVA 计算流体动力学 (CFD) 代码的优化方法应用于以二甲醚 (DME) 为燃料并采用化学计量燃烧的重型柴油机燃烧系统的设计。为系统配备三元催化器 (TWC) 以控制 NOx 排放。优化的目标是提高净指示效率 (NIE)，同时将氮氧化物排放、峰值压力和压力上升率保持在参考发动机水平以下。研究结果提供了一种优化配置，在满足限制的同时提供 0.6% 的 NIE 改进，并提供低于原始排放量 1% 的 NOx 值。由于该方法论，不仅提供了最佳燃烧系统配置，而且还识别和分析了最相关输入与优化输出的因果关系。新的几何形状通过最小化表面积来减少传热损失。注射压力和涡流被证明是克服化学计量操作增加的混合要求所必需的关键参数。发现 EGR 同时增加 NIE，同时控制 NOx 排放。结果表明，使用二甲醚作为保持类似柴油效率的有前途的途径的化学计量压缩点火操作的潜力，同时实现接近零的 NOx 和烟尘排放。注射压力和涡流被证明是克服化学计量操作增加的混合要求所必需的关键参数。发现 EGR 同时增加 NIE，同时控制 NOx 排放。结果表明，使用二甲醚作为保持类似柴油效率的有前途的途径的化学计量压缩点火操作的潜力，同时实现接近零的 NOx 和烟尘排放。注射压力和涡流被证明是克服化学计量操作增加的混合要求所必需的关键参数。发现 EGR 同时增加 NIE，同时控制 NOx 排放。结果表明，使用二甲醚作为保持类似柴油效率的有前途的途径的化学计量压缩点火操作的潜力，同时实现接近零的 NOx 和烟尘排放。