Stoichiometric industrial natural gas engines rely on robust design to achieve consumer driven up-time requirements. Key to this design are exhaust components that are able to withstand high combustion temperatures found in this type of natural gas engine. The issue of exhaust component durability can be addressed by making improvements to materials and coatings or decreasing combustion temperatures. Among natural gas engine technologies shown to reduce combustion temperature, dedicated exhaust gas recirculation (EGR) has limited published research. However, due to the high nominal EGR rate it may be a technology useful for decreasing combustion temperature. In previous work by the author, dedicated EGR was implemented on a Caterpillar G3304 stoichiometric natural gas engine. Examination of combustion statistics showed that, in comparison to a conventional stoichiometric natural gas engine, operating with dedicated EGR requires adjustments to the combustion recipe to achieve acceptable engine operation. This work focuses on modifications to the combustion recipe necessary to improve combustion statistics such as coefficient of variance of indicated mean effective pressure (COV of IMEP), cylinder-cylinder indicated mean effective pressure (IMEP), location of 50% mass fraction burned, and 10%–90% mass fraction burn duration. Several engine operating variables were identified to affect these combustion statistics. A response surface method (RSM) optimization was chosen to find engine operating conditions that would result in improved combustion statistics. A third order factorial RSM optimization was sufficient for finding optimized operating conditions at 3.4 bar brake mean effective pressure (BMEP). The results showed that in an engine with a low turbulence combustion chamber, such as a G3304, optimized combustion statistics resulted from a dedicated cylinder lambda of 0.936, spark timing of 45° before top dead center (°bTDC), spark duration of 365 µs, and intake manifold temperature of 62°C. These operating conditions reduced dedicated cylinder COV of IMEP by 10% (absolute) and the difference between average stoichiometric cylinder and dedicated cylinder IMEP to 0.19 bar.

化学计量工业天然气发动机依靠坚固的设计来满足消费者驱动的正常运行时间要求。该设计的关键是能够承受这种天然气发动机中高燃烧温度的排气部件。排气组件耐久性的问题可以通过改进材料和涂层或降低燃烧温度来解决。在显示出可降低燃烧温度的天然气发动机技术中，专用的废气再循环（EGR）限制了已发表的研究。但是，由于高的标称EGR率，它可能是一种用于降低燃烧温度的技术。在作者先前的工作中，在Caterpillar G3304化学计量天然气发动机上实施了专用EGR。燃烧统计数据显示，与传统的化学计量天然气发动机相比，使用专用EGR运行需要调整燃烧配方，以实现可接受的发动机运行。这项工作的重点是改进燃烧方法，以改善燃烧统计数据，例如指示平均有效压力（IMEP的COV），缸筒指示平均有效压力（IMEP）的方差系数，燃烧的50％质量分数的位置以及质量分数燃烧时间的10％–90％。确定了几个发动机运行变量以影响这些燃烧统计数据。选择了响应面方法（RSM）优化来查找可改善燃烧统计数据的发动机工况。三阶因子RSM优化足以找到3处的优化工作条件。4 bar制动器平均有效压力（BMEP）。结果表明，在低湍流燃烧室的发动机（例如G3304）中，优化的燃烧统计数据来自0.936的专用汽缸λ，上止点（°bTDC）前45°的点火正时，365 µs的点火持续时间，进气歧管温度为62°C。这些操作条件将IMEP的专用气缸COV降低了10％（绝对值），平均化学计量气缸与专用气缸IMEP之间的差异降低到0.19 bar。