Methane Conversion in Stoichiometric Natural Gas Engine Exhaust

Stoichiometric natural gas (CNG) engines are an attractive solution for heavy-duty vehicles considering their inherent advantage in emitting lower CO2 emissions compared to their Diesel counterparts. Additionally, their aftertreatment system can be simpler and less costly as NOx reduction is handled simultaneously with CO/HC oxidation by a Three-Way Catalyst (TWC). The conversion of methane over a TWC shows a complex behavior, significantly different than non-methane hydrocarbons in stoichiometric gasoline engines. Its performance is maximized in a narrow A/F window and is strongly affected by the lean/rich cycling frequency. Experimental and simulation results indicate that lean-mode efficiency is governed by the palladium’s oxidation state while rich conversion is governed by the gradual formation of carbonaceous compounds which temporarily deactivate the active materials. Lean/rich cycling around stoichiometry enables a higher CH4 oxidation as the oxygen storage seems to balance the individual effects of Pd oxidation and rich deactivation. In this work, the catalytic reaction mechanisms involved in CH4, CO and NOx conversion were studied by means of a multi-scale experimental campaign and mathematical modeling. Initially, a detailed kinetic study was performed on the synthetic-gas bench to understand the underlying phenomena and formulate the appropriate reaction mechanisms. The model was then evaluated under transient reactor experiments while final validation was performed against driving cycle measurements on the engine bench.

静止的天然气（CNG）发动机是重型车辆的有吸引力的解决方案，考虑到它们在发射较低的二氧化碳排放方面与柴油机相比，它们的后处理系统的成本较小，而NOX的降低可以与CO/HC氧化相同，而不是通过CO/HC氧化的表现，则可以通过三通猫（TWC）（TWC）（TWC）（TWC）（TWC）（TWC）（TWC）（TWC）。在狭窄的A/F窗口中，其性能最大化，并受到瘦/富循环频率的影响，而较稀有的氧化效率则在palladium的氧化状态下受到较长的综合，而不是在狭窄的A/F窗口中，与非甲烷的碳氢化合物相比，其性能最大化。 iometry可以较高的CH4氧化似乎在这项工作中平衡了PD氧化的单个效果，并通过CH4，CO和NOX转化的催化反应机制通过多尺度的实验运动和数学模型进行了详细的模型。评估在瞬态反应堆实验下，对发动机台上的驾驶周期测量进行了最终验证。