Reformed exhaust gas recirculation (REGR), which can generate onboard hydrogen-rich gas (i.e., the reformate including H₂, CO, unreformed hydrocarbon, etc.) via catalytic reforming of fuel and engine exhaust gas, is an attractive way to improve the performance and emissions characteristics of the engine fueled with liquefied natural gas (i.e., NG engine). However, the leakage during the valve overlap period and incomplete burning of the added reformate may lead to extra HC and CO emissions from the engine with REGR. In the present study, a multi-dimensional computation fluid dynamics model coupled with a detailed chemical kinetic mechanism was developed to investigate the effects of the ratio of reformate addition (R_ref) and exhaust valve closed (EVC) timing on the total emissions characteristics as well as the sources of HC and CO emissions from the engine. The emissions from the combustion and the leaking were included to calculate the total emissions. Moreover, the unburned CO from the added reformate was distinguished from the total CO emissions by adding marked-species. Results show that the unburned CH₄ in the cylinder is the main component of the total CH₄ emissions. Due to the increase of the concentrations of OH, O and H radicals during the combustion process, the oxidization of CH₄ is promoted with the increase of R_ref at high load, and therefore the total CH₄ emissions decrease. However, the total CO emissions increase with the increase of R_ref, and it is demonstrated that the unburned CO from the added reformate increases and turns to be the main sources of the total CO emissions. At R_ref of 10%, the total CH₄ and CO emissions firstly remain nearly constant and then increase dramatically with the delay of EVC timing. Therefore, low concentration of CO in the reformate and short valve duration are recommended to achieve low HC and CO emissions for the NG engine with REGR.

通过燃料和发动机废气的催化重整可产生机载富氢气体（即重整产物，包括H ₂，CO，未重整的烃等）的重整废气再循环（REGR）是一种改善燃料消耗的有吸引力的方法。以液化天然气为燃料的发动机（即NG发动机）的性能和排放特性。但是，气门重叠期间的泄漏和添加的重整油的不完全燃烧可能会导致带有REGR的发动机产生更多的HC和CO排放。在本研究中，建立了多维计算流体动力学模型并结合了详细的化学动力学机理，以研究重整产品添加比例（R _ref）和排气门关闭（EVC）定时，以了解总排放特征以及发动机中HC和CO排放的来源。燃烧和泄漏产生的排放包括在内，以计算总排放。此外，通过添加标记物种，将添加的重整产品中未燃烧的CO与总的CO排放区分开来。结果表明，气缸中未燃烧的CH ₄是总CH ₄排放的主要成分。由于在燃烧过程中OH，O和H自由基的浓度增加，在高负荷下，CH ₄的氧化随着R _ref的增加而促进，因此总的CH ₄排放量减少。然而，随着R _ref的增加，CO的总排放量增加，这表明添加的重整产品中未燃烧的CO逐渐增加，并成为CO的总排放量的主要来源。在R _ref为10％时，CH ₄和CO的总排放量首先保持接近恒定，然后随着EVC时序的延迟而急剧增加。因此，对于带REGR的NG发动机，建议重整产品中的CO浓度低且气门持续时间短，以实现较低的HC和CO排放。