The adoption of lean-burn concepts for internal combustion engines working with a homogenous air/fuel charge is under development as a path to simultaneously improve thermal efficiency, fuel consumption, nitric oxides, and carbon monoxide emissions. This technology may lead to a relevant emission of unburned hydrocarbons (uHC) compared to a stoichiometric engine. The uHC sources are various and the relative importance varies according to fuel characteristics, engine operating point, and some geometrical details of the combustion chamber. This concern becomes even more relevant in the case of engines supplied with natural gas since the methane has a global warming potential much greater than the other major pollutant emissions. In this work, a simulation model describing the main mechanisms for uHC formation is proposed. The model describes uHC production from crevices and flame wall quenching, also considering the post-oxidation. The uHC model is implemented in commercial software (GT-Power) under the form of “user routine”. It is validated with reference to two large bore engines, whose bores are 31 and 46 cm (engines named accordingly W31 and W46). Both engines are fueled with natural gas and operated with lean mixtures (λ > 2), but with different ignition modalities (pre-chamber device or dual fuel mode). The engines under study are preliminarily schematized in the 1D simulation tool. The consistency of 1D engine schematizations is verified against the experimental data of BMEP, air flow rate, and turbocharger rotational speed over a load sweep. Then, the uHC model is validated against the engine-out measurements. The averaged uHC predictions highlight an average error of 7% and 10 % for W31 and W46 engines, respectively. The uHC model reliability is evidenced by the lack of need for a case-dependent adjustment of its tuning constants, also in presence of relevant variations of both engine load and ring pack design.

稀薄燃烧概念在采用均质空气/燃料充量的内燃机中的应用正在开发中，作为同时提高热效率，燃料消耗，一氧化氮和一氧化碳排放量的途径。与化学计量发动机相比，该技术可能导致未燃烧碳氢化合物（uHC）的相关排放。uHC来源多种多样，相对重要性根据燃料特性，发动机工作点和燃烧室的一些几何细节而变化。对于使用天然气供应的发动机，这种担忧变得尤为重要，因为甲烷具有的全球变暖潜力远大于其他主要污染物的排放量。在这项工作中，提出了描述uHC形成主要机理的模拟模型。该模型描述了缝隙和火焰壁淬火产生的uHC，还考虑了后氧化。uHC模型以“用户例程”的形式在商业软件（GT-Power）中实现。参照两个大口径发动机（其口径分别为31和46 cm）进行了验证（发动机分别命名为W31和W46）。两台发动机均以天然气为燃料，并以稀薄混合气（λ> 2）运行，但点火方式不同（预燃装置或双燃料模式）。所研究的引擎已在1D模拟工具中进行了初步图示。根据BMEP，空气流量和涡轮增压器转速在负载扫描期间的实验数据，验证了一维发动机方案的一致性。然后，针对发动机输出测量值验证uHC模型。uHC的平均预测结果表明，W31和W46发动机的平均误差分别为7％和10％。uHC模型的可靠性是由于不需要根据情况调整其调整常数而得到证明的，而且还存在发动机负载和环形组件设计的相关变化。