High-pressure direct-injection (HPDI) of natural gas is one of the most promising solutions for future ship engines, in which the combustion process is mainly controlled by the chemical kinetics. However, the employment of detailed chemical models for the multi-dimensional combustion simulation is significantly expensive due to the large scale of the marine engine. In the present paper, a reduced n-heptane/methane model consisting of 35-step reactions was constructed using multiple reduction approaches. Then this model was further reduced to include only 27 reactions by utilizing the HyChem (Hybrid Chemistry) method. An overall good agreement with the experimentally measured ignition delay data of both n-heptane and methane for these two reduced models was achieved and reasonable predictions for the measured laminar flame speeds were obtained for the 35-step model. But the 27-step model cannot predict the laminar flame speed very well. In addition, these two reduced models were both able to reproduce the experimentally measured in-cylinder pressure and heat release rate profiles for a HPDI natural gas marine engine, the highest error of predicted combustion phase being 6.5%. However, the engine-out CO emission was over-predicted and the highest error of predicted NO_x emission was less than 12.9%. The predicted distributions of temperature and equivalence ratio by the 35-step and 27-step models are similar to those of the 334-step model. However, the predicted distributions of OH and CH₂O are significantly different from those of the 334-step model. In short, the reduced chemical kinetic models developed provide a high-efficient and dependable method to simulate the characteristics of combustion and emissions in HPDI natural gas marine engines.

天然气的高压直接喷射（HPDI）是未来船舶发动机最有希望的解决方案之一，其中燃烧过程主要由化学动力学控制。然而，由于船用发动机的大型化，因此用于多维燃烧模拟的详细化学模型的使用显着昂贵。在本文中，使用多种还原方法构建了由35个步骤的反应组成的还原正庚烷/甲烷模型。然后，利用HyChem（Hybrid Chemistry）方法将该模型进一步简化为仅包含27个反应。两者的实验测量点火延迟数据总体良好协议ñ对于这两个还原模型，获得了正庚烷和甲烷，并针对35步模型获得了对测得的层流火焰速度的合理预测。但是27步模型不能很好地预测层流火焰速度。此外，这两个简化的模型都能够再现HPDI天然气船用发动机的实验测量缸内压力和放热率曲线，预测燃烧阶段的最高误差为6.5％。然而，发动机排出的CO排放经预测和预测的NO的最高误差_X排放量为小于12.9％。35步模型和27步模型的温度和当量比的预测分布与334步模型的预测分布相似。但是，OH和CH ₂的预测分布O与334步模型的O显着不同。简而言之，所开发的简化化学动力学模型提供了一种高效可靠的方法来模拟HPDI天然气船用发动机的燃烧和排放特性。