柴油/天然气双燃料发动机数值优化

Numerical Optimization of Diesel/Natural Gas Dual-Fuel Engine

利用CONVERGE搭建了柴油/天然气双燃料发动机三维数值模拟平台,在大负荷工况下研究了压缩比和不同喷油策略对发动机燃烧性能的影响.研究结果表明,相同条件下,降低压缩比到14.8能够有效降低最大压升率,从而有助于进一步增大天然气的替代比例.采用单次喷射策略时,通过提高喷射压力并提前柴油直喷时刻,在最大压升率限值内,能在85%天然气替代比例的同时获得48.1%的热效率.采用两次喷射策略时,随着预喷油量的增加,缸内着火时刻提前.并且预喷时刻提前能够有效降低最大压升率.对比发现,与单次喷射策略相比,两次喷射策略能够实现更为灵活的缸内燃烧控制,获得90%的天然气替代比例.最终,两次喷油策略实现了48.4%的最高热效率.

A 3-dimensional numerical simulation platform for a diesel/natural gas dual-fuel engine was constructed by means of CONVERGE to investigate the effect of compression ratio and different injection strategies on the engine combustion performance under a high engine load condition.Results show that under the same conditions,the reduction of compression ratio to 14.8 leads to a significant decrease in peak pressure rise rate,which makes it possible to employ a higher natural gas substitution rate.Within the maximum pressure rise rate limit,a maximum thermal efficiency of 48.1%with an 85%natural gas substitution rate was obtained by increasing the injection pressure and advancing the diesel injection timing under a single direct injection strategy.With the employment of a split injection strategy,the increase of pilot fuel amount tends to trigger the earlier ignition,and the advancement of pilot injection timing can effectively reduce the peak pressure rise rate.Compared with the single injection strategy,the split injection strategy is more flexible in controlling the combustion phasing,making it possible to adopt a high natural gas replacement ratio(up to 90%)while maintaining a lower peak pressure rise rate.Finally,a peak indicated thermal efficiency of 48.4%is obtained by split injection strategy.