柴油/天然气双燃料发动机柴油燃烧策略的研究

Research on Combustion Strategy of Diesel/Natural Gas Dual Fuel Engine

基于自主研发的第三代并行式柴油/天然气双燃料发动机电控系统,利用FIRE软件建立柴油/天然气双燃料发动机柴油喷射系统的多次喷射模型。同时,通过进气压力控制过量空气系数,实现柴油/天然气双燃料发动机稀薄燃烧方式。针对高负荷工况,研究了多次喷射策略和稀薄燃烧方式对双燃料发动机最大压力升高率及NOx排放的影响。结果表明:发动机工作在高负荷及柴油替代率为80%时,采用双燃料稀薄燃烧方式能使NOx排放降低,但最大压力升高率仍可能超过安全临界值1MPa/(°)。采用合适的预喷射量与预喷射时刻能降低最大压力升高率。通过多次喷射和稀薄燃烧方式相结合的燃烧策略对缸内燃烧方式进行组织,可以实现双燃料发动机高替代率燃烧,并使高负荷时NOx排放达到或者低于国Ⅴ标准限值。

The multiple injection model of diesel fuel injection system was established for diesel/natural gas dual fuel engine by the FIRE software based on the third generation parallel dual fuel engine electronic control system. Meanwhile the lean burn combustion mode of dual fuel engine was realized by using intake air pressure to control excess air coefficient. And for the high load condition the effect of multiple injection strategy and lean burn combustion mode on maximum pressure rise rate and NOx emission was studied. The research shows that when the engine is running at high load with natural gas substitution rate of 80%, the dual fuel lean burn combustion mode can reduce the NOx emission, but it will make the maximum pressure rise rate exceed the safety threshold value of 1 MPa/（°） which could be reduced by using proper pilot injection quantity and injection timing. Using the combustion strategy of integrated multiple injection and lean burn combustion mode can realize high substitution rate combustion for dual fuel engine and make NOx emission meet or close to China V emission standard.