Effect of Ammonia Energy Fraction and Injection Strategy on Combustion and Emission of a Dual-Fuel Low-Speed Engine
In order to achieve high thermal efficiency and low nitrogen oxides(NOx)emissions for ammonia-fueled marine engines,a 3-D numerical combustion model was developed based on Converge software for a large-bore low-speed direct-injection ammonia-diesel dual-fuel engine.The combustion was mainly based on a premixed-diffusion control,in which partially premixed ammonia was formed by high-pressure direct injection.The influences of both single-and two-stage pilot diesel injection strategies,as well as ammonia energy fraction,on in-cylinder combustion,performance and NOx emissions were investigated.Results show that under the same ammonia energy fraction at full load,the single-stage injection of pilot diesel achieves higher indicated thermal efficiency(ITE),but the peak cylinder pressure and NOx emissions increase.Under 95％ammonia energy fraction,the two-stage diesel pilot injection strategy achieves a reduction of 29.6％and 17.7％in NOx emissions,and meanwhile maintains high ITE,compared to the single-stage injection strategy,due to reducing the high temperature and low ammonia mass fraction zone in the cylinder.In addition,it is found that,both the average and maximum of the rate of pres-sure rise are more sensitive to ammonia injection timing under both diesel pilot injection strategies.
dual-fuel enginehigh-pressure direct injectioninjection strategyammonia energy fraction
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