Study on the effect of blending hydrocarbon-based biodiesel on the performance of SCR system and urea calibration method for marine engines

In order to optimize the urea injection volume of the SCR system after fuel change, this paper constructs the three-dimensional models of the marine engine and SCR system. When the engine is doped with hydrocarbon-based biodiesel, this paper determines the optimal doping ratio and injection advance angle of the engine to be 10 % and 27°CA BTDC based on the economy. Under these parameters, the simulation obtains the exhaust parameters of the engine, determines the urea injection area of the SCR system, and calculates the theoretical urea injection volume to meet the urea injection temperature operating point. After blending hydrocarbon-based biodiesel, when the SCR system continues to use the calibrated urea injection volume in pure diesel mode, the requirements cannot be met, so it is necessary to re-calibrate the SCR system urea injection volume. Subsequently, this paper proposes a NOx target conversion rate allocation method based on the average ammonia-nitrogen consumption ratio and working condition usage frequency and taking the engine unit power urea consumption as the optimization target. The results show that the optimized average ammonia specific consumption of the SCR system is 21.45g/(kW⋅h), which is reduced by 6.95 % compared with original calibrated average ammonia specific consumption (22.94 g/(kW⋅h)).