Effect of Electric Supercharging on the Transient Loading Process Performance of Heavy-Duty Turbocharged Diesel Engine

To address the fuel-air ratio imbalance caused by the turbo lag during the loading process of conventional turbocharged diesel engines, a transient matching method for an electric supercharger was proposed, and the transient performance of a diesel engine was studied with a focus on fuel-air cooperative control. Based on a heavy-duty diesel engine, a one-dimensional simulation model was established. The electric supercharger was arranged upstream of the engine’s single-stage turbocharger. During a sudden, constant-speed loading process with a duration of 1.0 s and a speed of 950 r/min(load change: 0—90%), an electric supercharger selection scheme was determined through transient calculations using the proposed matching method. The selected motor had a rated power of 8 kW and a rated speed of 50000 r/min. Subsequently, a test bench of the electric supercharger system was constructed, and transient loading tests were performed for five types of fuel injection schemes and different electric supercharger intervention methods. The results showed that for a fuel injection scheme involving a 0.5 s ramp-up to 70 % load, the intervention of the electric supercharger accelerated the intake response speed during the transient process. As the intake mass flow rate was increased, the intake pressure increased and the mixture in the cylinder burned more completely. The peak in-cylinder pressure and peak heat release rate increased by 0.76 MPa and 30.03 J/(℃A), respectively, while the peak in-cylinder average temperature and combustion duration decreased by 49.17 K and 0.91℃A, respectively. Furthermore, the combustion center of gravity advanced, indicating an improved combustion effect. The peak equivalent ratio decreased to below the critical equivalent ratio of 0.80. The electric supercharger significantly reduced soot emissions while exerting only a minor effect on NO_x emissions. The lowest transient soot emission peak of 167.34 mg/m³ was achieved using an injection scheme featuring a step increase to 45% load at 0.1 s coordinated with the electric supercharger. Therefore, the control strategy combining the fuel injection scheme with electric supercharger intervention was an effective means to achieve low emissions.