Study of control strategy for cylinder-to-cylinder combustion homogeneity of marine medium-speed diesel engines

Closed-loop combustion control (CLCC) is an efficient method for minimizing cylinder-to-cylinder combustion variation by adjusting individual cylinder fuel injection parameters. It is complementary to the closed-loop speed control, which precisely controls the engine speed by manipulating the global fuel injection parameters. However, the application of CLCC changed the conventional closed-loop speed control to a complex control structure. In addition, the selection of combustion control parameters will not only influence the combustion heat release control precisely, but also lead to increased calibration effort for the combustion controller. In this research, a triple closed-loop control strategy, in conjunction with a set-point online generation method, was proposed to improve the cylinder-to-cylinder combustion homogeneity, maintain the desired engine speed, and reduce the calibration effort simultaneously. A coefficient of variation in crank angle domain was utilized to analyze the cylinder-to-cylinder combustion homogeneity. The triple closed-loop control strategy was implemented on a marine medium-speed diesel engine. The experimental results indicated that the proposed control strategy, compared with the speed & IMEP (indicated mean effective pressure) cooperative control and speed & MFB50 (crank angle when 50 % fuel is consumed) cooperative control, has a better potential to alleviate cylinder-to-cylinder pressure variations at the same crankshaft angle. The cylinder-to-cylinder variation of IMEP and MFB50 decreased by 61 % and 38 % compared to the closed-loop speed control, respectively. The cylinder-to-cylinder combustion inhomogeneity, resulting from engine long-time operation and ambient conditions change, was significantly reduced as well. Therefore, the proposed strategy provides a multi-objective precise control method that allows the extension to low-carbon and zero-carbon marine engines.