Experiment-based software optimization for multiple-injection control in a common-rail system

Abstract

Multiple-injection technology is being widely used in common-rail injection (CRI) systems for diesel engines. The precise control of the injected fuel quantity (FQ) and timing of every injection will directly affect the engine efficiency and exhaust performance. As the engine speed becomes faster, when more than five injections are engaged in per combustion cycle, the injection interval (between consecutive injections) will become increasingly shorter. In experiments based on the green diesel (GD)—CRI system applied in the YC6112 engine, the FQ of the main injection (MI) was found unbalanced when the pilot injection (PiI) is very close to it. According to the experimental analysis, this phenomenon was validated to mainly result from the electrohydraulic delay and the fuel pressure waves in the line leading from the rail to the injector. In order to minimize this influence, a software compensating strategy, which made an additive correction of the injection quantity, was developed. By this optimized software, not only does the MI FQ become steadily even when the PiI is very close to it, but also the conventional system-restricted injection interval can be decreased to as short as possible. This contributes to fulfilling the multiple-injection technology in the GD—CRI system and provides further benefit for the triple-injection function or greater. It also provides a successful example for up-to-date CRI systems to improve the multiple-injection performance in any other engine types by this software optimization method.