Pilot injections are normally used for the reduction of diesel engine emissions and combustion noise. Nonetheless, with a penalty on the indicated thermal efficiency. The cost is reduced by the minimization of the pilot mass, which on its counterpart increases the risk of pilot misfire. Pilot misfire can have a higher penalty on the indicated efficiency if it is not compensated adequately. This paper investigates how in-cycle closed-loop combustion control techniques can reduce the effects of pilot misfire events.
By closed-loop combustion control, pilot misfire can be detected and counteracted in-cycle. Two injection strategies are investigated. The first is the control of the main injection, the second includes an additional second pilot injection. Based on the in-cycle misfire diagnose, two architectures are investigated. The first uses a cycle-to-cycle controller to set the main injection under each scenario. The second is a fully in-cycle controller with feedback from predictive models. All the algorithms were tested experimentally in a Scania D13 engine.
The results confirmed that in-cycle closed-loop combustion control can effectively reduce the effects of pilot misfire. An error of +1.5CAD on the main SOC and −0.5bar IMEP on the engine load was reduced to 0±0.6CAD and 0±0.4bar IMEP using the cycle-to-cycle architecture. The predictive in-cycle control can further reduce the error of the main SOC to 0±0.4CAD and 0±0.2bar IMEP for the engine load. These two approaches had one degree of freedom, and therefore only one of the combustion timing parameters (SOC or CA50) was regulated successfully. With the additional degree of freedom of the second pilot injection, the misfire effects were not only reduced, but also fully counteracted.
The methods are limited by the time window where pilot misfire observability and controllability overlap. This is set by the injections’ separations and the respective ignition delays. The second pilot injection can be further improved by the regulation of its injection timing and duration. The results can enhance the nominal set-up optimization by including the in-cycle controllability and regulation performance in the constraints.
