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In-Cycle Closed-Loop Combustion Control for Pilot Misfire Compensation
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 15, 2020 by SAE International in United States
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. However, 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 compensated in-cycle. Based on the in-cycle misfire diagnose, three 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. The third approach investigates how the pilot misfire can be counteracted by a second pilot injection. 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 ±0.6CAD and ±0.3bar IMEP. The predictive in-cycle control can improve the cycle-to-cycle controller performance further to ±0.4CAD and ±0.2bar IMEP, but accurate predictive models are necessary. 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.