Transient prediction capabilities of a novel physics-based ignition delay model in multi-pulsed direct injection diesel engines

Abstract

This work is an extension of a novel physics-based ignition delay modeling methodology previously developed by the authors to predict physical and chemical ignition delays of multiple injections during steady operations in diesel engines. The modeling methodology is refined in this work to consider the influence of additional operating parameters such as volumetric efficiency, exhaust temperature and pressure on the ignition delay of multiple injections. Computational fluid dynamics predictions on two different engines indicated that the main spray encounters local temperatures about 60 K above average temperatures for about 1 mg of pilot. Hence, the modeling methodology was further refined to include this effect by considering the air mass trapped in pilot spray, computed based on the spray penetration and cone angle and tuned using results of the computational fluid dynamics studies. Comparisons of the ignition delay predictions with the stock boost temperature sensor and a specially incorporated, transient-capable fine wire thermocouple indicated that the measurements with stock sensor could be satisfactorily used for transients. Cycle-by-cycle changes in ignition delay could be predicted accurately when transients were imposed in boost pressure, rail pressure and main injection quantity in a turbocharged intercooled diesel engine controlled with an open engine control unit. Further validations were done even under a transient cycle when the engine was controlled by its stock engine control unit. The same tuning constants could be used for the prediction of the ignition delay under transients on another naturally aspirated engine. This indicates the suitability of the model for application in different engines. Finally, the model was incorporated within an open engine controller, and cycle-by-cycle prediction of ignition delays of the pilot and main injections were done in real time. It was possible to compute the ignition delays in less than 2 ms within engine control unit using the already available sensor inputs within an error band of ±60 µs.