Detection of Cylinder-to-Cylinder Injection Variation in a Four-Stroke Diesel Engine by Monitoring the Turbocharger Speed

In order to ensure a high level of performance and to comply with more severe limitations in term of fuel consumption and emissions reduction, a continuous supervision of the engine operating conditions, by monitoring several parameters, is needed. The growing use of turbocharger (TC) in ICE for automotive and industrial applications suggests to use the TC speed as a possible feedback of engine operating condition. Indeed, the turbocharger behavior is connected to the thermo-dynamic and fluid-dynamic conditions at the engine cylinder exit: this feature suggests that the turbocharger speed could give useful information about the engine cycle. In previous studies, a preliminary investigation of the relationship between the engine performance and the turbocharger speed of a four-stroke multi-cylinder turbo-diesel engine was carried out by varying the operating conditions of the engine such as fuel mass flow rate, EGR rate and back pressure at the turbine outlet. The analysis was performed by taking advantage of a 1D numerical model calibrated through the comparison with experimental data in the whole operating range of the engine. The numerical and experimental sensitivity analysis highlighted the link between the average TC speed and the engine torque. Moreover, the study underlined that the only use of the average TC speed does not allow one to univocally detect the cause of variations in the engine working conditions. Consequently, at least another parameter must be monitored. Furthermore, the previous numerical activity underline the sensitivity of the instantaneous TC speed to the cylinder-to-cylinder injection variation. The variation of the injection characteristics with respect to the nominal operating condition is usually due to the injector individual tolerance and the time degradation. In the present study, the authors focus on the experimental validation of the model in terms of instantaneous TC speed in the whole operating range of the engine. The model results was verified both in the standard engine operating conditions and in the case of non-uniform injected fuel quantity among cylinders. The numerical-experimental comparison confirmed that the instantaneous TC speed could be used to identify the cylinder-to-cylinder injection variation. In the future activity, an injection monitoring strategy based on the instantaneous TC speed will be defined by taking advantage of the numerical model, with the aim to quantify the injected fuel in each cylinder.