Modern internal combustion engine control systems require on-board evaluation of a large number of quantities, in order to perform an efficient combustion control. The importance of optimal combustion control is mainly related to the requests for pollutant emissions reduction, but it is also crucial for noise, vibrations and harshness reduction. Engine system aging can cause significant differences between each cylinder combustion process and, consequently, an increase in vibrations and pollutant emissions. Another aspect worth mentioning is that newly developed low temperature combustion strategies (such as HCCI combustion) deliver the advantage of low engine-out NOx emissions, however, they show a high cylinder-to-cylinder variation. For these reasons, non uniformity in torque produced by the cylinders in an internal combustion engine is a very important parameter to be evaluated on board.
This work describes a methodology that allows determining the difference between torque delivered by each cylinder and the mean value. These differences can be caused by different reasons, such as different air breathing or deposits on the injectors that do not allow injecting the desired quantity. Once the differences in cylinder to cylinder torque production have been evaluated, the engine control system can adopt the interventions that are needed to re-establish the nominal behavior.
The methodology presented in this paper requires no additional cost, because it is based on engine speed fluctuations measurement, that can be performed using the same phonic wheel already mounted on-board. This approach has been validated on an L4 Common Rail Multi-Jet Diesel engine mounted on-board a vehicle. In order to quantify the accuracy of torque non-uniformities estimation, specifically designed tests have been performed acquiring the instantaneous engine speed and the in-cylinder pressure signals (that allow evaluating indicated torque delivered by each cylinder) simultaneously.
The presented approach has been applied to a Common Rail Diesel engine, nevertheless this methodology is general, and it is suitable for torque non-uniformities evaluation in spark ignited engines as well.