Wang, J., Yang, F., and Ouyang, M., "Cylinder by cylinder indicated torque and combustion feature estimation based on engine instantaneous speed and one cylinder pressure through error similarity analysis," SAE Technical Paper 2015-01-1249, 2015, doi:10.4271/2015-01-1249.
There is increasing demand for engine diagnostic and control with in-cylinder pressure signal. However, the application of cylinder pressure sensors are restricted by the high cost of the sensor. Another possible way for engine combustion state estimation is by processing of instantaneous crankshaft speed signal, but it is limited by the precision and complexity of the algorithm. It could be a solution by processing one cylinder pressure signal in combination with a crankshaft speed signal. The indicated torque could be estimated through engine speed processing and also from the measure cylinder pressure for the reference cylinder. Measurement results from experiments show that the indicated torque error traces of different cylinder are similar in shape. According to this assumption, the reference cylinder with cylinder pressure signal available can serve as both a parameter calibration information source and an error reduction measure. An algorithm was designed to estimate cylinder wise indicated torque and combustion features based on the rigid crankshaft model and error similarity assumption. The indicated pressure torque estimation result can be used to obtain other combustion parameters, such as indicated mean effective pressure and the crank angle degree of the maximum combustion torque. The proposed method was validated with experimental data under both static and transient conditions.