The cylinder pressure signal is an optimum parameter for use in the detection of any anomalies present during the combustion process. The basic concept is to use vibration measurements from the engine surface and the engine structure function to perform a reconstruction of the cylinder pressure waveform. While measures of the acceleration signal contain all the necessary information for the reconstruction there is also contaminated by other sources such as impacting valves, piston slaps and combustion of adjacent cylinders. It has therefore been necessary to use advanced signal processing techniques to carry out an accurate reconstruction of the combustion pressure. Since cylinder pressure is an important parameter of engine operation, researchers have been seeking more efficient ways to measure its level.
Sensors can measure the cylinder pressure directly or indirectly.
This approach entails drilling a hole in the cylinder head and directly monitoring the cylinder pressure signal. This method has many disadvantages, such as, being inappropriate for on-board conditions, expensive to perform, and having a limited lifetime due to the harsh environment inside the combustion chamber. The reconstructed cylinder pressure was also used in this thesis research as input data to calculate the heat release rate and to define the start of the combustion process. The start of the combustion has a great importance for optimisation of the fuel injection rate. The heat release measured through the method described here can also be used to determine the efficiency of the engine.