BASIC FINDINGS OBTAINED FROM MEASUREMENT OF THE COMBUSTION PROCESS

The heat release of internal combustion engines decisively influences exhaust emissions, fuel economy, smoke and noise. Previously, however, the measurement methods were complicated and insufficiently accurate. Therefore heat release data were not often used. By means of an improved measurement and evaluation system it is now easier to determine the heat release with higher accuracy. The required combustion pressure diagram is recorded and then processed by means of a desk computer at the test stand. Because of the low calculation speed of desk computers, it is necessary to optimise carefully the algorithms in order to arrive at an acceptable computation time. To this end an approximative equation for the specific heat, a thermodynamic determination of the pressure diagram zero line and a simplified method of calculating the heat release are described, the use of which leads to an extremely short calculation time of about 5 seconds. This allows a quick evaluation of the rate of heat release directly at the test stand and so its immediate application in engine development. The kind of information which can be gathered from the rate of heat release is shown in some examples which compare typical results gained in an Otto cycle engine and three different direct injection diesel systems. The importance of determining the rate of heat release in unsteady operation is shown by the example of engine starting. (Author/TRRL)