THE MAXIMUM COMPRESSION PRESSURE POSITION RELATIVE TO TOP DEAD CENTERAS AN INDICATION OF ENGINE CYLINDER CONDITION AND BLOWBY

The compression curve of a DI (Direct Injection) diesel engine is affe cted by various parameters, such as heat loss, initial temperature and pressure, speed, compression ratio and blowby. Usually the engineer m akes use of the measured motored pressure diagram and especially of th e maximum compression pressure value to determine the engine condition (wear). However, in order to have an accurate indication of the engin e condition, one must consider accurately all the previous mechanisms. This poses a very difficult task since, for example, not even the com pression ratio is usually accurately known for an operating engine. Th us, a low maximum compression pressure value may not be caused by incr eased blowby rate, and so this may lead to a wrong indication of cylin der condition. The present work introduces a new method for determinin g cylinder condition (wear) and especially the blowby rate. The method is based on the determination of the position of the maximum compress ion pressure value relative to the TDC (Top Dead Centre) position. The maximum pressure position (before TDC) varies greatly with blowby rat e, but is practically unaffected by heat losses, initial temperature a nd pressure and compression ratio. Experiments have been conducted on a Ricardo E-6, DI diesel engine for various compression ratios, engine speeds and operating temperatures (cold and warm operation) under mot oring conditions. Pressure has been measured using a time step equival ent to 0.1-degree-CA, while the TDC position has been determined using a magnetic pickup device. A mathematical simulation accounting for he at losses and blowby has been used to examine the effect of various pa rameters on maximum compression pressure and its position relative to TDC. The results from both experiments and simulation are found to be in good agreement concerning pressure curves, maximum pressure positio n and their variation with the parameters examined. The results are pr omising, showing a high potential for determining any cylinder conditi on by processing the corresponding measured pressure diagram.