Effect of pressure transducer position on measured cylinder pressure diagram of high speed diesel engines
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Anestis, A
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Hountalas, DT
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The cylinder pressure diagram is a valuable source of information for reciprocating internal combustion engines. If processed, it provides information concerning the combustion process inside the engine cylinder. During this process, a problem that usually arises is the proper mounting of the pressure sensor on the cylinder head. The optimum is to flush-mount the transducer to the cylinder head so that it can be directly in contact with the gas. Unfortunately, in many cases, and mainly in small size, high speed commercial engines, this is not always possible. For this reason, the engineer must position the transducer in a location away from the cylinder head to bring it to continuous contact with the cylinder gas through a duct. From experiments, we find that this may result in errors in the measured values of the gas pressure that differ from the actual ones inside the combustion chamber. In the case of spark ignition engines, we face this problem by using pressure sensors mounted on the engine spark plug, but in the case of Diesel engines, we must mount the transducer separately. The main scope of the present work is to examine the effect of the transducer position on the measured pressure diagram in high speed diesel engines. For this purpose, in the present work, a theoretical investigation is conducted using a simulation model developed by the authors, where the unsteady Bow problem in the connecting pipeline from the combustion chamber to the transducer is solved using a finite difference scheme. A simple combustion model is used to simulate the operation of a high speed diesel engine at various conditions. The theoretical investigation involves the study of the effect of the connecting pipe geometry (diameter and length) and engine speed and load on the measured pressure diagram and on the parameters derived from it. From this investigation, important results are obtained that enable us to determine the magnitude of the error in pressure measurement that results from the positioning of the transducer away from the combustion chamber. The results reveal the limits within which the pressure measurements are reliable and may be possibly used to develop a method for correcting the measured pressure diagram. (C) 1998 Elsevier Science Ltd.
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