Research of Techniques for Low Pressure Indication in Internal Combustion Engines

In order to analyze the processes during the gas exchange in the engine, knowledge of pressure states in both inlet and outlet is required. This pressure measuring is known as “low pressure indication”. In the present work, three examples of controlling the quality of low pressure measurement are presented. An insight in the pressure waves in exhaust pipe, especially in the exhaust blow-off is given.

It was shown that: a small inaccuracy of measurement, lower than 10 mbar can be attained, the asymmetric course of the exhaust pulse can clearly be verified, and a protection screen for a sensor exposed to the exhaust blow-off pressure wave can be a tool to optimize between longlife and accuracy.

The most important statements are:

• both presented methods of low pressure indication - the direkt and the indirect yield the results with highest accuracy. The direct measuring method with a compensated piezoresistive sensor is to be recommended due to its simplicity and better applicability for dynamic measurements,
• the deformation of the blow-off pressure wave in the curve of the exhaust pipe was demonstrated, the sensors should not be installed at the external or internal positions due to deviating pressure values,
• the protecting screens used on the sensors in exposed positions have influences on the measured signals and shall be carefully choosen.