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Optical fiber pressure sensors developed recently have merits of compact size, installation ease and relatively low cost. However, they are normally not suitable for IMEP measurement due to the insufficient measuring accuracy in low frequency range, which is vital for the measurement of indicated mean effective pressure (IMEP). On the other hand, it is confirmed that the IMEP is determined by the frequency components which are equivalent to, or twice greater than those of the engine speeds included in the indicated pressure wave form. The IMEP calculation method discussed in the following is capable of accurate calculation of IMEP, by checking the characteristics of the pressure sensor in advance and correcting the primary and secondary components of frequency properly. This paper describes the correction method and reports the measured results obtained in actual engine operations.

Regarding measurement of the flow rate of exhaust gas or intake air of engines with several instruments, the pulsating flow in systems causes the error in indicated flow values. Usually a buffer tank is employed for decreasing the pulse. However the tank is rather inconvenient. The authors have developed the named “Surge Tube”, which is composed of a thin silicone rubber film tube having a considerable thermal and mechanical durability. In the conditions near atmospheric pressure, the effective volume as a buffer tank is over 100 times the free real tube volume, without any change in dead volume. The static relations between the inner volume change and the pressure are the most important characteristics, depending on the diameter, thickness, volume, and hardness of the silicone rubber film. The dynamic characteristics of the Surge Tubes are shown as the static pressure configurations at the inlet and outlet of the Surge Tube.