Measurement of Exhaust Gas Temperatures in a High Performance Two-Stroke Engine 983072

The performance characteristics of two-stroke engines are highly dependent upon the gas dynamic wave action in the exhaust system. In a tuned high performance exhaust system, negative suction pulses aid induction of charge into the cylinder, while positive waves aid its retention. The timing of these waves is closely related to the acoustic velocity, and is therefore dependent on the exhaust gas temperature (EGT).
In advanced engine management systems, the control strategy may be tailored to influence the EGT, and to maximize the beneficial influence of the gas dynamics in the exhaust. Therefore, accurate measurement of EGT is required for development purposes, and real-time feedback could potentially be used as an input to the management system. However, accurate measurement of exhaust gas temperature is fraught with difficulties due to a number of sources of error. Steady state errors can arise due to conduction and radiation of heat from the thermocouple junction, while in transient operation, additional errors arise due to the slow responses of the robust thermocouples which are required to survive the harsh environment.
In this study, the influence of the thermocouple geometry on the steady state errors has been estimated, and a technique has been developed to reconstruct mathematically the instantaneous temperature from the output of two dissimilar thermocouples. Results are presented to demonstrate that the reconstructed temperature correlates well with measurements from a fast-response thermocouple.


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