Investigation into relative temperature measurement of pulsed constrained gas flow using passive acoustic means

The requirement to measure the real time, dynamic temperature of exhaust system gases is becoming more and more important in the areas of aeronautics, automotive (cars, trucks, etc), marine and industrial/environmental applications, in particular on a cycleby-cycle (CBC) basis. Monitoring exhaust gas temperatures of any power-plant can give important diagnostic information for the monitoring of fuel mixture, combustion efficiency etc. This 'diagnostic' information can be used to help 'dynamically' tune the combustion process or engine operation to assist in reducing exhaust emissions, optimize fuel flow rates and help improve overall efficiency of the system or engine. In order to realize this capability, it is necessary to monitor the dynamic temperature of the exhaust flows with a temporal resolution in the millisecond range. The fastest response time achievable by currently available temperature sensors which are robust enough to survive in these very hostile environments is of the order of several hundred milliseconds or greater. To this end, conventional measurement systems such as resistive-temperature sensitive devices, bi-metallic solutions or even optical solutions are orders of magnitude too slow to be of any use. In order to achieve the temporal resolution required, a new measurement methodology has to be developed. This work presents a novel temperature measurement sensor methodology, based on passive acoustic tone generators and specifically the labial flue pipe, that respond to the constrained pressure pulses generated by a pressure release mechanism in an exhaust or blow-down system. The work includes the development of a unique software suite that allows optimal tone generator design parameters be determined and identifies a unique interaction between the Ising efficiency number and the Reynolds number pertaining to the jet mechanism of the tone generator. Experimental results presented indicate a sensitivity to tone generator oscillation frequency, with pre-oscillation of the tone generators shown to further enhance this sensitivity.