Instantaneous pressure measurement in pulsating high temperature internal flow in ducts

Research tasks in internal combustion engines often require instantaneous pressure measurement of the gases inside the exhaust manifold including absolute value information. In such environment, flow operation includes high temperature and extremely pulsating conditions. The work described in the paper identifies the problems that arise when acquiring absolute pressure with a piezoresistive transducer. A methodology based on using an additional cooler for a piezoresistive sensor placed between the duct and the original sensor cooler adaptor is proposed for dynamic pressure measurement. Specific tests have been performed in cold and hot pulsating flow in order to check the influence of the additional cooler geometry. It is possible to remove the effect of the additional cooler but the procedure depends on the pressure in the duct. If relevant frequencies in the signal are similar to the natural frequency of the cooler, a simple filtering technique is not recommended. In this case, direct application of the acoustic theory inside ducts allows the reconstruction of the instantaneous pressure in the duct. Comparisons between the reconstructed pressure and measurements carried out with piezoelectric transducers, which do not capture the absolute value of the signal but can be placed in the duct without using an additional cooler, in hot and pulsating flow are presented. Results confirm that the method for pressure reconstruction from additional cooled piezoresistive transducers provides accurate information for instantaneous pressure measurement in hot and pulsating flow conditions inside ducts.