Instantaneous Mass Flow Rate Measurements Via Transfer Matrix and Modal Analysis for an Internal Combustion Engine Application

Abstract

The gas flow through engines is governed by intake and exhaust pipe arrangements. The pressure waves generated at the valves interface interact with the geometry through reflection, transmission and propagation and induce a standing wave action inside the pipes. This in turn causes fluctuations of mass flow at the same characteristic frequencies. Therefore measurement of the unsteady behavior of mass flow is necessary in order to obtain an accurate understanding of the influence of wave action on engine performance and consumption. In this paper, an experimental mass flow impulse technique is employed to characterize dynamic pressure and mass flow inside a pipe equipped with two pressure sensors. The technique is based on a modal decomposition of resonant frequencies which is explained along with the calibration procedure to cover a sufficient frequency spectrum. The result is a transfer matrix formulation written in terms of pressure and mass flow that can be used to calculate instantaneous dynamic mass flow using the two pressure signals. This was done on three engine cases using GT-Power simulations, where the GT-Power mass flow results were compared to the ones given by the experimental transfer matrix. Finally the procedure of applying the transfer matrices methodology for more complex elements of engine is presented and explained. This methodology gives the possibility to measure instantaneous air mass flow rate on a real engine just by using two separate pressure taps anywhere on the line. Only two sensors at fixed positions are necessary without any calibration. Another possibility is to include this kind of transfer matrix in an ECU in order to improve the internal combustion engine control especially for the pollutant emissions reduction.