The flows at the intake and the exhaust of an internal-combustion engine are most of the time simplified to a single space dimension, and the hyperbolic partial differential equations that govern the compressible and unsteady air flow are discretized and solved numerically. This method is the basis of today's engine simulation codes. Models for complex parts such as the charge air coolers often need calibration with experimental engine data essentially for the pressure drop coefficients and the corrected lengths. Another technique for understanding wave action inside the pipes of an internal-combustion engine is to use the reciprocating nature of the engine itself and to gain access to the frequency spectrum of the pressure and the mass flow signals. This was achieved in this paper using a dedicated dynamic bench that identifies a transfer matrix which is defined in terms of the pressure and the mass flow rate. This new transfer matrix technique permits the dynamic pressure and the mass flow to be identified under similar conditions to those encountered in an engine. The transfer matrix is measured for two charge air cooler geometries and validated using experimental engine measurements. The results and methodology are explained in the frequency domain and the time domain, and the future objectives and perspectives discussed.

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