Transfer Matrix Computation for Intake Elements with Large Pressure Fluctuations under Mean Flow Conditions 2012-01-0672

A new methodology for modeling engine intake has been presented; it is based on a transfer function relating pressure response and mass flow rate that makes use of the corresponding frequency spectrum obtained on the so-called “dynamic flow bench”. This new approach provides a way to obtain fast and robust results, which take into account all the phenomena inherent to compressible unsteady flows. Recently the potential of this method has been explored by incorporating it in a GT-Power model to produce a coupled frequency - time domain simulation of a naturally aspirated engine. The method exhibited promising results.

One strategy utilized to combat the increasingly stringent emissions standards and reduce fuel consumption is to employ downsized turbocharged engines equipped with charge air coolers (CAC). Therefore, research and development must focus not only on naturally aspirated engines but also on turbocharged ones. Simulating such engines with the transfer function methodology is quite difficult, and identifying the transfer function of an air intake line with a CAC and turbocharger requires mounting it on the “dynamic flow bench”, which becomes impossible due to thermal and thermodynamic discontinuities. It is therefore necessary to split the intake line into separate elements, which leads us to transfer matrices.

In this work, a new method was developed to determine the transfer matrix across a simple element, it is capable to deal with any large pressure fluctuations and mass flow rates like the ones encountered on any engine without specific parameterization. It allows reconstruction of the matrix from a non-steady response to a nearly impulse excitation using the dynamic flow bench. Once the transfer matrix for a simple tube is calculated, it is validated by placing the corresponding tube in a GT-Power model of a single cylinder engine intake line.

In conclusion, the perspectives of such a technique are presented. It will allow the calculation of transfer matrices of a more complex system (CAC) intended to be later used for engine simulation purposes.