Paper 34: Effects of Variable Specific Heats and Gas Composition on Unsteady Flow Calculations

Abstract

A numerical method has been developed for the solution of one-dimensional non-steady flow problems including the effects of friction, gradual area change, heat transfer between the gas and the pipe wall, longitudinal variations, and discontinuities in gas composition and entropy. The fluid considered obeys the perfect gas equation of state, but the specific heats may vary with temperature. The method is not intended for use when shocks are present, but will give an approximate solution if shocks occur. The accuracy of the new method has been checked against existing methods for more simple cases, and although the new method has been found to be slightly superior it is more complicated, much slower, and the boundary conditions are more difficult to develop. For this reason, it is suggested that the new method be used to check on the adequacy of the existing simpler methods for each new application. The methods have been compared for the case of a typical diesel engine exhaust system and it has been found that the earlier methods are adequate for all practical purposes.

Modelling the Exhaust Noise Radiated from Reciprocating Internal Combustion Engines--A Literature Review

“…It was later extended to consider the case of variable specific heats and gas composition (Ref. 59), supersonic flow (Ref. 60), and ultimately to define gas composition along the path lines in terms of the molar concentrations of twelve different species, allowing chemical reactions along the path lines.'…”