PREDICTION OF THE PRESSURE WAVE IN AUTOMOTIVE EXHAUST PIPES

Elhadi Abujnah; Tuhami M Jaballa

doi:10.66411/jer.v16i.226

Authors

Elhadi Abujnah Mechanical and Industrial Engineering Department Faculty of Engineering- University of Tripoli, Libya Author
Tuhami M Jaballa Mechanical and Industrial Engineering Department Faculty of Engineering- University of Tripoli, Libya Author

DOI:

https://doi.org/10.66411/jer.v16i.226

Keywords:

Pressure Waves, Exhaust Pipes, MacCormack Method, Internal Combustion Engines

Abstract

Knowledge of the behavior of the flow of exhaust gases in the exhaust system of automotive engines help in the designing of a more efficient and more quite exhaust pipes and muffler. The exhaust valve opening and closure in a very short time while the pressure in the combustion chamber is high causes pressure waves traveling in the exhaust pipe. It is believed that these pressure waves are responsible for the unwanted noise produced by the internal combustion engines. A mathematical model is proposed for the calculation of the exhaust pipe flows, concentrating on the variation of pressure with time at different locations of the exhaust pipe. In order to simulate the complicated flow with the presence of heat transfer and friction, a system of quasi-one-dimensional model equations is employed. A FORTRAN program is developed to obtain the pressure and velocity of the exhaust gases in a 0.04m diameter, 6m long exhaust pipe. The model is using MacCormack method and a constraint for numerical stability. Results of the model showed that the shape of the pressure waves has the correct trend; however the shape does not have the well known inverted bell shape. Values of maximum pressure were predicted to within 3.5% from that found in literature. The pressure gradient along the exhaust pipe was predicted with an acceptable range depending upon the equation used for the friction factor

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