"The exhaust pressure against which an engine works affects the amount of pumping losses, the volumetric efficiency and the rate of advance of the flame front during the combustion process.
When the back pressure is decreased to the same pressure as the intake pressure, the amount of negative work done during the exhaust-intake process approaches the positive work done during the process. It can be seen from a PV diagram that it is possible to make this negative work less than the positive work and gain work during the process.
Because of the "15 to 30 degrees” of intake valve and exhaust valve overlap, exhaust gases may enter the intake manifold which has a pressure below atmospheric pressure. When the exhaust valve closes, this volume of residual gases may reenter the cylinder. This volume may be decreased by decreasing the exhaust pressure in the manifold.
The ratio of intake pressure to exhaust manifold pressure will have a great effect on the volumetric efficiency. High ratio values (1.75 - 2.00) will result in high volumetric efficiency. “While the loss (in volumetric efficiency) is only 5 or 10 per cent when the intake and exhaust manifold pressure are approximately equal, it becomes larger very rapidly as the ratio of intake to exhaust pressure is reduced.”
The decrease of back pressure will allow the exhaust gases in the cylinder to expand more and thus decrease the weight of the residual gases. The weight of the new charge entering the cylinder will increase as this weight of residual gases decreases. The volumetric efficiency will be increased as a result of this increased weight of the incoming charge"--Introduction, pages 1-2.
Miles, Aaron J.
Mechanical and Aerospace Engineering
M.S. in Mechanical Engineering
Missouri School of Mines and Metallurgy
vi, 50 pages
© 1951 James J. Trace, All rights reserved.
Thesis - Open Access
Internal combustion engines
Combustion gases -- Testing
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Electronic OCLC #
Link to Catalog Record
Trace, James J., "The effect of back pressure created by a venturi tube on power output and efficiency of an internal combustion engine" (1951). Masters Theses. 2981.