Abstract
In the paper the author discusses the cause of the loss of pressure in the induction system of an internal combustion engine, and also the essential difference between the breathing conditions of a carburetting engine and those of a compression-ignition engine, and the features which are peculiar to the latter. He gives particulars of some experiments on the influence of valve ports of different shapes upon the breathing of a given compression-ignition engine cylinder.
The experiments cover the measurement of the pressure loss under a steady air flow as well as the effect upon the volumetric efficiency under actual operating conditions. The effect of a change in valve lift is discussed also. The results of the experiments show that the governing factor in volumetric efficiency is the velocity of the air at the actual valve opening, and that a Venturi form of port provides much needed room for the accommodation of the fuel injector, without any sacrifice in volumetric efficiency, by allowing a material reduction in diameter of the port at a short distance ahead of the valve opening. It does not, however, possess any other great advantage over a parallel port with an equal diameter of valve seat.
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