From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Blowing tests to determine the effect of port shape on airflow through inlet valves.
| Identifier | ExFiles\Box 134\2\ scan0052 | |
| Date | 30th October 1935 | |
| AIR FLOW THROUGH INLET VALVES. It is generally realised that the air flow through an inlet port is governed by the valve diameter at small lifts but that at high lifts the shape of the port and the space between the valves and cylinder walls play a large part. In order to determine the effect of port shape and to assist in the design of inlet ports, blowing tests have been carried out in various types of cylinder and the results are given in the report. The cylinder to be tested was connected through a flowmeter to a blower with suitable adaptors and the air flow through the inlet valves was measured at various pressure drops and valve lifts and also with the valves removed to show the effect of port shape alone. The upstream pressure was measured close to the valve by a static tube and corrected for velocity head. The downstream pressure was assumed to be atmospheric, the bottom of the cylinder being open. With the high velocities common to inlet valves, the effect of adiabatic expansion is important and it cannot be assumed that the pressure drop varies as V². Nor can the usual adiabatic law be applied owing to the peculiar shape of the ports. It was found that the most satisfactory formula to fit the experimental results was :- Air Flow (lbs/min) = K * sqrt( (Pressure Drop ("Hg.) x P.in Cyl. ("Hg.)) / Absolute Temp. (°C.) ) The discharge coefficient K from this formula is plotted in the curves following and it should be noted that K applies to the whole cylinder head and not to a single valve. CURVE 1 gives the variation of K with valve diameter at a lift of 0.2" and shows that at small lifts the discharge coefficient depends only on the valve diameter, given a constant seat angle, of 45°. | ||