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Aviation History
1934
1934 - 1421.PDF
May 31, 1934 Supplement to FLIGHT iNHi FLIGHT" ENGINEERING SECTION Edited by C. M. POULSEN No. 100 (Vol^esIX) 9th year May 31, 1934 CONTENTS The Effect of Swirl on Petrol Engine Combustion Investigation into the Variation of Engine Power with Height Technical Literature— Summaries of Aeronautical Research Committee Reports Page 33 37 39 THE EFFECT OF SWIRL ON PETROL ENGINE COMBUSTION BY J. F. ALCOOK* " SWIRL," or rotation of the charge within the combus- tion chamber, is known to have a profound effect on combustion in Diesel engines, but its effect on petrol engines has not received much attention. The reason for this is that in the Diesel it is a valuable asset, easing as it does the critical problem of fuel distribu- tion, while in the petrol engine it is generally a nuisance. Until recently petrol engine swirl has been of no great importance, for in most engines of normal design the amount of swirl, if any, is so small that its effect is negligible. There are, however, a few known excep- tions to this rule, and perhaps a fair number of unsus- pected cases. Recently, however, the single sleeve valve engine has entered the aircraft field, and in this type of engine swirl is of far greater importance. As will be seen later, the method of inlet port control in these engines automatically produces a high rate of swirl, and pain- ful experience soon showed that it was a factor to be reckoned with. Method of Swirl Production In the single-sleeve engine the inlet ports are opened by the circumferential motion of the sleeve and closed by its upward motion. During the early opening period the orifice is faired on one side only by the edge of the cylinder port, and the mixture therefore enters obliquely, causing the charge to rotate in a direction opposite to that in which the sleeve is moving. Fig. 1 illustrates this effect. In the later part of the suction stroke the sleeve is moving vertically and no swirl is produced by the port • Mr. Alcock is on the Technical Staff of Ricardo & Co., Ltd., of Shoreham. SINGLE-SLEEVE-VALVE ENGINE: Diagram showing oblique inflow during early part of induction stroke. itself. At this time, however, the flow in the port nppi'oaches may be utilised to increase or reduce the •' natural " swirl previously produced by the port. Thus, in Fig. 2, which shows a section through the ports of the engine used for the tests described herein, the sleeve is moving anti-clockwise when the inlet ports open, and the natural swirl is therefore clockwise. If EXPERIMENTAL SINGLE-SLEEVE-VALVE ENGINE : tion through Ports. the mixture is admitted to the belt by the left-hand inlet, the flow in the belt is clockwise and reinforces the natural swirl, but if the right-hand inlet is used, the total swirl is decreased. These effects are clearly shown in Fig. 3, which shows the results of a " blow- ing " test on the above engine. In this type of test the engine is stationary, and air is blown through the inlet ports (the cylinder head being removed) and the rate of swirl is measured by a freely rotating vane within the cylinder. The test shows that the flow in D2540 a
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