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Aviation History
1940
1940 - 1231.PDF
25, 1940 14 THE AIRCRAFT ENGINEER SUPPLEMENT TOFLIGHT 391* Fig. 9. A multi-stage compressor. Figs. 3 (centre) and 4 (right) show two views of the ballistic velocity radial-flow turbo-supercharger. workers in research have established that once the exhaust port or valve is opened practically half the exhaust gases leave the cylinder with a velocity of the order of the speed of sound. Clearly, then, we have here the gas velocity required to operate the turbine, and there is no necessity to convert this velocity to a pressure head before reaching the tur- bine nozzles and then reconvert the pressure head back to a velocity of the order of its original magnitude. In addition, Kadenacy found that this ejection of the exhaust gas at ballistic velocity, was followed by a depression with the residue of the exhaust gas in the combustion chamber moving rapidly towards the exhaust outlet, and at the same time a series of gas oscillations occurred in the exhaust pipe system. From this it is quite evident that in a four-stroke engine, where the exhaust valve remains open for the usual period, high-temperature exhaust gases may flow past the exhaust valve in both directions several times before it closes. Ballistic Velocity Turbine In my patented design of '' ballistic velocity turbine'' the exhaust gases are directed into a radial outward flow turbine with a minimum of loss in their velocity, and further, the turbine blades are extended outwardly so as to act as centrifugal exhauster blades (see Figs. 3, 4, <5 and 7). With this method of operation an annular zone of accelerated outward gas flow is created around the tur- bine wheel, the depression in the exhaust pipe and system is maintained and prolonged, and return surges of gas and gas oscillations in the exhaust pipes are eliminated. Fur- thermore, the exhaust gas back pressure is eliminated, the temperature of the combustion chamber and exhaust valve are reduced, and more room is provided in the cylinder for a greater and denser charge of clean, fresh air or combustible mixture. In the turbine as illustrated in Figs. 3 and 4, the exhaust gases enter the turbine direct by way of pipes (1) and passages (2), and the jets of gas to drive the turbine leave the convergent nozzles (3) at an angle of 16 deg. to impinge on the turbine blades (4). In the passages be- tween the blades the path of gas flow is changed and it finally emerges from the blades almost radially. The exact exit angle is determined by the path of gas flow in the Wade passages, the peripheral velocity of the wheel, and the angle at the tips of the exhauster section of the blades. must not be thought, however, that the annular zone 01 accelerated cutward gas flow around the turbine wheel !s gained without expense, as part of the power output01 tne turbine is absorbed in the process. The curved convergent nozzles (3) are segments of a tube welded to «e disc (5), and the turbine blades (4) are designed to 6>vc streamline gas flow through the blade passages by combination of the elements shown in Figs. 2 and 8. They are machined from the solid metal of the rim of the turbine wheel, an exact but not difficult operation. Being solid with the rim, they provide an easy path for heat flow to the rim. We may now consider methods of cooling the blades and rim of the turbine. The top blade on the left of Fig. 2 shows the formation of one of a number of similar blades cooled by means of air passed through the interior com- partments of the blade. In addition, tests were performed with the turbine wheel and blades partly exposed to the slipstream. The results indicated that the turbine could be almost sufficiently cooled by these two methods in combination.* Recently Junkers have taken out a British patent in which they propose to cool the turbine by means of air taken from the delivery by the centrifugal air compressor. In the Biichi system, as applied to four-stroke compression ignition engines, the turbine is cooled by means of air supplied by the supercharger. This flows through the inlet valve port by way of the combustion chamber. 0 90 180 270 ' 360" 450 540 630 CRANKSHAFT TRAVEL IN DEGREES Fig. 5. Pressures in exhaust pipes. Full lines apply to two-stroke engine with ballistic velocity turbo-supercharger; dotted lines to the Biichi system on a four-stroke compress-ion-ignition engine. • " The Work of the DVL," by Dr. F. Seewald, flight. Nov. 24, 1938.
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