History of aicraft piston engines

Specifications and laboratory tests for antiknock

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Unformatted text preview: ines. Experimental work with leaded fuel continued thereafter at a rapid pace. It was officially adopted for use in aviation gasoline by the United States Navy in 1926 and by the Army in 1933, a nd has since become universally accepted as an additive for gasoline. A nother important contribution was Graham Edgar's work, about 1926, in determining the effect of fuel structure on antiknock quality and, 66 specifically, discovering the high antiknock properties of the branchedchain parafins such as iso-octane. Specifications and laboratory tests for antiknock quality of aviation fuels were sponsored by the Cooperative Fuel Research Committee in 1933, a nd led to good control of this quality in United States aviation fuels soon after. S. D. Heron was also an important contributor to this result. The " performance n umber" of a fuel, used from about 1942, is the ratio of k nock-limited indicated mean effective pressure (klimep) w ith that fuel, to the klimep in the same engine using iso-octane." Figure 63 shows the i mprovement in the performance number achieved both by the use of t etraethyl lead and the control of fuel composition. T he powerful effect of water or water-alcohol injection is also illustrated in figure 63. This development seems to have been started at Pratt & W hitney about 1940, and was continued by them, by the Army Air Corps a t Wright Field, and by the NACA laboratories. By 1946, water-alcohol injection was generally used for takeoff by both military and transport airplanes. The high consumption of the auxiliary fluid (about 50 percent of t he fuel flow) limits its use to short periods and to engines with sufficient s upercharging to take advantage of the increased knock limit. Altitude Performance and Superchargers T he fact that, as altitude increases, reduced air density reduces engine power m ust have been realized before it became obvious in 1909, when airplanes b egan to try for high-altitude flight. The advantage of altitude in military work became very apparent in World War I, but the only attempt at i mproved altitude performance used in World War I was embodied in the G erman BMW and Maybach engines, which were designed to be partly t hrottled near sea level, the throttle to be fully opened only above about 5,000 feet. Both engines were designed to be lighter in weight than would have been required for full-throttle operation at sea level, and the BMW also h ad higher compression ratios than could be used with full throttle at sea level without detonation. The advantage in altitude performance over an e ngine capable of full-throttle operation at sea level, however, was quite small. M easurement of engine performance at altitude was first seriously u ndertaken when the United States Bureau of Standards completed its a ltitude test chamber in 1918. S ubsequently a considerable literature on this subject developed (see bibliography). 67 T he Swiss engineer A. J. Buchi suggested the turbo-supercharger for aircraft in 1914. This type was then developed in France by...
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