High Octane Fuels: The Conditions Governing Their Use in Engines for Commercial Aeroplanes Available to Purchase

THE original work of Mr. H. R. Ricardo in 1919 showed some of the technical advantages of using fuels of high anti‐knock value. Since this time the development of aero‐engines in respect of power output and economy has depended more upon the fuels available than upon any other factor. Considerable progress has been made in the direction of improving the anti‐knock value of petroleum spirits, which constitute the bulk of the fuel used in aviation throughout the world. However, until very recently this progress had not been very rapid, and as Mr. Ricardo showed, far greater improvements in anti‐knock value could be achieved by the use of other fuels such as benzol, toluol and alcohol. On the octane scale benzol and toluol have a blending value by the C.F.R. motor method of about 90 in concentrations up to 50 per cent; that of alcohol being about 105. This is shown in Fig. 1, from which it will be observed that two curves are given for ethyl alcohol, one being obtained under motor method conditions (mixture temperature 149 deg. C.) and the other with the same heat input as required for a normal aviation gasoline. By this means the additional advantage of the higher latent heat of the alcohol blends is shown. Neither benzol, toluol nor alcohol is produced in very large quantities, and moreover, in times of national emergency they are likely to be required for purposes other than for use as aviation fuels.