RATING OF FUELS

Evening Post, Volume CXXV, Issue 148, 25 June 1938, Page 28

RATING OF FUELS

A TECHNICAL ADDRESS

A paper, with lantern illustrations, was.read at a meeting of the New Zealand branch of the Institution of Automobile' Engineers' by Mr. L. F. Elsby on the subject of "Knock Rating Laboratory- Test and Road Correlation." He dealt ,firpt with the early work of H. R. Ricardo in England and Midgley and Boyd in America.- With regard to knock rating determinations in octane numbers he pointed out , that octane itself gave a very poor ._. performance from the point of view of antiknock, whereas the reference fuel really used' was iso-octane,. and, in fact, iso-octane numbers were reported. Motor spirit contained so many chemical types of hydro-carbons that the subject was most complex, and it was because of this, fundamentally, that octane numbers Of a fuel did not predict its road performance. Petrols were composed today of straight-run spirits, "cracked," "reformed," "polymerised," blended with benzol and in some countries with alcohol, and ' also containing tetra ethyl lead. It was common knowledge among workers in this field that the octane number of any one particular fuel might be lower than another of different type, and yet give a much higher anti-knock performance on the road. In 1934, at Union Town, in America', actual field work was carried out in about 20 cars by 40 technical specialists representing 25 companies and institutions interested, and the total milage of the road test was estimated at something like 20,000. In modern makes of cars spark timing was automatically controlled by various' means with the object of advancing the spark as far as possible at medium road speeds enabling the car to run on a lean mixture and to give the highest possible milage per gallon. This was an added complication to knock testing correlation on the road compared with laboratory determinations of octane numbers. Portion of the lecture was devoted to technical progress in the rating of aviation fuels.

How much has been accomplished towards eliminating waste of power on its way from the engine to the driving wheels is indicated by the fact that the modern clutch, a hard-worked component, is very near 100 per cent, efficient, due to the use of ball or roller bearings, and the absence of slip between the friction surfaces. The gearbox of today has an efficiency percentage of about 92, while the latest propeller shaft and universal joints show practically no loss, their efficiency being rated at 99 per cent. In the final rear-axle gear drive the efficiency of the figure is around the 95 to 97 per cent, mark,