FUEL ECONOMY

Evening Star, Issue 23492, 5 February 1940, Page 11

FUEL ECONOMY

A NEW METHOD Surprising fuel economy results were recently obtained in England during some practical tests conducted with a view to ascertaining what fuel economy could be obtained by driving on the “open and shut ”, system, a practice which has. enabled many competition and expert motor drivers to obtain astonishing miles per gallon figures in fuel consumption tests on the opeli road. ’ Expressed shortly, the method consists of accelerating on full throttle on top,gear to about 40 m.p.h., then to shift the gear into neutral and let the car coast until the speed drops to about 15 m;p.h. with the engine idling. The operation is repeated as long as circumstances .permit, the gear being re-engaged-,hefore commencing to accelerate. .A,.skilful driver can make use of ■this* form of driving- without his passengers hardly being aware of the fact. At first sight, this may seem a queer way ,of progressing, but tests have disclosed tnat anyone who cares to adopt this style of driving can save considerable<fuel on a long trip. It should be borne in mind that thq petrol engine gives its highest efficiency on full throttle—that is to say, it consumes less fuel per brake horse-power per hour on full throttle. With a view to determining the precise effects in practice of driving on •long runs on the “ open and shut” principle- at varying speeds, etc., the Sdlex' Carburetter Company, England, recently carried out some actual tests, the results of -which are informative and interesting. , ’ Special testing apparatus,' devised by the company, was placed on a 10-h.p. car and the following tests carried out, with three passengers aboard, over two miles of flat toad at steady speeds. The figures given are'the. average of runs made in opposite directions. First of all, tests were made on normal fuel at four different average speeds to obtain a record of normal petrol consumption in the particular car used, in order to make relative comparisons with the results obtained in the “ open and shut ” style of driving. At 20 m.p.h. the fuel consumption was 42.3 m.p.g., at 30 m.p.h. 36.4 m.p.g., at 40 m.p.h. 33.7 m.p.g., and at 50 m.p.h. 28.9 m.p.g., figures which disclose how speed affects petrol consumption. The.car was then driven-to ascertain, the effect on consumption of acceleration on full throttle to 40 m.p.h. on top gear, then coasting in neutral, with idling engine, to 15 m.p.h. and repeat-' ing?,ihe operation. In the two miles, th&jphases or coasting operations varied from'five to eight, according to the direction of travel and traffic met. The average time taken to raise speed from 15 to 40 m.pdi. was 19 l-ssec, ftnd the average time to coast from 40 m.p.h. to 15 m.p.h. was 36sec. Roughly, the acceleration took about 0.1 mile and coastings rather over 0.2 mile.: The mean speed was 27.07'm.p.h. and average 1 consumption 39.9 m.p.g., as compared with 34.2 m.p.g. at 30 m.p.h. under normal conditions, a gain of about five m.p.g. A number of similar tests, under varied conditions as to maximum speed, and speed coasted to, were conducted. The best, fuel consumption resulted' from accelerating on top gear from 20 m.p.h. to 40 m.p.h., then coasting down to 20 m.p.h., using full throttle for accelerating. This gave 5J phases at a mean speed of 28.5 m.p.h, and a petrol consumption of 42.4 m.p.g. The time for acceleration from 20 to 40 m.p.h. was 15.2 sec. During The tests it was shown that, by switching off the engine while coasting. another three m.p.g. was obtained, also that increased maximum speed resulted in a loss of about two m.p.g. It must bo _ mentioned, says the ‘ Dunlop Bulletin,’ that the purpose of the tests was- to make clear exactly what real advantage could be' gained by the intelligent use of this method of driving on the open road in the event of a motorist being reduced to obtaining the utmost mileage from his supply of petrol. No doubt many motorists in this country, as a matter of interest, will determine for themselves actually what extra m.p.g. can be gained by the “ open and shut ” method of driving.