ECONOMY IN PETROL

Evening Post, Volume CXXIV, Issue 15, 17 July 1937, Page 26

ECONOMY IN PETROL

THE DRIVING FACTOR

WASTEFUL ACCELERATION

Given a car with standard tuning, which is in reasonably good mechanical condition, the rate of fue. consumption will be influenced to .an extraordinary extent by the way in which it is handled. Most people know that fast driving results in a heavier consumption, but few realise how great are the differences for which average speed is responsible. An English experimenter has carried out some, tests on a light, but powerful car, of the high-performance type which has a nominal consumption figure of 16-18 miles per gallon, according to the maker's catalogue. It was first driven in a normal manner, over a circuit selected to reproduce average road conditions, without taking the engine up to maximum revolutions on the intermediate gears; the capacity of the car for acceleration was not fully

employed, and at no time did the speed exceed 50 miles per hour. Careful measurement showed that under these conditions the car was covering exactly 17 miles per gallon.

■ As a second test, the car was driven over the same circuit in racing style—, in fact, it was treated more harshly than was fair to the mechanism-rthe engine being pushed up to maximum revs, on each gear, while full throttle was employed wherever possible; braking was left to the last moment on all ■corners. In these circumstances the fuel consumption worked out at 10-J miles per gallon. Just by way of contrast, a third test was made, in which the car was driven with the sole idea of obtaining a good consumption figure. Accelerator and brakes were treated gently, 40 miles per hour was never exceeded, and the average speed worked out at only 30 miles per hour. With this treatment the car gave 20J miles per gallon. All these tests were repeated three times, average figures being quoted, and were made in the course of a few hours, so as to rule out variations in weather conditions; no mechanical adjustments wers carried out in the course of the experiments. These results show clearly that driving methods make an enormous difference to fuel consumption and have been confirmed by experiences with many other types of car. Violent braking plays a part by causing the fuel to surge in the tank. and the float chamber; an effect which often leads to flooding and waste. Nowadays heavy traffic involves very frequent changes in road speed with fewer opportunities than formerly of sustaining a steady rate of travel. During acceleration, fuel consumption is heavy because the mass represented by the car has to be set in motion by energy supplied from the engine; after [this cruising at a steady speed needs much less petrol. Braking wastes the energy which has been so expensively stored in the moving car, and is followed, inevitably, by a further period of wasteful acceleration. The conditions are similar to those 'which apply when motoring in hilly country. . • It is obvious that the increase of consumption due to these factors is the more serious the heavier the car. The tendency towards bigger bodies besides adding weight has increased frontal areas and wind resistance, despite streamlining, and consequently more power is needed to push the car through the air. The more it is accelerated the. greater the demand on petrol consumption.