WASTE OF PETROL

Taranaki Daily News, 4 September 1935, Page 13

WASTE OF PETROL

USEFUL WORK 30 PER CENT.

POINT FOR MOTORISTS TO PONDER.

(By

“Spotlight.”)

When the average motorist has a gallon of petrol poured into the tank or his car he might ponder on the number of miles of travel he can expect for his 2s Id, but how many stop to think how that gallon is employed? Whether the motorist meditates on the point or not he would be amazed at the proportion of his 2s Id that is absorbed in various directions apart from driving the car. With a certain model of a popular American make 30 per cent, of useful work is obtained from a gallon of spirit, the other 70 per cent, being eaten up by various factors that contribute nothing to moving the car. For instance the water in the jackets in the cylinder block and in the radiator absorbs heat estimated to use 25 per cent, of the energy in the gallon of petrol, another 25 per cent, is wasted in exhaust, _ bevel gears demand 10 per cent., the universal joint accounts for 5 per cent, and friction for 5 per cent. With later models of the same make and with other makes the proportion between the percentage of useful work and waste varies a little from the figures quoted according to the size and design of the car, but any motorist may rest assured that he is not getting much more than 30 per cent, of tractive effort for his 2s Id. Water and exhaust are the two greatest sources of waste. The terrific heat generated by the explosion of the gas on the power stroke has to be absorbed, and while air cooling has been used for car engines, water jackets and radiator are the common method of cooling. Thus on the one hand the engine is generating heat while the radiator dissipates it. One of the main points for which the manufacturer seeks in an engine is a design that ensures the freest possible getaway for the exhaust gases in order that the new charge from the carburettor may be fresh when it is compressed on the power stroke and not contaminated or weakened by the burned gases of the previous explosion. Yet the efforts that are made to that end result in 25 per cent, of the value of a gallon of petrol disappearing to no good purpose down the exhaust pipe. Those are two examples of the mass of contradictions that exist in the internal combustion engine, but if the service station man told the motorist that about 70 per cent, of the gallon of “juice” he was buying was going to be wasted the motorist could not contradict him. TIME LAG FACTOR ITS EFFECT QN SAFETY. AVERAGE MORE THAN SECOND. One of the greatest dangers of motoring the world over is a purely inherent personal factor known as the lag, or lapse, that is inevitable between the observation and the act of applying the brakes, says the latest safety first message of the Automobile Association (Canterbury). This phenomenon is altogether outside the scope of the engineer. It is a retarded muscular function with which the physician alone can deal. Just how serious a bearing time lag has on motoring safety may be gathered from the recital of a few facts, the results of exhaustive tests overseas.

It was found that the lag varied considerably between car drivers selected at random, from three-fifths of a second in the case of a number of taxi-drivers, up to two seconds for another class who might have been expected to react much more quickly. Others again failed to respond to the expected signal, even after repeated trials. The general outcome of the tests indicated that a lag of three-fifths of a second was the minimum, and one and one-fifth of a second •a fair average for a considerable number of keen and experienced men.

The significance of these very short intervals of time is not apparent until their effect is realised in actual braking performances. As an example let it be assumed that the driver of a car running at 40 miles an hour is required to apply the brakes with maximum force when a selected spot is reached, and not before. His lag is three-fifths of a second, with braking efficiency 75 per cent. The car will cover 106 feet from the selected place before it -stops. Another driver with one second and one-fifth lag repeats the performance with the same car, but this time it will travel through 141 feet and will be running at. 28 miles an hour when it passes the spot at which the first man stopped. If the car weighed one ton it would have a striking force of about 29 tons at that point. In result, instead of an actual braking efficiency of 75 per cent, the corresponding efficiencies would be reduced to' 50 per cent; in the first case and to 38 per cent, in the second —very substantial differ-

ences. If by any means the lag period could be reduced to no more than three-fifths of a second ail round it may be taken for granted that accidents would be reduced substantially in number and the extent of peisonal injuries and damage to vehicles and other property.