MOTOR NOTES

Evening Star, Issue 23682, 16 September 1940, Page 10

MOTOR NOTES

fßy ‘ Radiator.’]

LIGHTING-UP TIMES To-day .., .... ... ... 6.27 Tuesday 0.28 Wednesday •..., .... 6.29 Thursday ... ... 6.30 Friday ••• 6.31 Saturday ... ... ••• 6-36 Sunday 6.34 This month’s coupons—B and 9. EXHAUST VALVE COOLING One of the problems facing designers and manufacturers of internal combustion engines is the increasing exhaust valve temperatures brought about by the higher compressions and increased speeds of modern automobile and aircraft engines. Operating temperatures of exhaust valves increase not only with engine speed, but also with the valve diameter —that is to say, with the cylinder bore. The heat absorbed by the valve head during the power and exhaust strokes is dissipated in part through the exhaust valve seat and in part through the valve stem and its guide. Many methods have been tried to dissipate this heat, which has a considerable bearing on the life of the valves and the efficiency of the engine. The problem of finding effective coolants for exhaust valves is to-day more acute in aircraft engines than in automobile engines, owing to the fact that the latter are water cooled, whereas most aeroplane engines are air cooled. Mercury was tried many years back and used to wet the inside surface of valve stems. This method, while effective, proved to be poorly adapted to quantity production. Water sealed in the valve stem was also tried, resulting in reducing the valve head temperature by from 600 to 700 deg. P., but steam generated to about 10,0001 b per square inch in the interior of valve stem precluded satisfactory operation. Other substances were also tried, but they quickly decomposed at high temperatures and formed into carbon. Oil circulation through the hollow valve stem and cooled in a separate radiator had to be discarded owing to its complications. An aluminium rod in the hollow valve stem was also experimented with, but the heat expansion of the aluminium being about twice that of steel, rendered this scheme impractical. Experiments continued over many years, until it was discovered that a mixture of salts composed of sodium and potassium, with a ’melting point of more than 900 deg F., was an excellent cooling medium when used as a filling for hollow stemmed valves. Research continued and finally led to the adoption of metallic sodium, which has a much lower melting point (208 deg F.) and a much higher boiling point (1,616 deg P.) than salts. So successful has this coolant proved that both the stem and head of exhaust valves of most high powered air cooled_ aircraft engines are now cooled by this engenious method. If the compression ratios of the power units of modern motor car engines are raised much higher, with a view to gaining greater efficiency and power from a given engine capacity, the practice of using sodium cooled exhaust valves in high powered aeroplane engines may have to be adopted by motor car manufacturers, unless the rotary valve type of power unit comes into the automobile field. RUBBER FROM PETROL A synthetic rubber produced from petroleum is announced by the Goodrich and Standard Oil Companies of America. So successful is it claimed to he that America may be freed of its worries at a future date over the supply of natural rubber. GERMAN FUEL SUPPLIES States the ‘ Motor ’ (England) In our issue of June 19 we endeavoured to give some estimate of the German fuel position, and we concluded that the German home-produced fuel, plus reserves, would be for them to carry on the war for a considerable time. Unknown to us, the ‘ Engineer ’ of approximately the same date had an article dealing with the same matter, and although the evidence they put forward differs somewhat from ours, it is interesting to note that their conclusions are the same. They estimate an average number of German aircraft engaged on day-to-day operations as 2,000, with a consumption of 4,000 tons per day, and, adding service vehicle, etc., makes the total consumption of the Luftwaffe 4,500 tons daily. The use of 4,500 tanks per day is also assumed with a consumption of one ton per tank per day. With an allowance made for fuel consumed in naval and transport vessels and industry, it is assumed that the total German demand on oil resources is about 13,500 tons per day, or 5,000,000 tons per annum. ... Against this it is reckoned that 500,000 tons of oil were seized in Denmark and Norway, and that the fuel derived from the Polish oilfields, plus synthetic production, probably amounts to about 2,500,000 tons per annum. There is no doubt, says the ‘ Engineer,’ that Russia or Rumania can separately supply the balance of fuel required by Germany. Thus there is no reasoned basis for the belief that her collapse through shortage of oil supplies is likely to occur in the measurably near future. The advantage of access to unlimited supplies of liquid fuel lies with Great Britain, but to make this advantage decisive we must exploit it in increasing measure.

MOTOR CYCLING

FIXTURES. To-night.—Monthly meeting,