At The Wheel

NZ Truth, Issue 1200, 29 November 1928, Page 18

At The Wheel

Some Temperatures Reached By Modern Engines

11l a fairly efficient high-compression engine, such as that of a sports motor-cycle, the explosion temperature will range from 1500-2200 deg. centigrade, the boiling point of water being 1 100 deg.

piSTON heads reach a temperature 1 of 250 to 500 cleg., and the piston walls about half this figure. Cylinder walls keep rather cooler, their temperature ranging from 100 to 150 deg., while the crankcase varies between 50 and 150. In the case of water-cooled engines, the cylinder temperatures are kept lower, because the boiling: point of water imposes an extreme limit of just under 100 deg. For this reason more heat which might usefully be used for power production is wasted, which is one of the reasons why air-cooling is becoming so popular for aviation engines. One of the greatest difficulties en-

countered by designers is the uneven temperatures attained by various engine parts. While the exhaust valve port is. one of the hottest portions, the neighboring inlet valve is being cooled by the incoming gas. Unless the metal is very carefully disposed, and the arrangement of coolIng fins is correct, cylinder distortion ensues, and it is this fault which causes the falling off m power so noticeable m some machines when they are driven all out for considerable periods. ■ The absence of distortion under extreme heat, due to more symmetrical design, is one of the reasons for the success of overhead valve engines m racing.