"STAIR CASE" PISTONS

Evening Post, Volume CXII, Issue 51, 28 August 1926, Page 18

"STAIR CASE" PISTONS

. The problem of "pinking" and autolgnition in motor engines is a highly technical one, involving investigations into the explosion of hydro-carbons in closed vessels, by no means so simple as it looks. The main avenue to higher efficiency in the case of internal combustion engines is the raising of the compression ratio. This can be done by introducing into the combustible mixture a minute proportion of "antiknock" compound such as tetra-ethyl lead, but the advantage is gained at the cost of a certain amount of risk with exhaust gases.- The maximum ordinary compression ratio is 5 to 1, beyond which auto-ignition starts with all its dangers. By the use of tetra-ethyl lead the ratio can be raised to 0.5 to 1.

An exceedingly novel and ingenious proposal' to secure similar results without the use of lead or other compounds is described in the latest issue of 'The Motor" (London) to hand. Thesis to shape the piston-crown like a staircase in a series of steps down from the points of the plug. The invention is that of a Frenchman, M. Dumanois, who claims to have secured by his stepped piston a compression ration of 6.7 to 1, without "pinking," on a fuel consisting of 77 per cent, of petrol and t!-3 per cent, of paraffin.