James Keilar, of Christchurch, asks :-

During the second world war powerful sleeve valve engines were developed for British fighter aircraft. Why hasn't the motor vehicle industry used these engines in production cars?

John Smaill, a mechanical engineer at the University of Canterbury, responded.

One hundred years ago car engines were noisy and unreliable, often breaking valve springs. Charles Knight decided to try and solve these problems by changing the way the gases flowed into and out of the cylinder.

The conventional four-stroke engine has the piston moving in a steel cylinder. The fuel/air mixture was drawn into the cylinder through a spring-activated inlet poppet valve and following combustion the exhaust gases were discharged via a similar outlet valve. In modern conventional engines a camshaft controls how and when these valves are opened and closed.

Mr Knight developed an engine with two moving concentric sleeves around the piston. These sleeves have slots machined into them and an additional drive causes them to move with respect to each other and the engine block. At given positions, as the piston moves up and down in the inner sleeve, the slots in both the inner sleeve and outer sleeve line up with the inlet or outlet ports of the engine block.

The removal of the poppet valves stopped the noise they made when they closed while the presence of a lubrication film on the sleeves also helped to quieten the engine. An additional advantage of the sleeve valve system was that the top of the cylinder could be hemispherical and combined with a better flow pattern for the gases this improved the efficiency of the engine. Unfortunately by the time Mr Knight had got the sleeve-valve engine to run successfully, the conventional poppet valved engine had also been improved. Therefore most automobile manufacturers did not change to this new engine and only a half million vehicles powered by sleeve valve engines where produced in the United States of America by 1933. Because it was so quiet some luxury car companies in Europe, such as Daimler, used the sleeve-valved engine manufactured under licence.

While the sleeve valve engine is efficient, it produces exhaust gases that contain an unacceptable volume of pollutants and the engine could not satisfy the current anti-pollution laws of most countries.

In 1932 the Bristol Engine Company, under the guidance of Sir R Fedden, adopted a sleeve valve engine design using a single moving sleeve and produced an aircraft engine called the Perseus. The company continued to design and manufacture sleeve valve engines with one of the last being the Centaurus that developed up to 1850Kw. This was the one of the most powerful aircraft petrol engines manufactured and was used in the Tempest and Sea Fury fighter aircraft.