A SOUPED-UP version of a Second World War aero engine could save millions of
litres of fuel a year, according to a Texan engineer. Dimitrios Dardalis of the
University of Texas in Austin says his improvements to the engine will cut the
fuel consumption of heavy lorries by 5 per cent, and reduce maintenance costs
into the bargain.
The Sabre engine was originally created by British engineering company Napier
to power the Hawker Tempest and Typhoon fighters in the Second World War. The
Napier designers wanted to eliminate the valves on the top of each cylinder to
make the engine smaller and reduce drag on the plane.
So they designed an engine with rotating sleeves inside the cylinder. The
valves were incorporated in the rotating sleeve, which had holes to let fuel in
and exhaust out. The engine鈥檚 performance surprised Napier because the reduction
in friction 鈥渄ecreased the cylinder wear rate by ten times the normal rate,鈥�
Dardalis says.
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The reason for this, says Dardalis, is that in a typical engine, oil is
sprayed on the side of the piston at the bottom of each stroke. As the piston
moves up the cylinder it carries with it a film of oil that lubricates the
cylinder wall. But as the piston approaches the top of its stroke, it stops
moving the oil up the cylinder, accelerating wear at this point. In Napier鈥檚
design the rotating cylinder sleeve continues to smear oil on the piston, even
at the top of the stroke.
In Dardalis鈥檚 improved engine, the moving sleeve also lubricates the cylinder
wall. But this time the exhaust and inlet valves are in the cylinder head where
they control emissions better than sleeve valves, which tend to leak. The Napier
engine suffered from high oil consumption and emissions, explains Dardalis, who
has patented his combination of features.
Dardalis says his engines could be used in heavy lorries or for power
generators. From Napier鈥檚 fuel consumption data from the 1940s, plus computer
modelling of his design, Dardalis estimates that the fuel consumption will be
between 4.5 and 5.5 per cent better than a conventional diesel.
The university is now building a one-cylinder diesel prototype. John Crane of
Chicago has helped to design the critical head seal, where the rotating sleeve
meets the cylinder head. The seal will be made of hardened steel or tungsten
carbide.
Dardalis admits that the seal and the gearing that rotates the liners will
add up to $3400 to the cost of the engine. 鈥淏ut even at US fuel prices
that will be paid back several times over the life of the engine,鈥� he says.
