Why change current engine designs? (Continued)
In 1995, Automotive Mechanical Engineer, Brad
Howell-Smith was researching the internal combustion
engine and its efficiency and losses. He found that if a
typical engine’s Mean Effective Pressure map from the
combustion cycle was simulated against a conventional
crankshaft device, that the efficiency of that device
was only 65% efficient.
For an example, at 10-30 degrees After Top Dead Centre
(ATDC) when the pressure in the cylinder is at its
highest, a crankshaft connecting rod arrangement
provides low mechanical transfer to rotational force.
Most of the force is applied downwards on the main
journals and is wasted as a mechanical loss. At between
70-80 degrees ATDC, the crankshaft mechanical device has
high efficiency because the connecting rod is around 90
degrees to the crank.
At the crankshaft’s point of highest efficiency, the
piston has travelled approximately 40% down the stroke,
and the pressure in the cylinder is around half of peak.
This interesting finding meant that the formula for
working out engine losses must include the mechanical
losses caused by the poorly efficient crankshaft device.
It is believed that all losses have been accounted for
in the formula.
|
The Dream of an Engine
After the theory was realised, Brad literally
dreamt the Revetec engine design. After graphing the
performance of the new engine design, it was realised
that it is possible to increase an engine’s efficiency
to a much higher level. In some initial designs it was
calculated that a petrol engine of this design could
reach 50% efficiency, which is deemed as unachievable in
the industry.
Breaking the Theory
Over the last decade, six different versions of
Revetec engine designs have been prototyped. The latest
version was designed as a development engine for the
aviation industry, and in early 2008 it was
independently tested by Orbital Australia. The X4v2
engine has a very basic top end featuring only two
valves per cylinder operated by push rods. It features
no variable valve timing nor variable length intake
ports which are common in many current late model
vehicles.
The X4v2 Prototype petrol engine achieved a
Brake Specific Fuel Consumption (BSFC) of 207g/(kW-h) or
39.5% efficiency. The figure achieved was deemed as
impossible, given the knowledge of engine losses and
that various current engines achieve an efficiency in
the range of 27-32%. |
