http://www.sae.org/mags/aei/7160
Automotive Engineering
International
Supercritical Fuel
Injection and Combustion
Recent work by Mike Cheiky,
a physicist and serial inventor/entrepreneur, is focusing on
raising not only the fuel mixture’s pressure but also its
temperature.
Cheiky's aim, in fact, is to generate a little-known,
intermediate state of matter — a so-called supercritical (SC)
fluid — which he and his co-workers at Camarillo, CA-based
Transonic Combustion believe could markedly increase the fuel
efficiency of next-generation power plants while reducing
their exhaust emissions.
Transonic’s proprietary TSCi fuel-injection systems do not
produce fuel droplets as conventional fuel delivery units do,
according to Mike Rocke, Vice President of Marketing and
Business Development. The supercritical condition of the fuel
injected into a cylinder by a TSCi system means that the fuel
mixes rapidly with the intake air which enables better control
of the location and timing of the combustion process.
The novel SC injection systems, which Rocke calls “almost
drop-in” units, include “a GDI-type,” common-rail system that
incorporates a metal-oxide catalyst that breaks fuel molecules
down into simpler hydrocarbon chains, and a precision,
high-speed (piezoelectric) injector whose resistance-heated
pin places the fuel in a supercritical state as it enters the
cylinder.
Company engineers have doubled the fuel efficiency numbers in
dynamometer tests of gas engines fitted with the company’s
prototype SC fuel-injection systems, Rocke said. A modified
gasoline engine installed in a 3200-lb (1451-kg) test vehicle,
for example, is getting 98 mpg (41.6 km/L) when running at a
steady 50 mph (80 km/h) in the lab.
The 48-employee firm is finalizing a development engine for a
test fleet of from 10 to 100 vehicles, while trying to find a
partner with whom to manufacture and market TSCi systems by
2014.
“A supercritical fluid is basically a fourth state of matter
that’s part way between a gas and liquid,” said Michael Frick,
Vice President for Engineering. A substance goes supercritical
when it is heated beyond a certain thermodynamic critical
point so that it refuses to liquefy no matter how much
pressure is applied.
SC fluids have unique properties. For a start, their density
is midway between those of a liquid and gas, about half to 60%
that of the liquid. On the other hand, they also feature the
molecular diffusion rates of a gas and so can dissolve
substances that are usually tough to place in solution.
To minimize friction losses, the Transonic engineers have
steadily reduced the compression of their test engines to
between 20:1 and 16:1, with the possibility of 13:1 for
gasoline engines.
