Page 26 - MotorTrend (March 2020)

NEWS I OPINION I GOSSIP I STUFF
Frank Markus
Technologue
Might This New-Concept
Rotary Range Extender Fly?
urbine cars seemed inevitable in 1963, when 50
Chrysler Turbine demonstrators hit the streets.
Low parts count, reduced maintenance, and abso-
lute smoothness were the selling points, but by
T1979 efficiency and emissions woes scuppered the
automotive turbine.
Now, micro-turbine range extenders like those in
Jaguar’s C-X75 and Mitsubishi’s MI-Tech concepts are
beginning to hit the road. What’s more, there’s a new
patent-pending rotary-engine concept that promises
to combine turbine- and piston-engine advantages for
even greater efficiency and lower emissions.
In a traditional turbine, burning fuel isn’t contained
and forced to act on a crankshaft. Rather, expanding
gases blow against fan blades to rotate a shaft, and excess
air provides cooling.
However, Astron Aerospace’s new trademarked Omega
One rotary engine contains the combustion like in
piston engines, improving torque and simplifying emis-
sions control while retaining turbine advantages like
air cooling, low parts count, compact size, and smooth
operation. The Omega is primarily meant for aviation,
but a range extender application for electric
cars is being codeveloped. It incorporates
various Technologue “greatest hits,” including
June 2006’s split-cycle concept of conducting
compression and combustion in separate
spaces, and homogeneous-charge compression
ignition (HCCI).
Imagine a smooth gear featuring a single,
wide tooth rotating against another perfectly
smooth gear incorporating one notch to fit the
first gear’s tooth. These rotate in a housing machined to
fit tight (0.001-0.005-inch clearance) to the surface of the
notched gear and to the outer edge of that single tooth.
Side plates complete each enclosure with similar oper-
ating clearance to the rotors. The tooth is not expected
to need seals, dramatically reducing friction.
In one gear pair, the tooth separates the intake and
compression volumes; in the other, combustion and
exhaust. The compression one is about a third
larger, which allows it to “supercharge” the
combustion chamber via a small air storage
tank that sits between these rotor pairs. Blow-
off valves regulate intake pressure (180 to 320
psi is the expected range).
Intake air enters the combustion
chamber when a port in a rotating plate
in the compression tank aligns with a
hole in the rotor side plate, positioned
where the combustion tooth emerges
26 MOTORTREND.COM MARCH 2020
from its notch to begin another rotation. As compressed
air enters this large and unrestricted port, fuel is supplied
by port and/or direct injectors that provide stratified
charge (rich near the plug) at lower rpm or homogeneous
charge at higher rpm. Spark-assisted HCCI is possible
up to 10,000 rpm.
Once combusted, the expanding gases push the back
side of that tooth most of the way around its circular
path, providing loads of time to extract work from the
fuel. Then the exhaust leaves through an open port near
where the tooth re-enters its notch, pushed by
the front side of the tooth on its next pass. This
port can be ducted to a turbo and/or a catalyst.
In the computer, this 14 x 15 x 23-inch
engine whirs out 600 hp at 15,000 rpm and
1,000 lb-ft, achieving 80 percent thermal
efficiency(!). Cooling air from a turbine-
like fan blows through the large, hollow
shafts supporting the rotor pairs and past
the finned outer housing. Only these shafts’
bearings are lubricated, so the combustion
chamber is never exposed to lubricant. And
the HCCI flash combustion plus
low combustion chamber surface
area should lower engine-out NOx
sufficiently to eliminate the three-
way catalyst, which doesn’t work
with excess air. There will be
excess air, especially under
low-load conditions in “skip-
fire” mode, when the engine
doesn’t fire every revolution.
These are Astron’s claims. But enough smart
people (including some at Los Alamos Labo-
ratory) saw sufficient merit in the concept
to fully fund the venture in a matter of days.
Now comes the hard part: building and
operating a proof-of-concept engine. I’m
concerned about the lack of seals and lubrication
of the rotors operating at relatively close tolerances, Intake and
and I worry that parts exposed to varying compression
happen in the
amounts of heat will expand at different green area;
rates, causing interference. Exotic compressed air is
stored in the blue
materials and tight tolerances can
tank, compression
be budgeted into a pricey aviation and exhaust in the
engine, but can this be made to work red. The light blue
ports above are
on an automotive range extender where compressed
budget? Color me intrigued and opti- air exits the
compression rotor
mistic about the aviation engine’s
and enters the
future, a bit more skeptical of its combustion one.
automotive prospects. Q