Truck & Off-Highway Engineering - October 2021 - 6

TECHNICAL INNOVATIONS
PROPULSION
Extending a Wankel future on hydrogen fuel
engines used air to cool the rotor, in place of
oil-cooling systems used in automotive applications.
Particularly in the UAV engines, this
resulted in some wet oil mist being emitted,
making them unsuitable for ground use.
In 2008, Garside patented a self-pressurBaseline
for Garside's
modular series of hydrogen
rotaries is a 225-cc engine with an
initial test power rating of 16 hp
based on a UAV engine weighing
22 lb. Applications would be urban
taxis and smaller cargo vans.
Could the Wankel rotary engine have a major future as a hydrogen-fueled,
zero-emissions range-extender engine?
Alternative fuel cells are still under development and there are
technical hurdles and production costs to overcome.
Reciprocating engines are generally too heavy and complex
for range-extender application, experts believe. Furthermore,
hydrogen fuel - necessary for zero emissions - presents
many difficulties when used in reciprocating engines. These
issues are evaded in the rotary engine where the cool intake
chamber is remote from the combustion zone.
" The overall objective is to create a range-extender power
unit that exceeds the efficiency of the best fuel cells; with
lower weight, higher TBO [time between overhauls] and at a
fraction of the manufacturing cost, " said veteran Wankel development
engineer David Garside. He expects that after
2030, the majority of the world's larger electric vehicles will
be fitted with range extenders of this type.
Air-cooled rotary
The proposed basic technology for the rotary has for many
years been extensively used in the engines for powering military
UAVs (unmanned aerial vehicles, or drones), but further
key technical advances now are incorporated.
Garside has been involved with rotary-engine R&D since
1964, initially working at Rolls-Royce. He believes the design
can make a major contribution as a hydrogen-fueled range
extender. Having developed the successful Norton and UAV
rotaries, Garside, now formally retired, has continued his involvement
in rotary engine technologies. The Norton and UAV
6 October 2021
In a motoring friction comparison of the Wankel rotary and reciprocating
engines, the air-cooled rotary (ACR) has lower friction than the oil-cooled
version (OCR) because the ACR has no oil scraper ring friction (or need of
the space for them); no oil 'cocktail shaker' losses; it has rolling-element
bearings and no oil pump to drive; and its lower R/e ratio (reduced rotor
size) results in reduced friction from all the gas seals as they sweep
reduced areas at a reduced velocity. An engine operating with H2
fuel and
50% stoichometric mixture strength results in zero NOx, Garside claims.
Inevitably BMEP is reduced with this weak mixture, so an engine with
lower friction losses has an important advantage.
TRUCK & OFF-HIGHWAY ENGINEERING
ized air-rotor cooling system (SPARCS) which
eliminated that problem. " The internal cavity
of the rotor becomes part of a closed cooling
system " he explained. " A small engine-shaftmounted
centrifugal fan circulates the air at
high speed through the rotor, where heat is
gathered and through an air/water heat exchanger
where it is rejected. The advantage is
that the circulating gas becomes pressurized
to the average pressure in the engine working
chambers via the very small two-way leakage
of gases past the rotor side seals. "
In an engine at wide-open throttle, the
cooling system is pressurized and hence densified,
to about 5-6 bar (72.5-87 psi), Garside
noted. " Since the rate of heat transfer is proportional
to gas density to the power of 0.8,
we obtain a gain of more than two or three in
the rate of rotor cooling, meaning we have a large margin of
cooling of the rotor in UAV applications, " he said.
" Furthermore, there is now zero loss of wet oil particles out of
the sealed system. "
BOTH IMAGES: DAVID GARSIDE
Truck & Off-Highway Engineering - October 2021

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