Automotive Engineering - October 2021 - 24

EXTENDING THE WANKEL'S FUTURE ON
HYDROGEN
FUEL
The rotary, from bikes to aerial drones
The 1960s and 1970s saw a significant number of industrial
companies, including Curtiss-Wright and automakers that
included Mazda and GM, purchase Wankel production
rights from patent owner NSU/Audi. Motorcycle OEMs were
interested in the engine's packaging benefits, smooth running,
low mass and performance potential. Suzuki's RE-5,
produced from 1974-76, was the most commercially successful
rotary bike, but Hercules/DKW, Kawasaki and
Yamaha also trialed the technology in both single- and
twin-rotor form. The most successful efforts were made by
the small British manufacturer Norton, whose project was
led by David Garside. His team's work was described in an
SAE Technical Paper in 1982 (SAE821068).
In 1984, the Norton rotary engine technology was liIn
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.
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. "
Garside believes that this technology is key to the air-cooled-rotor
Wankel's future successful application as a hydrogen-fueled rangeextender
engine, especially when compared to rotary designs using
oil-cooled rotors. He lists these as more compact geometry, higher
mechanical efficiency, reduced size, weight and production cost,
improved combustion efficiency and hence overall brake thermal
efficiency (BTE).
This fits well with the engine characteristics that Garside has identified
as necessary in providing a lightweight, low-cost range-extender
engine with zero NOx and negligible HC emissions. All sizes of the engine
use just a single rotor, which only ever operates at a single load
and single speed. Provision of a weak (50% excess air) hydrogen fuel /
air mixture results in both zero NOx and excellent thermal efficiency.
A single-rotor design with a larger chamber size has fewer components
and reduced heat losses and gas leakage, contributing to the
high BTE. Such an engine still has zero radial vibrations and the same
instantaneous torque vibrations as a 3-cylinder reciprocating engine.
It can be rigidly mounted, saving cost and space, and is ideal for driving
an integrated electrical generator. " A single-rotor Wankel's largediameter
output shaft allows the generator rotor to be compactly
cantilever-mounted on the engine shaft without additional bearings, "
Garside detailed.
Since speed and load remain constant in operation, the quantity
and timing of hydrogen injected per cycle also remain constant, permitting
the use of a rotary valve operating at half engine speed to
control the supply of hydrogen gas to the engine. The valve opens
24 October 2021
censed to U.S.-based Teledyne Continental Motors company
for application in light aircraft. This led Norton into
rotary engine development specifically for unmanned aerial
vehicles (UAVs). In 1992, Garside led a management buyout
of that UAV business from Norton and the company he
created, UAV Engines Ltd., has built many thousands of
engines for military and civilian drone aircraft applications.
John Kendall
Suzuki's RE5 was only produced
from 1974-76; examples are rare today.
precisely as the engine air intake port closes, with injection
operating at about three bar (43.5 psi) pressure
and completed within approximately the first 15%
of the succeeding compression stroke. The valve inlet
is fed with H2 gas direct from the supply tank with no
requirement for an additional pressure pump.
Garside's plan is to develop a modular series of
range-extender engines sizes aimed at different vehicle
sectors, starting with a 225-cc engine with an
initial test power rating of 12kW (16 hp) at 5,000 rpm,
based on a 30-kW (40 hp) UAV engine with a core
engine weight of 10 kg (22 lb). Applications would be
urban taxis and smaller cargo vans.
AUTOMOTIVE ENGINEERING
FROM LEFT: DAVID GARSIDE; GTREGS75 VIA WIKICOMMONS
Automotive Engineering - October 2021

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