UNDERTHE SKINJESSE CROSSE

THE AGE OF AQUARIUS HERALDSTINY, 10KG HYDROGEN ENGINEA NEW,LIGHTWEIGHT hydrogen engine concept fromIsraeli ﬁrm Aquarius Engines has been under development
since 2014 and is close to maturity. Powered by hydrogen,the Aquarius Two Sided Free Piston Linear Engine (FPLE)
is designed to generate electricity for plug-in series
hybrids or range-extenders.
The tiny engine consists of a mere 20 components, only
one of which moves. Although originally designed to burnpetrol, it could conceivably operate on a variety of fuels
including the latest ‘dropin’ carbon-neutral, synthetic
liquid fuels, and a hydrogen version of the engine has beendeveloped and tested. The Aquarius is called a linear
engine, because instead of converting reciprocating forces
into rotating forces via a crankshaft like a conventional
piston engine, the single piston rod moves to and fro on a
two-stroke cycle, ﬁring on each stroke of the piston, at
each end of the cylinder.
The Aquarius engine comprises one piston rod (a long barwith a piston at its mid-point); a small cylinder block inwhich the piston slides; two cylinder heads, one on eachend of the block; two inner bearings and two outer
bearings, which support the piston rod. The air-cooledengine needs no lubrication and instead has graphite
piston rings and special coatings to reduce friction. The
lack of oil rules out any chance of leaks or unburnedhydrocarbons being produced during combustion and it
simpliﬁes servicing, which, its designers say, is minimal
and required only every 1000 hours of operation. In thattime, a hybrid car could comfortably travel more than
50,000 miles.
As the piston moves from side to side in the single
cylinder, it expels exhaust via ports in the wall of thecylinder like a conventional two-stroke engine, then draws
in air through a patented air ﬁltration system and via ports
in a hollow section of the piston rod. There are no poppet
valves like a conventional engine or a highly stressedvalvetrain to soak up energy in effort and friction.
There are four injectors in total, two in each cylinder headat each end of the engine. On each stroke, the hydrogen is
injected into the fresh air by a pair of injectors, themixture is compressed and ignited by a spark plug and thewhole sequence begins again. A patented system ofbalance weights reduces noise and vibration.
The engine drives a generator that feeds the battery or
traction motor of a series hybrid with electricity.
Regenerative braking works in exactly the same way aswith any all-electric or hybrid car, the traction motor
switching to generator mode when the car slows to recoverenergy into the battery.
There are no production dates yet but a hydrogen-fuelled
version of the engine has undergone independent testingby AVLSchrick in Austria and work continues on reducing
noise levels from the electrical generator. Apart fromhybrid cars, the engine is designed for use as a generator in
telecommunications centres, microgrids, as an auxiliary
power supply (APU) in large trucks, marine applications
and for use in drones or APUs in aviation.

One they made earlier
The Aquarius engine is already running in a driverlessskateboard chassis to show its potential. The
demonstrator vehicle is a petrol series hybrid at themoment but it could equally run with the latesthydrogen-fuelled version of the engine. The fact that theengine/generator unit can be used for so many different
applications should make it more commercially viable
than single-use systems.