I agree, it is an unbalanced double action pneumatic actuator.

The video briefly shows two parallel shafts which would help with the balance, but as mentioned, no explanation of how that power is coupled to a generator. Also, there's no mention of fuel consumption per Kw output. It looks like a simple two stroke principal to me.

In another video I saw on this engine they showed a reciprocating generator very briefly. The principle was the same as kids' shake-to-charge flashlight. The coil looked like it surrounded the piston rod extending out of the engine housing. Presumably the piston rod has magnets inside, like the shake charge flashlight, or a special wound armature fed through slip (or in this case slide) rings.

Doesn't say so in the blurb, but I think the benefit of this type of engine depends on how it's used. The generator, not described, is important too.

Conventional IC engines spin a rotary alternator by wastefully driving a heavy crankshaft with several bearings, and the alternator probably has to be geared up as well – more waste in the transmission. There are circumstances in which a few percent better efficiency is valuable, especially if the power comes in a compact format.

A linear engine like the Aquarius could drive a pair of linear alternators, each perhaps as simple as a supermagnet oscillating to and fro inside a solenoid. It would produce variable frequency AC well above 50Hz. High frequency variable AC doesn't matter if the generator is used to top up a battery powered vehicle, because such AC can be immediately rectified into DC.

A linear arrangement could be quite compact, and being able to run on Hydrogen is a useful bonus. Obviously not a plug-in substitute for the petrol engine in my car, but potentially useful in an EV/Hybrid. This class of vehicle has an important future. All my motoring could easily be done with a pure battery car, but there are plenty of other use-cases where longer legs and more stamina are needed. Hybrids are almost certainly part of the answer, but the IC part need not be based on an 1886 Karl Benz Motorwagen! .

Dave

Dunno about the Aquarius engine, but Toyota claim 42% for their free-piston engine, which is rather better than the average reciprocating engine, which are usually less than 30% efficient, even when not idling at traffic lights.

Choosing a motor isn't simply about efficiency though because different motor types suit different operating conditions:

• Turbines are highly efficient,- well over 30%, and reliable but only at constant high rpm, no reverse. They easily outperform reciprocating IC in long-haul aircraft and for generating electricity, but are terrible for variable speed applications like road vehicles.
• Reciprocating IC engines are complicated (more maintenance), don't reverse, and are relatively inefficient, but they have a high power to weight ratio, convenient fuel, and can vary RPM over a reasonable range. Supported by a gearbox, they do well in road vehicles.
• Steam reciprocating engines have high start torque, but low efficiency (<5%), and massive boilers. Main advantage, they aren't fussy about fuel quality. Otherwise, almost entirely obsolete.
• Electric motors are efficient (>60%), high torque over a wide range of RPM, reversible, simple and reliable. Their Achilles heel is the need for a power supply, but whenever mains power is available, they slaughter other types of motor.

Free piston engines look to be a good option for Hybrid EVs. They're compact and don't need a big engine compartment. And their high efficiency is well suited to generating electricity. May only be a niche application, but the type could be important in future.

Dave

Hi,

2 stroke engines run forwards and backwards.

Maurice

Having owned not one but two Bond Minicars (built by Sharps Commercials who also produced the Bond Bug, I can remember them well!

The engine and gearbox was a modified Villiers motorcycle unit and available in 200cc and a heady 250cc variants. The reverse was effected by the Siba 'Dynastart' motor/dynamo on the end of the crankshaft, opposite the transmission. This could be run in reverse to start the engine in reverse, from a shielded second position on the ignition-switch; but I forget if the engine had two contact-breakers timed on either side of, or a single one on, TDC.

Whether a two-stroke engine is more or less efficient than an equivalent 4-stroke I do not know, but having no valves does mean slightly less power absorbed within the machine itself.

Very large marine Diesel engines are or were built in two-stroke form, as were some 4-stroke ones reversible via the valve-timing.

.

Missing from your list is the Steam Turbine.

As with the reciprocating engine the overall efficiency is let down by the need for a large boiler, hence external combustion; more than the engine itself. Nevertheless, power-station and marine steam-turbine sets achieve significantly better than 5% overall efficiency, thanks to long, steady running against fairly constant loads, full pressure-range through the engine to the condenser, and the heat-recovering economiser and feed-water heater.

Some ships, including the three Titanic class liners, used reciprocating engines followed by exhaust-steam turbines, to gain maximum expansion from HP inlet to the condenser's partial vacuum.

Two-stroke have a higher power-to-weight ratio than 4-stroke, but 4-stroke are more fuel efficient and the exhaust is cleaner. Being more complicated 4-stroke are more expensive to make. So you tend to get 2-stroke engines when a cheap dirty noisy inefficient light-weight power unit is beneficial: usually open-air stuff like lawn-mowers, chainsaws, ATVs etc. 4-stroke engines win as soon as fuel economy, quiet, or cleanliness matter. Motorbikes are interesting because they straddle the line: sometimes 2-stroke, sometimes 4.

Whilst it's possible to build a reversible reciprocating IC engine, it's rarely done. 2-strokes don't require much modification, basically move the timing and spin it backwards. It's a cheap way of providing vehicles that rarely reverse with the ability. Might ask if it does the engine any harm, and the answer is yes, after a while, but not so it matters for occasional reversing. Did 2-stroke Bubble Cars have reverse? I seem to remember people had to get out and push!

Reversible 4-stroke engines need a complete second set of valve control gear, making them extra complicated. Sometimes done in ships to avoid installing a monster gearbox, but generally avoided. The lengths shipbuilders go to avoid fitting gearboxes is another story!

Dave