Page 63 - Energize July 2022

TECHNICAL

Central single piston dual chamber(Aquarius) allows for a unique marriage between cycle-to-cycle flexibility and the
The central single piston system uses dual combustion chambers on HCCI combustion mode. Cyclic variations are sympathetic with the
either side of the central piston (see Figure 9). The two chambers freedom of the translator to naturally increase or decrease its stroke
fire alternately to give a dual power stroke, without an air spring. length which acts as feedback for subsequent cycles of operation. 2

Dual piston system Controls
The dual piston system uses a single piston rod with pistons A FPLG requires controls to operate efficiently. The speed and
attached to each end, housed in separate combustion chambers. position of the piston is controlled by an electronic control system
The pistons operate in anti-phase, i.e., one piston is in compression which regulates the intake and outlet valves as well as the total
while the other is in expansion. There is no gas spring or rebound load on the system. The load is varied electronically by the current
device, since the power for the return stroke is provided by the flowing in the stator coils.
opposite piston. This allows close control of motion within the
stroke, and better control over power. Engine start up
A FPLG does not have a flywheel and cannot be started using the
Central combustion system (opposed piston system) conventional rotary starter motor. Instead the role of the generator
In the central combustion system, the air-fuel mixture is is reversed and used as a linear motor in an oscillatory cycle until
compressed in the centre reaction zone until a low temperature sufficient pressure has built up to allow the fuel cycle to take over.
reaction occurs. The reaction drives the two oscillators outwards. Finally, the system reaches its stable amplitude oscillation state. The
Outer springs, or an air spring in the bounce chamber, are final achieved compression ratio is determined by the energy balance.
compressed to return the oscillators for the next cycle.
Examples of commercial systems
Cycle efficiency compared to a conventional IC engine Although most of the available literature covers laboratory models,
The movement of the piston is not restricted by a crankshaft and there are several working systems available on the market.
flywheel, and this allows full expansion of the hot gas, resulting in
higher efficiency. Typical efficiency figures are claimed to be in the Mainspring
same range as fuel cells. The company produces a FPLA with an output of 73 kW (Figure 12).
The unit is a dual generator using a single central reaction zone.
Flame free combustion (reaction) Reaction of the fuel with air forces the rotor outwards against the
In the FPE, the stroke length of the rotor and compression ratio are air spring. Release of pressure in the reaction zone allows the air
not geometrically constrained as they are in a crankshaft driven spring to return the piston to its original position.
engine. Instead, they are allowed to vary from stroke to stroke. This In Mainspring’s linear generator, electrically controlled linear
variability, while presenting difficulty in terms of system control, motion of rotors compresses a fuel and air mixture until the
mixture reacts uniformly and near instantaneously without a flame
or burning. Since there is no flame or burning (i.e., no combustion),
the reaction occurs at low temperatures (less than 1500°C) and, as
a result, produces near-zero NOx emissions. The energy from the
low-temperature reaction drives linear motion of the oscillators,
which is directly converted into electricity, and the electrically-
controlled linear motion of the oscillators drives the reaction.

Figure 9: Central piston engine (Aquarius)

Figure 10: Dual piston system 4

Figure 11: Central combustion or opposed piston system 4 Figure 12: The Mainspring FPLG (Mainspring)

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