Free Piston Power Pack (FP3)
FP3 design is based on "free pistons" being driven back and forth inside cylinders
by controlled internal combustion. Permanent magnets are attached to the pistons.
As the magnets move, electric power is generated in coils placed around the magnets.
The module represents a fresh approach in free piston engine/generator design. Novel
features include passive intake valves, located in the crown of the piston and an
integral charge compressor.
These improvements eliminate problems hampering earlier free piston engine designs,
such as ported cylinder walls with associated piston ring wear and the need for
a bulky, external charge compressor. The result is a significant increase in power
density (1kW per kg or 1.93 kW per litre).
Mechanical simplicity (software "replaces" the crankshaft), high pressure direct
fuel injection, variable exhaust valve lift and timing as well as variable stroke
and compression ratio all contribute to excellent fuel efficiency and low levels
of harmful exhaust emissions.
The FP3 is an extremely compact, efficient, clean, low-cost, scaleable electric
generator with an output up to 450kW. It can be modified to operate on diesel, ethanol,
LPG and hydrogen.
Passive Intake Valves
Four passive intake valves are located in the crown of each piston. They are seated
poppet valves and form the intake ports through which fresh air enters the combustion
chamber. The intake valves operate in a completely passive manner, i.e. there are
no external controls. The opening and closing of the intake valves is governed by
the pressure differential that exists between the compressor and the combustion
chamber. The passive intake valves provide three major benefits:
- Uni-flow gas exchange
- Elimination of intake and exhaust slots in the cylinder wall resulting in reduced
piston ring wear
- Axial module length reduction by allowing the generator to overlap the combustion
chambers
Charge Compressor
Two compressors, driving the gas exchange process, form an integral part of the
FP3. This eliminates the need for a bulky, external charge compressor.
Linear Generator
The linear generator is highly integrated into the design of the FP3. It consists
of eight ring-shaped NeFeB permanent magnets located on the mover assembly and an
eight coil stator. The coils are connected to IGBT inverters which convert the generator
output to direct current.
The inverters are controlled by a digital signal processor system maximising the
efficiency of the power conversion process.
The generator acts as a linear motor when starting the FP3; power is applied to
the stator coils in sequence causing the piston to move.
Electro-Pneumatic Exhaust Valve
The exhaust valve is driven by a high speed, software controlled actuator. The actuator
contains two opposing solenoids that open and close the valve. Each solenoid incorporates
a gas spring that stores energy required to generate the high forces necessary for
rapid operation. The exhaust valve is capable of opening to a stroke of over 7 mm
and closing again in 5 ms. The seat diameter of 36 mm provides a large aperture
for rapid removal of exhaust gases.
Graph of a test result
Mover Bearing
The interface between the mover and stator is the only major bearing in the FP3.
Because the FP3 is not subjected to dynamic lateral piston forces, the contact pressure
in the bearing is less than 0.02 MPa. Since the mover speed is less than 10 m/s
there is plenty of scope for the design of a lubrication-free bearing.
Piston Seal
The FP3 uses an advanced seal rather than conventional piston rings. The main pressure
seal is fitted into the inside surface of the bottom of the cylinder. It is subject
to relatively low temperatures. Above the main seal is a labyrinth seal that provides
a significant pressure reduction, allowin the use of a low pressure type seal. The
prevailing conditions allow for the design of a lubrication-free piston seal.
The FP3 can take advantage of current research in materials and cooling to achieve
a minimal crevice volume. This may allow the use of a contact-less piston seal.
Frequency of Operation
The power delivered by the engine and generator can be increased by raising the
operating frequency. To achieve this, the mover of the FP3 has been designed for
minimum mass (5.2 kg).
A simple analysis shows that the operating frequency can also be increased by around
60% by sub-dividing the unit into four quarter-size sub-modules.
Graph of a test result
Features
- Significant technical innovation (protected by international patents)
- Exceptional power density (compared to current engines and fuel cells)
- Unrivalled high fuel economy
- Ultra-low or zero harmful exhaust emissions
- Mechanical simplicity (software "replaces" conventional crankshaft
- Maintenance-free and lubrication-free
- Long service life
- Electronically variable
- Spark ignition timing
- Exhaust valve timing and lift
- Direct fuel injection timing and quantity
- Compression ratio
- Multi-fuel capability
- Gasoline
- Diesel
- Hydrogen
- Ethanol
- LPG
- etc.
Gas Exchange
Specifications
- 100 kW peak electrical output power
- Four free piston engine sub-modules
- 8 cylinders
- 2.82 litre displacement
- 30 Hz operation (equivalent to 1800rpm in a two stroke crankshaft engine)
- 280x280x660 mm dimensions
Orthodox Internal Combustion Engine Vehicle Technology
The established internal combustion engine powered vehicle has benefited from over
100 years of research, development, testing and refinement. This has produced designs
that have good fuel efficiency, low manufacturing cost and excellent reliability.
However, planet earth requires transportation solutions that are more fuel efficient,
environmentally responsible and sustainable. It is difficult to further improve
existing vehicle design to achieve these goals without recapturing the vehicle’s
kinetic energy lost when slowing down and braking. It is our opinion that the Series
Hybrid Electric Vehicle with the FP3 as a clean and efficient power source will
attain these objectives.
Series versus Parallel Hybrid Electric Vehicles Existing and proposed Parallel Hybrid
Electric Vehicles are driven, in the main, by an internal combustion engine connected
mechanically to the wheels. In parallel is installed an electric motor/generator
and battery combination also connected to the wheels, via a separate gear train.
With this combination it is difficult to go beyond 25% power regeneration. In contrast,
Series Hybrid Electric Vehicles have no mechanical drive. The electric output power
of the FP3 is fed directly to a battery and to four electric wheel motors via a
power electronic control system. This permits 100% power regeneration of the vehicle’s
kinetic energy when slowing down or braking. The result is:
- significantly smaller, lighter and simpler design
- improved fuel economy
- lower harmful emissions
- quieter operation
- fewer moving parts
- much lower manufacturing cost
When installed in a typical series hybrid family sedan, the following specifications
apply: 100 kW FP3 complete with electronic control Installed Lithium-Ion Battery
Power 164 kW Electric Wheel Motors 4x50=200 kW 200 kW Wheel Motor Drives Wheel Motor
Gear Ratio 6.75:1 Torque on Wheels:
- 0-100 km/h (62 mph) 2122 Nm (1563 ft-lb)
- 150 km/h (93 mph) 1415 Nm (1042 ft-lb)
- Acceleration 0-100km/h (62 mph) in 5.4 seconds
- Curb Weight 1300 kg (2860 lb)
- 100% Regenerative Power
- Overall efficiency of 45% (compared to a current 25%)
FP3 versus Fuel Cell Technology
The fuel cell is under development by many automotive manufacturers and has been
released on the market in limited numbers. The manufacturing cost of fuel cells
is a major obstacle and experts agree that this cost will remain high for many years
to come. It has been suggested that it will take at least 10 years for fuel cell
vehicle prices to fall below US$100,000. This makes the free-piston concept a much
more cost-effective power plant for automobiles.
Fuel cells use hydrogen as a fuel source. The safe storage of hydrogen in a motor
vehicle is a major concern. Another limitation of fuel cells in the short and medium
term is the lack of a hydrogen distribution infrastructure. Industry analysts predict
that it may take 20 years to establish such an infrastructure. If and when hydrogen
starts to replace gasoline and diesel, the FP3 can run on this harmful emissions-free
fuel (a low cost, mechanical fuel cell).
It can be argued that the reduction in fossil fuel consumption as well as improvement
in air quality will be far greater as a result of the sale of millions of low cost,
series hybrid electric vehicles equipped with efficient, clean FP3s, rather than
from limited sales of expensive “Zero Emission Vehicles”.
Other Applications
- HEV passenger vehicles (up to 100 kW, gasoline or diesel)
- HEV trucks (up to 450 kW, diesel) in combination with Pempek Systems’ patented Electric
Differential Drive Axle
- Public transportation, eg. buses
- Leisure craft
- Static and portable power generation
- Auxiliary electric power generation
Proposed Series HEV
INTERNAL COMBUSTION ENGINE & LINEAR GENERATOR MODULE:
- Linear Generator Power 40 kW
- Dimensions 225 mm x 225 mm x 520 mm
- Mass 40 kg
- Combustion Engine Cylinders 8
- Bore 52 mm
- Stroke 80 mm
- Capacity 1.36 l
- Power 40 kW
- Cylinder Heads 2 Exhaust Valves 22 mm bore (one actuator)
- 1 Fuel Injector
- 1 Spark Plug
- Pistons 3 Passive Intake Valves 20 mm bore
- Generators Mover OD 80 mm
- Mover Length 140 mm
- Number of Coils 6
- Stator OD 110 mm
- Frequency 36 Hz
BATTERY ASSEMBLY:
- Batteries: Power 37.5 kW x 3 = 112 kW
- Dimensions 180 x 590 x 170 mm x 3
- Mass 23 kg x 3 = 69 kg
- 56 Li-Ion Cells VL7P
- Voltage 200 V
- Power 37.5 kW
- Energy 1.4 kWh
WHEEL MOTORS:
- Traction Motor: Power 30 kW x 4 = 120 kW
- Dimensions Ø120 x 200 mm
- Mass 13 kg x 4 = 52 kg
- Gear ratio 6.75 : 1
Predicted Performance:
Acceleration for a vehicle mass of 1000 kg from 0 to 100 km/h: 6 seconds
Regenerating Capacity for a vehicle mass of 1000 kg:
Vehicle Speed Retardation
< 43 km/h 10.0 m/s²
50 km/h 8.6 m/s²
60 km/h 7.2 m/s²
80 km/h 5.4 m/s²
100 km/h 4.3 m/s²
120 km/h 3.6 m/s²
Fuel consumption in city traffic measured in accordance with NEDC: 1.6 l/100 km
Who knows this morning what will happen tonight? (Chinese Proverb)
