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Presented by:
Himanshu Sekhar Bal
Reg. No- 1101298386
Mechanical Branch
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The free-piston engine is a linear, 'crankless'combustion engine, in which the piston
motion is not controlled by a crankshaft but
is a result of the interaction of forces from
the combustion cylinder gases, a rebounddevice(e.g., a piston in a closed cylinder)
and a load device(e.g. a gas compressor or a
linear alternator).
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The free-piston diesel engine concept was
developed by Pescara, and engines of various size
were manufactured between 1930-1960 by GM,Ford, Renault, Junker, Sigma and others.
General motor XP-500
It is a combination of reciprocating engine and a
rotary turbine.
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Bounce Chamber Intake Air valve Scavenge Air Box Supercharge pump
Exhaust gas receiverPower turbine
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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
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A cycle starts with the pistonplunger
combination in BDC: most to the right. Theelectronic control opens the frequency control
valve. This increases the pressure in the
compressor cylinder, moving the piston-
plunger to the left. Simultaneously, air is
compressed in the combustion cylinder and oilis sucked into the power cylinder.
When the piston-plunger arrives in TDC fuel is
injected and ignites. The expanding gases will
force the piston plunger to move back to BDC.
Oil is pumped to the high pressure side.
The burned gases are replaced by fresh air
due to the loop scavenging process. In the BDC
the piston-plunger will wait until the
electronic control gives a new starting signal
to the frequency control valve.
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Efficiency-During tests, the free piston engine reached an
indicated efficiency of more than 50%.
Emissions-It was proven that the combination of a high
efficiency combined with low soot and low NOx emissions
is possible.
Power density-The Chiron has an net effective power of
approximately 17kW.Compared with a conventional
diesel engine and pump combination, the number of
parts of the Chiron is reduced to approximately 40%.
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Infinia is a well renowned company that utilizes
free piston technology in three types of machines.
Generators
Cryocoolers Infinias unique stirling design
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1-2: Adiabatic compression
in compressor cylinder
2-a: Adiabatic compression
a-b: Engine combustion
b-3: Adiabatic expansion or
power stroke in dieselcylinder
3-4: Mixing of m2 kg engine
exhaust and m2 kg bypass air
4-5: Adiabatic expansion in
turbine
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LP HP A simple design with high
controllability is the main strength of
the single piston design compared to
the other free-piston engineconfigurations.
The rebound device gives the
opportunity to accurately control the
amount of energy put into the
compression process and thereby
regulating the compression ratio andstroke length.
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LP
HP
Dual piston engine configuration
eliminates the need for a rebound
device, as the (at any time) working
piston provides the work to drive
the compression process in the othercylinder.
It has a simple and more compact
design with higher power to weight
ratio.
The control of piston motion, in
particular stroke length andcompression ratio, has proved
difficult.
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Combustion chamber
Piston synchronization
Bounce chamber
It was exclusively used in theearly free-piston engine designs
(1930-1960).
The perfectly balanced and
vibration- free design is the
exclusive feature of this design.
Due to elimination of cylinderhead, heat transfer losses are
also reduced allowing uniflow
scavenging giving better
efficiency.
The piston synchronization
mechanism and dual set of main
components makes it a bulky and
complicated design.
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Inward compression type
Outward compression type
The basic difference between them is that
inward types compress air during inwardmotion of the piston while the outward types
compress air during the outward motion of the
piston. Furthermore, inward type is simpler,
has less number of working parts and possessbetter accessibility for maintenance than
outward type.
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Two- stroke, since power stroke required
on every cycle.
Though performance gap is decliningbetween 2-stroke and 4-stroke engines
due to recent increase of interest in 2-
stroke engine.
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No motion control and no energy storage.
May lead to less or more compression ratios and
less time for scavenging.
Absence of crank mechanism andflywheel leads to :-
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Motion is controlled by sum of forces acting on
piston at any time.
Interaction of forces must be arranged in
acceptable limit of motion.
Due to bounce spring nature of combustionchamber and bounce chamber, appropriate load
must be used.
Measures to previous problems :-
< F
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System behaves as a spring-mass system and
have natural frequency given by
= K/m ; where K = F/x
therefore stroke length must be
appropriately chosen to match any of the
natural frequencies.
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No energy storage, as in flywheel, therefore
misfiring may be a problem if engine fails to
build up sufficient compression.
Though practically, misfiring has not been
mentioned in any of the reported
experiments.
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Load must be linear and provide efficient
energy conversion comparable to rotatingloads in conventional engines.
Load is directly connected to mover,
therefore has high mechanical requirements.
Load device may be subjected to heattransfer from engine cylinder.
Generally, Free Piston Engine loads are :-
1. Electric Generators
2. Hydraulic Pumps
3. Air Compressors
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Low frictional losses
Reduced manufacturing cost
Compactness
Low maintenance cost and increased lifetime
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High speed around TDC results in more
turbulence, better mixing of air-fuel and
better combustion.
Rapid expansion due to high piston speedresults in less NOx formation.
Variable compression ratio allows
optimization of combustion process.
Suitable for multi-fuel operation.
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Balancing is a problem but can be sorted out
using mechanical linkages between the
pistons.
Though, using mechanical linkages putconstraint on piston motion and also there is
danger of breaking of linkages at high
speeds.
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Effect of fuel Supply
Effect of Bounce Cylinder Pressure
Effect of Working Pressure
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Simple design with few moving parts reduces
the frictional losses
Compact and low maintenance costs
High power to weight ratio Possible operation on multiple fuels due to
variable compression ratio
Fuel air mixing is enhanced
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Poor fuel economy as specific fuel
consumption is high
Requires a certain quantity of fuel per stroke
that varies according to load causingminimum stability problems
Due to high supercharge rate of combustion
per cylinder volume is high
Reduction Gearing
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Early applicationsa) Widely used as submarine air compressor units
b) Suitable for power generation in mediumpower range
c) They have also been tried in ship propulsion ,road and rail traction
d) High speed centrifugal air compressors andwater pumps can be directly driven by it
e) A mixed gas steam cycle also offers the
possibility of improving the efficiency Modern applications
a) Hydraulic free piston engines
b) Free piston engine generators
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Automotive application is that studied by
most current free-piston engine developers.
The free-piston engine generator is a very
attractive candidate as a prime mover in
series hybrid vehicles or as a range extender
in plug-in hybrids.
It can provide high thermal efficiency
(including high part load efficiency), lowemissions, fuel flexibility, and high power to
weight ratio through a compact design and a
flexible engine layout.
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The piston engine can provide substantial advantages in this
respect, with
Extremely low friction: all frictional losses associated with the
crank system are eliminated and piston friction is reduced due to
no side forces acting on the piston
no load-carrying bearings, allowing operation at high compression
ratios; and
very high piston acceleration around top dead centre, reducing
the time spent in the high-temperature parts of the cycle and
thereby reducing heat transfer losses and emissions formation.
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AIR COMPRESSORS
The first successful application of the free-piston engine
concept was as air compressors. In these engines, air
compressor cylinders were coupled to the moving pistons,
often in a multi-stage configuration. Some of these engines
utilized the air remaining in the compressor cylinders to return
the piston, thereby eliminating the need for a rebound device.Free-piston air compressors were in use among others by the
German Navy, and had the advantages of high efficiency,
compactness and low noise and vibration.
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Besides advantages regarding efficiency,
the free piston compressor offers on-demand start and stop (since there is no
compression stroke in the engine side)
cool operation (given that the
combustion products are greatly dilutedwith air after expanding down below
atmospheric pressure)
quiet operation (given that there is noexhaust of high-pressure gasses)
simple
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efficiency is achieved by matching the dynamic
load of the compressor to the ideal adiabaticexpansion of the hot gas combustion products
The device proposed exploits this fact by
converting thermal energy into kinetic energy ofthe free piston, and then utilizes this stored
kinetic energy to compress and pump air on the
opposite side of the piston toward the end of
the stroke.
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After the success of the free-piston aircompressor, a number of industrial researchgroups started the development of free-pistongas generators. In these engines there is no loaddevice coupled to the engine itself, but the
power is extracted from an exhaust turbine.(The only load for the engine is thesupercharging of the inlet air.)
A number of free-piston gas generators weredeveloped, and such units were in widespread
use in large-scale applications such as stationaryand marine powerplants [3]. Attempts were madeto use free-piston gas generators for vehiclepropulsion (e.g. in gas turbine locomotives) butwithout success.
http://dictionary.sensagent.com/free-piston+engine/en-en/http://dictionary.sensagent.com/Gas_turbine_locomotive/en-en/http://dictionary.sensagent.com/Gas_turbine_locomotive/en-en/http://dictionary.sensagent.com/Gas_turbine_locomotive/en-en/http://dictionary.sensagent.com/free-piston+engine/en-en/8/11/2019 Magnet Piston Engin
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Free-piston engines could be used togenerate electricity as efficiently as, and lessexpensively than, fuel cells.
It could be used to generate electricity as
efficiently as fuel cells yet cost less.Having a cheap and efficient way to generate
electricity is becoming more important asautomakers develop electric vehicles with
onboard generators for recharging thebattery pack and extending range. Suchvehicles, called series plug-in hybrids orextended-range electric vehicles
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Automakers such as GM, Lotus, and Volvo have
started to investigate the possibility of using
such engines in future vehicles.
To generate electricity, the pistons could be
equipped with rows of magnets that shuttle past
metal coils to create an electrical current.
The free-piston design can also allow the engine
to be instantly optimized for different fuels,
such as hydrogen, natural gas, ethanol, gasoline,
and diesel. Ideally, drivers could use whatever
fuel is cheap and readily available.
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Sound of the engines: the fast explosions are
very loud and will be difficult to muffle.
The biggest issue is control: it makes
necessary some sort of active controlmechanism to ensure that each cycle is the
same, variations could cause poor
performance and increased emissions.
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These engines are commonly of the single
piston type, with the hydraulic cylinder
acting as both load and rebound device using
a hydraulic control system. This gives the
unit high operational flexibility, and
excellent part load performance has been
reported for such engines .
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The Chironfree piston engine is an integratedcombination of an internal combustion engineand a hydraulic pump.
The core of this engine is a combustion piston
directly coupled to a hydraulic plunger. The piston is not connected to any mechanism
but is free to move within the limitations of thecylinders. In this way the energy of thecombustion process is almost directly converted
into hydraulic energy. Compared to a conventional combination of a
pump and a combustion engine, the number ofparts is reduced to approximately 40%.
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The HyDrid is a hydraulic hybrid drive train forroad vehicles. In this new concept, the completemechanical transmission of a car is replaced by afull hydrostatic transmission, allowing energyrecuperation and an efficient operation.
The concept requires extremely efficienthydrostatic pumps, motors and transformers,which have been developed recently.
Simulation by the German Institute for FluidPower Drives and Controls (IFAS) at RWTH Aachen
University proved that an average fuelconsumption of 3.1 liter per 100 km (or 77 MPG)is possible for a mid-sized (1450 kg) passengercar.
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TWO CARS: SAME
WEIGHT, SAME SIZE,
SAME ENGINE,SAME TRACTION, SAME
PERFORMANCE
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This can be achieved with a series hydraulic
hybrid drivetrain, called the Hydrid, which
is developed by the Dutch company INNAS.
In this new concept, the complete
mechanical transmission of a car is replaced
by a full hydrostatic transmission, allowing
energy recuperation and an efficient engine
operation.
The concept requires extremely efficient
hydrostatic pumps, motors and transformers,
which have been developed recently.
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Engine control problem which is fully solved
only in single piston hydraulic engine
Influence of cycle to cycle variations in the
combustion process
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