seminar report on free piston engine

“FREE PISTON

SUBMITTED IN PARTIAL FULFILMENT OF THE REQ

BACHELOR OF TECHNOLOGY

MECHANICAL ENGINEERING

RAJASTHAN TECHNICAL UNIVERSITY, KOTA

PACIFIC COLLEGE OF ENGINEERING, UDAIPUR,

A

Seminar Report

on

FREE PISTON LINEAR ENGINE”

SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIRMENT FOR AWARD OF

THE DEGREE OF

BACHELOR OF TECHNOLOGY

IN

MECHANICAL ENGINEERING

SUBMITTED TO


SUBMITTED BY

(SHIVAM KUSHWAH)

13EPAME064

FEBRUARY, 2017


RAJASTHAN

UIRMENT FOR AWARD OF



i

DECLARATION

I, Shivam Kushwah here by declare that this report is the record of authentic work carried by me

during the academic year 2017

Signature of the student

(H.O.D. Of Mechanical Engg.)

ii

ACKNOWLEDGEMENT

We are greatly thankful to all those who have given me the opportunity of doing

Seminar in Pacific College of Engineering.

Also thanks for support by Mr. Akshat Singh Jhala for his unwavering assistance

in making Report on Stirling Engine.

We are very grateful for the encouragement, guidance and assistance that he

accorded us from the beginning of the Presentation to its successful completion.

Date..................... (Shivam Kushwah)

iii

ABSTRACT

Free-piston engines are under investigation by a number of research groups

due to potential fuel efficiency and exhaust emissions advantages over

conventional technology. The main challenge with such engines is the control of

the piston motion, and this has not yet been fully resolved for all types of free-

piston engines.

This Report discusses the basic features of a single piston free-piston engine

generator under development at Newcastle University and investigates engine

control issues using a full-cycle simulation model. Control variables and

disturbances are identified, and a control strategy is proposed. It is found that the

control of the free-piston engine is a challenge, but that the proposed control

strategy is feasible. Engine speed control does, however, represent a challenge in

the current design.

iv

INDEX

Declaration i

ACKNOWLEDGEMENTS ii ABSTRACT iii TABLE OF CONTENTS iv

1. Introduction 1

2. Principal 2

3. Features 2-3

4. Piston Configurations 3

4.1 Single Piston 4

4.2 Dual Piston 4

4.3 Opposed Piston 5-6

5. Applications 6

5.1 Free Piston Air Compressor 6-10

5.2 Hydraulic free Piston-Engine 10-11

5.3 Free Piston Engine Generator 11-12

Conclusion 13

Reference 14

1

1. Introduction

The development of industry and technology had led to a massive energy

crisis, environmental pollution and consequently, high levels of fuel prices present a

great challenge for internal combustion engine designers. More research efforts are

put into engine technology to explore and study more efficient unconventional

engines, aiming at reducing engine emissions and improving efficiency. The free

piston engine is a kind of unconventional engine with the characteristics of

simplicity and operational flexibility, which draw a great amount of attention from

engine researchers. The advanced microprocessor-based control systems and

modern engine technologies significantly promote the development of this research

as a result of improved operational control of the free piston engine, along with

enhanced optimization possibilities for various operating conditions.

Literature Review

The free-piston engine, proposed by Pescara, during 1930‟s was a successful

alternative to conventional engines and gas turbines as it was suitable to be used as

air compressors or gas generators. However, as conventional engine and gas turbine

technology matured, the free-piston engine concept was abandoned in the early

1960s. After being abandoned, free-piston engines are being investigated by a

number of research groups worldwide as an alternative to conventional engine-

generator sets or for generating hydraulic power in off- highway vehicles. The

experimental analysis on hydraulic free piston engine. and free piston engine

generator a wide scope for such an unconventional engine in the future.

2. Principle

The piston is „free‟ because its motion is not restricted by the motion of a

rotating crankshaft, but that the piston is free to move between its endpoints, only

influenced by the gas and load forces acting upon it. By coupling with a suitable

2

load device, it can be used as air compressor, gas generator, hydraulic pump or

generator.

This can be written as:

∑ F = mp (d2x/dt2)

Where FC is the combustion chamber force, FR bounce chamber /rebound force, FL

load force, x mover position and mp piston mass [4].

Free piston engines usually works on two-stroke compression ignition or spark

ignition operating principle, as a power stroke is required on every cycle.

3. Features

The free-piston engine has a number of unique features, some give it

potential advantages and some represent challenges that must be overcome for the

free-piston engine to be a realistic alternative to conventional technology.

As the piston motion between the endpoints is not mechanically restricted by

a crank mechanism, the free-piston engine has the valuable feature of variable

compression ratio, which may provide extensive operation optimization, higher part

Fig.3 Feature of Free Piston Engine

3

load efficiency and possible multi-fuel operation. These are enhanced by variable

fuel injection timing and valve timing through proper control methods.

Variable stroke length is achieved by a proper frequency control scheme such as

PPM (Pulse Pause Modulation) control [1], in which piston motion is paused at

BDC using a controllable hydraulic cylinder as rebound device. The frequency can

therefore be controlled by applying a pause between the time the piston reaches

BDC and the release of compression energy for the next stroke.

Since there is few number of moving parts frictional losses and manufacturing cost

reduces. The simple and compact design thus requires less maintenance and this

increases lifetime.

The purely linear motion leads to very low side loads on the piston, hence lesser

lubrication requirements for the piston.

The combustion process of free piston engine is well suited for Homogeneous

Charge Compression Ignition (HCCI) mode, in which the premixed charge is

compressed and self-ignited, resulting in very rapid combustion, along with lower

requirements for accurate ignition timing control. Also, high efficiencies are

obtained due to nearly constant volume combustion and the possibility to burn lean

mixtures to reduce gas temperatures and thereby some types of emissions [4].

By running multiple engines in parallel, vibrations due to balancing issues may be

reduced, but this requires accurate control of engine speed. Another possibility is to

apply counterweights, which results in more complex design, increased engine size

and weight and additional friction losses.

With the absence of an energy storage device, like flywheel in conventional

engines, it will not be capable of driving the engine for several revolutions. Hence,

if the engine fails to build up sufficient compression or if other factors influence the

injection/ignition and combustion, the engine may stop. This result in misfiring and

the need for accurate speed control.

4. Piston Configurations

Free-piston engines are usually divided into three categories based on the

piston / cylinder configuration.

4

4.1 Single Piston

It consists of a combustion cylinder, a load device and a rebound device,

which accurately controls the amount of energy put into the compression process

and thereby regulates the compression ratio and stroke length. A simple design with

high controllability is the main strength of this design compared to others.

Fig. 4.1 Single piston hydraulic free-piston engine

4.2 Dual Piston

In this design, the need for a rebound device is eliminated since the working

piston itself acts as rebound device. This allows a simple and compact device with

higher power to weight ratio. The control of piston motion has proved difficult since

small variations in the combustion in either of the two cylinders will have high

influence on the next compression.

Fig. 4.2 Hydraulic dual piston free-piston engine

4.3 Opposed Piston

This design consists of two single piston units with a common combustion

chamber. Each piston requires a re

coupled to one or both of the

pistons ensure symmetric piston motion. The main advantages are

Fig.4.3.1_Free_opposed_pistion_Hydraulic_Pump

5


chamber. Each piston requires a re-bound device, and a load device may be

coupled to one or both of the pistons. Mechanical linkages connecting the two

pistons ensure symmetric piston motion. The main advantages are

Fig.4.3.1 Free opposed pistion Hydraulic Pump


bound device, and a load device may be

pistons. Mechanical linkages connecting the two

pistons ensure symmetric piston motion. The main advantages are perfectly

6

Fig.4.3.2 Free Opposed Piston Generator

balanced and vibration-free design and reduced heat transfer losses due to the

elimination of the cylinder head. But, it is seen that the need for a piston

synchronization mechanism together with the dual set of the main components

makes the engine complicated and bulky.

5. Applications

Since the free-piston engine was first developed around 1930, a number of

different designs have been proposed using the free-piston concept. The majority of

these were, however, not commercially successful. This section gives an overview

of known free-piston engine developments, with an emphasis on engines where

experimental results or operational performance data have been reported.

5.1 Free Piston Air Compressors

The original free-piston configuration proposed by Pescara was an air

compressor. These engines were of the opposed piston type, making them vibration-

free. 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 clearance of compressor cylinders to return the piston, thereby

eliminating the need for a rebound device.

In the figure shown, during the expansion stroke, the air in the compressor

cylinder is compressed along with the sc

combustion chamber by the scavenging pump. In the compression stroke, which

results from the bounce chamber, the charge is compressed and ignited

One of the earliest successful free

described by Toutant, developed by German company Junkers and was used by

the German Navy during World War II to provide compressed

torpedoes. It had the advantages of high efficiency, compactness and low noise and

vibration. Superior fuel economy is possible due to the on/off control regulating the

delivery of compressed air, where conventional engine

The lack of success of the free

possible factors, including

Fig.5.1.1_Free_Piston_Air_Compressor

7


cylinder is compressed along with the scavenging of influx charge to the


results from the bounce chamber, the charge is compressed and ignited

One of the earliest successful free-piston engine air compressors was

escribed by Toutant, developed by German company Junkers and was used by

the German Navy during World War II to provide compressed air for launching

. It had the advantages of high efficiency, compactness and low noise and

fuel economy is possible due to the on/off control regulating the

delivery of compressed air, where conventional engine-compressor sets run idle.

The lack of success of the free-piston air compressor may be due to some

possible factors, including

Fig.5.1.1 Free Piston Air Compressor


avenging of influx charge to the


results from the bounce chamber, the charge is compressed and ignited [5].

piston engine air compressors was

escribed by Toutant, developed by German company Junkers and was used by

air for launching

. It had the advantages of high efficiency, compactness and low noise and

fuel economy is possible due to the on/off control regulating the

compressor sets run idle.

piston air compressor may be due to some

8

(a) Stationary installations tended to use cheaper electric motors to drive

compressors.

(b) Demand for variable power output disfavored the narrow-output free-piston air

compressor for portable applications.

(c) Limited market for such applications discouraged the development of such

unconventional design.

Fig. 5.1.2 Pescara Free Piston Gas Turbine

In the late 1940‟s the free-piston gas generator attracted interest for use in

large-scale power plants, marine installations and later also for vehicle propulsion.

These engines were typically diesel powered, opposed piston engines with

9

mechanical synchronization of the two pistons. The most important

advantages were: low fuel quality requirements, vibration-free design, good dynamic

response and low turbine material requirements due to lower inlet temperatures.

These engines were highly supercharged and operated on higher mean effective

pressures than conventional diesel engines.

The working of a free piston gas turbine starts with the influx air being

compressed by the piston that rebounds from the cushion cylinder. The pressurized

air then flows though the delivery valves to the combustion chamber, where

combustion occurs, producing the power stroke. The exhaust gases will be

scavenged by the further flow of fresh air and is passed to the turbine.

The model GS-34 free-piston gas generator manufactured by Société

Industrielle Générale de Mécanique Appliquée (SIGMA) in France was one of

the most successful free-piston engine gas generators ever made.

Still, free-piston gas generator never became a real competitor to either the

diesel engine or the gas turbine. Some of the reasons for its limited success are:

a) The mismatching of a pulsating-flow compressor with a continuous-flow turbine,

giving low part-load efficiency and limiting the gas generator to constant power

applications.

b) High failure rates and low lifetime were reported, related to high pressure and

temperature operation.

c) No large advantages in weight or fuel economy compared to conventional

engines and could not compete with the power to weight ratio of the gas turbine.

5.2 Hydraulic Free-Piston

The hydraulic free piston engine integrates the

and the hydraulic pump. The energy released from combustion process is converted

directly into hydraulic energy. They may apply a hydraulically rebound device,

using part of the produced hydraulic energy to return the piston, or

chamber.

Experimental tests on the prototypes show generally good fuel economy and

high part load efficiency by using the PPM (Pulse Pause Modulation) control [1].

Many of the modern approaches in free

engines. Most of these units are aimed at vehicles such as fork

system. The piston assembly consists of the power piston, rebound piston and pump

piston which are rigidly connected by the piston rod. The HEUI (Hydra

Electronic Unit Injector)

reversible energy storage device to supply energy for the compression stroke.

Frequency control valve controls the supplied energy from the accumulator, which

determines the operational frequency of the engine.

Fig.5.2_The_hydraulic_free_piston_engine

10

Piston Engines

The hydraulic free piston engine integrates the internal combustion engine



using part of the produced hydraulic energy to return the piston, or



Many of the modern approaches in free-piston engine technology are hydraulic

engines. Most of these units are aimed at vehicles such as fork- lift trucks and earth


piston which are rigidly connected by the piston rod. The HEUI (Hydra

nit Injector) is equipped for fuel injection. The accumulator is used as a



onal frequency of the engine.

Fig.5.2 The hydraulic free piston engine

internal combustion engine



using part of the produced hydraulic energy to return the piston, or a bounce



piston engine technology are hydraulic

lift trucks and earth-


piston which are rigidly connected by the piston rod. The HEUI (Hydraulic

is equipped for fuel injection. The accumulator is used as a



The working process can be described as follows: Hydraulic energy from

accumulator pushes the piston thereby compressing the gases in the combustion

cylinder along with the sucking of low pressure oil through the suction valve.

During the expansion stroke, high

valves by the pump piston and compression piston pushes the compression oil to

accumulator again.

Since the piston motion is determined by the instantaneous balance of the

cylinder gas pressure, the hydraulic forces and the friction forces, the exhaust valves

need to be driven accurately and quickly according to piston position. Since this

cannot be done by the c

valves system is developed and equipped in the cylinder head.

Thus, a number of prototypes have been developed in recent years and

experimental results from these are currently being reported. The D

Innas BV [1] is among the research leaders within free

They have developed a single piston, diesel powered, hydraulic free

5.3 Free-Piston Engine

The free piston engine generator essentially

coupled to a linear electric machine. The high efficiencies of electrical machinery,

along with flexibility and controllability, make this an interesting concept.

A driving force behind the interest and researches in free

generators is the increasing interest in hybrid

electric ship concept.

Fig.5.3.1_free_piston_linear_enginegenerator

11



with the sucking of low pressure oil through the suction valve.

During the expansion stroke, high-pressure oil is outputted through the pressure


iston motion is determined by the instantaneous balance of the



cannot be done by the conventional camshaft timing system, the hydraulic exhaust

valves system is developed and equipped in the cylinder head.


experimental results from these are currently being reported. The D

Innas BV [1] is among the research leaders within free-piston technology today.

They have developed a single piston, diesel powered, hydraulic free-piston engine.

Piston Engine Generators

The free piston engine generator essentially consists of a free



A driving force behind the interest and researches in free

generators is the increasing interest in hybrid-electric vehicle technology and all

Fig.5.3.1 free piston linear engine generator



with the sucking of low pressure oil through the suction valve.

pressure oil is outputted through the pressure


iston motion is determined by the instantaneous balance of the



onventional camshaft timing system, the hydraulic exhaust


experimental results from these are currently being reported. The Dutch company

piston technology today.

piston engine.

consists of a free-piston engine



A driving force behind the interest and researches in free-piston engine

electric vehicle technology and all-

12

In this machine, the piston will move freely between its two endpoints, its

motion being determined by the instantaneous balance of cylinder gas forces,

electric machine force and frictional forces. The bounce chamber will be a closed

cylinder with pressure control valves to regulate the amount of gas trapped in the

bounce chamber, and thereby the gas pressure force on the piston. Thus the piston

motion is controlled.

The engine will operate on a turbocharged two-stroke diesel cycle with

direct injection / electronically controlled fuel injection like CRDI. Scavenging is

provided through scavenging ports in the cylinder liner and electro-pneumatic

exhaust poppet valves in the cylinder head.

The linear electrical machine is taken as a permanent magnet machine. By

employing appropriate power electronics, this setup may allow the use of the

electric machine in motoring mode to aid engine control and for starting.

Fig.5.3.2 Free Piston Power Pack with the specifications.

The design of the electric machine will have a high influence on the

performance since the alternator translator forms a part of the moving mass.

Increasing the moving mass reduces the bouncing frequency of the system, whereas

a low moving mass is expected to give high engine speeds. Also, due to low speed,

higher mass have more time available for scavenging, allowing lower scavenging

ports height and nearly constant volume combustion. This increases the efficiency.

But the resulting high temperatures and pressures causes appreciable heat transfer

losses. Hence an appropriate weight is required in order to achieve an acceptable

power to weight ratio and optimum efficiency.

13

Conclusion

Free piston engines have been proved as a promising technology with several

developments showing favorable performance compared to conventional technology

by fully utilizing the powers of modern, microprocessor-based, control techniques.

Although several reports have confirmed that the free-piston engine is a viable

concept, with further work focusing on the parameters that influences engine

performance, such as optimal control of piston motion, combustion process,

emissions measurement etc., free piston engines can be developed as an alternative

for conventional engines.

14

References

1. R. Mikalsen, A.P. Roskilly, “A computational study of free-piston diesel engine

combustion”, Applied Energy, 2009

2. https://www.google.co.in

3. https://www.bing.com

https://www.bing.com/