28
Liquid Piston Engines
Scrivener Publishing
100 Cummings Center, Suite 541J
Beverly, MA 01915-6106
Publishers at Scrivener
Martin Scrivener ([email protected])
Phillip Carmical ([email protected])
Liquid Piston Engines
Aman Gupta, Shubham Sharma, and Sunny Narayan
This edition first published 2017 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA
and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA
© 2017 Scrivener Publishing LLC
For more information about Scrivener publications please visit www.scrivenerpublishing.com.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or
transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or other-
wise, except as permitted by law. Advice on how to obtain permission to reuse material from this title
is available at http://www.wiley.com/go/permissions.
Wiley Global Headquarters
111 River Street, Hoboken, NJ 07030, USA
For details of our global editorial offices, customer services, and more information about Wiley products
visit us at www.wiley.com.
Limit of Liability/Disclaimer of Warranty
While the publisher and authors have used their best efforts in preparing this work, they make no rep-
resentations or warranties with respect to the accuracy or completeness of the contents of this work and
specifically disclaim all warranties, including without limitation any implied warranties of merchant-
ability or fitness for a particular purpose. No warranty may be created or extended by sales representa-
tives, written sales materials, or promotional statements for this work. The fact that an organization,
website, or product is referred to in this work as a citation and/or potential source of further informa-
tion does not mean that the publisher and authors endorse the information or services the organiza-
tion, website, or product may provide or recommendations it may make. This work is sold with the
understanding that the publisher is not engaged in rendering professional services. The advice and
strategies contained herein may not be suitable for your situation. You should consult with a specialist
where appropriate. Neither the publisher nor authors shall be liable for any loss of profit or any other
commercial damages, including but not limited to special, incidental, consequential, or other damages.
Further, readers should be aware that websites listed in this work may have changed or disappeared
between when this work was written and when it is read.
Library of Congress Cataloging-in-Publication Data
ISBN 978-1-119-32295-5
Cover images: Irrigation, Elswarro | Dreamstime.com. Plant, lofoto | Dreamstime.com
Chimneys, Piotr Majka | Dreamstime.com
Cover design by Kris Hackerott
Set in size of 11pt and Minion Pro by Exeter Premedia Services Private Ltd., Chennai, India
Printed in the USA
10 9 8 7 6 5 4 3 2 1
v
Contents
Abstract ix
List of Symbols xi
1 Introduction 11.1 Background 11.2 Types of Stirling Engines 21.3 Stirling Engine Designs 41.4 Free-Piston Stirling Engines 61.5 Gamma Type Engine 18References and Bibliography 27
2 Liquid Piston Engines 292.1 Introduction 292.2 Objectives 322.3 Brief Overview of Pumps and Heat Engines 332.4 Heat Engine 382.5 Clever Pumps 422.6 History and Development of Stirling Engines 452.7 Operation of a Stirling Engine 482.8 Working Gas 532.9 Pros and Cons of Stirling Engine 53
2.10 Low Temperature Difference Stirling Engine 542.11 Basic Principle of a Fluidyne 552.12 Detailed Working of a Fluidyne 572.13 Role of Evaporation 612.14 Regenerator 612.15 Pumping Setups 622.16 Tuning of Liquid Column 632.17 Motion Analysis 642.18 Losses 652.19 Factors Affecting Amplitude 662.20 Performance of Engine 67
vi Contents
2.21 Design 672.22 Assembly 702.23 Calculation 712.24 Experiments 722.25 Results 742.26 Comparison Within Existing Commercial Devices 762.27 Improvements 782.28 Future Scope 792.29 Conclusion 802.30 Numerical Analysis 80References and Bibliography 83
3 Customer Satisfaction Issues 873.1 Durability Issues 873.2 Testing of Engines 883.3 Design of Systems 883.4 Systems Durability 89References and Bibliography 89
4 Lubrication Dynamics 914.1 Background 914.2 Friction Features 934.3 Effects of Varying Speeds and Loads 944.4 Friction Reduction 944.5 Piston-Assembly Dynamics 954.6 Reynolds Equation for Lubrication Oil Pressure 964.7 Introduction 1024.8 Background 1044.9 Occurrence of Piston Slap Events 105
4.10 Literature Review 1104.11 Piston Motion Simulation Using COMSOL 1144.12 Force Analysis 1174.13 Effects of Various Skirt Design Parameters 1204.14 Numerical Model of Slapping Motion 1314.15 Piston Side Thrust Force 1324.16 Frictional Forces 1334.17 Determination of System Mobility 1334.18 Conclusion 143
Contents vii
5 NVH Features of Engines 1455.1 Background 1455.2 Acoustics Overview of Internal Combustion Engine 1465.3 Imperial Formulation to Determine Noise Emitted
from Engine 1495.4 Engine Noise Sources 1515.5 Noise Source Identification Techniques 1545.6 Summary 157 References and Bibliography 158
6 Diagnosis Methodology for Diesel Engines 1616.1 Introduction 1616.2 Power Spectral Density Function 1626.3 Time Frequency Analysis 1626.4 Wavelet Analysis 1636.5 Conclusion 164References and Bibliography 165
7 Sources of Noise in Diesel Engines 1677.1 Introduction 1677.2 Combustion Noise 1687.3 Piston Assembly Noise 1687.4 Valve Train Noise 1707.5 Gear Train Noise 1707.6 Crank Train and Engine Block Vibrations 1717.7 Aerodynamic Noise 1717.8 Bearing Noise 1717.9 Timing Belt and Chain Noise 172
7.10 Summary 174 References and Bibliography 175
8 Combustion Based Noise 1798.1 Introduction 1798.2 Background of Combustion Process
in Diesel Engines 1808.3 Combustion Phase Analysis 1838.4 Combustion Based Engine Noise 1848.5 Factors Affecting Combustion Noise 1868.6 In Cylinder Pressure Analysis 1878.7 Effects of Heat Release Rate 1878.8 Effects of Cyclic Variations 1888.9 Resonance Phenomenon 189
viii Contents
8.10 In Cylinder Pressure Decomposition Method 1898.11 Mathematical Model of Generation of
Combustion Noise 1928.12 Evaluation of Combustion Noise Methods 1938.13 Summary 199References and Bibliography 199
9 Effects of Turbo Charging in S.I. Engines 2039.1 Abstract 2039.2 Fundamentals 2049.3 Turbochargers 2059.4 Turbocharging in Diesel Engines 2069.5 Turbocharging of Gasoline Engines 2079.6 Turbocharging 2089.7 Components of Turbocharged SI Engines 2089.8 Intercooler 2139.9 Designing of Turbocharger 213
9.10 Operational Problems in Turbocharging of SI Engines 2229.11 Methods to Reduce Knock in S.I Engines 2239.12 Ignition Timing and Knock 2239.13 Charge Air Cooling 2249.14 Downsizing of SI Engines 2259.15 Techniques Associated with Turbo Charging
of SI Engines Boosting Systems 225
10 Emissions Control by Turbo Charged SI Engines 231
11 Scope of Turbo Charging in SI Engines 233
12 Summary 235
13 Conclusions and Future Work 23713.1 Conclusions 23713.2 Contributions 23713.3 Future Recommendations 238References and Bibliography 240
List of Important Terms 243
Bibliography 247
Glossary 249
Index 251
ix
Abstract
Engines and pumps are common engineering devices which have become essential to the smooth running of modern society. Many of these are very sophisticated and require infrastructure and high levels of technological competence to ensure their correct operation. For example, some are com-puter controlled, others require stable three-phase electrical supplies, or clean hydrocarbon fuels. The first part of the project focuses on the iden-tification, design, construction and testing of a simple, yet elegant, device which has the ability to pump water but which can be manufactured easily without any special tooling or exotic materials and which can be powered from either combustion of organic matter or directly from solar heating.
The device, which has many of the elements of a Stirling engine, is a liquid piston engine in which the fluctuating pressure is harnessed to pump a liquid (water). A simple embodiment of this engine/pump has been designed and constructed. It has been tested and recommendations on how it might be improved are made. The underlying theory of the device is also presented and discussed.
The second portion deals with noise,vibration and harshness perfor-mances of internal combustion engines. Features of various sources of noise and vibrations have been discussed and major focus has been on combustion based noise and piston secondary motion.Various equations of piston motion were solved and effects of various parameters on it were analyzed.
xi
List of Symbols
Symbol Definition Units
V Volume cm3
P Pressure Bar
T Temperature Kelvin
R Gas Constant J/K-mol
v Voltage Volt
I Current Ampere
Q, V Volume flow Rate cm3/s
Qe
Heat Absorbed Joules
A Tube Area cm2
q Charge coulomb
Cp
Specific Heat J/Kg-K
η Kinematic Fluid Viscosity m2/S
ω Frequency Hz
Rt
Radius Of Tube cm
X Fluid Displacement cm
ρ Fluid Density kg/m3
U Heat Transfer coefficient W/m2-k
L,l Tube length cm
g Acceleration due to gravity m/s2
1
1Introduction
1.1 Background
The Stirling engine system was studied years ago. Such engines have merits the basis of sealings, materials, heat transfer rate, size, and weight issues. During past years the major focus has been on various designs of Stirling engine systems.
This engine is based on a heated reciprocating system. The gas receives heat and expands at constant temperature. Rate of transfer is higher, which is a major drawback of these engines. In contrary the internal combustion (IC) engine is operated by combustion of air-fuel mixture which results in higher heat and pressure rise which is converted to useful work. The temperature varies with the combustion and piston motion. As the heat is supplied externally the following varieties of sources can be used:
Heat from gaseous, liquid, or solid fuelSolar energyRecycled Waste heat
2 Liquid Piston Engines
Cooling in a Stirling engine cycle can be done in the following ways:
Convection coolingUse of cooling fluids like water, ethylene glycol, or a mixture
Reversible nature of Stirling engine differentiates it from IC engines. Combustion outside results in lower emissions as well as less noise and vibration.
Solar energy may also be harnessed using parabolic dish.As a smaller number of fuel types or heat sources are available, a Stirling
system may be designed as such. This system may use solar heating as the primary heat source, as well as a natural gas burner as an auxiliary unit during nights and cloudy periods.
1.2 Types of Stirling Engines
Using basic concepts of heat engineering many designs of Stirling engines have been proposed over past years. These engines may be classified on the basis of mechanical design features as:
Kinematic designs: These engines operate on basis of crank-shaft and linkage mechanisms in which the motion of the piston is limited by configuration of linkages.Free-piston designs: In these engines the oscillatory motion of the piston in a magnetic field generate electric power. Pressure gradient cause tuned spring-mass-damper motion of displacer. Such machines are simple to operate but more complex on basis of dynamics and thermodynamics. For cooling purposes, the piston may be driven by a motor.
Stirling engines may also have alpha, beta, or gamma configurations which are discussed as follows:
Alpha engines which are seen in Figure 1.1 have two separate pis-tons that are linked and oscillate showing some phase lag. The working gas moves to and fro passing through a cooler, regenerator, and a heater between the cylinders. These engines are kinematic engines which need proper sealings.
Beta engines that are seen in Figure 1.2 have a displacer-piston arrange-ment that are in phase with one another. The displacer pushes the gas to and fro between the hot (expansion area) and cold ends (compression
Introduction 3
area). As the working gas moves, it passes through a cooler, regenerator, and heater. Beta engines can be either kinematic or free-piston engines.
Gamma engines which are shown in Figure 1.3 have a system wherein the displacer and power pistons operate in separate cylinders. The displacer moves the working gas to and fro between the hot and cold ends. The cold
Regenerator
Hot endCold end
Crank shaft
Gas motion
Figure 1.1 Alpha engines.
Regenerator
Cooler
Heater
Power piston
Hot end
Cold end
Displacer
Figure 1.2 Beta engines.
Figure 1.3 Gamma engine.
Regenerator
Cooler
Heater
Powerpiston
Hot end
Cold end
Displacer
4 Liquid Piston Engines
area has cold side of the displacer and power piston. As the gas moves, it passes through a cooler, a regenerator, and a heater. These engines can be either kinematic or free-piston type.
1.3 Stirling Engine Designs
The power piston in the engine is connected to an output shaft by linkages. Kinematic design of the engine has following merits:
Coordination of various parts for proper motion during start-up, normal operation, and fluctuations of loads.
Some disadvantages of such a design include:
Need of lubrication due to rotating parts.Need of more maintenance.Proper sealing needed.
Some of the novel designs of kinematic engines are discussed next.
Wobble-plate Mechanisms
The wobble-plate that is seen Figure 1.4 has a wobble plate which is in a sliding contact with the crankshaft pivoted by connections to pistons as well as connecting rods. This ensures straight travel inside the cylinder with out rotation. The thrust is transferred to the crank at an offset angle
Wobbleplate
Crankshaft
Piston
Figure 1.4 Gamma engine.
Introduction 5
to wobble plate which acts as a double-acting engine using the power stroke of one cylinder to compress the cold gas for the adjacent cylin-der. The power piston for one cylinder is the displacer piston for another cylinder.
The Z-crank shape that the same to the wobble plate design has pis-tons connected directly to the crankshaft. Pivot points are made in order to ensure axial motion of the piston in the cylinder. Such design is more com-pact as compared to a single-piston Stirling engine. However these engines have certain demerits:
Cyclic load and wear of pivots is quick as they are under compression and bendings.Piston-lubrication is a major issue. Oil flow may cause fouling and lesser external heat transfer so reducing the efficiency.
Swash Plate Drive mechanisms – This drive has may same features as wobble plate. Bearings are used to connect the swash plate to the crank-shaft and rotates with the crankshaft, but the wobble plate which remains fixed is attached to the shaft. This design has many merits:
Quiet operation, better sealings with lesser lubrication problems.Design of swash plate may be changed for better stiffness and power transfer.The balancing of swash plate can be done built by adding additional sets of pistons. This in turn increases the power output and reduces the power-to-weight ratio.
Rhombic Drive – In this mechanism, yokes connect the power piston and the displacer piston. These are linked to twin crankshafts by means of connecting rods, as seen in Figure 1.6. In this drive mechanism power
Swashplate
Crankshaft
Power piston
Power piston
Figure 1.5 Swash plate engines.
6 Liquid Piston Engines
piston and the displacer piston move with constant lag. The rhombic drive has many benefits:
The engine has less vibrations due to complete balance of various lateral forces.These engines operate at higher power outputs due to higher pressures.Many units can move at same time in order to provide power to a multi-cylinder engine.
1.4 Free-Piston Stirling Engines
These engines have two oscillating pistons that are not connected as seen in Figure 1.7. The displacer piston has a smaller mass compared to the power piston. The heavier piston moves undamped. Motion of the displacer is simulated by springs or by the compressible working gas. The springs placed between the displacer and the power piston provide harmonic oscil-lations of the displacer. These oscillations are maintained by temperature difference, and so the system operates at the natural frequency.
The power in a free-piston system is generated by a linear alternator. Recently some of the designs have been using a hydraulic drive to run the crankshaft. Use of these hydraulics is good in engines having more torque which reduces the lateral forces in such systems.
Regenerator
Powerpiston
Connectingrod
Yokepower
Gear
CrankdiscDisplacer york
Displacerpiston
Figure 1.6 Rhombic drive engine.
Introduction 7
Free-piston systems have major advantages:
Less lateral forces and lubrication needs due to absence of rotating parts.Less maintenance.Properly sealed units prevent loss of the working gas.
These systems have following disadvantages:
Need of complex calculations to ensure proper working.Lower response time as compared to kinematic and IC engines.Piston position is an important parameter to control system as oscillations may become unbalanced.
The Alpha configuration of engine is the simplest form having two pis-tons and two cylinders connected by a regenerator. Both these cylinders are normal to one another connected by a flywheel. The hot piston is in contact with located high-temperature source while the cold piston is with the low-temperature reservoir. The pistons are arranged in a manner that the linear motion is converted to rotatory motion and a constant phase difference is maintained. The pistons are joined at a common point on flywheel.
As compared to the other basic designs the alpha type engine has greater volume due to higher compression ratios.
Hot endHeater
Cooler
Regenerator
Cold end
Alternator
Electricoutput
Displacer
Figure 1.7 Free piston engine.
8 Liquid Piston Engines
WORKING OF ENGINES: working of a Stirling engine can be divided into four operations steps that are similar to I.C. engine. Heat is added and removed at constant temperatures. The working of I.C. Engines occurs on the basis of Otto and Diesel cycles, respectively. Mechanisms of these engines is complex as motion is based on movements of multiple pistons.
Working of an Alpha Stirling can be analyzed as follows:
1. Transfer of working gas from cold side to hotter side:Flywheel moves clockwise, the hot piston moves towards right hand side towards Dead Centre and the cold piston moves up towards Top Dead Centre (TDC) as seen in Figure 1.9.
Figure 1.8 An Alpha Stirling engine.
Cold end
Hot end
Figure 1.9 Alpha engine - Transfer phase.
Introduction 9
The regenerator connects both pistons and operates at hotter temperatures.
The pistons move in such a manner that the change in the engine vol-ume is minimum and heat addition occurs at constant volume.
Towards end of the process, the working gas will be hotter and the major portion of remains in the hot cylinder. This is similar to suction stroke.
2. Power strokeAs flywheel roates by 90°, the majority of the working gas is now in the hot-ter cylinder and volume of the engine is minimum.
The fluid receives heat from a hot source. It expands moving the fly-wheel further. This is similar to power stroke of the engine and all energy is derived from this stroke.
As the hot piston moves towards right side due to gas pressure, the gas expands, with a portion passing through the regenerator.
As the heat added to the system at constant temperature it is converted to work, with a little rise in temperature. A perfect isothermal processes will cause a phase change.
This may be compared to the power stroke.The working fluid expands to about three times its original volume.
The flywheel turns by another quarter rotation and the hot piston starts to move to Dead Centre. The cold piston moves downwards. The regenerator gets heated up as the hot fluid passes by.
Heat rejection occurs at constant volume and can be seen as the exhaust stroke of the engine.
Cold end
Hot end
Figure 1.10 Alpha engine - Power stroke.
10 Liquid Piston Engines
3. Compression strokeThe crank moves by quarter of rotation. The cold piston is at the bottom dead center location and the hot piston moves towards inner dead center.
The working gas has major portion in the cold cylinder which cools down rejecting heat to cold reservoir. As the cold piston moves to the top dead center, volume is reduced and the working gas is compressed.
During Isothermal Compression the working gas rejects heat and gets compressed. There is minimum change in the internal energy and work needed is also minimum. Towards the end of the process, almost all the gas
Figure 1.11 Alpha engine - Transfer stroke.
Figure 1.12 Alpha engine - compression stroke.
Introduction 11
is in the cold piston, so volume reduces to about one-third of its original and the cycle goes on.
This final stroke may be compared to action of a supercharger or turbo-charger. There is no need of compression inside the power piston.
This mechanism was first proposed by Andy Ross. This linkage makes design more compact as connecting rods move in a straight line. This in turn reduces the force on the pistons and thus improves performance of the engine. Wear is less due to less friction and life is also increased.
The double-acting-engine has four cylinders. The pistons act as the expansion space of one engine and at the same time as compression space
Hotcylinder
Coldcylinder
Triangleconnectingrod
Figure 1.13 Ross engine.
Heater
RegeneratorExpansionspace
CoolerCompressionspace
Figure 1.14 Double-acting engine.
12 Liquid Piston Engines
of a neighbouring one. Thus this is the same as four Alpha engines. Sir William Siemens has done major work to develop these engines.
The cylinders are connected in a circular manner with cold and hot regions of neighbouring cylinders connected by a reservoir. Hence the out-let of the last cylinder is connected to the first one. So this system is more compact and with high specific power output. All the pistons move at a phase difference of 90°.
Maintaining the phase difference between the pistons and harnessing power is complicated.
All the above mentioned mechanisms face problems due to excessive side thrust and excessive wear and they have lower life and reliability.
Pistons
Bearing
Power shaft
Figure 1.15 Rocking yoke.
Pistons
Gears
Crank shaft
Powershaft
Figure 1.16 Gear mechanism.
Introduction 13
William Beale later designed an engine in which a turbine was used to har-ness power out.
Such mechanism that is seen in Figure 1.18 uses gas compressors to run turbines. Double-acting compressors may be used for more pulses of air per cycle but at lesser specific power of the engine. Uniform loading and lesser thrust force also increases life of the engine.
WORKING: Working of the double acting Stirling engine can be under-stood from the design of Alpha Stirling engine. Various engines in alpha design can have the same stroke. For that the phase lag between any two adjacent pistons must be 90°.
PistonCooler
Heater tubes
Combustor
Swash platedrive
Regenerator
Figure 1.17 Swash plate mechanism.
Compressionspace
Expansionspace
Turbine
Manifold
Valve
Cooler
Heater
Regenerator
Figure 1.18 Beal engine.
14 Liquid Piston Engines
As shown in Figure 1.18, first see the first piston moving downwards. The engine between the last and the first cylinder may be considered as a fourth engine. The first and second piston move downwards at the same time, this transfers the working gas to the hotter side with negligible change in volume.
Hence the first engine is working on Isochoric heat transfer in work-ing fluid. The second one is vicinity of the BDC and third piston moves upwards. The second one is in power stroke, and the volume of fluid is maximum. Similarly, other engines are in transfer stroke which moves fluid from hot to cold end. A Beta configuration of engine has a displacer and piston in same cylinder with a 90° phase difference. Robert Stirling was first to invent a Beta Stirling engine that was an inverted beam engine. It was similar steam engine having a beam linkage.
These are more suited for space limited applications, but output is lower than other engines. Use of a regenerator is complex in absence of insula-tion between the hot and cold ends. There is loss of RPM of the engine and hence its output.
WORKING: The basic working of a Beta Stirling engine is similar to that of Alpha Stirling engine. The difference lies in the way the working gas
Figure 1.19 Beta engine.
Piston Compressionspace
Expansionspace
Displacer
CoolerRegenerator
Heater
Beta engine
Figure 1.20 Beta engine in working.
