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Design and Simulation

of Two-Stroke Engines

Gordon P. Blair

Professor of Mechanical Engineering

The Queen's University of Belfast

Published by:

Society of Automotive Engineers, Inc.

400 Commonwealth Drive

Warrendale, PA 15096-0001

U.S.A.

Phone: (412) 776-4841

Fax: (412) 776-5760

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Library of Congress Cataloging-in-Publication Data

Blair, Gordon P.

Design and simulation of two-stroke engines / Gordon P. Blair.

p. cm.

Includes bibliographical references and index.

ISBN 1-56091-685-0

1. Two-stroke cycle engines—Design and construction. I. Title

TJ790.B58 1996

621.43-dc20

95-25748

CIP

ISBN 1-56091-685-0

Cover photo courtesy of Mercury Marine, a Brunswick Company (3.0-liter V-6 outboard engine).

Permission to photocopy for internal or personal use, or the internal or personal use of specific clients,

is granted by SAE for libraries and other users registered with the Copyright Clearance Center (CCC),

provided that the base fee of $.50 per page is paid directly to CCC, 222 Rosewood Dr., Danvers, MA

01923. Special requests should be addressed to the SAE Publications Group. 1-56091-685-0/96 $.50.

SAE Order No. R-161

A Second Mulled Toast

When as a student a long time ago

my books gave no theory glimmers,

why two-strokes ended in second place slow,

and four-strokes were always the winners.

Williams and Craig were heroes enough

whose singles thumped to Tornagrough,

such as black 7R or silver Manx,

on open megas they enthused the cranks.

Wallace and Bannister gave me the start

into an unsteady gas dynamic art,

where lambdas and betas meshed in toil

for thirty years consumed midnight oil.

With the parrot on Bush a mental penny

into slot in brain fell quite uncanny.

Lubrication of grey cells finally gave

an alternative way to follow a wave.

That student curiosity is sated today

and many would describe that as winning.

Is this then the end of the way?

No, learning is aye a beginning.

Gordon Blair

July 1994

Foreword

Several years ago I wrote a book,

The Basic Design of Two-Stroke Engines.

It was no

sooner published than a veritable revolution took place in several areas of two-stroke design

and development. Thus, some time ago, I settled to update that book to a Second Edition. It

soon became very obvious that the majority of the material was so different, and the changes

so extensive, that to label the book as simply a "second edition" was not only unreasonable

but would be both inaccurate and misleading. Nevertheless, the basic premise for providing

the book had not changed so the original Foreword is still germane to the issue and is pro-

duced below, virtually in its entirety. The fundamental approach is no different the second

time around, simply that the material is much more detailed and much more extensive. So

here it is, with a postscript added:

This book is intended to be an information source for those who are involved in the design

of two-stroke engines. In particular, it is a book for those who are already somewhat knowl-

edgeable on the subject, but who have sometimes found themselves with a narrow perspec-

tive on the subject, perhaps due to specialization in one branch of the industry. For example,

I am familiar with many who are expert in tuning racing motorcycle engines, but who would

freely admit to being quite unable to design for good fuel economy or emission characteris-

tics, should their industry demand it. It is my experience that the literature on the spark-

ignition two-stroke engine is rich in descriptive material but is rather sparse in those areas

where a designer needs specific guidance. As the two-stroke engine is currently under scru-

tiny as a future automobile engine, this book will help to reorient the thoughts of those who

are more expert in designing camshafts than scavenge ports. Also, this book is intended as a

textbook on design for university students in the latter stages of their undergraduate studies,

or for those undertaking postgraduate research or course study.

Perhaps more important, the book is a design aid in the areas of gas dynamics, fluid me-

chanics, thermodynamics and combustion. To stop you from instantly putting the book down

in terror at this point, rest assured that the whole purpose of this book is to provide design

assistance with the actual mechanical design of the engine, in which the gas dynamics, fluid

mechanics, thermodynamics and combustion have been optimized so as to provide the re-

quired performance characteristics of power or torque or fuel consumption.

Therefore, the book will attempt to explain, inasmuch as I understand, the intricacies of,

for example, scavenging, and then provide you with computer programs written in Basic

which will assist with the mechanical design to produce, to use the same example, better

scavenging in any engine design. These are the very programs which I have written as my

own mechanical design tools, as I spend a large fraction of my time designing engines for test

at The Queen's University of Belfast (QUB) or for prototype or production development in

Design_and_simulation_of_two-stroke_engines.pdf

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