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Gas engine design
GAS ENGINE DESIGN
BY CHARLES EDWARD LUCKE
NEW YORK, D. VAN NOSTRAND COMPANY, 1905
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PREFACE
The purpose of this book is to present in a compact form those principles which underlie the design of gas-engines, together with such data on the subject as seem reliable for the use of those engaged in building this kind of machinery, and who are familiar with its characteristics. The qualitative or inventive side of design, such as is treated in all the books that have so far appeared, except Guldner in German, is here entirely omitted and familiarity with such presupposed. This book is concerned entirely with the quantitative side of design, and treats solely of the forces in, and the energy transforming power of the standard mechanism of, the exploding gas-engine.
All those whose interests have demanded such a quantitative knowledge of the gas-engine, either for probable output and economy or for the stresses in and proper strength of resisting engine parts, have met with difficulty in finding reliable data for reference,, as there is no book in English treating exclusively of this side of the subject. The data here presented are the result of many years' collection and personal experience, and were first classified in the present form for lecture use before my classes at Columbia University. The increase in quantity of material during the last few years made it seem desirable to publish the notes in as closely condensed a form as possible consistent with clearness.
The work is divided into three parts. The first, treating of power, efficiency, and economy, gives the material necessary for deciding on the necessary piston displacement for any specified output for any kind of gas, and enables the designer to approximately predict economy. The second part contains the data and method for determining the stresses in the parts and the number and arrangement of cylinders necessary for balance or turning effort to meet the specifications. The last part is entirely concerned with the dimensions of the parts to resist, the stresses, both by theoretic analysis and by empirical formulae, showing between what limits every principal dimension should lie.
These results apply to all classes of gas-engines, from the small high and variable-speed automobile and boat engine to the large 5000-H.P. constant-speed station engine.
The method of treatment used in the first part is believed to be new. A standard reference indicator card is established and, by comparison with tests, a diagram factor found by which the probable M.E.P. for any fuel and compression can be predicted. It is further shown that this same diagram factor, applied to the efficiency of the standard card, will give the probable efficiency of the engine as well as the economy when applied to the standard economy. The diagram factor can therefore be used for three purposes, making calculations easy and certain; quite contrary to steam work, where the M.E.P. diagram factor is very different from the ratio of theoretic to actual water-rate, or efficiency. In the second part means are given for drawing the probable indicator card and, by tables and curves, the probable inertia diagram for any engine yet unbuilt. From these the stresses are found, as well as the turning effort, for all conditions of load, ignition, charge, mixture, speed, weight of parts, and combinations of cylinders. Means are also presented here for quickly estimating the conditions of balance and the unbalanced force, from the inertia diagram. The third part of the work, by the application of a method too little used in designing, enables the exact calculations for the dimension of a part to be made, and for a check the limits between which the result should lie are presented. These limits also permit of very quick approximate design when used as empirical formulae. Variations of the limits for size, speed, or other conditions are pointed out.
The large amount of computation and numerical work involved makes it unlikely that the book is free from errors, and I will gratefully acknowledge notice of any errors or discrepancies. In this connection I am very much indebted to my associate Prof. Amasa Trowbridge for his valuable suggestions in the reading of the manuscript.
All those whose interests have demanded such a quantitative knowledge of the gas-engine, either for probable output and economy or for the stresses in and proper strength of resisting engine parts, have met with difficulty in finding reliable data for reference,, as there is no book in English treating exclusively of this side of the subject. The data here presented are the result of many years' collection and personal experience, and were first classified in the present form for lecture use before my classes at Columbia University. The increase in quantity of material during the last few years made it seem desirable to publish the notes in as closely condensed a form as possible consistent with clearness.
The work is divided into three parts. The first, treating of power, efficiency, and economy, gives the material necessary for deciding on the necessary piston displacement for any specified output for any kind of gas, and enables the designer to approximately predict economy. The second part contains the data and method for determining the stresses in the parts and the number and arrangement of cylinders necessary for balance or turning effort to meet the specifications. The last part is entirely concerned with the dimensions of the parts to resist, the stresses, both by theoretic analysis and by empirical formulae, showing between what limits every principal dimension should lie.
These results apply to all classes of gas-engines, from the small high and variable-speed automobile and boat engine to the large 5000-H.P. constant-speed station engine.
The method of treatment used in the first part is believed to be new. A standard reference indicator card is established and, by comparison with tests, a diagram factor found by which the probable M.E.P. for any fuel and compression can be predicted. It is further shown that this same diagram factor, applied to the efficiency of the standard card, will give the probable efficiency of the engine as well as the economy when applied to the standard economy. The diagram factor can therefore be used for three purposes, making calculations easy and certain; quite contrary to steam work, where the M.E.P. diagram factor is very different from the ratio of theoretic to actual water-rate, or efficiency. In the second part means are given for drawing the probable indicator card and, by tables and curves, the probable inertia diagram for any engine yet unbuilt. From these the stresses are found, as well as the turning effort, for all conditions of load, ignition, charge, mixture, speed, weight of parts, and combinations of cylinders. Means are also presented here for quickly estimating the conditions of balance and the unbalanced force, from the inertia diagram. The third part of the work, by the application of a method too little used in designing, enables the exact calculations for the dimension of a part to be made, and for a check the limits between which the result should lie are presented. These limits also permit of very quick approximate design when used as empirical formulae. Variations of the limits for size, speed, or other conditions are pointed out.
The large amount of computation and numerical work involved makes it unlikely that the book is free from errors, and I will gratefully acknowledge notice of any errors or discrepancies. In this connection I am very much indebted to my associate Prof. Amasa Trowbridge for his valuable suggestions in the reading of the manuscript.
CONTENTS
- POWER EFFICIENCY ECONOMY.
- FORCES IN THE ENGINE DUE TO GAS PRESSURE AND INERTIA
- DIMENSIONS OF THE ENGINE PARTS
PART I – POWER – EFFICIENCY - ECONOMY
I. Introduction - It is from a comparatively simple though comprehensive statement of a guarantee to a buyer that the engineer must design and construct his engine. This statement of guarantee is the initial specification for which the designer must elaborate the details with sufficient minuteness to enable workmen to construct the machine.
Five facts are of prime importance to the buyer: first, the capacity of the engine in brake horse-power; second, its performance in B.T.U. per hour necessary to maintain each B.H.P.; third, the adaptability of the engine to the service. This is a factor of no little importance to the buyer, but is not always a feature of guarantees. When it is not, it certainly has weight in the decision of the buyer with what builder he will place his order. It may be that a certain firm has a reputation for building a better balanced engine than another, either because of owning certain useful patents or because of employing better designers; another firm may be in a position to build an engine with better speed regulation. To the former the boat-builder or owner whose building must not be shaken will apply, to the latter the buyer who intends to run dynamos in parallel. When incorporated in the guarantee this adaptability clause is mainly confined to regulation of engines to run dynamos.
The last two factors that concern the designer in the closing of the contract are the cost and workmanship. Cost is the last thing also that is learned by either designer or builder, and is determined only by experience in manufacture, not by any abstract or deep knowledge of technology, while workmanship is likewise difficult to predict.
The building of an engine to meet requirements of power economy or adaptability in balance or regulation is a thing that can be set down as a technical problem and solutions found from endless comparisons of what by mathematical analysis should be under ideal conditions and the determination by test of what is or can be under practical conditions. It is the business of the designer to know all the available results of such comparisons, for these enable him to take cognizance of conditions that are unknown or unknowable and thus to design for any specifications that are within possibility and to know just as surely what cannot be done.
Power depends on mean effective pressure and piston speed. Mean effective pressure depends in gas-engines primarily on the kind of gas and secondly on the treatment of the gas. Piston speeds in gas-engines depend on nearly the same conditions as in steam-engines. Economy is a factor in gas-engines that depends on the kind of fuel and its treatment.
Regulation depends on the method of governing, the combination of cylinders or treatment of the gas, to produce uniformity of turning effort and permit of quick change to meet loads.
Balance in gas-engines is controlled by the same laws as in other machines. The dimensions of the parts which are covered in the guarantee under the head of workmanship depend on a knowledge of the stresses in all the parts and the resisting power of the various metals.
The stresses in gas-engines depend primarily on the kind of gas and the treatment, and secondly on the inertia of parts, just as in other engines.
It thus appears that the design of a gas engine to meet a given guarantee involves many problems of steam engine or ordinary machine design, but a knowledge of these alone is useless; it must be supplemented with the data on the behavior of gas when mixed with air and burned by the explosion method in a water-jacketed cylinder.
It is intended, after the first brief treatment of the condition surrounding the output or power and the economy, to consider the forces produced in the gas-engine cylinder, their variation throughout the stroke, and the effects of these forces on the other parts of the mechanism. The forces due to mass and motion will be next treated for balance, their combination with the forces due to the gas pressure behind the piston, for turning effort and strength in parts.
The analysis of stresses in the separate parts and their dimensions as determined by present-day practice, furnish the main part of the work and are based naturally on what precedes.
DOWNLOAD OLD AUTOMOTIVE BOOK: Gas engine design
Five facts are of prime importance to the buyer: first, the capacity of the engine in brake horse-power; second, its performance in B.T.U. per hour necessary to maintain each B.H.P.; third, the adaptability of the engine to the service. This is a factor of no little importance to the buyer, but is not always a feature of guarantees. When it is not, it certainly has weight in the decision of the buyer with what builder he will place his order. It may be that a certain firm has a reputation for building a better balanced engine than another, either because of owning certain useful patents or because of employing better designers; another firm may be in a position to build an engine with better speed regulation. To the former the boat-builder or owner whose building must not be shaken will apply, to the latter the buyer who intends to run dynamos in parallel. When incorporated in the guarantee this adaptability clause is mainly confined to regulation of engines to run dynamos.
The last two factors that concern the designer in the closing of the contract are the cost and workmanship. Cost is the last thing also that is learned by either designer or builder, and is determined only by experience in manufacture, not by any abstract or deep knowledge of technology, while workmanship is likewise difficult to predict.
The building of an engine to meet requirements of power economy or adaptability in balance or regulation is a thing that can be set down as a technical problem and solutions found from endless comparisons of what by mathematical analysis should be under ideal conditions and the determination by test of what is or can be under practical conditions. It is the business of the designer to know all the available results of such comparisons, for these enable him to take cognizance of conditions that are unknown or unknowable and thus to design for any specifications that are within possibility and to know just as surely what cannot be done.
Power depends on mean effective pressure and piston speed. Mean effective pressure depends in gas-engines primarily on the kind of gas and secondly on the treatment of the gas. Piston speeds in gas-engines depend on nearly the same conditions as in steam-engines. Economy is a factor in gas-engines that depends on the kind of fuel and its treatment.
Regulation depends on the method of governing, the combination of cylinders or treatment of the gas, to produce uniformity of turning effort and permit of quick change to meet loads.
Balance in gas-engines is controlled by the same laws as in other machines. The dimensions of the parts which are covered in the guarantee under the head of workmanship depend on a knowledge of the stresses in all the parts and the resisting power of the various metals.
The stresses in gas-engines depend primarily on the kind of gas and the treatment, and secondly on the inertia of parts, just as in other engines.
It thus appears that the design of a gas engine to meet a given guarantee involves many problems of steam engine or ordinary machine design, but a knowledge of these alone is useless; it must be supplemented with the data on the behavior of gas when mixed with air and burned by the explosion method in a water-jacketed cylinder.
It is intended, after the first brief treatment of the condition surrounding the output or power and the economy, to consider the forces produced in the gas-engine cylinder, their variation throughout the stroke, and the effects of these forces on the other parts of the mechanism. The forces due to mass and motion will be next treated for balance, their combination with the forces due to the gas pressure behind the piston, for turning effort and strength in parts.
The analysis of stresses in the separate parts and their dimensions as determined by present-day practice, furnish the main part of the work and are based naturally on what precedes.
DOWNLOAD OLD AUTOMOTIVE BOOK: Gas engine design
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