Tips and tricks
Gas engine ignition
GAS ENGINE IGNITION
BY EARLE B. NORRIS, ROBERT K. WINNING AND WILLIAM C. WEAVER
McGRAW-HILL BOOK COMPANY, NEW YORK, 1916
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Gas engine ignition
PREFACE
This volume has been developed to satisfy the demand for a systematic course of instruction dealing with the ignition systems used on stationary and automobile internal combustion engines. In preparing the text, the authors have had in mind the needs of the men in the factories and repair shops who have to install, adjust, and repair ignition systems. For this reason, a few systems have been included which are no longer manufactured, but which are to be found in operation in large numbers.
The division of the text matter into chapters has been made with the idea of making uniform assignments of work for home study, rather than of following any more logical classification.
The authors wish to express their appreciation of the hearty co-operation received from the manufacturers in supplying the cuts for the illustrations of the book.
The division of the text matter into chapters has been made with the idea of making uniform assignments of work for home study, rather than of following any more logical classification.
The authors wish to express their appreciation of the hearty co-operation received from the manufacturers in supplying the cuts for the illustrations of the book.
CONTENTS
- CLASSIFICATION: THE MAKE-AND-BREAK SYSTEM
- JUMP-SPARK BATTERY SYSTEMS; VIBRATING COILS
- NON-VIBRATING COILS
- BATTERIES
- LOW-TENSION MAGNETOS ARMATURE TYPE
- OSCILLATOR MAGNETOS; INDUCTOR MAGNETOS
- LOW-TENSION FOR JUMP-SPARK IGNITION
- HIGH-TENSION MAGNETOS
- DIRECT-CURRENT GENERATORS
- MISCELLANEOUS IGNITION SYSTEMS
CHAPTER I - CLASSIFICATION; THE MAKE-AND-BREAK SYSTEM
1. Methods of Ignition. In the development of the internal combustion engine, a number of methods of igniting the explosive charge within the cylinder have been tried. These can be grouped in the four following classes:
1. Ignition by an open flame.
2. Ignition by a hot tube or bulb.
3. Ignition by the heat of compression.
4. Ignition by an electric spark.
The first method named was tried only for a short period and did not prove satisfactory; hence, it may be given only passing notice here. It consisted of two gas jets or burners, one outside the combustion chamber and the other inside of a revolving cock or valve which was alternately connected to the outside flame and then to the combustion chamber. The jet outside the cylinder was kept burning all the time. The revolving cock surrounding the second jet was first turned to connect with this out- side flame, thus lighting the gas at this second jet. The cock was then turned to communicate with the combustion chamber at the desired instant for ignition of the charge. The explosion which followed extinguished this flame and made necessary the outside flame for reigniting it after each explosion.
The other three methods of ignition have all survived and are used in different types of internal combustion engines. The method of electric ignition is the most common and is found in many diverse forms.
2. Hot-tube Ignition. The hot tube as a means of ignition was the prevailing method for a number of years and is still used to some extent, especially in the natural gas regions, where gas is cheap. As shown in Fig. 1, this system consists of a small tube having the outer end closed and having the open inner end connected to the combustion chamber of the engine. Surrounding the tube is a chimney, usually of cast iron lined with asbestos. A gas or gasoline burner at the base of this chimney surrounds the tube with flame and keeps it at a red heat. The temperature of this tube on the inside is sufficient to ignite the explosive mixture within the cylinder when it comes into contact with the tube.
The control of the time of ignition is effected in the following manner: After a working stroke of the engine the tube is filled with burnt gases. During the exhaust stroke most of the burnt gases are exhausted from the cylinder, but the tube remains filled with the dead gases at atmospheric pressure. On the compression stroke of the piston these dead gases are compressed into the upper end of the tube and the fresh mixture follows it up into the tube, where it is ignited by the hot metal. This flame then shoots back into the main combustion chamber and fires the charge in the cylinder. If the flame which heats the tube is too close to the lower end, the fresh charge will reach the hot part of the tube too soon on the compression stroke and ignition will be too early. This will cause the explosion pressure to act against the motion of the piston during the balance of the compression stroke and will cause the engine to "pound." On the other hand, if the heating flame is too far out from the cylinder, the fresh gases may not reach the hot part and ignition may not occur. It will thus be seen that the time of ignition may be varied by changing the location of the heating flame on the outside of the tube. It may also be controlled by using tubes of different lengths, since a longer tube will permit the fresh gases to enter it farther during the compression stroke. It will be evident that this method of ignition does not offer an accurate and ready control of the time of ignition and that the matter of ignition control for starting is especially difficult, since ignition cannot be retarded until after the end of the compression stroke. The common method of starting such an engine is to turn it by hand until the cylinder has been charged and then to turn it backward against the compression until ignition occurs. The engine is then driven forward by the force of the explosion, which occurs before the piston has reached the end of the backward stroke.
One difficulty with this method of ignition is that the iron or steel tubes are burned out by the action of the heating flame and by the combustion on the inside. To partially overcome this, nickel-steel tubes have been used as they resist this corrosive action longer than mild steel or wrought iron. Porcelain has also been used to some extent as it does not burn out like iron or steel.
Several minutes are required to start an engine equipped with hot-tube ignition, as the tube must first be brought to a red heat. With the advent of gasoline as a fuel for internal combustion engines this difficulty became doubly serious, as it became necessary first to generate gas for the heating flame from the gasoline before the tube itself could be heated. This led to the development of electric ignition. The advent of the automobile gave added impetus to the cause of electric ignition, as hot-tube ignition was almost out of the question for this use, although some of the early machines did use hot-tube ignition.
There were several modifications of the hot tube from that shown in Fig. 1. Some engines used a small valve to control the time at which the fresh charge was allowed to enter the tube. Others provided a small opening at the upper end of the tube to permit the escape of the dead gases and the admission of the fresh mixture into the tube. In still another form, a small tube within the hot tube led nearly to its upper end and was provided with a valve to release the dead gases from the tube at the desired instant.
3. Hot-bulb Ignition. The hot bulb is frequently spoken of as being a modification of the hot tube. Instead of the hot tube, a large proportion of the combustion chamber is formed into a bulb-shaped cylinder head, as shown in Fig. 2. Heat is applied from without only for starting. After starting, the bulb is kept hot by the combustion occurring on the inside during the regular operation of the engine. This form is used quite generally for engines using kerosene and heavier oils, the bulb furnishing heat to assist in vaporizing the fuel as well as in igniting the mixture after it is formed.
The control of ignition in this system is effected in various ways. It is evident that the temperature of the bulb will vary with the load on the engine. Under a heavy load with full charges in the cylinder the bulb will receive more heat than under light loads. Where the bulb is depended upon for the vaporization of the fuel, this is compensated to a greater or less extent by the additional heat taken from it to vaporize the increased amounts of oil. In addition, the Hornsby-Akroyd engine shown in Fig. 2 is provided with a water jacket at the base of the bulb. By controlling the water supply to this jacket the temperature of the bulb may be regulated. In the Mietz & Weiss hot-bulb engine shown in Fig. 3 the control is effected by steam admitted to the cylinder with the charge. This steam is generated in the cylinder jacket and therefore its amount will be proportional to the amount of fuel burned in the cylinder. The addition of steam to the combustible mixture in the cylinder increases the capacity of the mixture for absorbing heat and also raises the temperature at which ignition takes place, thus requiring a greater amount of heat from the bulb at the times when the bulb is hottest.
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1. Ignition by an open flame.
2. Ignition by a hot tube or bulb.
3. Ignition by the heat of compression.
4. Ignition by an electric spark.
The first method named was tried only for a short period and did not prove satisfactory; hence, it may be given only passing notice here. It consisted of two gas jets or burners, one outside the combustion chamber and the other inside of a revolving cock or valve which was alternately connected to the outside flame and then to the combustion chamber. The jet outside the cylinder was kept burning all the time. The revolving cock surrounding the second jet was first turned to connect with this out- side flame, thus lighting the gas at this second jet. The cock was then turned to communicate with the combustion chamber at the desired instant for ignition of the charge. The explosion which followed extinguished this flame and made necessary the outside flame for reigniting it after each explosion.
The other three methods of ignition have all survived and are used in different types of internal combustion engines. The method of electric ignition is the most common and is found in many diverse forms.
2. Hot-tube Ignition. The hot tube as a means of ignition was the prevailing method for a number of years and is still used to some extent, especially in the natural gas regions, where gas is cheap. As shown in Fig. 1, this system consists of a small tube having the outer end closed and having the open inner end connected to the combustion chamber of the engine. Surrounding the tube is a chimney, usually of cast iron lined with asbestos. A gas or gasoline burner at the base of this chimney surrounds the tube with flame and keeps it at a red heat. The temperature of this tube on the inside is sufficient to ignite the explosive mixture within the cylinder when it comes into contact with the tube.
The control of the time of ignition is effected in the following manner: After a working stroke of the engine the tube is filled with burnt gases. During the exhaust stroke most of the burnt gases are exhausted from the cylinder, but the tube remains filled with the dead gases at atmospheric pressure. On the compression stroke of the piston these dead gases are compressed into the upper end of the tube and the fresh mixture follows it up into the tube, where it is ignited by the hot metal. This flame then shoots back into the main combustion chamber and fires the charge in the cylinder. If the flame which heats the tube is too close to the lower end, the fresh charge will reach the hot part of the tube too soon on the compression stroke and ignition will be too early. This will cause the explosion pressure to act against the motion of the piston during the balance of the compression stroke and will cause the engine to "pound." On the other hand, if the heating flame is too far out from the cylinder, the fresh gases may not reach the hot part and ignition may not occur. It will thus be seen that the time of ignition may be varied by changing the location of the heating flame on the outside of the tube. It may also be controlled by using tubes of different lengths, since a longer tube will permit the fresh gases to enter it farther during the compression stroke. It will be evident that this method of ignition does not offer an accurate and ready control of the time of ignition and that the matter of ignition control for starting is especially difficult, since ignition cannot be retarded until after the end of the compression stroke. The common method of starting such an engine is to turn it by hand until the cylinder has been charged and then to turn it backward against the compression until ignition occurs. The engine is then driven forward by the force of the explosion, which occurs before the piston has reached the end of the backward stroke.
One difficulty with this method of ignition is that the iron or steel tubes are burned out by the action of the heating flame and by the combustion on the inside. To partially overcome this, nickel-steel tubes have been used as they resist this corrosive action longer than mild steel or wrought iron. Porcelain has also been used to some extent as it does not burn out like iron or steel.
Several minutes are required to start an engine equipped with hot-tube ignition, as the tube must first be brought to a red heat. With the advent of gasoline as a fuel for internal combustion engines this difficulty became doubly serious, as it became necessary first to generate gas for the heating flame from the gasoline before the tube itself could be heated. This led to the development of electric ignition. The advent of the automobile gave added impetus to the cause of electric ignition, as hot-tube ignition was almost out of the question for this use, although some of the early machines did use hot-tube ignition.
There were several modifications of the hot tube from that shown in Fig. 1. Some engines used a small valve to control the time at which the fresh charge was allowed to enter the tube. Others provided a small opening at the upper end of the tube to permit the escape of the dead gases and the admission of the fresh mixture into the tube. In still another form, a small tube within the hot tube led nearly to its upper end and was provided with a valve to release the dead gases from the tube at the desired instant.
3. Hot-bulb Ignition. The hot bulb is frequently spoken of as being a modification of the hot tube. Instead of the hot tube, a large proportion of the combustion chamber is formed into a bulb-shaped cylinder head, as shown in Fig. 2. Heat is applied from without only for starting. After starting, the bulb is kept hot by the combustion occurring on the inside during the regular operation of the engine. This form is used quite generally for engines using kerosene and heavier oils, the bulb furnishing heat to assist in vaporizing the fuel as well as in igniting the mixture after it is formed.
The control of ignition in this system is effected in various ways. It is evident that the temperature of the bulb will vary with the load on the engine. Under a heavy load with full charges in the cylinder the bulb will receive more heat than under light loads. Where the bulb is depended upon for the vaporization of the fuel, this is compensated to a greater or less extent by the additional heat taken from it to vaporize the increased amounts of oil. In addition, the Hornsby-Akroyd engine shown in Fig. 2 is provided with a water jacket at the base of the bulb. By controlling the water supply to this jacket the temperature of the bulb may be regulated. In the Mietz & Weiss hot-bulb engine shown in Fig. 3 the control is effected by steam admitted to the cylinder with the charge. This steam is generated in the cylinder jacket and therefore its amount will be proportional to the amount of fuel burned in the cylinder. The addition of steam to the combustible mixture in the cylinder increases the capacity of the mixture for absorbing heat and also raises the temperature at which ignition takes place, thus requiring a greater amount of heat from the bulb at the times when the bulb is hottest.
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