The autocar handbook

Within the space at one's disposal in a handbook of this elementary nature, it is quite impossible to deal with any degree of completeness or at adequate length with the theories which govern the functions of various parts of the motor car. Information on this subject may be divided into three classes: The things one MUST know; the things one SHOULD know; and the things one need NOT know; the last-named being those things knowledge of which, although exceedingly interesting and valuable, is, however, of no immediate utility as regards the successful running and keeping in order of a car. This it is that forms the raison d'etre of this book. Roughly speaking, then, the information one must have will enable one to keep one's car running in good order, whilst what one should have will result in the car being actually improved, although the line of demarcation between these two classes of knowledge is not very apparent.

The question which faces, has faced, and will face, every prospective buyer of a motor car is this: Here is a machine at one end of which we have a tank full of petrol, at the other end the wheels go round. How is this brought about? We  will therefore trace the course of the petrol with which the car is driven, from the tank in which it is contained to the carburetter wherein it is vaporised and mixed into an explosive gas to the engine, where the explosions of this gas are caused to revolve a flywheel, and hence to the passage of the exhaust gases into the open air. We shall see also as we go along how the potential energy that is, energy due to its constituents of the petrol is transformed into kinetic energy, whereby the car is propelled. A motor car may be briefly described as a framework mounted on four road wheels and driven by a gas engine in fact, that is a motor car reduced to its essential ends. First of all, the engine must be supplied with gas, and for this purpose a gas works is required, and this is formed by a supply of petrol and a carburetter, which we will now briefly consider. The name petrol properly applies to a spirit of a specific weight about 68% as much as water that is, not quite 7 lbs. to the gallon at 60 F. Of recent years, however, the name has been stretched to cover lower qualities of spirit of a much higher specific gravity, and may be described as a sort of petroleum, only very much thinner and more volatile and with a different smell. Petrol in common with numerous other spirits has the quality of readily evaporating, and forms  a highly inflammable gas; and it is this gas which is used on a car as fuel for the engine whereby it is driven. The carburetter or gas works in which the liquid petrol is transformed into gas, and mixed with the quantity of air requisite to provide an explosive mixture, is an instrument consisting essentially of three parts.

First, an apparatus for maintaining a constant level of petrol in a subsidiary tank, or float chamber, which is kept supplied by the main reservoir; secondly, a device whereby the petrol is adequately vaporised and mixed with air; thirdly, a tap or throttle, by means of which the supply of explosive gas to the engine can be regulated.


The Principle of the Explosion Engine.

It is a matter of common knowledge that if ordinary lighting gas be left turned on in a room for any length of time, and that if it be ignited there will be an explosion which will result in the side of the room, if not of the house, being forcibly blown out. In a petrol engine we have essentially a room of very strong material, one side of which, however, is free to move within a guide provided for the purpose. The room, or cylinder, is filled with gas made as we have seen by petrol. This gas is then ignited, its ignition resulting in an explosion which causes the movable side of the chamber or piston to be violently driven outwards along its guide. By means of a crank this linear motion is transformed into a rotary one. It will be seen, therefore, that, first of all, it is necessary to fill one's. cylinder with explosive gas ; secondly, to ignite it; and thirdly, to get rid of the products of combustion of the explosion, so that the cylinder may be filled again with fresh explosive gas. It has been found, however, that if the explosive gas be compressed that is to say, forced to occupy a smaller space than it would otherwise do at normal temperature and pressure it is capable when ignited in that state of causing a very greatly enhanced explosion, just as the old muzzle loader was found to carry much farther according as the wads were rammed more tightly home and the powder squeezed into as small a space as possible. The gas engine must therefore provide for the following sequence of operations: The filling of the cylinder with explosive gas, compression of the gas, ignition and explosion of the compressed gas, and exhaustion. of the uninflammable products of combustion. This is known, after its discoverer, as the Otto Cycle, and it is upon this principle that all internal combustion engines operate.

It will now be understood that during the performance of these four functions the piston has travelled twice outwards and twice inwards in the cylinder, and this movement has been accompanied, therefore, by two revolutions of the flywheel, which is driven by the crank, as mentioned above. There is accordingly only one explosion that is to say, only one power impulse during every two revolutions of the crankshaft, whence engines of this type in which each function is performed by a separate stroke are known as four-stroke motors.