Alcohol-Acetylene Gas for Motor Vehicles.
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All attempts to use denatured alcehol as fuel for the motor in test runs made with motorcars have clearly demonstrated the unsuitability of the new hydrocarbon for use in the highspeed, low-compression motorcar engines now manufactured. It is impossible to start cold on alcohol alone, because it is much less volatile than petroleum spirit and has a higher ignition temperature, so that without the application of external heat the air taken in through the carburetter will not evaporate enough alcohol to form an inflammable vapour. When the -engine has been started on petroleum spirit and warmed up to a temperature at which alcohol would vaporise satisfactorily, it was determined that the compressien of 6o to 70 pounds per square inch in the engine was insufficient for the best results, and that the alcohol vapour burned so slowly that much of the energy was lost in the exhaust when running the engine at normal speed. Stationary alcohol engines, which have been brought to a high state of perfection in France and Germany, have compression as high as 120 pounds, and operate most efficiently at from 200 to 300 revolutions per minute. As a result of these conditions, there was a great waste of fuel in the motorcar test runs and, although they showed that the cars would run on alcohol alone after being started, they failed to demonstrate any economy in the use of alcohol, even upon the assumption that eventually the new fuel will be marketed at a price to compete with petroleum spirit, as the cars would not run more than seven miles on a gallon. To overcome these objections, and to make it possible to utilise commercial alcohol in the present type of internal-combustion engine, without any alteration further than a change of carburetters, or the addition of a supplemental device, a new process known as the Barker-White system was invented and patented last year by F. W. Barker and Thomas L. White, of New York City.
During the past winter, a series of laboratory experiments with this system has been made by Joseph Tracy, until results have been attained that warrant the statement that the new fuel develops as great efficiency in a givep engine as petroleum spirit, and that the motor can be started cold with it. The invention is, broadly, " the process of producing a gas for power purposes which consists in carburetting air with dilute alcohol and then bringing such carburetted air into contact with calcium carbide." By passing the vapour of alcohol and air as formed in the ordinary spray carburetter through a layer of calcium carbide, a variety of effects, all desirable, are secured. The first is to extract from the alcohol the greater part of the water contained in it, which, in commercial alcohol, is present to the amount of in per cent. or more. As water has no fuel value, and its only effect when present in the cylinder is to reduce the temperature and, consequently, the efficiency of the engine, it is altogether desirable to remove it. This is done by the carbide, which dehydrates the vapour on its way to the cylinder. As the water unites with the carbide, it is dissociated into hydrogen and oxygen, the former combining with the carbon in the carbide to form acetylene gas, and the oxygen uniting with the calcium chloride and
forming calcium oxide or lime. The chemical reaction generates heat, which assists further to volatilise the alcohol before it enters the explosion chamber, and the liberated acetylene gas commingles with the aicchol vapour, effecting both a mechanical mixture and a subtle chemical combination, the exact nature of which has not yet been determined. Acetylene burns with great rapidity, offsetting the slow burning of the alcohol, the resulting effect being that the whole charge burns much more quickly than would alcohol vapour alone. In brief, the two gases have a counteracting effect that can, by proper regulation of the quantity of water present in the alcohol, be made to approach very closely the
properties of the ordinary petroleum spirit. The more nearly one can approach to complete combustion at the instant of maximum pressure, or minimum volume, utilising the entire downward stroke of the piston for expansion only, the greater the efficiency developed.
With the alcohol-acetylene mixture, which has been given the distinctive name " Alkoethine," combustion occurs early in the piston-stroke, and only expansion later, so that, before the exhaust valve opens, combustion has been completed, which is not true of alcohol vapour when the engine is run at high speed.
A decided advantage is that an excess of water in the alcohol as purchased is dot an objection ; on the contrary, the greater the quantity of water the more rapidly the engine will run. In the tests as carried out by Mr. Tracy, with the single-cylinder De Dion engine of 3 to 31 horse-power, it has been found that the addition of water to up to a total of 18 per cent. gives the best results, increasing the proportion of acetylene gas in the ultimate explosive mixture to an amount that gives results most nearly approaching these of petroleum spirit. There is, however, a wide latitude of choice, ranging from alcohol undiluted to a solution containing 25 per cent. of water. Since the addition of water increases the bulk of the fuel, and water costs nothing, it offsets the cost of the carbide consumed.
No quantitative tests have yet been made with the apparatus, which is merely a large brass cylinder Connected with the cylinder of the engine, and with an ordinary float-feed spray carburetter, by copper piping, and has a 'diaphragm of wire netting upon which lies the layer of calcium carbide of quarter-inch size. Therefore . the -proportions of carbide and water used to a gallon of commercial alcohol consumed to produce a given indicated horse-power have not been determined; roughly, however, about i pound of carbide is used to one gallon of the IS per cent. solution of alcohol and water. In the experiments that have been conducted it has been found that all the heat that could be collected from the exhaust by means of a long sleeve is just sufficient fully to vaporise the alcohol in the carburetter. To start cold the engine is " primed " by throwing a wine-glass full of alcohol solution directly into the carbide chamber to generate an excess of acetylene. The chemical action liberates heat from the carbide, which further evaporates the alcohol just before it enters the engine cylinder. As pound of carbide contains goo British thermal units, and there are approximately 450 British thermal units. of latent heat in I pound of alcohol, the decomposition of a pound of the former will supply enough heat to evaporate fully 2 pounds of alcohol from a liquid state. The size of the carbide lumps and their disposition in the carbide chamber are of considerable importance, as the vapour must .pass through the mass freely, and, at the same time, come in contact with a large surface of the carbide. Experiments are to be made in the near future to ascertain what size will give the best general results, and to settle a few other important constructional details.
It has been found that perfect combustion of the mixture takes place through a wider range of proportions of gas and air than is the case with petroleum spirit. With petroleum spirit and air the range is from one part of liquid to eight parts of air to one part of liquid to fourteen parts of air, whilst with pure acetylene and air the range is from one to three all the way to one to twenty-two parts. The range with the alcohol-acetylene combination is about halfway between these, varying according to the quantity of water contained in the alcohol. " Alkoethine "can be regulated so that it will ignite at the same sparking point as petroleum spirit, whilst with -pure alcohol, which is slow burning, it is necessary to advance the spark much more. When the mixture begins to get so rich that it deposits soot, ignition becomes difficult and even ceases at times.
Indicator diagrams taken with manog,raph instruments during the tests, and at the demonstration before the Press representatives on March 5th, showed results quite as good as cards taken from the same engine using petroleum spirit. With a compression of 65 pounds, and advanced ignition, a very high peak was obtained; with maximum pressures. of more than 240 pounds. Whilst the engine used developed highest efficiency at 1,100 revolutions per minute when running on petroleum spirit, with " Alkoethine " the efficiency. did not decrease until i,eoo revolutions per minute were attained, and, whilst the maximum speed on petroleum spirit was 1,700, the motor has been run up to 2,100 on the alcohol-acetylene combination.—From the " Motor Age," New York.