regulated the pumps which compressed the explosive mixture in the cylinder, and at the same time varied the composition of the explosive mixture so as to always be proportional to the work which was required to be done. When we come to consider that this engine was brought out in the year 1833, it is wonderful that it did not meet with greater success, but this was probably due to the fact that the steam engine was at that period coming greatly into favour, and for the time being completely eclipsed all other forms of motive power.
About this time a double-acting gas engine was devised by Johnston, using pure hydrogen and oxygen as the explosive mixture, in the proportion of two volumes of hydrogen to one of oxygen. After the explosion and driving forward of the piston, the combined gases being cooled were precipitated as water, and a partial vacuum obtained which was used during the return stroke. This idea was a highly ingenious one, but failed owing to the high price of hydrogen and oxygen, but perhaps some day, when these obstacles have been removed, this idea may once more be taken up.
In 1838 William Barnett took out a patent for an engine based on the same principle as that of Lebon. Two pumps compressed separately the combustible gas and the air and forced the mixture under pressure into the cylinder. The explosion was caused by a small gas-jet, communication between it and the cylinder being set up at the right moment by a revolving valve. The gas-jet was situated in the valve itself, and was so arranged that during half a revolution it was turned towards the outside, and was then lighted by a second jet, and during the remainder of the revolution it communicated with the interior of the cylinder and ignited the explosive mixture. This was the first gas motor in which the ignition was from the outside, and in which the explosive gases were at the same time under pressure. In most modern gases the same result is obtained, but the original and rather crude method of obtaining it has of course been much modified and improved. During the next few years several patents were taken out relating to the same subject. In 1844 John Reynolds suggested using a battery which should white-heat a platinum wire in order to ignite the gases, the ignition taking place at the required moment by means of an automatic switch closing the battery circuit.
In 1850 Stéphard recommended a magneto-electric machine driven by the engine itself instead of the primary battery.
Barsanti and Matteucci described in 1857 an atmospheric motor, their arrangement of the parts being afterwards adopted by Otto and Langen. A Bunsen cell supplied current to a De la Rive multiplier, causing a stream of sparks to pass between two fine points situated within the combustible mixture. In 1858 and 1859 Degrand explained in two patents a gas engine in which the gases were compressed in the cylinder itself. Owing to mechanical difficulties his machine was impracticable, but the idea forms an important step in the history of gas engines.
In 1860, when the Lenoir motor appeared, no other existed which was capable of regular and comparatively efficient work.
This machine, devised by Lenoir and constructed by Marinoni, had the appearance of a double-acting horizontal steam engine. The explosive mixture was ignited by an electric spark produced by a Ruhmkorff coil and a primary battery. The machine ran smoothly and regularly and its cost was moderate: among the advantages which it possessed at that time over other forms of motive power, were the absence of a cumbrous boiler and costly foundations, and the little care and attention necessary to keep it in working order. So great was its success at the time, that many people prophesied that the steam engine would soon become extinct.
In spite of this the Lenoir motor possessed many defects which engineers were not slow to recognize. The enthusiasm which it had aroused soon cooled down when it became known that for steam and gas engines of equivalent power, the steam engine was considerably cheaper. It required in fact 3000 litres of gas to produce one horse-power hour, and to cool the cylinder of such a motor a volume of water was necessary four times as great as that required to produce the steam of a steam engine of equal power. Besides this, the machine had to be kept flooded with lubricating oil. In consequence of these various defects the Lenoir motor disappeared almost as rapidly as it had arisen. In spite, however, of this apparent failure, it did some good, for it once more directed the attention of inventors to the problem of a practical gas engine.
Among the numerous patents taken out in consequence of this reaction, the most important, filed in 1860 by M. Hugon, related to a gas motor with a flame ignition, and in which the cylinder was cooled by injecting into it a very fine spray of cold water. Experiments were made upon it in 1876 by M. Tresca, and it was found that the motor consumed 2445 litres of gas per horse-power hour. The temperature of the exhaust gases was 180° C., while in the Lenoir motor they were about 280° C. The diminution in temperature was probably due to the better method of cooling the cylinder, and was found to be a great improvement, the cylinder requiring much less lubrication. In 1861 Kinder and Kinsey somewhat modified the existing arrangements of the parts, but otherwise their motor embodied no new ideas. Another motor was devised about this time by Millon, once more bringing forward Lebon’s idea of compressing the gases in the cylinder itself.
We have now reached the year 1862, which may be considered a memorable one in the history of the gas engine, for it was in this year that a patent was taken out by M. Beau de Rochas, setting forth from a theoretical point of view the best working conditions for a gas engine. During the forward stroke of the piston the explosive mixture was to be drawn into the cylinder, during the return stroke this volume of gas being compressed; at the dead point at the beginning of the second forward stroke the explosion was to take place, driving the piston forward, the gases being expelled during the second return stroke. The whole principle will be seen to consist of four distinct operations, forming what is known as the Otto cycle, for reasons which we will presently explain.
The peculiar part of the patent was its purely theoretical explanation. Whilst giving all the honour due to the inventor, and recognizing that he fully understood what he was talking about, we must not forget that there was nothing whatever in the patent indicating how the ideas embodied therein might be carried into practice. No drawings were appended to the text, explaining how the gases were to be ignited, or how the exhausted gases were to escape; it contained nothing, in fact, but the plain statement of the most efficient cycle of operations.
M. de Rochas did not construct a machine on this principle, and as he omitted to pay his patent fee for the second year, the idea became public property. For these reasons no attention was drawn to it until ten years afterwards, when it came to light during some patent litigation undertaken by Dr. Otto in 1878.
In 1867 at the International Exhibition at Paris a vertical atmospheric motor was to be seen working, based on the primitive principle of the gunpowder pump of De Hautefeuille. This machine was constructed by two German engineers, Otto, and Langen of Deutz near Cologne, and was a perfected form of the Barsanti and Matteucci motor invented ten years previously. The explosion of the gases in the cylinder only served to obtain a partial vacuum underneath the piston, which was therefore forced down by the excess of atmospheric pressure above it. This arrangement had one great advantage over the Lenoir and Hugon motors, it only burnt 1350 litres of gas against their 2500 or 3000 per horse-power hour, and consequently it rapidly came into favour, and the lucky inventors were able to sell no less than 5000 motors in a few years.
The motor itself was very rough and had many defects: the gear-wheels rattled and made a furious noise, the igniting flame kept up a continuous roar, and above the noise of clanking machinery the explosion of the gases could be heard like a cannon going off; in fact, no one could say that the ideal of domestic motors had been attained; but as the motors constructed in 1872 only consumed 800 litres of gas per horse-power hour, rendering power produced by this means cheaper than steam, its success was assured in spite of the defects.
The success of these early attempts stimulated Dr. Otto to further efforts, and in 1878 he brought out his famous gas engine, which has earned a world-wide reputation by reason of its incontestable merits. It was based on the principle explained in the De Rochas patent which we have spoken of, but Otto undoubtedly knew nothing of this patent, and his invention
