Gas and Petroleum Engines

by H. de Graffigny

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 was perfectly independent and fresh as far as the world was concerned. The enormous success to which the new motor attained naturally led to many unscrupulous imitations, and legal proceedings were instituted in England and France. In this country the validity of Otto’s patents were upheld, but in France the De Rochas patent was for the first time brought to light, and the verdict went against him. This verdict has been attributed to malice on the part of the French judges, for at that time the French nation would have probably conceded as little as possible to a German; but whether that be so or not, we are indebted to Dr. Otto for having made the gas motor a really practical engine after many years of patient experiment and study. At the same time as the Otto engine three other motors appeared at the Exhibition of 1878: the Bisschop gas engine constructed by Mignon and Rouart, and two others by Simon and Ravel. The Simon motor, of which only a very small number were constructed, was very interesting from the economy point of view. The explosion of the mixed gas was not allowed to take place suddenly, but proceeded gradually as the piston moved forward, and the heat which in the Otto engine is carried off by the water jacket, was made use of, as in the old Hugon motor, to vaporize a spray of cold water, and thus adding to the total force behind the piston. This process was so effective, that on shutting off the supply of gas the motor continued to revolve for a considerable period by means of the vaporized water. About 800 litres of gas were consumed and four litres of water per horse-power hour, a very good result. The Ravel motor used even less, about 500 or 600 litres only, but owing to the bad arrangement of the parts the mechanical efficiency was very low.

Such was the position of the gas engine in 1878. A standard type had been adopted and worked excellently. It merely required to be perfected in detail and simplified in order to make it still more economic, and capable of holding its own against its powerful rival the steam engine.

Many modifications of the Otto gas engine have appeared since that date, among the most important being those by—Dugald-Clerk, in 1879, a motor which compressed and exploded the gases once in every revolution; Lenoir, in 1833, the cylinder being cooled by currents of air; and in the same year appeared the Griffin gas engine, with a complete cycle of operations every three revolutions.