Frustrated by the failure to avoid destruction of the gas combustion engine Otto returned to the atmospheric gas engine. In his "Memories" of 1889 [1] he wrote:

The experience with the four stroke engine were so depressing, that at the time I doubted if someone would ever be able to build a direct acting gas engine. I tried now to build atmospheric gas engines, where the explosive force of a mixture of gas and air is used to create an air diluted mixture space. The over pressure of the external atmosphere would become the driving force ...

From his experiments of the Lenoir gas engine Otto had learned, that after the expansion of exploding gases in a cylinder, as the gases cooled down and created a vacuum the piston was sucked back into the cylinder. To reduce the destroying forces of the explosions Otto used a second piston for evacuating the explosion gases. At the beginning of March 1863 a prototype was ready to be tested. The illuminating gas was ignited by an electrically generated spark.

The results were promising and Otto filed on 16 April 1863 for a patent. His request was denied as the atmospheric principle was already known, the small differences to the known principles did not justify a patent, and various technical details were not sufficiently disclosed [2]. At this point, Otto needed financial support to perfect his atmospheric gas engine to be ready for use in practice. With Eugen Langen not only an engineer but also with the wealthy back ground of a sugar manufacturers family he founded on 31 March 1864 "N.A.Otto & Cie", a limited commercial partnership.

Eugen Langen realized that the source of the problem was the transfer of the piston forces to a crank shaft. Decoupling the piston from in the explosion phase allowed for the piston to be flung as far as the explosion was driving it without hitting any obstacle. Thus a destruction of the cylinder or other parts could be avoided. Only on the way back into the cylinder the piston engaged with a pinion rack gear and transferred the force of the falling piston to a fly wheel. They filed on 8 February 1866 was finally successful and resulted in a patent granted on 21 April 1866 for the period of 5 years. This machine was presented on the Paris Exhibition of 1867.  

DE 778 Langen-Otto Patent

The granted patent did not have claims in our todays requirements. At the end of the patent specification it has a statement as follows:

With respect to earlier gas engines the inventors emphasize especially as novel and peculiar:

  1. the interrupting mode of action of the piston.
  2. the switch mechanism or the mechanisms which by friction transfer the force that is established, when the piston is descending, to the fly wheel.
  3. the construction of the control mechanism and the slider.
  4. the power control of the machine by changing the number of piston strokes at a constant revolution speed of the fly wheel shaft.


The US patent US 67,659 "Improvement in air-engines", granted 13 August 1867, has more detailed drawings and only three claims:

  1. the peculiar mode of communicating the downward or backward motion of the piston under atmospheric pressure only to the engine-shaft, by means of a clutch apparatus, so arranged that the speed of the piston is rendered independent of the speed of the engine-shaft.
  2. The cams or eccentrics S arranged for controlling the valves or slides for the admission of the combustible gas into, and exit of the products of combustion from, the cylinder, when actuated in such a manner from the engine-shaft through the mediation of the eccentric or cam S, pawl x, ratchet-wheel Q, and disengaging-catch w, that such admission and exit of gases, and consequently the number of strokes of the piston, may be varied independently of the speed of the engine shaft, substantially as and for the purpose hereinbefore set forth.
  3. The combination of the several parts K, h, P, T, U, Q, S1, S2, v', w, and x', operating in manner and for the purposes substantially as set forth.


At the international industrial exhibition in Paris in the year 1867 were exhibited 8 gas machines of the type Lenoir, 6 gas machines of the type Hugon and one of the type Otto-Langen. During this exhibition the efficiency of these machines were tested and compared. The machines from type Lenoir were consuming appr. 2.8 cubic meter illumination gas per horse-power and hour, the machines form type Hugon 2.6 cubic meter per horse-power, whereas to everybody's astonishment the consumption of the Otto-Langen atmospheric gas engine was as low as appr. 1.0 cubic meter illumination gas per horse-power and hour. Despite this improved efficiency the costs were still 2.66 times more than the fuel costs for a steam engine. The author however could not deny that the big advantage of the gas engines is that they can easily be switched on and off, whereas a steam engines need to be heated at least for 30 minutes before there was sufficient steam to put it in operation. 

source: G. Delabar, "Die Gasmaschinen auf der Allgemeinen Industrieausstellung zu Paris im Jahre 1867", Polytechnisches Journal 1868, Vol. 187, pages 1-12.




Gas machines type Otto-Langen in use


Gas engines of the type Otto and Langen are availble only from the "Gasmotorenfarbrik Deutz". They are build in six sizes: 1/4 horse power, 1/2 horse power, 3/4 horse power, 1 horse power, 2 horse power and 3 horse power. End of May 1875 one thousand nine hundred eighty seven machines were in use, 500 for water supply, 400 for printing presses and 1087 machines in small trade.


[1] Hans. L. Sittauer, Nicolaus August Otto /  Rudolf Diesel, Springer Fachmedien Wiesbaden GmbH 1978, 4. Auflage 1990, ISBN 978-3-322-00762-9, S. 26

[2] S. 28