Otto engine

This article is about the stationary engine. For a discussion of related thermodynamic principles, see Otto cycle.

Otto Engine Types

There are three types of internal combustion engines designed by Nikolaus August Otto and his partner Eugen Langen. In 1862 Otto attempts to develop an explosion motor, which fails. In 1864 he does succeed in developing the Atmospheric Engine. Finally in 1876 after 14 years of effort Otto develops the layered charge Otto engine.

Timeline

Nikolaus August Otto as a young man was a traveling salesman for a grocery concern. In his travels he encountered the internal combustion engine built in Paris by Belgian ex-patriot Jean Joseph Etienne Lenoir. In 1860 Lenoir succeeded in creating a double acting engine which ran on illuminating gas at 4% efficiency. The 18 liter Lenoir engine was able to produce only 2 horsepower. The Lenoir engine ran on the illuminating gas that was made from coal which had been developed in Paris by Philip Lebon.

In testing a replica of the Lenoir engine in 1861 Otto became aware of the effects of compression on the fuel charge. In 1862 Otto attempted to produce an engine to improve on the poor efficiency and reliability of the Lenoir engine. He tried to create an engine which would compress the fuel mixture prior to ignition, but failed as that engine would no more than a few minutes prior to it's destruction. Many engineers were also trying to solve the problem with no success.

In 1864 Otto and Eugen Langen founded the first internal combustion engine production company NA Otto and Cie (NA Otto and Company). Otto and Cie succeeded in creating a successful atmospheric engine that same year. This is an engine that burned fuel without first trying to compress the fuel/mixture. TheOtto/Langen Atmospheric engine ran at 12% efficiency. This engine produced 0.5 HP at 80 RPM. In competition at the 1867 World Exhibition in Paris it easily bested the efficiency of the Lenoir engine and won the Gold Medal, thus paving the way for production and sales which funded additional research.

The atmospheric engine used a gas flame ignition system and was made in output sizes from 0.25 to 3.0 hp. The factory ran out of space and was moved to the town of Deutz in 1869 where the company was renamed to Deutz Gasmotorenfabrik AG (The Deutz Gas Engine Manufacturing Company). Gottleib Daimler was technical director and Wilhelm Maybach was the head of engine design. Daimler was a gunsmith who had also worked on the Lenoir engine previously.

By 1876 Otto and Langen succeeded in creating the first internal combustion engine that compressed the fuel mixture prior to combustion for far higher efficiency than any engine created to this time. This is the engine that used four cycles in it's creation of power. It is known now as the Otto Cycle engine. The is the engine that was unsuccessfully attempted in 1862. Otto succeeded in creating a stratified charge method of introducing the fuel mix into the cylinder which resulted in a controlled combustion which prevented the explosive combustion of the fuel mixture and provided a steady push throughout the power cycle. This principle was not understood by the engineers of the time and resulted in one of his patents being overturned later.

Atmospheric Engine

The Otto/Langen Atmospheric Engine

The Original Otto Atmospheric Engine running on Youtube

The first version of the Atmospheric engine used a fluted column design which was the design of Eugen Langen. The Atmospheric engine has it's power stroke delivered upward using a rack and pinion to convert the piston's linear motion to rotary motion. The expansion ratio of this engine was much more effective than that of the 1860 Lenoir engine and gave the engine it's superior efficiency.

The first versions of the atmospheric engine used a frame to stabilize the rack but this was soon dispensed with as the engine design was simplified. Later engines dispensed with the fluted cylinder as well.

Otto Cycle Engine

The Otto Engine of 1876

An Otto engine with slide valve ignition

After 14 years of research and development Otto succeeded in creating the compressed charge internal combustion engine. It operated over four cycles and produced two crankshaft revolutions for every power pulse. In order to overcome the explosive detonation that had destroyed all engines prior to this time that attempted to compress the fuel mixture prior to ignition Otto found a way to layer the fuel mixture into the cylinder to cause the fuel to burn in a progressive, as opposed to explosive fashion.

The engine featured a slider control with gas flame ignition, which overcame the problems that Lenoir could not overcome with electric ignition which was unreliable at that time. In the 15 years prior to the development of the Otto engine power output never exceeded 3 hp. In a few years after the Otto engine was developed engine power rose until it reached 1000 hp.

Deutz also developed the carburetor and a reliable low voltage ignition system in 1884. This allowed the use of Liquid Petroleum fuel for the first time.

In 1886 the German patent office nullified the Deutz patent that would have run until 1891 due to the discovery of a previous patent for a four cycle engine by Frenchman Beau De Rochas. Deutz was unable to show that his stratified charge induction system was unlike that described in the Rochas patent and lost his monopoly and 1 of his 25 patents. By 1889 more than 50 companies were manufacturing Otto design engines. Website for the Otto Museum

Spark plug firing

The Otto is one of the first engines to use a spark plug, which is a device that produces a small electric spark to ignite the fuel charge. Otto engines were equipped with a number of different mechanism designs to trigger sparking. This usually consisted of a pivoting trip-arm that briefly grabs a power switch lever and gives it a quick pull. The switch lever is then released and allowed to snap back to its original position in preparation for the next cycle. This system requires an external electric battery, ignition coil, and electric charging system similar to modern automobile engines.

Later Otto engines employed a small magneto directly on the engine. Rather than tripping a switch, the spark plug firing arm applies a quick rotation to the magneto rotor, which then snaps back under spring tension. This quick rotation of the magneto coil produces a very brief current flow that fires the spark plug and ignites the fuel. This design has the advantage of requiring no external battery, and is how modern portable gas engines operate, incorporating the magnet portion of the magneto into the flywheel. Modern portable engines excite the magneto with every flywheel rotation, and so use a cam-operated electric switch to prevent plug firing except for the power stroke of the engine (see wasted spark).

Engine speed regulation

This is a video montage of the Otto engines running at the Western Minnesota Steam Threshers Reunion (WMSTR), in Rollag, Minnesota. (2min 16sec, 320x240, 340kbit/s video)

How the governor regulates engine speed on an Otto engine. This particular engine operates on natural gas; the large disk-shaped object below the engine is the gas pressure regulator. (22sec, 320x240, 320kbit/s video)

Close-up view of the governor wheel either riding up over the fuel intake cam or sliding to the right and coasting. (14sec, 320x240, 250kbit/s video)

This is a demonstration of how the speed regulation works in the Otto engine. The spinning balls are the centrifugal governor, and as the machine runs slower the small wheel moves to the left, inserting the rod into the nearby roller and pushing it up to trigger the intake of fuel to fire the engine for one revolution.

If the machine is under load and still running too slowly, the cam continues to stay inserted and makes the engine fire repeatedly for each ignition cycle. When the engine speed increases, the governor pulls the small wheel to the right and the machine coasts without injecting any fuel, though the spark plug continues to fire with no fuel in the cylinder.

This method of speed-control is often referred to as the Hit or Miss method because the engine mis-fires (for lack of fuel-mixture) on those power-strokes where the engine is running faster than the governed speed, but will hit (fire) on power strokes where the speed is too low. Note that no fuel is used on the mis-fire strokes.

Cylinder cooling

Otto engines use a flowing water jacket around the cylinder wall, similar to modern engine cooling systems. The stationary Otto engines on display at the Western Minnesota Steam Threshers Reunion all share a single large heat radiator outside the building. This centralized distant heat dissipation system also helps to keep the engine building cool.

History

The first person to actually build a vehicle with this engine was German engineer Gottleib Daimler a former employee of Otto's who helped design Otto's engines. The four-cycle compressed charge spark ignited engine today is commonly known as the Otto cycle engine. The Otto cycle consists of adiabatic compression, heat addition at constant volume, adiabatic expansion and rejection of heat at constant volume. In the case of a four-stroke Otto cycle, there are also an isobaric compression and an isobaric expansion, usually ignored since in an idealized process those do not play any role in the heat intake or work output.

References

1. Thinkquest Otto Engine
2. Otto Museum
3. Nikolaus Otto
4. Photograph of Nikolaus August Otto
5. Photograph of Jean Joseph Etienne Lenoir
6. Encyclopedia Britannica article on Etienne Lenoir