Combustion chamber
Otto cilco thermal engine

Used spark plugs
Petrol engine

Otto Motor

Otto Motor

The Otto engine is a type of alternative thermal engine that works through the Otto cycle. It is an alternative engine capable of converting the chemical energy of fuel into mechanical energy through a thermodynamic reaction.

Due to the characteristics of this type of thermal engine it can receive several names.

  • Gasoline engine. Due to the fuel used.
  • Otto Engine. Because it works through the otto cycle.
  • Spark ignition engine. Due to the way to start the ignition of the fuel. The ignition starts through a guspira generated by a spark plug.

Use of the Otto motor

Most motor motors belong to the category of Otto engines (gasoline engine or spark ignition engine). Although in recent years the diesel engine has also become very popular. A large part of the motors for industrial traction, all motors for motorcycles and aircraft and a good part of the motors for nautical and agricultural applications use the Otto cycle.

The Otto motor can operate in 4 or 2 cycle cycles. However, the Otto 2-cycle cycle is little used because of the mixing losses that occur through the exhaust and the consequent high fuel consumption.

Therefore, the vast majority of otto engines operate according to the 4-stroke operating cycle. The 2-stroke spark ignition engine is only adopted in particular cases, such as outboard engines and small motorcycle engines.

Fuel used in an Otto engine

The fuel for an Otto engine is gasoline. Gasoline is formed by light hydrocarbons of high calorific value, which evaporate easily. Gasoline is obtained from petroleum, a fossil fuel that is extracted underground.

The Otto engine can also use gaseous fuels or liquefied gas, but its use is less practical and, therefore, much less widespread.

Gasoline is obtained from crude oil in a refinery. In general, it is obtained from direct distillation naphtha, which is the lightest liquid fraction of oil (except gases). Naphtha is also obtained from the conversion of heavy fractions of petroleum (vacuum gas oil) into process units called FCC (fluidized catalytic cracking) or hydrocracatge.

A series of specifications required for the engine to function well and others of environmental type, both regulated by law in most countries, must be met. The most characteristic specification is the octane rating, which indicates its tendency to detonate.

There are different types of commercial gasoline, classified according to their octane number.

Otto motor power supply

Otto engines can be powered by carburetion or by injection. In otto engines fed by injection, the gasoline is mixed into the air by injecting it into the suction duct at the valve intake, or directly into the combustion chamber. Between the two methods of lamintenación of the fuel, the most used is the fed by carburación.

The injection feed of the otto motor, in the case of multi-cylinder engines, has the following advantages:

  • Distribute the fuel evenly in the various cylinders.
  • Not sensitive to acceleration
  • Not subject to ice formations.

By contrast, this type of gasoline engine feed has the following disadvantages which is more complicated and expensive, especially as regards regulation.

Otto Cycle

The Otto engine is governed by the so-called Otto cycle or Beau de Rochas cycle. The Otto cycle is the ideal thermodynamic cycle that is applied to internal combustion engines that ignite (gasoline engines). It is characterized by the fact that, in a first theoretical approach, all the heat is supplied at constant volume.

Efficiency of the Otto cycle

The efficiency or thermal performance of a motor of this type depends on the compression ratio, ratio between the maximum and minimum volumes of the combustion chamber. This ratio is usually from 8 to 1 up to 10 to 1 in most modern Otto engines. Larger proportions can be used, such as 12 to 1, thus increasing engine efficiency, but this design requires the use of high octane fuel to avoid detonation.

A low compression ratio does not require high octane fuel to avoid this phenomenon, in the same way, a high compression requires a high octane fuel, to avoid the effects of detonation, that is, a self-ignition of the fuel before producing the spark in the spark plug. The average performance of a good Otto 4-stroke engine is 25 to 30%, lower than the performance achieved with the diesel engine. Diesel engines reach yields of 30 to 45%, due precisely to their higher compression ratio.

History of the Otto engine

Nikolaus August Otto - Inventor of the Otto cycle engine

The spark ignition engine was invented, practically in parallel, by two different inventors: Alphonse Beau de Rochas and Nikolaus August Otto.

The first inventor of the Otto engine, around 1862, was the Frenchman Alphonse Beau de Rochas. The second, towards 1875, was the German doctor Nikolaus August Otto. As none of them knew about the other's patent until engines were manufactured in both countries, there was a lawsuit. Finally, De Rochas earned a certain sum of money, but Otto was left with fame and name.

The thermodynamic principle of the four-stroke engine is still called the otto cycle.

Otto built his motor in 1866 together with his compatriot Eugen Langen. It was a gas engine that soon after gave rise to the four-stroke internal combustion engine. Otto developed this machine in four and two-stroke versions. Then, this machine would carry its name: otto cyclic motor.

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Last review: May 3, 2018