Otto cycle


The operation of a certain engine can be defined depending on the cycle that your engine uses , currently, most engines use the Otto cycle , when they run on gasoline. In order to understand it, it is necessary to remember that the pistons are those that can move inside the cylinder alternately, generating the force that will move towards the crankshaft .

What is the Otto cycle?

The Otto cycle is the mechanism by which internal combustion can function properly , this because the mechanical energy that arises from combustion is produced within a chamber that has been designed for this purpose to produce the movement of the piston.

  • Characteristics of the Otto cycle
  • Story
  • Phases of the Otto cycle
  • How the four-stroke Otto cycle works
  • How the two-stroke Otto cycle works
  • Efficiency
  • Otto cycle applications
  • How it differs from the diesel cycle
  • Importance

Characteristics of the Otto cycle

The main characteristics of the Otto cycle are the following:

  • This cycle is typical of internal combustion engines .
  • It is a thermodynamic type cycle .
  • It works on two-stroke and four-stroke engines .
  • Its efficiency depends on the thermal performance.
  • In this cycle, mechanical energy is produced inside the chamber.


Nikolaus Otto was a renowned German engineer is the man who initiates the history of the Otto cycle , it was he who invented and developed the-cycle engine internal combustion four – stroke as a practical alternative to the steam engine . It was in 1876 that he built this engine and it was later patented in 1862 by Alphonse Beau de Rochas , a French engineer.

Phases of the Otto cycle

There are six phases that occur during the Otto cycle, these are:

  • Intake : in it the intake valve is opened so that the mixture of air and gasoline can enter the cylinder.
  • Adiabatic compression: the mixture is compressed isentropically and the piston reaches its top dead center.
  • Explosion : the spark plug is activated creating a spark to ignite the mixture.
  • Adiabatic expansion : the mixture is able to expand and the chemical energy is transformed into mechanical energy.
  • Isochoric cooling : the pressure is reduced and the mixture is cooled.
  • Exhaust : the exhaust valve opens and the combustion products are expelled.

How the four-stroke Otto cycle works

The four – stroke engines are those having one or more pistons in the cylinder and each has two valves for intake and two valves leak . In this type of engines there are four stages which are well defined and which include the intake , compression , explosion and finally, the exhaust . It is during these stages that two turns are produced in the crankshaft , this because the piston goes up in times 1 and 2 and then goes down in times 3 and 4. For them, follow the following steps:

  • The piston descends with the intake valves open while the exhaust valve remains closed, forming a mixture of air and fuel that is then drawn in by the piston.
  • Before the piston reaches its lowest point, the valves close and it begins to rise compressing the mixture . This is a very fast process and does not release heat.
  • The mixture which has been compressed with the valves closed and the highest point of the piston, occurs combustion form explosive of the mixture which has been initiated by the spark .
  • The mixture, being subjected to high pressure , manages to expand causing the piston to go down and the valves remain The work of the piston is positive and is transmitted to the crankshaft thus producing the motive force.
  • The burned mixture is then expelled through the valve that remains open while the intake valve is closed.

How the two-stroke Otto cycle works

This type of two-stroke operation is mainly used in engines that have small displacement and are simpler . Provides more power but tends to be less efficient . The steps for the operation of the cycle are:

  • Compression and aspiration that occur when the piston rises and manages to compress the air, oil and fuel mixture . This causes a vacuum to form in a part known as the crankcase and then, when the stroke ends, the piston leaves a hole to suck in the mixture again.
  • The next step is the explosion and escape . These are made by the spark plug that is responsible for forming a spark that has the function of igniting the compressed mixture causing an explosion that causes the piston to move downwards.
  • Then the performance is given , this because the Otto cycle must work with a certain amount of air and fuel and this must be balanced. This type of ratio is called a lambda, and it has 7 parts air to one part fuel .


The efficiency of an Otto cycle depends solely on the compression ratio . In order to find it, it is necessary to apply a formula known as Poisson’s ratio , which reads as follows:

Then the performance can be expressed as:

with r = VA / VB the compression ratio between the initial and final volume.

Otto cycle applications

The Otto cycle is widely used in the automotive industry , mainly in low-weight vehicles such as cars and motorcycles . It is also used in the different types of stationary applications that are used for the production of electrical energy, such as emergency plants, and it is also used in machines when there is electrical power. It is also used in an important way in engines that work with internal combustion , those of two and four times.

How it differs from the diesel cycle

Although the Otto cycle and the diesel cycle are two types of heat engines that work through a series of thermodynamic reactions , they present some differences that separate them. The first and perhaps most important is based on the theoretical cycle indicating that the otto cycle works through the ignition of the spark while diesel cycle operates according to the ignition by compression .

In the otto cycle , the ignition is carried out by means of a spark which is caused by means of the spark plug , which is why it is known as the spark cycle , on the other hand, in the diesel cycle , the ignition is done by means of the compression of the fuel and therefore is known as compression – ignition.


The Otto cycle is of vital importance for the field of motorsports because it is in charge of providing the energy for most of the transports and for this reason it is considered essential for the modern world. Specifically, the vast majority of cars on the road today need of the Otto cycle to convert the gasoline in motion .

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