Cycle

Stirling Cycle

The Stirling cycle is a thermodynamic cycle that describes the operation of a class of equipment (generating or operating machines). The cycle describes the original Stirling engine that was invented and patented in 1816 by the Reverend Robert Stirling, helped substantially by his brother engineer.

The Stirling engine is an external combustion engine. This characteristic differentiates it from other types of engines such as the otto engine or the diesel engine which are internal combustion engines. Both engines operate according to the otto cycle and the diesel cycle respectively.

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Theoretical and real cycles Cycles

Cycles theoretical endothermic engines

For theoretical cycles, commonly used approaches aproximacióna by the real conditions are three:

• real cycle
• air cycle
• air-fuel cycle.

A theoretical these cycles are compared in practice the actual cycles, which are obtained experimentally by means of the indicators, for this reason, the actual cycle also indicated cycle is called.

Although the theoretical cycles do not correspond to actual cycles, provide a useful reference for the thermodynamic study of internal combustion engines,…

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Otto cycle

The theoretical Otto cycle is the ideal cycle of the Otto engine. The Otto engine is also known as a spark ignition engine because the ignition of the fuel is done through a spark caused by a spark plug. It is also known as a gasoline engine because of the type of fuel it uses.

One way to study the performance of this engine is by analyzing its theoretical cycle. The theoretical cycle is an approximation to the real cycle with many simplifications. In practice, there are so many variables that affect the performance of the engine that calculating the actual cycle is practically impossible.…

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Atkinson cycle

The Atkinson cycle engine is a type of reciprocating internal combustion engine invented by James Atkinson in 1882. It is practically a common Otto cycle engine, but with a crank modified crank to obtain greater efficiency at the expense of a reduction in the power. The objective was to compete with the Otto cycle without infringing any patent.

In its original version, the Atkinson cycle requires a single rotation of the crankshaft to complete a cycle of operation, keeping the phases of the Otto cycle engine intact: intake, compression, expansion (useful phase) and discharge. However,…

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Theoretical diesel cycle

The theoretical diesel cycle is the theoretical cycle of a diesel engine, also known as a compression ignition engine.

The theoretical cycle of a thermal engine is a theoretical approximation of its operation to calculate its performance.

The cycle of an internal combustion engine is constituted by the physical and chemical transformations suffered by the fuel during its passage inside the engine.

The study of a real cycle taking into account all the numerous variables, represents a very complex problem. For this reason, it is usually simplified by resorting to theoretical…

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Cycles of the thermal engines

The operating system of the thermal engines is based on a cycle that is constantly repeated. In the case of internal combustion engines this cycle consists of the fuel input (admission), combustion of the fuel, expansion of the cylinder and expulsion of the gases produced. This cycle generates a mechanical movement, if the cycle repeats we will have a constant mechanical movement.

A thermal engine can work through many different cycles. In this section we will explain the different operating cycles that an internal combustion engine can have, the real cycles and the theoretical cycles.

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Comparison between the three theoretical cycles

To compare cycle just discussed, it is necessary to refer some of the factors whose value depends on the shape and surface, such as: the compression ratio, the maximum pressure, the amount of heat supplied and the heat subtracted useful work.

The following figure are plotted the curves of the ideal thermal performance variations by varying the ratio of co

RINTING for three cycles: Otto, Diesel and Sabathé. For Diesel cycles and Sabathé has chosen a constant pressure…

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Difference between real and theoretical Otto cycles

Between the Otto real cycle and the corresponding theoretical Otto there are substantial differences. Some of these differences can be observed when comparing the diagram of the real cycle with the theoretical cycle diagram. The other differences that we are going to analyze refer to the differences between the temperature and pressure values of the two Otto engine cycles.

Differences in the form of the diagram

The difference in shape of the diagram between a real Otto cycle and a theoretical Otto cycle consists of a different profile in the expansion and compression curves, in…

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Sabathé mixed cycle

The actual operating conditions of diesel engines differ markedly from those that are represented in the ideal Otto and Diesel cycles. For diesel engines, the combustion process transformational approaches a constant pressure only in case of unusually large motors and slow.

The actual plot shows that, under normal conditions, the combustion takes place, in Diesel engines, according to a process that approximates a transformational combustion and a constant volume at pressures n…

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Differences between the real and theoretical diesel cycle

Between real and theoretical diesel cycles there are differences and similarities in the form and in the values of pressures and temperatures. Differences that also appear in the otto cycle. Some of these similarities correspond to those of the otto cycle; for example, the similarities due to the variation of the specific heats, to the loss of heat and to the opening time of the exhaust valve.

Others differ in part and are caused by dissociation and loss by pumping. Finally, one is peculiar to the diesel engine, namely; the one concerning that the combustion is not verified at constant…

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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…

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Real cycles of thermal engines

The actual cycle of a thermal engine is the one that reflects the effective conditions of its operation. These conditions are identified with the diagram of average pressures in the cylinder in correspondence to the different positions of the piston. The pressure shown in a mean pressure diagram is the so-called average pressure indicated.

The indicated diagram is the graph that represents this cycle.

Simplified operation of the indicator

The indicator is a device used to obtain the indicated diagram of a thermal engine cycle.

In the indicator of the indicated diagram,…

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I cycle indicated provided

It is necessary to know the cycle, not only to check if the thermal engine operation is correct, but also to determine the value of the forces acting on the engine components. When in the design phase is to establish the dimensions of the engine components, proceed to the calculation of stresses based on an expected cycle. This similarity can be drawn by motor cycles parangonables with that study, but also obtained a simple and fast way, ore than with a sufficient approximation, using the following method is set forth by way of example and recommend as applicable to the case engine 4-stroke…

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Internal combustion engines, external and electric

In this website we try to explain the operation of the main types of engines from a theoretical point of view. We present schematically the parts, operating cycles and characteristics of the following types of engines:

• The thermal engine or internal combustion engine. Inside the thermal engines we explain the gasoline engine (or otto engine) and the diesel engine).
• The electric motor. This engine has undergone a great evolution throughout history and right now is one of the most used types of engines and with more projection of the future. We will analyze direct current…

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4-stroke engine

A four-stroke engine is a type internal combustion engine, an alternative engine. It can work both in diesel cycle and Otto cycle (gasoline engine). It is therefore a thermodynamic and combustion motorcycle.

The most important feature is that you need to perform four strokes of the piston or plunger to complete the cycle. During these 4 races the crankshaft makes two full turns. These four times are: admission, compression, combustion or explosion and escape.

In 1861, the German Otto experimented with his first 4-stroke gas engine. Otto had to abandon the project due to technical…

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Operating cycle

By operating cycle of a thermal engine we understand the succession of operations that the active fluid executes in the cylinder and repeats periodically. The duration of the operating cycle is measured by the number of strokes made by the piston to perform it.

In this sense, there are two types of thermal engines:

• 4-stroke engine. In the four-stroke engine the cycle is carried out in 4 strokes of the piston. This engine makes a cycle every two revolutions of the motor shaft.
• 2-stroke engine. The two-stroke cycle is carried out only in 2 strokes of the piston. Two-stroke…

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Differences between the Otto engine and the diesel engine

The Otto engine and the diesel engine are two types of thermal engines. These are two types of endothermic engines that, through thermodynamic reactions, convert the internal energy of the fuel into mechanical work. However, there are certain differences between them.

The most important difference is found in its theoretical cycle. The Otto engine operates according to the Otto cycle by spark ignition while the diesel engine is controlled according to the diesel cycle by compression ignition.

The other important difference is in the ignition of the fuel. In the Otto engine the ignition…

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Types of heat engines

The heat engines can be classified in many different ways. Then classify heat engines, taking into account six different aspects:

• They Depending on where is combustion.
• Depending on the fuel used and the type of lighting.
• Depending on the movement of moving parts.
• Depending on how realizes the cycle.
• Depending on the number of cylinders
• Depending on the arrangement of the cylinders
Types of heat engines depending on where combustion takes place

Depending on where combustion takes place two types:

Stirling engine applications

The Stirling engine applications can be divided into three main categories:

• Mechanical propulsion
• Heating and cooling
• Power generation systems

A Stirling engine is a thermal engine that works by cyclic compression and expansion of air or other gas, the working fluid. During the Stirling cycle there is a net conversion of heat to mechanical work. The Stirling cycle engine also operates in reverse, using a mechanical energy input to drive the heat transfer in a reverse direction (ie, a heat pump or refrigerator).

Generation of electrical energy…

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Exam of the indicated diagram

What is the indicated diagram?

The indicated diagram is the diagram that represents the real cycle of a heat engine (a diesel engine or an Otto engine).

The actual cycle of a thermal engine reflects the effective operating conditions. These conditions are identified with the diagram of average pressures in the cylinder in correspondence to the different positions of the piston. The pressure shown in a mean pressure diagram is the so-called average pressure indicated.

Study of the indicated diagram

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Stirling engine

The Stirling engine is an external combustion thermal engine. Originally it was conceived as an industrial main engine to compete with the steam engine, but in practice, for more than a century it was only used for domestic applications and for low power engines.

The Stirling engine was invented in 1816 by Robert Stirling, a Scottish priest. One of the concerns of the time was the safety of steam engines. Stirling's goal was to get a less dangerous engine than the steam engine.

The operation of the Stirling engine is based on the expansion and contraction of a gas that can be…

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2-stroke engine, 2-stroke

In the 2-stroke motors, the operating cycle is carried out in two races. The admission of the active fluid must be made during a fraction of the compression stroke, and the exhaust must be produced during a fraction of the working stroke.

For this to be verified, it is necessary that the active fluid be pre-compressed to be able to enter the cylinder and that the exhaust of the combustion gases be carried out by its own pressure.

The 2-cycle cycle was conceived to simplify the distribution system, eliminating and reducing the number of valves, and to obtain a greater power with…

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History of the diesel engine

The diesel engine was invented by Rudolf Diesel, in the year 1893. Rudolf Diese was a German engineer, employed by the firm MAN.

Rudolf Diesel studied high thermal efficiency engines, with the use of alternative fuels in internal combustion engines. Diese's goal was to replace the old steam engines that were inefficient, very heavy and expensive.

First steps before reaching the diesel engine

In 1806, brothers Claude and Nicéphore Niépce developed the first known internal combustion engine and the first fuel injection system. The two brothers tested systems…

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Pressure diagram for a 4-stroke engine

Next we analyze the diagram of the pressures of a real cycle as a function of the angular displacement of the axis for a 4-stroke engine.

Knowing the indicated cycle, the immediate thing is to draw the diagram of the pressures in the cylinder of the thermal engine as a function of the angular displacement of the crank, instead of depending on the volumes or the reciprocating movements of the piston. In doing so, we take into account the kinematic relationship that links the latter with the axis rotation.

The diagram related to a 4-stroke engine is shown in the figure. In the real…

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Diesel engine

Diesel engines are also known as compression ignition engines. The diesel engine is a type of internal combustion engine that uses gas oil as fuel for the diesel thermodynamic cycle.

The actual performance of diesel cylinder thermal engines is between 35% and 40% and is widely used to propel vehicles.

Diesel engines can operate with 4-cycle and 2-cycle cycles. 2-stroke engines do not consume more fuel than engines with 4-stroke cycles, because the cylinder is swept with pure air and not with the fuel mixture. This is the reason why there is no loss of fuel through the exhaust.

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Heat engine

Heat engines are a type of alternative engines. Actually, they are the most popular alternative engines.

This type of engine uses the thermal energy caused by the combustion of a fuel (usually gasoil or gasoline) to convert it into mechanical energy.

Heat Machines

The concept of a thermal engine is often confused with that of a thermal engine. These terms are related but not exactly the same. A thermal machine is a device or system that works by establishing exchanges of heat and work with its environment. To achieve this, the machine transforms a substance through a cyclic…

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Types of engines

A motor or motor is a machine designed to convert a form of energy into mechanical energy . An engine can be classified into a category according to two criteria: the form of energy it accepts to create movement and the type of movement it produces.

As a general rule, engines have an axle, which in rotary offset and through mechanical devices such as drive gears. The exceptions are rocket motors and linear motors . Nowadays, combustion engines…

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Second law of thermodynamics

The second law of thermodynamics is a principle of classical thermodynamics that establishes the irreversibility of many thermodynamic events, such as the passage of heat from a hot body to a cold one. Unlike other laws of physics such as the law of universal gravitation or Maxwell's equations, the second principle is fundamentally linked to the arrow of time.

The second principle of thermodynamics has several equivalent formulations, one of which is based on the introduction of a state function, entropy: in this case the second principle states that the 'entropy of a system isolated…

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Analysis of a cycle and its thermal performance

Second law of thermodynamics

No real or ideal engine can turn all the heat introduced into mechanical work.

Therefore, only a fraction of the heat supplied by the combustion will be converted into work; This fraction represents the thermal performance of the engine. Then we define,

Ideal thermal performance

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Relation between the amount of heat transformed into useful work and the amount of heat supplied to the fluid.

As useful work equals the difference between the supplied…

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Compression ignition

The compression ignition engine is the diesel or diesel cycle engine. This qualification refers to the way fuel combustion starts inside the piston.

In this type of motor, what enters the chamber initially is only air; the diesel is injected more or less near top dead center. The fuel enters the liquid state, but it is dense. The dense fuel must be vaporized, mixed with the air and reach the conditions of pressure and temperature appropriate to ignite. The time that this process takes is the self-ignition delay and limits the speed at which the engine can turn and, therefore, its maximum…

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First law of thermodynamics

The first law of thermodynamics, also called by extension, the law of conservation of energy, is a fundamental assumption of the theory of thermodynamics.

The first law of thermodynamics is a formulation of the principle of conservation of energy and states that:

"The internal energy of an isolated thermodynamic system is constant."

A thermodynamic universe, which consists of the system and its environment, is an isolated system. Energy is not created or destroyed, but is transformed from one form to another: energy can be transferred through the exchange of heat (heat…

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