Steam engines are mechanical devices capable of transforming heat energy into mechanical energy in a rotating axis. This heat energy takes advantage of the energy contained in water vapor at high pressure and temperature.
We consider steam engines all those machines that transform the thermal energy of a fluid into mechanical energy. In general, the fluid must be pre-heated and at the outlet of the steam machine it must be cooled to repeat the process.
Steam machines can be classified into these two types:
- Plunger steam engine
- Turbine steam engine
A first example of the history of the known from rotary to alternative movement is the crank mechanism. The oldest manual cranks appeared in China during the Han Dynasty (202 BC-220 AD). Several sawmills in Roman Asia and Byzantine Syria during the III-VI centuries AD had a connecting rod mechanism that converted the rotary motion of a water wheel into the linear movement of the saw blades. In 1206, the Arab engineer Al-Jazari invented a crankshaft. Piston motor
A free piston engine is a linear internal combustion engine, in which the movement of the piston is not controlled…
In this section we describe the different parts of a thermal engine. Of thermal engines have many types, however we will focus on the diesel engine and the gasoline engine (otto cycle).
Despite being different engines share many parts in common, so the scheme presented will serve to indicate the nomenclature of each element.
The most important elements of internal combustion engines, common to diesel and explosion engines, we classify them in two large groups:
- Fixed elements of a heat engine: block, cylinder head, crankcase.
- Moving parts of a heat engine:…
A piston is an element formed by two pieces: a piston that moves in a rectilinear alternative movement and a shirt or guide to which it moves. In principle, the piston has a cylindrical shape and is usually made of metal, although it could be of any material.
The guide is actually a cavity that can be integrated into a different part. It is part of the piston-crank-crank system that serves to transform rectilinear movements into rotary and vice versa. Function of the piston in a thermal engine
In an automotive engine, the piston is traditionally called a cylinder. The cylinder,…
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,…
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…
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…
The reciprocating engine uses the reciprocating motion of one or more pistons to convert the pressure into a working fluid. Generally this work is in the form of rotation movement, that is, we obtain mechanical energy. In the opposite direction we find ourselves with the rotating machines in which the movement of the parts of the machine is already rotating like the turbines or the Wankel engine.
The reciprocating engine is also known as a piston engine. The most common alternative engines are internal combustion engines. These thermal engines are widely used in motor vehicles.
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.…
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…
The cylinder of an engine is the enclosure by which a piston moves. The cylinder name comes from its practically cylindrical form.
The materials used to make the cylinders are specific to each type of engine. The way of building and the chosen materials of the cylinder makes vary the performance of the engine. A cylinder made of a gray cast matrix with laminar graphite provides good sliding properties. A motor cylinder made of high quality alloys such as molybdenum, chromium, nickel and manganese, improves hardness and resistance to wear and corrosion.
Engine cylinders are characterized…
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…
The heat engines can be classified in many different ways. Then classify heat engines, taking into account six different aspects:
Types of heat engines depending on where combustion takes place
- 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
Depending on where combustion takes place two types:
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…
The crank shaft is the force that makes the whole rod-crank crank. Its function is to transform rotational movements in alternative movements (combustion engines, for example) or vice versa (Eccentric mechanical presses).
In the heat engine crankshaft collects forces originated during the explosion and turns through the rod, linear motion into rotary motion of the piston alternative. Transmits the movement and the driving force transmission elements that are coupled. Is subjected to bending and torsion efforts, and has a strong structure and very resistant. The crankshafts, which can…
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.…
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…
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…
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…
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…
The uses of the steam engine have been changing with the passage of time.
Initially, since the early eighteenth century, steam engines have been used to power a multitude of uses. At first, the steam engine was used as a piston pump. A piston pump is a hydraulic pump that generates movement in it by the movement of a piston.
Subsequently, from the years 1780 began to appear alternative engines. With the alternative motors a new use of the steam engine appears: to give power to the factories and to the industrial one. At the beginning of the 19th century, steam…
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
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…
The first figure shows a diagram of a typical indicated 2-stroke engine. We need not make a detailed description thereof will suffice to clarify some obscure points, examination of the corresponding path diagram as a function of angular displacement of the crank. This diagram illustrates the second figure.
Nor is there, in this case, correspondence between "time" and "race", for convenience of exposition we have matched the start of the two-stroke points that correspond, respectively, at the beginning of phase COMBUSTION , n at the start of the scanning phase.
A) First Half. Point…
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