# Pressure

## Definition of pressure

In everyday life we find many examples of pressure we often use: atmospheric pressure to talk about time changes, blood pressure to talk about health, pressure of the car's wheels in the engine field. We even talk about pressure on issues that have no link with physics: the pressure of a job interview.

Force and pressure are very different concepts. The pressure (symbol P) is the physical quantity that measures the instantaneous force in a unit of surface, applied in a direction perpendicular to it. Its unity in the SI is the Pascal. Pascal is equivalent to one Newton per square meter…

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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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## 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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## 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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## 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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## Types of steam engines

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

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## Pascal - Pressure unit

The pascal (symbol: Pa) is a unit derived from the International System used to measure internal pressure, mechanical stress, Young's modulus and tensile strength. It is defined as one newton per square meter. It is called in honor of the French mathematician Blaise Pascal.

Some common multiples of the pascal are the hectopascal (1 hPa = 100 Pa), which is equivalent to one millibar, the quilopascal (1 kPa = 1000 Pa), the megapascal (1 MPa = 1,000,000 Pa) and the gigapascal (1 GPa = 1,000,000,000 Pa).

The unit of measure called standard atmosphere (atm) is defined as 101,325 Pa…

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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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## Steam. What is it?

Steam is a substance in the gas phase that is at a temperature lower than the critical point. Due to this characteristic, the vapor can be condensed in a liquid or a solid increasing its pressure without reducing the temperature.

That is, the vapor is a gas that can be condensed at a constant temperature, increasing the pressure. On the other hand, to convert a non-vaporous gas to liquid, it is not enough to increase the pressure, but the temperature must be lowered.

For example, water has a critical temperature of 374 ° C (647 kelvin), which is the highest temperature at…

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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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## 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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## Diagram shown as a function of crank angle for a 2-stroke engine

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…

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## Safety in steam engines

Safety in steam engines is an important issue that needs to be studied and prevented due to the characteristics of this type of machine.

The composition of the steam machines formed by boilers and other components under pressure causes fluids with a very high potential energy to be stored. Due to the high pressure and temperature with which you work any steam or explosion leaks can be very harmful for the safety of people.

Throughout the history of steam engines there have been very serious accidents that have involved considerable material damage and even the loss of human lives.

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## Steam engine

A steam engine is a device that produces mechanical energy through the use of water vapor. In particular, thermal energy is transformed into mechanical energy by means of steam. Heat is typically produced by burning fossil fuels, particularly coal, but it can also come from wood, hydrocarbons or nuclear reactions.

Description of steam engines

An essential part of the system that includes the steam engine is the steam generator, or the boiler. In the boiler water vapor is obtained by the administration of heat to liquid water. The steam is then sent to the engine, which can be…

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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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## Refinery

An oil refinery is an industrial plant, of the oil raw material by purification and distillation under normal pressure and under vacuum in fractions with a defined boiling range transferred. The additional refinement of the boiling cuts is done by methods such as extraction or chemical cleaning methods. To increase the quality of products, such as their octane number, conversion processes such as isomerization or catalytic reforming are used. In addition, additives are added to products that improve or suppress certain properties.

Higher value products are obtained, such as gasoline,…

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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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## Advantages of the diesel engine

Diesel engines have several advantages over other internal combustion engines:

Advantages related to diesel engine fuel

The fuel of a diesel engine has a higher energy density and a smaller volume of fuel is required to perform a specific amount of work.

Diesel engines inject fuel directly into the combustion chamber, have no air intake restrictions other than air filters and intake pipes and have no vacuum in the intake manifold to add parasitic load and pump losses to push the pistons down against the vacuum of the intake system. Cylinder filling is aided by atmospheric…

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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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## History of the steam engine

The first reference of the steam engine is found in the Hellenistic period. Then we talk about experiments to take advantage of the expansion of the compounds due to the change of the liquid phase to the gas (vapor) phase: in particular, the Aeolus cell of the heron. It is a hollow metal sphere filled with water, with the arms tangential to the outlet hole: when water is heated, it vaporizes and the water vapor that comes out of the holes, by rotating the ball itself.

You should also remember the attempts to use Leonardo da Vinci's steam with his car called the Architano. In 1606 the…

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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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## 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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## What is spark ignition?

We call it by spark to the one of the forms in which it ignites a thermal engine. The engines starting with spark ignition are Otto cycle gasoline engines.

In this type of engines there is an element, the spark plug, which is capable of causing a spark when it receives electric energy. In this way, the spark plug is capable of transforming the electrical energy coming from the battery into a spark.

Around the spark causing the spark plug creates the so-called initial ignition source. In the initial ignition focus fuel combustion is spread forming a flame front.

As the flame…

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## 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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## Parts and components of a heat engine

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:…

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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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## 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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## Thermodynamic transformations

Thermodynamic transformation is a process by which a thermodynamic system passes from a state of thermodynamic equilibrium to another.

A thermodynamic system is in principle in a state of thermodynamic equilibrium when the main variables of the system (ie pressure, volume and temperature) do not experience any additional variation over time.

In the event that two or all of the above variables change (the variation of only one of them is impossible because they are all interconnected by an inverse or direct proportion ratio) we are in the presence of a thermodynamic transformation,…

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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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## 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:

## 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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