Diesel engine.
Diesel cycle

Endothermic engine
Gearbox

Pressure

Definition of 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…

Pressure diagram for a 4-stroke engine

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…

Exam of the indicated diagram

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

Real cycles of thermal engines

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,…

Difference between real and theoretical Otto cycles

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…

Types of steam engines

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

Pascal. What is it?

Pascal. What is it?

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…

Theoretical diesel cycle

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…

Steam. What is it?

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…

Differences between the Otto engine and the diesel engine

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…

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…