The principle of operation of the internal combustion engine. Operating cycles of an internal combustion engine.

There are several different types of engines, and in wheeled, tracked, water and sometimes even air transport (trucks and cars, special equipment, motor boats, airplanes, etc.), you can often find an internal combustion engine (ICE).

Internal combustion engines are gasoline and diesel, and can also successfully run on gas and even hydrogen (hydrogen internal combustion engine). Motors also differ in design and layout; they are two-stroke and four-stroke.

One way or another, a power unit of this type has become widespread due to its autonomy, versatility, as well as a number of other advantages. At the same time, the units have many different parameters and characteristics, among which it is worth highlighting the operating cycle. Next, we'll talk about what the duty cycle of an automobile internal combustion engine means.

What is a 2 stroke motor?

A 2-stroke engine is a type of piston engine in which the working process is completed in two strokes of the piston. Such an engine has only 2 strokes, a compression stroke and a power stroke. Moreover, cleaning and filling the cylinder with the combustible mixture is carried out not in separate strokes, as in a 4-stroke engine, but in joint ones.

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How does a four stroke engine work?

Structurally, the working cycle of a typical four-stroke unit is ensured by the operation of the following elements:

• cylinder;
• piston - performs reciprocating movements inside the cylinder;
• intake valve – controls the process of supplying the air-fuel mixture to the combustion chamber;
• exhaust valve – controls the process of exhaust gases expelling from the cylinder;
• spark plug – ignites the resulting air-fuel mixture;
• crankshaft;
• camshaft - controls the opening and closing of valves;
• belt or chain drive;
• crank mechanism - translates the movement of the piston into rotation of the crankshaft.

Operating cycle of a four-stroke engine
The operating cycle of such a mechanism consists of four strokes, during which the following processes are implemented:

1. Intake (fuel and air injection). At the beginning of the cycle, the piston is at TDC. At the moment when the crankshaft begins to rotate, it acts on the piston and moves it to BDC. This leads to the formation of vacuum in the cylinder chamber. The camshaft acts on the intake valve, gradually opening it. When the piston is in its extreme position, the valve is completely open, resulting in intense injection of fuel and air into the cylinder chamber.
2. Compression (increasing the pressure of the combustible mixture). In the second stage, the piston begins to move back to the top dead center of the compression stroke. The crankshaft makes another turn and both valves are completely closed. The internal pressure increases to 1.8 MPa and the temperature of the combustible mixture rises to 600 C°.
3. Expansion (working stroke). When the piston reaches the top position in the combustion chamber, the maximum compression is set to 5 MPa and the spark plug is fired. This leads to combustion of the mixture and an increase in temperature to 2500 C°. Pressure and temperature lead to an intense impact on the piston, and it begins to move back to BDC. The crankshaft makes another turn, and thus the thermal energy is converted into useful work. The camshaft opens the exhaust valve, and when the piston reaches BDC, it is fully open. As a result, the exhaust gases begin to gradually leave the chamber, and the pressure and temperature decrease.
4. Exhaust (removal of exhaust gases). The engine crankshaft turns and the piston begins to move to the top point. This leads to the expulsion of exhaust gases and an even greater decrease in temperature and a decrease in pressure to 0.1 MPa. Next, a new cycle begins, during which these processes are repeated again.

During each stroke, the engine crankshaft rotates 180°. During a full working cycle, the crankshaft rotates 720°.

The four-stroke engine has become widespread. It can work with both gasoline and diesel fuel. The difference between the operating cycle for a diesel engine is that the ignition of the air-fuel mixture does not occur from a spark, but from high pressure and temperature at the end point of the compression stroke.

Origin information

When choosing a name for a child, parents can pay attention to every detail. They are interested not only in what impact this or that way of naming the baby will have on the fate

The history of the name, existing versions of its origin and even rarity of use come into the field of attention.

There are several versions about the origin and meaning of the name Eliana. Among them, three main ones stand out. Each offers its own interpretation of where this female name came from.

The first is based on the Roman origin and meaning of the name Eliana. History says that it was formed from the generic or personal nickname Aelianus. In turn, this nickname takes its roots from the Greek word “helios”. In this case, the name carries the meaning of “sunny”, which makes it somewhat related to Elena.

The second version indicates that the name Eliana is of Jewish origin. In this version, the translation sounds like “God answered me” or “my God is my family.”

The third version of where the meaning of the name Eliana comes from is French. According to this theory, the word has two translations. The first sounds like “daughter of the sun,” which overlaps with Greco-Roman theory. In the second version - as “good day”.

Expanded classification of thermometers

Let us make a reservation that in the framework of the review we will not separate pyrometers from the topic. This is a slightly different class of devices, actively used for similar purposes as temperature sensors. So, it is customary to distinguish:

Expansion thermometers. Based on the ability of bodies to change geometric dimensions:

1. Glass liquid thermometers are outside the window. Already considered temperature sensors. Mercury is most often used as a liquid for a number of reasons: it retains its state of aggregation in a wide range of environmental conditions, does not wet glass, and is easily extracted from natural components. Disadvantages include toxicity, low coefficient of thermal expansion and solidification even at minus 35 degrees Celsius. This reminds us of the benefits of alcohol thermometers.
2. Manometric thermometers are based on the dependence of the vapor pressure of a substance in the working chamber on temperature. Such systems are readily used as thermostats in old refrigerators that do not have electronics. Pros: the system does not require electrical power, which greatly simplifies the design of the device. These temperature sensors are located in the evaporator area and are connected through a tube to the regulator (located in the refrigeration compartment), where the relay is located.

Thermometric sensors and resistance thermometers include thermocouples and thermistors. This is a hackneyed topic, we’ll touch on it a little lower. Metals, semiconductors, and other classes of the periodic table are used as materials for these temperature sensors.

Resistance thermometer

What are the main differences?

Features of operation require consideration first in order for the comparison to be correct:

• In diesel engines, the air-fuel mixture is formed much faster when compared to a unit running on gasoline. In the cylinders of such engines, only air is compressed, the temperature of which corresponds to approximately 900 degrees. Gasoline is supplied separately to the compartment for subsequent combustion. Small fragments of diesel fuel evaporate at an accelerated rate and combine with the air mass. Due to the sufficiently high temperature effect, the resulting mixture is easily ignited without the need for ignition with a spark. Such engines consume significantly less oil.
• Air and fuel in gasoline engines are combined in a specially designed exhaust manifold, after which the fuel enters the compartment for further combustion. When the compression stroke is completed, the final stage of formation of the fuel-air composition is completed and its subsequent distribution throughout all compartments of the cylinder. After squeezing, the resulting mixture reaches a temperature of approximately 500 degrees, and then the procedure of igniting it using a candle is performed.

Torque and horsepower

Car enthusiasts often debate with each other about whose engine is more powerful. But sometimes they have no idea what this parameter consists of. The generally accepted term "horsepower" was coined by inventor James Watt in the 18th century. He came up with it while watching a horse that was harnessed to a mechanism that lifted coal from a mine. He calculated that one horse could lift 150 kg of coal to a height of 30 meters in a minute. One horsepower is equivalent to 735.5 watts, or 1 kW is equal to 1.36 hp.

First of all, the power of any engine is assessed in horsepower, and only then do they remember the torque. But this traction characteristic also gives an idea of ​​the specific traction and dynamic capabilities of the car. Torque is an indicator of the operation of the power unit, and power is the main parameter for performing this work. These indicators are closely related to each other. The more horsepower an engine produces, the greater the torque potential. This potential is realized in real conditions through the transmission and axle shafts of the machine. Connecting these elements together determines exactly how power can be converted into torque.

The simplest example is comparing a tractor with a racing car. A racing car has a lot of horsepower, but torque is required to increase speed through the gearbox. To make such a car move forward, very little work is needed, because the bulk of the power is used to develop speed.

As for the tractor, it may have an engine with the same displacement that produces the same horsepower. But in this case the power is used not to develop speed, but to generate traction (See traction class). To do this, it is passed through a multi-stage transmission. Therefore, the tractor does not develop high speeds, but it can tow large loads, plow and cultivate the land, etc.

In internal combustion engines, force is transmitted from the gases of the burning fuel to the piston, from the piston it is transmitted to the crank mechanism, and then to the crankshaft. And the crankshaft, through the transmission and drives, spins the wheels.

Naturally, engine torque is not constant. It is stronger when a greater force acts on the shoulder, and weaker when the force weakens or ceases to act. That is, when the driver presses on the gas pedal, the force acting on the shoulder increases, and, accordingly, the engine torque increases.

Power ensures overcoming all kinds of forces that prevent the car from moving. This is the friction force in the engine, transmission and drives of the car, aerodynamic forces, wheel rolling forces, etc. The more power, the greater the resistance of forces the machine will be able to overcome and develop greater speed. However, power is not a constant force, but depends on engine speed. At idle the power is the same, but at maximum speed it is completely different. Many car manufacturers indicate at what speed the maximum possible power of the car is achieved.

It must be taken into account that maximum power does not develop immediately. The car starts from a standstill at almost minimum speed (slightly above idle), and it takes time to mobilize full power. This is where engine torque comes into play. It will depend on it how long it will take for the car to reach its maximum power - that is, the dynamics of its acceleration.

Often the driver is faced with situations where it is necessary to give the car significant acceleration in order to perform the required maneuver. Pressing the accelerator pedal to the floor, he feels that the car is accelerating weakly. Fast acceleration requires powerful torque. It is this that characterizes the car’s throttle response.

The main force in an internal combustion engine is generated by the combustion chamber, in which the fuel-air mixture is ignited. It drives the crank mechanism, and through it the crankshaft. The lever is the length of the crank, that is, if the length is longer, then the torque will also increase.

However, it is impossible to increase the crank arm indefinitely. After all, then you will have to increase the stroke of the piston, and with it the size of the engine. At the same time, the engine speed will decrease. Engines with a large lever crank mechanism can only be used in large-sized boats. But in passenger cars with small crankshaft sizes you cannot experiment.

Operation - Duty Cycle

The work cycle operations are regulated automatically using a time relay, without the use of manual labor.  

Each operation of the work cycle is specified by one command.  

The four operations of the working cycle are automatically controlled by a time relay. Typically, calculating a material balance requires about 30 cycles, during which time it is possible to collect cracking products in quantities sufficient to determine all components. The temperature is regulated by automatic point devices (regular pockets are used to insert thermocouples) and is automatically recorded. Each reactor has two thermocouples installed in the lower and upper zones of the catalyst bed. Temperature measurements at these two locations indicate whether the catalyst bed is sufficiently mixed.  

Of all the operations in the centrifuge operating cycle, the most power consumed is Unloading. In this case, the power is spent on overcoming the forces of inertia and adhesion of particles of the rotating layer of sediment, directed by the cutting mechanism for unloading. The lowest load is observed during the Drying operation, when power is spent mainly on ventilation losses and to a small extent on friction in the bearings.  

Thanks to this, all operations of the working cycle are controlled using two handles located on both sides of the steering wheel in the range of the driver’s hands. The design of the handles allows you to move them not only back and forth and left and right, but also in any other direction. When the lever moves diagonally, two hydraulic valve spools are simultaneously activated and the two working movements in the cycle are combined in time.  

The working process of an excavator includes the operations of the work cycle and the operation of moving the machine, which is carried out after it becomes impossible or inconvenient to excavate the soil from the parking lot.  

Depending on the sequence of operations of the working cycle, the loading process of the engine of a single-bucket excavator is formed. The methods outlined in the specialized literature make it possible to determine the average power removed from the engine crankshaft during each operation of the operating cycle.  

It has a number of devices that allow you to automate most of the operations of the working cycle, in particular the supply of pipes to the inspection area, its rotation during the inspection process and the removal of the pipe after the end of the inspection to the rack.  

Machines of this type are characterized by continuous rotation, frequency of work cycle operations and automation of these operations. Loading the centrifuge, the jointing process itself, washing, removing and unloading the sediment are carried out strictly periodically, at certain intervals; they also continue for a certain time and are controlled by a special automation system that manages and controls all operations. The worker's functions are reduced solely to starting the machine, which can then work without stopping for an indefinitely long time.  

Advanced crane operators widely combine crane operating cycle operations when loading and unloading containers. Simultaneously with the movement of the container in the transverse or longitudinal direction, the container is raised or lowered to a height that ensures the safety of further movement. When operating gantry and overhead cranes, just like when operating jib cranes, a combined loading and unloading method is used. To combine individual operations in the work cycle, it is advisable to use the method of parallel processing of platforms and vehicles. To do this, cars approach certain areas, and the crane, moving along the front, simultaneously processes the platforms and cars. The downtime of individual vehicles is increasing slightly, but the average downtime of vehicles at the container site is decreasing.  

Branch broaching can be done with one or three cores. All operations of the working cycle - loading, supply of blank pipes, removal of bends from the core - are carried out mechanized.  

By introducing the method of Stalin Prize laureate F.L. Kovalev into excavation work, one can achieve great success in increasing the productivity of the machine. Different Stakhanovites perform the operations of the excavator working cycle using different techniques, so the duration and effectiveness of these operations are not the same for different excavator operators. Kovalev allows you to select, study and implement only the best techniques of the Stakhanovites and thereby achieve the greatest productivity.  

Natural science. Grade 11

Lesson summary

Science, 11th grade

Lesson 9. Design of heat engines

List of issues discussed in the topic:

• What types are real heat engines divided into?
• What are the main components of heat engines, and what functions do they perform?
• By what criteria are heat engines evaluated?

Glossary on the topic

:

Top dead center

(TDC) - the position of the piston in the cylinder of an internal combustion engine, corresponding to the maximum distance between any point of the piston and the axis of rotation of the crankshaft (conditionally the initial position of the crankshaft, zero degrees of crank rotation).

Bottom dead center

- the position of the piston in the cylinder, corresponding to the minimum distance between any point of the piston and the axis of rotation of the crankshaft.

The stroke of the piston during which no work is done by the gas is called the idle stroke.

.

Working stroke

– stroke of the piston under the pressure of gases formed during combustion of the working mixture, moving from the T.M.T. (top dead center) to B.M.T. (bottom dead center).

Design features

In addition to differences in operating principles, these motors also have design features.

The 2-stroke engine is structurally simpler. The gas distribution mechanism is an additional engine equipment that complicates the design.

A 2-stroke engine does not have this mechanism and its role is played by the piston, opening and closing certain windows.

In addition, this engine does not require a lubrication system. This is due to the fact that the under-piston space, where the knees are located, is also involved in the work process. shaft.

But since the crank mechanism requires lubrication, in this engine it is produced together with fuel, that is, engine oil is added to the fuel, and when fuel enters this space, the existing oil lubricates the mechanism.

For 4-stroke engines, the design includes both a gas distribution mechanism and a separate lubrication system.

This significantly complicates the design, however, these engines are a higher priority than two-stroke engines due to a number of operational shortcomings of the latter.