Read At Home: 8 Shameful Questions About How An Internal Combustion Engine Works

2023 Author: Natalie MacDonald | [email protected]. Last modified: 2023-11-26 13:59

We all seem to know that under the hoods of most cars driving on our roads are internal combustion engines. But what does the phrase "internal combustion engine" actually mean? How does it work, why does it need valves, cylinders and what is a camshaft? We answer eight simple and by no means embarrassing questions about the internal combustion engine

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To begin with, a few formalities: an internal combustion engine is an engine that converts the energy of fuel combustion into mechanical work. And the word "internal" means that combustion takes place in the working chamber (cylinder) inside engine. How else, you ask? Easy: Steam engines, for example, use the heat from the combustion of fuel to heat a liquid that turns into steam to do work. Such engines are classified as "external combustion engines". Is it logical?

How exactly does the internal combustion engine use the energy of the fuel?

He burns it - that's why the internal combustion engine and ecologists don't like it. Combustion takes place in the heart of the engine - a hollow cylinder, the volume of which can change due to the piston moving inside it. Fuel - or rather, the fuel-air mixture - burns very quickly, practically explodes. As a result of combustion, a lot of gas is formed, which becomes cramped in the cylinder - and already its pressure forces the piston to move with force from the position when the volume of the cylinder is minimal (it is called the "top dead center", TDC), to the maximum volume reached in the "bottom dead point "(NMT).

And in order for this process to continue continuously, four stages of one cycle, the so-called "ticks", must be performed sequentially: 1) filling the cylinder with a mixture (inlet), 2) compressing the mixture, 3) working stroke (combustion) and 4) releasing the expanded gases. In four strokes, the piston travels twice from TDC to BDC, and back.

In a car engine, there is usually more than one cylinder - most often there are four, six or eight, arranged in a row, V-shaped, or opposite each other. There are, of course, 10, 12 and even 16, but these are already special cases. The number of cylinders, their volume, compression ratio (the ratio of the maximum volume to the minimum) determine such properties of the engine as power, thrust and maximum possible revolutions.

Cycle strokes pass sequentially in each cylinder - thus, in a 4-cylinder engine, every half-turn of the crankshaft, one of the pistons makes a working stroke, and the rest are doing other things at this time

But the piston goes up and down - how does the internal combustion engine rotate the wheels?

To translate the translational movement of the pistons (up and down) into rotation, there is a crankshaft inside the motor. Pistons through levers (they are called connecting rods) press on the necks (sections) of the crankshaft, offset relative to its axis - in the same way as a person presses on the pedals of a bicycle, forcing the sprocket-gear to rotate, which then sets the chain connected to the drive wheel in motion.

To make the rotation of the crankshaft uniform, a massive disk (flywheel) is bolted to it. And in some engines, special balance shafts rotate along with the crankshaft, which reduce vibrations that inevitably occur due to fuel explosions inside the engine.

How does the fuel get into the cylinder, which must be sealed during the compression stroke?

To do this, each cylinder has an intake and exhaust valve. The first one opens on the intake stroke - at this moment the piston moves down and helps to suck the fuel mixture into the cylinder. The exhaust valve opens at the last stroke, when the piston, after the working stroke, begins to rise to the top dead center and pushes exhaust gases through the opened hole, making room for a new portion of fuel.

In most modern engines, there are not two valves, but four (some have five) - this is done in order to fill the cylinder with a large amount of mixture in one stroke and get rid of exhaust gases faster and more efficiently.

The camshaft (or several shafts) is responsible for the synchronization of the valves with the pistons. There are special thickenings (cams) on the camshafts, when the shaft rotates, they press on the valves, and they open. As soon as the camshaft stops pressing on the valve, it returns to the closed state under the action of the spring. The camshaft rotates exactly two times slower than the crankshaft, making one revolution in four cylinder strokes, and the order and duration of valve opening are regulated by the location and size of the cams on it.

What fuel does the internal combustion engine use?

Modern cars usually use one of two types of fuel - gasoline or diesel fuel (diesel fuel). Accordingly, engines are divided into gasoline and diesel. But in order for the engine to work normally, it needs a strictly defined amount of fuel, which depends on the load and speed. And he also needs air - without it, gasoline or diesel fuel will not burn in the cylinders. The supply system of the internal combustion engine is the power supply system - it measures the required portions of fuel and air, mixes them and feeds them to the intake.

What is the difference between gasoline and diesel engines?

By the way the fuel mixture is prepared and measured in them. The operation of the gasoline engine is regulated by the amount of air that the power supply system passes into the cylinders - by pressing the gas, the driver opens the throttle (throttle) at the intake, informing the mechanism of his desire to go faster, that is, to increase the engine output. The electronics that control the engine, based on the readings of the sensors, estimates how much air will enter the intake, calculate and measure the required amount of gasoline, which is then mixed with air before entering the cylinder or directly in it. The resulting mixture is then ignited with a spark - a small artificial lightning that is generated by a spark plug installed in the cylinder. In early cars, the power system was completely mechanical.

In a diesel engine, revolutions and recoil are regulated only by the amount of diesel fuel, which is injected into the cylinder under enormous pressure, atomized into tiny droplets. Air intake is not limited to the dampers, but it is compressed much more in the cylinder than in a gasoline engine. From this, the mixture is very hot and flares up without any spark. Therefore, in diesel engines, ignition is said to be from compression.

What happens to the combustion products?

At the exhaust stroke, the piston pushes out of the cylinder the gases formed during the combustion of fuel and having already performed useful work. But you can't release them into the atmosphere right away. They are very hot, "spit out" very often and with great speed. Because of this, the exhaust fumes are deafeningly loud. To calm them down, they need a muffler - a metal box with tubes and partitions inside that form a labyrinth on their way. Passing through the muffler, the exhaust gases lose energy - they slow down, cool down and almost silently go outside through the exhaust pipe. In modern cars, gases are also passed through a catalytic converter - in it, the most toxic combustion products are converted into less harmful ones (for example, carbon monoxide - into carbon dioxide). And only then they get into the atmosphere.

And the engineers figured out how to use the energy of the exhaust gases to the advantage. To do this, a turbocharger (a wheel with blades) is installed at the outlet of the engine, which rotates a very fast gas flow. The turbine, in turn, turns the compressor wheel, which pumps air into the motor. The more air (and thus fuel) enters the cylinders, the higher the engine power can be.

Does the ICE use all the energy in the fuel?

Alas, no - even the most perfect engine does more than just useful work. Part of the energy of the burning fuel is spent on heating the engine itself. But he cannot be too hot, otherwise the details will not withstand and collapse. Therefore, the motor has to be cooled. Its hottest parts are washed with a special coolant, which is then pumped into the radiator (cooler), where it gives off excess degrees to the atmosphere and returns back to heat up again from the engine and cool down again. The circulation of liquid through the system is maintained by a water pump (pump), and the required temperature is controlled by a thermostat.

What else does the motor need for normal operation?

First of all, oil. It is required to lubricate moving parts - this reduces friction and therefore wear. Oil from the bottom of the engine (sump) is taken by the oil pump - through a system of channels and pipes, it is supplied to the crankshaft and camshaft, valves and pistons, and then, having lubricated all important components, the oil flows back into the sump. From where it is pumped out again.

The engine also needs … electricity. Gasoline - to ignite the mixture in the cylinders. And to start any internal combustion engine, at least one revolution of the crankshaft is required - it is performed by a small electric motor (starter). Electronics controls the operation of modern motors. And the car also has bulbs, headlights, music, electric windows … Therefore, the car cannot do without a generator that generates electricity (it is driven by a belt from the engine), and a battery that accumulates excess electricity in reserve.

This is roughly how any car internal combustion engine works. Although modern units are, of course, much more complex in design. They are equipped with turbocharging, their efficiency is increased by optimizing the combustion process, camshafts, valves and throttle valves are deprived … But more about this, probably some other time.