Principle of internal combustion engine operation

We have already written in more detail about the structure of a car engine. In a nutshell, a piston engine consists of a casing, individual mechanisms, and intake, exhaust, fuel, ignition, cooling, lubrication and control systems. So how does the combination of piston, connecting rod, cylinder, crankshaft and other engine parts work?

An internal combustion engine operating cycle

The duty cycle of an internal combustion engine is the number of processes that take place in each of its cylinders.

Let's look at the operating principle on a four-stroke petrol engine.

The operating cycle of any engine is a series of processes that take place sequentially in each cylinder.

The process that takes place in the time it takes for the piston to move from top dead centre towards the bottom dead centre is called a stroke. A complete work cycle takes place in two full revolutions of the crankshaft, which is four strokes.

The process that takes place during the time it takes the piston to move from top dead centre to bottom dead centre is called a stroke.

1. Input.
   In the first cycle «intake» the piston from the maximum upper point descends down – to the lower point. The volume of space in the cylinder above the piston increases (increases), rarefaction is created, the intake valve is simultaneously opened and the combustible mixture is sucked into the cylinder space from the intake duct..
2. Compression.
   Within the second stroke, the moving piston (due to the work of other cylinders) rises to the TDC, the duct is closed by the intake valve and the combustible mixture is compressed.
3. Extension (expansion).
   In the expansion stroke, a spark leaps between the electrodes of the spark plug placed in the cylinder head. It ignites the combustible mixture, which generates a pressure wave that pushes the piston away, causing it to act on the connecting rod and transmit mechanical force to the crankshaft connecting rod journals.
4. Releasing.
   In the last stroke of the release, the piston returns to its original state, i.e. moves upwards again. The exhaust valve opens and the exhaust gases exit the cylinder through the appropriate channel..

This completes one engine cycle. And at this point, the next one begins.

In addition to four-stroke engines, there are also two-stroke engines. In these engines, the duty cycle is completed by a compression stroke and a subsequent stroke. They are not used in the automotive industry today.

What are the differences between diesel engines?

Diesel engines do not have an electromagnetic nozzle. The fuel is ignited without additional ignition devices, namely spark plugs. Instead of an ignition system, there is a high-pressure injector in the cylinder head.

In the intake stroke, the piston does not draw a combustible mixture into the cylinder, but simply pure air.

In the compression stroke, the air is compressed so hard by the piston that its temperature exceeds 700 °C. At this temperature, the diesel fuel that is injected by the injector (at the moment of maximum compression of the air) ignites. Similar to the previous variant, the explosion forms a wave that pushes the piston to bottom dead centre. This process is the «expansion» tact (or working stroke). The «release» tact fully reproduces the above tact in a petrol engine. One engine cycle is completed, then all the cycles are repeated to form the next cycle.

The sequence of working processes in the cylinders of an engine

Different cycles occur in different cylinders at each instant of time. The alternation or sequence of the same cycles in different cylinders is called the engine sequence. It is usually determined by the «working stroke» stroke. For example, a four-cylinder engine with a 1-3-4-2 – order of operation is a type of engine in which the stroke (expansion) in the cylinders occurs first in the first cylinder, then in the third, in the fourth and finally – in the second.

There are 4-cylinder engines with the 1-2-4-3 work order, 6-cylinder engines – with the 1-5-3-6-2-4 work order, 8-cylinder engines – with the 1-5-4-8-6-3-7-2 work order and others.

Cylinder layout features

If the cylinders are arranged in a single row, such engines are called in-line engines.

If two connecting rods are placed on the same crankshaft crankpin (fix the lower split head) at an angle of 90° one to the other, this kind of engine is called a V-type engine. It will be twice as short. And if you place two pistons on the same connecting rod journals opposite each other, you get an opposition engine.

In fact, the engine's duty cycle and crankshaft rotation are not that slow. On the dashboard, there is a tachometer scale that shows how often the crankshaft rotates in one minute (the value we see on the scale should be multiplied by 100). On a warmed up engine, this is a rotation frequency of about 700-900 revolutions per minute. If the engine is not warmed up, the rotational speed is about 1300-1400 (so-called warm-up revolutions). As the engine warms up, it drops to normal. In order to change gears from lower to higher, the engine spins up from 2500-3500 revolutions. If you press the accelerator pedal so that the tachometer arrow goes to the red line, the fuel supply to the injector simply stops.

That's about the principle of operation – that's it. Obedient cars and good roads to you! Read the full list ofworkshop equipment in our catalogue.