INTERNAL COMBUSTION ENGINES

An internal combustion engine is a machine that converts heat from the combustion of various substances into mechanical energy.
This type of engine can consist of one or more cylinders, inside of which pistons slide.
The active fluid, i.e. the fluid that does the work, consists of the products of combustion, which, in addition to an increase in temperature, also undergo a rise in pressure. The expansion of these products, therefore, moves the pistons. The pistons, therefore, set the crankshaft in motion, which acts as the drive shaft for the vehicle's traction.
Internal combustion engines have cyclic operation, which can be either '2-stroke (2T)' (one cycle for every revolution of the shaft) or '4-stroke (4T)' (one cycle for every two revolutions of the shaft). Either way, the cycle begins with the fresh fluid (charge) entering the cylinder and ends with the expulsion of the combustion gases.
The characteristic phases of a two-stroke engine are:
- compression;
- expansion.
The characteristic phases of a four-stroke engine are:
- intake;
- compression;
- expansion;
- expulsion.
The fluid injected into the cylinders may be air and fuel in the form of a mixture or air and fuel supplied separately.
Both engine characteristics and performance depend on the type of fuel, which can be liquid (petrol, diesel,...) or gaseous (methane, LPG,...).
Since petrol has a high degree of volatility, in positive ignition (CA) engines it can be introduced into the cylinder in a mixture with the combustion agent.
In this case, combustion can be triggered by a spark ignited on each cycle.
Since diesel fuel is not very volatile, in compression-ignition (C.I.) engines it can be injected into the cylinder by finely pulverising it in the combustion mass, so as to facilitate the ignition of combustion when the temperature of the mixture rises due to compression.
Compression-ignition engines are also called 'compression-ignition' engines.