Internal Combustion Engine (ICE)

What is an internal combustion engine ?

An internal combustion engine (or ) is a thermal engine that uses the explosion of pressurized gas to produce mechanical force. This is why we also speak of an explosion engine.

The combustion of gas under overpressure takes place inside one or more cylinders equipped with pistons, hence the concept of internal combustion.

Actuated by the combustion of the gas, the pistons can be used to:

  • produce torque on a shaft, in the case of gasoline, diesel or gas ignition (LPG type) engines ;
  • or provide thrust by ejecting fluid through a nozzle, as in the jet engines used on board aircraft.


The specificities of an internal combustion engine

An internal combustion engine needs a fuel and an oxidizer to function. Depending on the technology, the fuels used in internal combustion engines can be of a different origin and nature.

They can be:

  • fossil fuels derived from petroleum, called hydrocarbons: for example, gasoline, diesel or LPG (Liquefied Petroleum Gas) ;
  • biofuels from non-fossilized plants or animals such as bioethanol or biodiesel ;
  • liquid propellants, when the engines are used outside the atmosphere, for example, on rockets.

The high of these fuels gives vehicles with internal combustion engines with a great autonomy.

However, the combustion involved in their operation causes polluting emissions (such as CO2 and greenhouse gases) that contribute to global warming. In cars and other transport vehicles, internal combustion engines are being replaced little by little by hybrid or electric engines that are less polluting for our environment.


Examples and practical application

In general, internal combustion engines are used for the propulsion of transport vehicles. The gasoline or diesel engines of our cars are thus MCI. Some mobile tools (chainsaws, lawnmowers) or fixed installations (pumps, generators) also use this type of thermal engine.

There are two main categories of internal combustion engines:

  • spark-ignition engines (usually gasoline or gas) in which the fuel is premixed with the oxidizer ;
  • compression ignition engines, known as Diesel engines, in which the fuel ignites on contact with hot air.

Internal combustion engines usually follow a 4-stroke cycle: intake of air and/or fuel by suction, compression of the space within the cylinder, combustion and exhaust of the gases. There are also 2-stroke engines that only need 2 piston movements to operate.


Internal combustion engines in figures

While they will still represent the majority of sales in 2021, vehicles with internal combustion engines will see their market share decline.

In October 2021, out of a total of 118, 517 registrations:

  • 42, 621 (or about 35.9 percent) were for MCI gasoline-powered vehicles, down 43 percent from 2020 ;
  • 22, 885 (19.3%) were MCI diesel vehicles, down 57.8% from the previous year.

Hybrid and plug-in hybrid vehicles that use an internal combustion engine (gasoline or diesel) combined with an electric motor, however, accounted for 33, 424 registrations in 2021, or 28.20 percent of new vehicles sold.

In comparison, 15,582 new electrically powered vehicles were sold over the same period, representing 13.1% of the market share, up 55.2% from 2020.


Regulatory framework

In order to combat climate change, all new vehicles sold in Europe since 1991 must meet certain pollution standards set by the European Union. These are the anti-pollution standards known as " Euro ".

These European standards differ according to:

  • the type of vehicles (heavy trucks, buses and coaches/cars and light commercial vehicles/2 wheels, motor tricycles and quadricycles) ;
  • and the type of engine used in the vehicles (spark ignition engines: gasoline, LPG, LNG, CNG, etc. or diesel engines).

They apply checks during the approval new vehicles.

For cars and light commercial vehicles, the Euro standards set an emission limit based on the distance travelled (g/km), for heavy vehicles these limits are based on the energy developed (in g/kWh).

  • Regulation no. 595/2009 of the European Parliament and of the Council of 18 June 2009, known as the Euro VI standard ;
  • Commission Regulation (EU) No 2016/1718 of 20 September 2016 ;
  • Order of June 21, 2016 establishing the nomenclature of vehicles classified according to their level of emission of air pollutants pursuant to Article R. 318-2 of the Highway Code

These emission requirements are reinforced every 5 years and particularly affect vehicles with internal combustion engines. For example, the Euro 6 standard for light vehicles will be replaced in 2025 by a Euro 7 standard whose requirements could condemn the sale of internal combustion vehicles.