Trucks and buses face many mechanical forces when being driven (see longitudinal dynamic section). They need to be equipped with an internal unit generating mechanical energy in the right form to compensate these forces. This is the role of the vehicle’s powertrain.
Vehicle powertrain refers to all components that generate mechanical energy and deliver it to the driving wheels. Components generating mechanical energy are parts of the engines. Components transferring and transforming the mechanical energy between the engines and the driving wheels are parts of the drivetrain. One vehicle has generally one engine and one drivetrain, but there are some exceptions where several engines can be used with one or more drivetrains. However, the maximum number of drivetrains equals the number of engines.
Diesel engines are the most popular type of engine being used today in the trucking industry. Buses are using a greater variation of fuels: methane, electricity, and hydrogen. Decarbonisation needs to make these fuels relevant as well for trucks in the future. In the following, engines and drivetrains will be analysed in couple per type of fuel. As several fuels share the same type of drivetrain, it will make sense to create three main powertrain types: one based on internal combustion engines, one based on electrical engines, and one based on fuel cells. Another section is being added to these three, to include hybridation and dual fuelling.
Beforing going into technical details, a short explanation is needed on why vehicle’s combustion engines are said internal.
Internal and external combustion engines are two types of engines that convert fuel into mechanical energy, but they do so in different ways.
An internal combustion engine, as the name suggests, burns fuel inside the engine itself. The combustion of fuel occurs within the engine, typically in a combustion chamber, and the resulting hot gases are used to push a piston, a turbine blade, or some other movable part of the engine. The movement of this part then generates mechanical energy (work). Common examples of internal combustion engines include those that run on gasoline or diesel, such as those found in most cars and trucks.
On the other hand, in an external combustion engine, the combustion of fuel takes place outside the engine. The heat produced from this external combustion is then used to heat a separate working fluid, which then moves through the engine to perform work. Examples of external combustion engines include steam engines or Stirling engines. In these engines, the fuel is burned in an external furnace and the heat is transferred to the engine through a working fluid, such as steam or hot air.
One key difference between these two types of engines is their efficiency. Internal combustion engines tend to be more efficient than external combustion engines because they convert more of the fuel's energy directly into mechanical work. External combustion engines, however, can be more flexible in terms of the types of fuels they can use, as they can burn almost any type of fuel in the external furnace.
In the case of trucks and buses, internal combustion engines (ICE) burn mostly two types of fuel: Diesel and methane. Some ICE burns also gasoline and LPG but they won’t be cover here. However, ICE burning hydrogen will be covered here as they offered great potential for decarbonise road transport.
A dedicated page has been created to cover Diesel powertrain