Engines today


By the turn of the millennium, the priorities had been set for engine development well into the 21st century. Most passenger cars and light commercial vehicles on our roads still contain four-stroke petrol or diesel engines. However, new technologies are changing the industry and offering a wider choice than ever before. It’s time to have a look at the main engine types and fuelling options available to the drivers of today – and tomorrow.

A two-stroke engine fires once every revolution, unlike a four-stroke engine which only fires once every second revolution. (A revolution consists of two strokes, down and up.)


So why are two-stroke engines not used universally? The answer is that their disadvantages outweigh the benefits when it comes to cars.

- They are less fuel efficient, making them expensive to run.

- They don’t have a dedicated lubrication system. Instead, oil is mixed in with the fuel/air mixture before combustion. As this is less efficient, the engine parts wear out more quickly.

- They produce more pollution and fail to meet many environmental regulations.


Petrol or diesel?

The most important difference occurs in the ignition stage. Rather than needing a spark to induce combustion, diesel engines simply rely on compression. Compression causes the temperature to rise so that when diesel is sprayed into the cylinder, it combusts spontaneously. This means that the diesel engine doesn’t need a spark plug. If the engine is too cold for ignition, a glow plug is used to raise the temperature to the necessary level for combustion.

The benefits of diesel generally outweigh its disadvantages and diesel engines are becoming more and more popular.





Natural Gas & Petroleum Gas

Natural Gas - Liquified (LNG) and Compressed (CNG)

Gas engines run on a gas fuel such as coal gas, biogas, landfill gas or natural gas. They work on the same basic principles as petrol engines – natural gas is mixed with air in the cylinder and ignited by a spark plug. However, some modifications are needed. These include high-compression pistons, hardened exhaust valve seats, a methane-specific catalytic converter and a gaseous fuel-injection system.

Liquified Petroleum Gas (LPG)

LPG is a mixture of propane and butane which, when compressed, becomes liquid. It offers the same advantages as natural gas but is still not as widely available as CNG.

Some passenger cars are sold already prepared for LPG, but more often it is necessary to convert the vehicle. This is quite expensive, although the cost is usually recuperated quickly repaid in fuel savings.



Hydrogen can be produced from a wide range of sources. It is a very clean solution, producing no emissions.
Hydrogen can be used to power engines in two ways. It can be burned in an internal combustion engine in the same way that petrol is. It can also be reacted with oxygen in a fuel cell to run an electric motor.

Electric vehicles

Electric vehicles are not propelled by an engine but by at least one electric motor, using electrical energy that is usually stored in a lithium-ion battery pack. Other possibilities such as capacitors and flywheel energy storage devices are also being explored. Electric vehicles are on the increase but there are still some significant hurdles to overcome before they will be embraced by all drivers.


Hybrid technology

A hybrid vehicle is any vehicle that combines two power sources. Most hybrid cars on the road today combine petrol or diesel with an electric motor and battery. They combine the advantages of both power sources: the power, range and refuelling convenience of petrol or diesel with the low emissions and low cost of electricity.

There are two main drivetrain configurations for hybrid vehicles: Parallel hybrid and Series hybrid.

Plug-in Hybrid Electric Vehicle (PHEV)

This is a hybrid vehicle with increased energy storage capacity, usually in the form of Li-ion batteries. It can be connected to a mains electricity supply after each journey to avoid using the internal combustion engine and thus decrease emissions. In one innovative new system the electric motor is powered by a small internal combustion engine if the battery is flat.

Fuel cell/electric hybrid vehicle 

This type of vehicle is equipped with a fuel cell as well as an electric battery. The fuel cell powers the battery when it is empty, using hydrogen as a fuel.





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