Glossary of Terms

Here's a quick guide to some of the terms you'll find on our website:

Petrol engines
With petrol engines, fuel enters the cylinders and is ignited by spark plugs. The fuel then burns very quickly and the engine runs at higher revs to produce more power than a similar sized diesel engine.

Diesel engine
With a diesel engine, pistons rapidly compress the air inside the cylinders creating heat. Diesel fuel is then injected into the cylinders and ignites spontaneously. Road diesel is designed to lubricate the injection system and burn cleanly. Even so, diesel engines produce more 'particulates' than petrol engines because the fuel is less refined.

Revs
Revs is short for 'revolutions per minute' (or rpm). When an engine's revs are high, the engine is turning quickly - when low, it is turning more slowly. A change of gear affects the revs of an engine, with the higher gears creating lower revs.

Torque
Torque is the 'turning force' an engine produces. The higher the torque, the more 'pulling power' is produced. Diesel engines generally deliver a higher torque at lower engine speeds when compared to petrol engines. (Torque and engine speed multiplied together give the engine's power.)

Power
For vehicles, power is the amount of mechanical energy delivered to propel the vehicle per second. Its units are either horsepower (hp) or kilowatts (kW).

Hybrid car
A hybrid car has at least two power sources - either petrol and electricity or diesel and electricity. Each power source can power the vehicle individually or in combination with the other. Many hybrid vehicles can store the energy normally wasted when braking, and re-use it again when accelerating. This means less fuel is burned so CO₂ emissions can be reduced.

Petrol
Petrol is a fossil fuel refined from crude oil. It evaporates easily and is mixed with air before it enters the engine to burn more cleanly.

Diesel
Diesel is also a fossil fuel that is refined from crude oil. It does not evaporate easily and is ideally suited for burning in diesel engines.

Fuel efficiency
This is how efficiently a vehicle converts fuel into useful powerforce. The more efficient the engine the more driving force from a measured amount of fuel, which can also mean more miles to the litre. Carbon dioxide (CO₂) is a greenhouse gas and is produced by cars as they burn fuel. The more fuel burned the more CO₂ is produced which contributes to climate change. CO₂ emissions are not currently regulated by the EU but under voluntary agreements vehicle manufacturers in the EU aim to reduce CO₂ emissions from the cars they produce.

Tailpipe emissions
These are emissions that come out of a car's exhaust pipe and are measured when a new car is tested to ensure that it meets the necessary standards needed for sale in the UK or Europe. These emissions are also known as tank-to-wheel emissions.

Particulates or Particulate Matter (PM)
These are the elements of a car's tailpipe emissions that are either solid or liquid droplets. Most particulate matter is solid carbon particles and most is too fine to be detected by the naked eye. Particulates can be harmful to respiratory and cardiac functions.

Emissions testing
A process that involves the testing of a vehicle in laboratory controlled conditions to assess the emissions they produce.

Euro standards
Euro standards are the air quality pollutant emission standards that all new cars have to reach before they can be sold in Europe. These standards have been in place since 1970 but have become more stringent over time. The first Euro standard for cars required petrol engines to be fitted with catalysts and was known as Euro 1. This was followed by Euro 2 then Euro 3. The current Euro standard for cars is now Euro 4. Euro 5 will become compulsory for new cars from 1 January 2011.

Smarter Driving
Smarter Driving is a style of driving that helps the engine burn fuel in the most efficient way and so helps to keep CO₂ emissions to a minimum. An important part of Smarter Driving is looking ahead so you can anticipate the actions of other road users and recognise potential hazards early, so it's also safer driving.

Climate change
Our world is surrounded by a blanket of gases which keeps the surface of the earth warm and able to sustain life. This blanket is getting thicker as we burn fossil fuels which produces greenhouse gases, trapping heat and changing our climate drastically.

Greenhouse gases
This is a term used to refer to a number of gases that form a blanket around the planet. As this blanket thickens it traps in more heat strengthening the 'greenhouse effect'. The most significant greenhouse gas is CO₂.

Carbon dioxide (CO₂)
The most abundant of the greenhouse gases which is released by burning fossil fuels.