# Combustion road vehicles

Cars, trucks and buses burning petrol, diesel, CNG or LPG.

Source page: https://www.materialinsights.org/energy/e_road_ice/

Conversion and use · Transport systems · No. 111

- Conversion and use
- Typical efficiency: About 25-30% (petrol engine)
 Conversion and use · Transport systems · Foundation · Energy

A petrol car wastes about three litres of every four as heat, yet road engines burn a fifth of world energy.

Chart: Illustration: Combustion road vehicles

##### Where it comes from

Chart: Map of where it comes from

Burning fuel in a sealed cylinder pushes a piston, and the crankshaft turns that push into rotation. The more the charge is squeezed first, the more heat becomes work, which is why diesels beat petrol engines.

##### Three things to know

1. An ideal petrol engine at a compression ratio of 13 could reach 64%, but Toyota's best production engine peaks at 40%.
2. In city driving, idling alone wastes about 6% of a car's fuel, which stop-start systems and hybrids remove.
3. Electric trucks made up 9% of global truck sales in 2025, so most freight still runs on diesel.

##### The journey

1. 1 **Fuel tank**Petrol, diesel, CNG or LPG on board
2. 2 **Combustion**Compressed charge burns into hot gas
3. 3 **Pistons**Expanding gas turns the crankshaft
4. 4 **Driveline**Gearbox sends power to the wheels
5. 5 **Exhaust**Catalysts clean gases; most heat escapes

##### Go deeper pick a tab to open it in full

## Other sections

- [Overview](https://www.materialinsights.org/energy/e_road_ice/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_road_ice/correlation/index.md)
- [Science and limits](https://www.materialinsights.org/energy/e_road_ice/science/index.md)
- [Value chain](https://www.materialinsights.org/energy/e_road_ice/valuechain/index.md)
- [Unit economics](https://www.materialinsights.org/energy/e_road_ice/economics/index.md)
- [Engineering methods](https://www.materialinsights.org/energy/e_road_ice/methods/index.md)
- [Equipment and suppliers](https://www.materialinsights.org/energy/e_road_ice/equipment/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_road_ice/links/index.md)