Petrol vs. Diesel: What's the Difference?
Read the comparison below, or explore it visually. Create a visual lesson comparing petrol and diesel using available credits or plan allowance.
A petrol engine mixes fuel with air and ignites it with a spark plug, while a diesel engine squeezes air so hard that it becomes hot enough to ignite fuel sprayed into it, with no spark needed. Diesel's higher compression and denser fuel give better fuel economy and strong pulling power at low speed, which is why trucks, buses and tractors usually run on diesel.
At a glance
| Petrol | Diesel | |
|---|---|---|
| Ignition | Spark plug ignites a fuel-air mixture | Heat of compressed air ignites injected fuel |
| Compression ratio | Lower, roughly 8:1 to 12:1 | Higher, roughly 14:1 to 22:1 |
| Fuel properties | Light, volatile, rated by octane number | Heavier, oily, rated by cetane number |
| Efficiency and torque | Less efficient, revs higher | More efficient, more torque at low revs |
| Main pollutants | Carbon monoxide, hydrocarbons | More nitrogen oxides and soot particles |
Which should you use?
Petrol suits light vehicles that travel short distances and rev freely, such as the scooters and motorcycles that fill Indian city streets, which are cheaper and quieter as petrol machines.
Diesel suits heavy loads and long distances, such as trucks, buses, tractors, generators and trains on non-electrified lines, where its fuel economy and low-speed pulling power pay off.