Both gasoline (petrol) and diesel engines are internal combustion engines, but they differ in their ignition system and fuel properties:
1. Ignition System:
* Gasoline Engines: Use spark plugs to ignite the air-fuel mixture. This process is called spark ignition.
* Diesel Engines: Use high compression of air to ignite the fuel. This process is called compression ignition.
2. Fuel Properties:
* Gasoline: More volatile and flammable, igniting easily with a spark.
* Diesel: Less volatile and less flammable, requiring higher pressure and temperature to ignite.
Here's a breakdown of the differences:
| Feature | Gasoline Engine | Diesel Engine |
|---|---|---|
| Ignition System | Spark Ignition | Compression Ignition |
| Fuel | Gasoline (petrol) | Diesel fuel |
| Compression Ratio | Lower (8-12:1) | Higher (14-25:1) |
| Fuel Injection | Typically injected before intake valve | Injected directly into cylinder |
| Operating Temperature | Lower | Higher |
| Efficiency | Lower | Higher |
| Power Output | Higher at lower RPMs | Higher at higher RPMs |
| Noise Level | Quieter | Louder |
| Emissions | Higher emissions of NOx and hydrocarbons | Lower emissions of NOx and hydrocarbons, but higher particulate matter |
| Fuel Economy | Lower | Higher |
| Maintenance | Less demanding | More demanding |
| Cost | Lower initial cost | Higher initial cost |
Why these differences matter:
* Compression Ignition: Diesel engines use the heat generated by compressing air to ignite the fuel, making them more efficient but also requiring a heavier engine structure.
* Fuel Properties: Diesel fuel has a higher cetane number (indicating its ability to ignite quickly under compression), allowing for higher compression ratios and better fuel economy.
* Power Output: Diesel engines produce higher torque at lower RPMs, making them ideal for heavy loads and slow-speed applications.
In summary:
Gasoline engines are more common for passenger cars due to their lower initial cost and smoother operation, while diesel engines are favoured in heavy-duty vehicles, trucks, and some passenger cars due to their higher efficiency and durability.
