Let’s go in detail about petrol used in automobiles:
In this article:
1. Definition of Petrol
Petrol, also called gasoline, is a flammable liquid fuel derived from crude oil.
- It is specifically refined for internal combustion engines (ICE) in cars, motorcycles, and light vehicles.
- Petrol is composed mainly of hydrocarbons—alkanes, cycloalkanes, and aromatic compounds.
2. Purpose of Petrol in Automobiles
- Energy Source for Engines:
- Provides chemical energy, which is converted into mechanical energy by combustion in the engine cylinder.
- Enables Vehicle Mobility:
- Powers the engine to rotate the crankshaft, which moves the wheels.
- Supports Engine Efficiency and Performance:
- Proper combustion ensures smooth acceleration, high speed, and fuel economy.
3. Composition of Petrol
| Component | Typical Hydrocarbon Type | Purpose |
|---|---|---|
| Alkanes | C5–C12 straight/branched | Burns easily, high energy content |
| Cycloalkanes | Cyclopentane, Cyclohexane | Stable combustion, reduces knocking |
| Aromatics | Benzene, Toluene, Xylene | Boosts octane rating, anti-knock properties |
| Additives | Detergents, anti-oxidants | Prevent engine deposits, improve performance |
Properties of Petrol:
- Color: Usually colorless to pale yellow
- Density: ~0.71–0.77 g/cm³
- Boiling point: ~40–205°C
- Octane rating: 87–100+ (depends on grade)
- Energy content: ~44 MJ/kg
4. Grades of Petrol
| Grade | Octane Rating | Use |
|---|---|---|
| Regular | 87–91 | Standard passenger cars |
| Premium | 91–95 | High-compression engines, turbocharged vehicles |
| Super Premium | 95–100+ | Sports cars, high-performance engines |
| Racing / Specialized | 100+ | Motorsports, track vehicles |
Octane rating indicates resistance to engine knocking (pre-ignition) under high compression.
5. How Petrol Works in an Automobile Engine
- Fuel Delivery: Petrol is injected into the intake manifold or cylinder via a carburetor or fuel injector.
- Air-Fuel Mixture: Petrol mixes with air to form a combustible mixture.
- Ignition: Spark plug ignites the mixture at the right moment.
- Combustion: Burns rapidly, producing high-pressure gases that push the piston down.
- Mechanical Work: Piston movement turns the crankshaft → powers wheels.
6. Advantages of Petrol for Cars
- High Energy Density: Provides sufficient power for acceleration and high speed.
- Smooth Combustion: Minimal vibration in spark-ignition engines.
- Widely Available: Infrastructure exists globally.
- Easy Handling and Storage: Less viscous than diesel, ignites easily.
7. Disadvantages of Petrol
- Lower Torque at Low RPM: Compared to diesel engines.
- Volatile and Flammable: High risk of fire if mishandled.
- Pollutant Emissions: Produces CO, NOx, and unburned hydrocarbons.
8. Petrol vs Diesel
| Feature | Petrol | Diesel |
|---|---|---|
| Engine Type | Spark-ignition | Compression-ignition |
| Ignition Method | Spark plug | Compression of air |
| Energy Density | High | Slightly higher per liter |
| Torque | Moderate | High |
| Efficiency | Moderate | Higher fuel efficiency |
| Emissions | CO, HC | NOx, soot |
| Cost | Usually higher per liter | Usually lower per liter |
✅ Summary
- Petrol (gasoline) is a light, volatile hydrocarbon fuel for spark-ignition engines.
- Purpose: Powers the engine, provides mobility, and ensures performance.
- Grades: Regular, Premium, Super Premium, Racing (octane 87–100+).
- Advantages: High energy, smooth combustion, easy handling.
- Disadvantages: Volatile, flammable, moderate efficiency, pollutant emissions.
💡 Tip:
- Using the recommended octane rating is critical. Low-octane petrol in a high-compression engine can cause knocking, reducing performance and damaging the engine.
Other courses:
