Overview
Gasoline (petrol) is a refined petroleum product consisting of a mixture of hydrocarbons (predominantly C₄-C₁₂, boiling range ~30-200°C) optimized for spark-ignition internal combustion engines. It is one of the most widely handled flammable liquids in the world. Density, volatility (Reid vapor pressure), and octane rating are the primary engineering properties.
Physical Properties
| Property | Value (typical, 20°C) |
|---|---|
| Density | 720-780 kg/m³ (average 750 kg/m³) |
| Density (summer blend) | ~760 kg/m³ (heavier components) |
| Density (winter blend) | ~740 kg/m³ (more volatile for cold starts) |
| Dynamic Viscosity | ~0.6 × 10⁻³ Pa·s (0.6 cP — less viscous than water) |
| Kinematic Viscosity | ~0.8 cSt |
| Specific Heat | 2200 J/kg·K |
| Thermal Conductivity | 0.13 W/m·K |
| Boiling Range | 30-200°C |
| Flash Point | -43°C (-45°F) — extremely flammable |
| Autoignition Temperature | ~280°C |
| Reid Vapor Pressure (RVP) | 7-15 psi (seasonal) |
| Octane Rating (AKI/RON) | 87-93 AKI (91-98 RON) |
| Lower Heating Value | 44 MJ/kg |
Volatility Classes (Reid Vapor Pressure)
RVP is a key specification controlling gasoline volatility, regulated seasonally and geographically:
| Class | RVP (psi) | Season | Purpose |
|---|---|---|---|
| Summer blend | 7.0-9.0 | Hot months | Minimize evaporative emissions, prevent vapor lock |
| Transition | 9.0-11.5 | Spring/fall | Moderate conditions |
| Winter blend | 11.5-15.0 | Cold months | Good cold start, easy vaporization |
Octane Rating
Octane rating measures resistance to engine knock (auto-ignition under compression):
- AKI (Anti-Knock Index): U.S. pump rating, (RON+MON)/2 — typically 87 regular, 89 mid, 93 premium
- RON (Research Octane Number): Europe/Asia rating — typically 91, 95, 98
- Higher octane allows higher compression ratios (more power/efficiency) but does not contain more energy per liter
Energy Content
Gasoline energy is ~44 MJ/kg, which is ~34 MJ/liter due to density of 750 kg/m³. Diesel has similar energy per kilogram but ~12% more per liter due to higher density.
Engineering Applications
Storage & Handling
- Underground/above-ground storage tanks (UST/AST) at gasoline stations — typically double-wall fiberglass/steel
- Vapor recovery systems mandatory in most jurisdictions (Stage I/II) to capture VOC emissions
- Hydrostatic pressure in tanks: ~7.5 kPa per meter depth (vs 10 kPa/m for water)
- Tank material compatibility: steel, HDPE, fiberglass (NOT natural rubber, certain plastics)
Fuel Dispensing
- Submersible turbine pumps or suction pumps dispense at ~0.2-0.5 MPa
- Metered delivery to 0.5% accuracy (legal metrology requirements)
- Vapor recovery nozzles for emissions control
Pipeline & Transport
- Batched in multi-product pipelines (between diesel and jet fuel, separated by interface)
- Lower density means pump power is 25% less than water for equivalent flow
- Centrifugal pump performance unaffected by gasoline viscosity (much less viscous than crude oil)
- Pipeline leak detection: gasoline floats and spreads rapidly
Environmental Considerations
- LUST (Leaking Underground Storage Tanks) historically major groundwater contamination source
- MTBE phased out as oxygenate; replaced by ethanol (E10, E85)
- Ethanol-blended gasoline behaves differently — phase separation with water, different material compatibility
Summary
Gasoline (density ~750 kg/m³) is the lightest common refined fuel, highly volatile and flammable. Its low density reduces pump power requirements compared to water or diesel, but its extreme flammability (flash point -43°C) governs all storage, dispensing, and transport design. Seasonal RVP and density variations (winter/summer blends) affect both engine performance and storage tank design.
Gasoline Density vs Temperature
| Temperature (°C) | Density (kg/m³) | Notes |
|---|---|---|
| 0 | 752 | Winter blend, denser |
| 5 | 749 | |
| 10 | 746 | |
| 15 | 743 | Reference temperature |
| 20 | 740 | Standard measurement |
| 25 | 737 | Summer blend |
| 30 | 734 | Hot climate |
| 40 | 728 |
Gasoline density decreases by approximately 0.65 kg/m³ per °C — slightly less temperature-sensitive than diesel.
Gasoline vs Diesel vs Jet Fuel Comparison
| Property | Gasoline | Diesel | Jet A-1 |
|---|---|---|---|
| Density (15°C) | 715-770 kg/m³ | 820-845 kg/m³ | 775-840 kg/m³ |
| Flash Point | -43°C | >52°C | >38°C |
| Auto-ignition | ~280°C (spark) | ~210°C (compression) | ~210°C |
| Energy per liter | 32 MJ/L | 36 MJ/L | 34.8 MJ/L |
| Octane/Cetane | RON 91-98 | CN 40-55 | — |
| Viscosity (40°C) | 0.5-0.8 cSt | 2-4.5 cSt | 1.2-1.7 cSt |
Gasoline Weight Calculation
Example: 1000 liters of gasoline at 20°C:
- W = 1.0 m3 x 740 kg/m3 = 740 kg
- Compare: 1000 liters diesel = 840 kg (gasoline is ~12% lighter)
- Compare: 1000 liters water = 1000 kg (gasoline floats on water)
Gasoline Grades and Octane Ratings
| Grade | RON | AKI (US) | Use |
|---|---|---|---|
| Regular | 91 | 87 | Most passenger cars |
| Mid-grade | 93 | 89 | Some turbocharged engines |
| Premium | 95-97 | 91-93 | Performance engines |
| Racing fuel | 100+ | 93+ | Motorsport, aviation |
| E10 (10% ethanol) | 91-93 | 87-89 | Standard in many countries |
| E85 (85% ethanol) | 100+ | 94+ | Flex-fuel vehicles |
Higher octane resists knocking (pre-ignition) but does not inherently produce more energy — it allows higher compression ratios which improve efficiency.
Engineering Applications
Storage and Handling
- Underground storage tanks (UST): double-wall FRP or steel with leak detection
- Above-ground tanks: must meet fire codes (NFPA 30), minimum separation distances
- Vapor recovery systems (Stage I: tank filling, Stage II: vehicle refueling)
- Reid Vapor Pressure (RVP): summer max 7.0-9.0 psi, winter max 13.5-15.0 psi
Pipeline Transport
- Density 740 kg/m3 means pump power is 26% less than water at same head/flow
- Low viscosity (0.5-0.8 cSt) means minimal friction losses
- Batched with jet fuel and diesel in multi-product pipelines
Fire Safety
- Flash point -43°C means gasoline is extremely flammable at all ambient temperatures
- Area classification: Zone 0/1/2 (vapor-air mixture may be present)
- Explosion-proof equipment required within classified zones
- Minimum ignition energy: 0.25 mJ (very low — static sparks can ignite)
Related Engineering Tools
- Diesel Density & Properties — Compare with diesel fuel
- Fluid Density Calculator — Calculate any fluid density
- Tank Volume Calculator — Fuel storage tank sizing
- Pump Power Calculator — Fuel pumping requirements
- Heat Transfer Calculator — Fuel heating/cooling
Frequently Asked Questions
What is the density of gasoline? Gasoline density at 15°C ranges from 715 to 770 kg/m3, with a typical value of approximately 743 kg/m3. This is about 10-12% lighter than diesel (820-845 kg/m3) and 25% lighter than water.
How much does 1 liter of gasoline weigh? One liter of gasoline at 20°C weighs approximately 0.74 kg (740 grams). This is lighter than water (1.0 kg/L) and lighter than diesel (~0.84 kg/L).
What is the specific gravity of gasoline? Specific gravity (SG) of gasoline at 15°C is approximately 0.74 (relative to water at 4°C). API gravity is approximately 59-65 degrees.
What is the flash point of gasoline? Gasoline flash point is approximately -43°C, meaning it is extremely flammable at all normal ambient temperatures. This is vastly different from diesel (flash point >52°C), which is classified as combustible rather than flammable.
How does ethanol affect gasoline density? Adding ethanol increases density slightly. E10 (10% ethanol) has density approximately 745-750 kg/m3 vs 715-740 for pure gasoline. E85 (85% ethanol) has density approximately 775-785 kg/m3.