There are a few key reasons why cars do not use jet fuel like airplanes do. While jet fuel and gasoline may seem similar since they both power transportation vehicles, there are some important differences that make jet fuel impractical for use in cars.
What is Jet Fuel?
Jet fuel refers to the specialized kerosene-based fuels used to power jet engines on aircrafts. There are several different types and grades of jet fuel, but they all have certain properties in common:
- High energy density – Jet fuels contain a large amount of energy per unit volume, which is important for powering aircraft over long distances.
- Low freezing point – Jet fuels do not freeze at the very cold temperatures encountered at high altitudes, allowing them to flow and be burned properly.
- Optimized thermal stability – Jet fuels are designed to withstand the high temperatures found within jet engines for extended periods of time without breaking down.
- Low volatility – Jet fuels evaporate much more slowly than other fuels like gasoline, which is important in aircraft fuel systems.
The most common types of jet fuel used today are Jet A and Jet A-1. They have very similar properties and are suitable for powering both civilian and military jet aircrafts. Jet fuel is precisely refined and tested to meet stringent technical specifications for use at altitude.
What is Gasoline?
Gasoline is the ubiquitous fuel used for powering automobiles, motorcycles, boats, small engines like lawn mowers, and some aircraft. Gasoline is sometimes shortened to gas. Compared to jet fuel, gasoline has some different key properties:
- Lower energy density – Contains less potential energy per gallon than jet fuel.
- More volatile – Gasoline evaporates relatively easily, which is important for use in spark-ignition engines.
- Varies seasonally – The composition of gasoline is adjusted seasonally to control evaporation and burn properties in different weather conditions.
- Contains additives – Gasoline contains additives like detergents to keep engines clean and reduce build-up.
- Lower combustion temperature – Gasoline is designed to burn at lower temperatures than jet fuel for engine longevity.
The most common types of automotive gasoline are 87 (regular), 89 (midgrade) and 93 (premium), indicating the octane rating. Higher octane gasolines provide improved anti-knock properties.
Key Differences Between Jet Fuel and Gasoline
While they are both petroleum-based fuels, jet fuel and gasoline are engineered with quite different properties and considerations in mind. Here are some of the key differences:
| Property | Jet Fuel | Gasoline |
|---|---|---|
| Energy density | Higher | Lower |
| Freezing point | Very low | Higher |
| Boiling point | Higher | Lower |
| Thermal stability | Excellent | Lower |
| Volatility | Low | Higher |
| Combustion temperature | Very high | Lower |
This table summarizes how jet fuel is engineered to have a higher energy density to maximize range, low freezing point for high altitude use, higher boiling point and thermal stability for hot turbine engines, and low volatility for fuel systems. Gasoline is designed very differently for automotive use, with lower energy density, higher volatility for ease of vaporization, lower combustion temperatures, and additives like detergents.
Why Cars Don’t Use Jet Fuel
Based on the major differences between jet fuel and gasoline, there are a few key reasons why cars cannot use jet fuel:
- Energy density – Jet fuel’s higher energy density would provide excess performance in cars that is not needed. It would be an unnecessary waste to use such a potent fuel.
- Freezing point – The very low freezing point of jet fuel is not needed for automotive use and could actually cause problems in cold weather.
- Boiling point – With a much higher boiling point, jet fuel does not vaporize as easily as gasoline. This would cause issues for the spark-ignition engines used in cars.
- Thermal stability – Gasoline engines do not reach the extreme temperatures of jet turbine engines, so the thermal stability of jet fuel is excessive.
- Volatility – Jet fuel’s lower volatility makes vaporization difficult in a car engine without fuel injection. Gasoline’s higher volatility is desirable for mixing of the fuel-air charge.
- Combustion temperature – The high combustion temperatures of jet fuel could damage automotive engine components over time, reducing engine life.
- Additives – Jet fuel lacks the detergent additives present in gasoline to help keep fuel systems clean.
- Cost – Jet fuel has historically cost approximately 50-100% more than automotive gasoline, making it uneconomical for routine use in cars.
In summary, the technical requirements for an aircraft operating at altitude are so different from a passenger car that their respective fuels have evolved quite differently over decades of engineering. Using jet fuel in automobiles would offer no benefits, and would come with several disadvantages and drawbacks. Modern gasoline has been extensively optimized for the operating conditions found in reciprocating engines used in cars and trucks.
Rare Exceptions
While jet fuel is generally not used in cars, there are a couple rare exceptions worth noting:
- Some high performance sports cars with racing heritage and very high compression ratios recommend using higher octane jet fuel instead of premium gasoline for maximum performance. Examples include the Aston Martin Vulcan.
- Certain modified diesel pickup trucks and tractors can safely combust jet fuel in their engines without issue. This is sometimes done in remote areas when gasoline is not available.
- Jet fuel may be used as an emergency fuel in gasoline cars when gasoline supplies are severely disrupted, such as during natural disasters and wars. But long-term use can damage engines.
However, for the vast majority of passenger cars and light trucks on the road today, jet fuel is simply not the proper fuel for regular use. Only gasoline engineered to rigorous automotive specifications should be used.
Can Gasoline Be Used in Airplanes?
Just as jet fuel is generally incompatible with automobiles, the reverse is also true – gasoline is typically not a suitable fuel for aircraft jet engines. There are a few primary reasons:
- Lower energy density provides less range for the airplane.
- Higher freezing point can cause issues at high altitudes.
- Lower thermal stability and boiling point affects engine performance.
- Higher volatility increases risk of vapor lock in fuel system.
- Knock resistance properties are not optimized for turbojets.
Gasoline is sometimes used in small piston engine airplanes with spark ignition engines, however. And in emergency situations, gasoline has been used in jet engines but with less than optimal performance. Like cars using jet fuel, it is not recommended except for very rare circumstances.
Future Fuels
As research continues to develop new fuel sources that can provide energy security as well as environmental benefits, there is interest in alternatives to petroleum-based fuels. Some future fuels that could potentially be used in both jet aircraft and automobiles include:
- Biofuels – Renewable fuels like sustainably-sourced biofuels can reduce lifecycle carbon emissions.
- Hydrogen – Hydrogen fuel cells may power electric aircraft and hydrogen internal combustion engines.
- E-fuels – Synthetic electrofuels offer carbon neutral potential.
- Liquified natural gas – An interim option cleaner than jet fuel and gasoline.
With further development, these new fuels could optimize energy density, thermal stability, engine performance, and emissions properties for both aerospace and ground transportation applications. But until then, jet fuel will continue powering aircraft while gasoline dominates the automotive sector due to their specialized properties.
Conclusion
In summary, jet fuel and gasoline have evolved quite differently over the past century to meet the vastly different engineering requirements of jet aircraft versus passenger vehicles. Jet fuel is specially formulated for high altitude use in hot turbine engines and lacks the volatility and additives desired in car engines. Gasoline is designed for optimal vaporization, emissions, and durability in spark ignition reciprocating engines. While there are a few niche cases where jet fuel can be used in automobiles, and vice versa, these fuels have specialized properties incompatible with switching applications in most transportation sectors. As future fuels emerge, we may eventually see new options viable for both jets and cars.
