Why Jet Planes Use Kerosene: A Comprehensive Guide
In the world of aviation, jet planes are powered by kerosene rather than gasoline. This choice is driven by several factors, including cost, volatility, and the extreme temperatures experienced at high altitudes. Let's delve into the reasons why kerosene is the preferred fuel for jet engines.
The Cost-Effective Advantage of Kerosene
One of the primary reasons jet planes use kerosene over gasoline is cost. Kerosene is generally cheaper to produce and purchase, making it a more economical choice for airlines. Although kerosene is more refined, it is still shunned by the mass consumer market, which is why it isn't readily available at the pump. However, this refined nature is a valuable trait for aviation purposes, as it ensures cleaner operation and reduces odors, making jet planes far less obnoxious than they might otherwise be.
Volatility and Temperature Considerations
Another crucial factor in jet fuel selection is volatility. Kerosene's high vapor point and low freezing point make it ideal for aviation purposes, especially during extended flights at high altitudes. The lower stratosphere, where most jet planes fly, experiences temperatures that can drop to as low as -60°C (-51°F) or even -80°C (-112°F) at the tropopause. This severe cold would cause gasoline to freeze, disrupting fuel flow and engine performance.
Case Study: The Concorde and Fuel Management
The Concorde, a supersonic airliner, demonstrated sophisticated fuel management techniques. During takeoff and acceleration, the SST would "cold-soak" its fuel load, warming the fuel through the kinetic energy generated. This process would distribute the heat from the cockpit and other heated parts to the fuel tanks in the wings. This strategy maintained the fuel's flowability and prevented the fuel from freezing, ensuring consistent performance throughout the flight.
Why Not Diesel or Other Fuels?
While diesel and other oils like heating oil also have high energy content per pound, they are not suitable for jet engines due to their high viscosity. Specifically, diesel fuel can become very thick, like maple syrup, even at a moderate temperature of -5°F. As altitude increases, the temperature drops, and by 35,000 feet (the typical cruising altitude for commercial jets), the temperature can drop to temperatures where diesel fuel would solidify, rendering it useless for fuel lines. This is where kerosene excels.
Practical Solutions: Kerosene and Additives
Despite the potential issues with kerosene, modern aviation has developed solutions. A key additive used in jet fuel is prist, which helps lower the pour point of the fuel, allowing it to flow more freely in the harsh conditions encountered during high-altitude flights. This additive is crucial in maintaining the efficiency and reliability of jet engines.
Conclusion
In summary, the choice of kerosene as the primary fuel for jet planes is a result of a combination of cost, structural properties, and environmental considerations. While gasoline has its advantages, the need for a cost-effective, heat-resistant, and fluid fuel for high-altitude flight drives the preference for kerosene. The development of additives and advanced fuel management systems ensures that jet planes can operate efficiently and safely under extreme conditions.
For further reading, explore the importance of fuel in aviation, the differences between diesel and kerosene, and the future of sustainable aviation fuels.