Why do cars run on gasoline, trucks on diesel, airplanes on kerosene, and ships on heavy fuel oil?
In short: if a specific fuel best meets the operational needs of a particular mode of transport, then it is the most suitable fuel for that vehicle.
Does that sound a bit confusing? Let me break it down for you.
1
Gasoline and Cars
Gasoline is a relatively light petroleum fraction; it has low density, low calorific value, and high volatility. It burns extremely fast compared to heavy oils-think of the difference between igniting gunpowder and lighting a campfire.
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Gasoline engine
As for the engines themselves: compared to those in ships (cruise liners or warships) or aircraft (airliners or fighter jets), the technical specifications required for car engines are quite modest. However, cars demand rapid acceleration and compact engine sizes. High-performance sports cars, for instance, often accelerate from 0 to 100 km/h in under five seconds. Consequently, the engine needs to respond quickly, making gasoline-with its "explosive" burning characteristics-an ideal match for cars.
2
Kerosene and Aircraft
Aviation kerosene is refined through multiple processes from substances like naphtha and paraffinic oils. Compared to gasoline-which distills off earlier in the refining process-kerosene is much more stable; it has low density, high calorific value, and low volatility. Yet, within the unique combustion environment of a turbine engine, it actually burns just as fast as gasoline.
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Five-cylinder radial engine
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Turbofan engine
There are many types of aircraft. Most WWII-era planes used radial internal combustion engines-essentially reciprocating engines-which mostly ran on gasoline. Modern turbine engines only began appearing on aircraft (starting with fighter jets) toward the end of WWII, marking a massive leap in performance.
Gasoline is unsafe for aircraft because it evaporates easily at high altitudes (meaning a hit from enemy fire could cause an explosion). Kerosene, which offers superior performance, is used instead (handling rotational speeds of over 10,000 RPM). Another advantage kerosene has over gasoline is that it is less prone to carbon buildup-a crucial factor for high-precision aircraft engines.
Why not use diesel? It's simple: it burns too slowly (especially in the cold temperatures of high altitudes), which would severely compromise an aircraft's maneuverability. 3
Diesel and Trucks
If gasoline is described as "volatile" and kerosene as "lively," diesel's personality is best described as "steady." It comes in two varieties: light diesel (for cars and trucks) and heavy diesel (for heavy machinery and small-to-medium vessels). Compared to the light version, heavy diesel is denser, has a higher calorific value and ignition point, and is more viscous.
Because of its stable characteristics and ignition properties, diesel can undergo compression ignition without the risk of uncontrolled detonation (knocking). This allows for the design of large combustion chambers-something not feasible with gasoline engines.
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Large diesel engine
For certain ships and heavy industrial machinery, the priority is handling heavy loads rather than rapid acceleration; instead, high power and-crucially-high torque are required. Diesel's high calorific value, combined with the high compression ratio of diesel engines, allows for efficient energy utilization. Although they do not reach high RPMs, they deliver immense power that gasoline engines simply cannot match.
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Light diesel engine
For trucks and some passenger vehicles using light diesel, the lack of a need for rapid acceleration allows the advantages of light diesel engines-such as simpler construction, high reliability, and low fuel consumption-to shine compared to gasoline engines. Additionally, while diesel engines do accumulate carbon deposits, they are relatively insensitive to the negative effects of this buildup; heavy-duty diesel engines, in particular, are barely affected by it.
4
Ships and Heavy Fuel Oil
Heavy fuel oil is the viscous residue left behind after most of the lighter components of crude oil have been distilled off. It is dense and energy-rich-a small bottle's worth can burn for over an hour-though insufficient oxygen causes it to billow black smoke (composed of carbon particles from incomplete combustion).
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Steam turbine
In the past, this type of oil could not be used in internal combustion engines because it was impossible to inject effectively; instead, it was burned directly in boilers to generate steam for driving turbines. With the maturation of technology, however, heavy fuel oil can now be used in the massive two-stroke diesel engines found on commercial ships. These engines operate at low speeds-barely over 100 RPM-but because lower speeds yield higher efficiency, they are far more efficient than the engines used in automobiles. Most importantly, heavy fuel oil is very inexpensive-and it is worth noting that ship fuel consumption is measured in tons. However, engines that burn heavy fuel oil have poor responsiveness; consequently, ships must switch to diesel engines when entering port to handle the frequent acceleration, deceleration, and course changes required.
