Kerosene and diesel are both common liquid fuels derived from petroleum, a naturally occurring fossil fuel formed over millions of years from decaying organic matter. These hydrocarbon mixtures are separated from crude oil through a process called fractional distillation. While both serve as important energy sources, a common question arises regarding their burning characteristics, specifically which one burns hotter. Understanding the differences between these fuels involves examining their energy content, chemical makeup, and practical applications.
Comparing Heat Release
The heat of combustion, or calorific value, quantifies the energy liberated during complete burning. Diesel generally releases more heat per unit of mass or volume than kerosene. For instance, diesel fuel typically has a calorific value ranging from 42 to 46 megajoules per kilogram (MJ/kg), with some values reported around 45.6 MJ/kg. Kerosene usually falls in a range of approximately 43.1 to 46.2 MJ/kg.
The slightly higher energy density of diesel means it contains more potential energy. While the overall energy content is a primary factor for a “hotter burn,” the actual flame temperature can also be influenced by factors such as the efficiency of combustion and the air-fuel mixture during burning. Considering the inherent energy, diesel typically offers a greater energy yield upon complete combustion.
Underlying Chemical Differences
The variations in heat release stem from the distinct chemical compositions of kerosene and diesel. Both are complex mixtures of hydrocarbons, but they differ in the average length of their carbon chains. Kerosene is composed of lighter hydrocarbon chains, typically containing between 9 and 16 carbon atoms per molecule (C9-C16). Diesel, by contrast, consists of longer and heavier hydrocarbon chains, commonly ranging from 10 to 22 carbon atoms per molecule (C10-C22). Longer carbon chains generally contain more chemical bonds, which translates to a higher energy content.
These chemical differences also influence other burning characteristics, such as flash point and autoignition temperature. The flash point is the lowest temperature at which a liquid produces enough flammable vapors to ignite. Kerosene typically has a flash point ranging from 38°C to 72°C (100°F to 162°F). Diesel generally has a higher flash point, often above 52°C and potentially up to 100°C (126°F to 212°F).
The autoignition temperature is the lowest temperature at which a substance will spontaneously ignite. Kerosene’s autoignition temperature is around 220°C to 295°C (428°F to 563°F), while diesel’s is similar, ranging from approximately 210°C to 280°C (410°F to 536°F).
Practical Considerations and Uses
The differing burning characteristics of kerosene and diesel lead to their distinct practical applications and safety considerations. Kerosene’s properties, including its cleaner and more consistent burn, make it suitable for various uses. It is a common fuel for lamps and some heating applications, especially in less developed regions. Refined kerosene, known as jet fuel (Jet A/A-1), is also the primary power source for most aircraft engines due to its stable properties at high altitudes.
Diesel’s higher energy content makes it an optimal fuel for compression-ignition engines. These engines, found in trucks, buses, trains, and heavy machinery, rely on the fuel’s ability to ignite under high compression. Diesel fuel is also utilized for heavier heating oils and as a backup power source in generators.
Regarding safety, the flash points of these fuels are particularly relevant. Kerosene’s generally lower flash point means it can produce ignitable vapors at lower ambient temperatures, which can necessitate careful handling and storage. Diesel, with its higher flash point, is considered less volatile than fuels like gasoline and safer to store and handle. When combustion is incomplete, diesel, being a heavier fuel, tends to produce more soot compared to kerosene.