Both kerosene and diesel fuel are refined petroleum distillates derived from crude oil. They are widely used globally as sources of heat and power, from home furnaces and lamps to industrial engines and jet aircraft. Determining which fuel burns “hotter” is complex, depending on the fuel’s theoretical energy content versus its performance in a specific, real-world application. A comparison of their chemical composition, combustion properties, and application is necessary to understand how each fuel delivers thermal energy.
Defining the Contenders: Composition and Refinement
The fundamental difference between kerosene and diesel lies in the length of their hydrocarbon chains, which are separated during the refining process. Crude oil is heated in a distillation column, and products condense at different temperature levels based on their boiling points. Kerosene, the lighter and more refined fuel, is extracted first, typically between 150°C and 275°C.
Kerosene molecules have carbon chains generally in the C9 to C16 range, and the resulting liquid is clear and less viscous. Diesel fuel (No. 2 distillate) is pulled at a higher temperature range, usually between 200°C and 350°C. This fraction contains longer, heavier chains (C10 to C22), giving diesel higher viscosity and an oilier consistency. The shorter, more uniform chains in kerosene allow it to burn cleaner, reducing soot and deposits in heating systems.
Key Combustion Properties: Flash Point and Energy Density
The two most important metrics for determining a fuel’s burning characteristics are its flash point and energy density. Flash point is the lowest temperature at which a liquid produces enough vapor to form an ignitable mixture with air near its surface. Kerosene typically has a flash point of about 38°C (100°F), placing it near the boundary between flammable and combustible liquids.
Diesel fuel, with its longer, heavier molecules, is less volatile and has a much higher flash point, generally ranging from 52°C to 96°C (126°F to 205°F). This difference means kerosene is much more likely to release ignitable vapors at typical room temperature than diesel.
Regarding energy density, both fuels have a very similar heat of combustion by mass, releasing approximately 43 megajoules of energy per kilogram. However, because diesel is slightly denser than kerosene, a volume of diesel holds a greater mass of fuel molecules. This results in diesel having a marginally higher energy density per unit of volume, theoretically releasing slightly more total heat than an equivalent volume of kerosene.
Combustion Efficiency and Heat Output in Practical Use
The practical heat output, or how “hot” the fuel burns, depends heavily on the device used and its efficiency in achieving complete combustion. In atmospheric burners, such as certain home heating systems or lamps, kerosene’s cleaner composition minimizes soot production. This leads to less fouling of the equipment, allowing the appliance to operate at a higher, more consistent thermal efficiency over time.
Kerosene, often used as jet fuel, is designed for clean, high-temperature, and continuous combustion in gas turbine engines. Its properties allow for superior atomization and mixing with air, which maximizes heat release.
Diesel is engineered for compression-ignition engines, where its combustion is triggered by heat generated from high compression. While kerosene can be used in a diesel engine, its lower density and lubricity can result in a measurable decrease in engine power and efficiency compared to standard diesel fuel.
Safety and Storage Considerations
The difference in flash points dictates the safety and regulatory classifications for handling and storing the two fuels. Kerosene’s flash point of 38°C means it is classified as a combustible liquid but is much closer to the threshold for a highly flammable liquid. Consequently, it requires careful handling to prevent the accidental ignition of its vapors, which are more readily produced at ambient temperatures.
Diesel’s higher flash point, well above 52°C, classifies it as a combustible liquid that poses a lower fire hazard under normal storage conditions. This property is why a lit match dropped into a pool of diesel will often extinguish itself, whereas a similar action with kerosene could lead to ignition. Due to kerosene’s increased volatility, specific regulatory guidelines often require its storage in clearly identifiable containers to prevent accidental mixing or misuse.