Kerosene releases heat when burned, making it useful as a fuel. Its heating value, or heat of combustion, is around 18,500 Btu/lb, or 43.1 MJ/kg, making it similar to that of diesel.
Kerosene is obtained from the fractional distillation of petroleum at 150 °C and 275 °C (carbon chains from the C12 to C15 range).
Typically, kerosene directly distilled from crude oil requires some treatment, either in a Merox unit or a hydrotreater, to reduce its sulfur content and its corrosiveness. Kerosene can also be produced by a hydrocracker, which is used to upgrade the parts of crude oil that would otherwise only be good for fuel oil.
At one time it was widely used in kerosene lamps and lanterns. Now it is mainly used in fuel for jet engines (more technically Avtur, Jet-A, Jet-A1, Jet-B, JP-4, JP-5, JP-7 or JP-8). A form of kerosene known as RP-1 is burned with liquid oxygen as rocket fuel. These fuel grade kerosenes meet specifications as to smoke points and freeze points.
Diesel is produced from petroleum, and is sometimes called petrodiesel when there is a need to distinguish it from diesel obtained from other sources such as biodiesel. It is a hydrocarbon mixture, obtained in the fractional distillation of crude oil between 200 °C and 350 °C at atmospheric pressure.
Petroleum derived diesel is composed of about 75% saturated hydrocarbons (primarily paraffins including n, iso, and cycloparaffins), and 25% aromatic hydrocarbons (including naphthalenes and alkylbenzenes).[5] The average chemical formula for common diesel fuel is C12H26, ranging from approx. C10H22 to C15H32.
The density of diesel is about 850 grams per liter. When burnt, diesel typically releases about 40.9 megajoules (MJ) per liter.
In short, they are similar but are by no means the same. You would not want to run full strength kerosene in your modern diesel engine, it wouldn't last long. However, when used in ratio's of up to about 1/4 kerosene to "cut" diesel fuel it has no real adverse effects.