Major advantages

Diesel engines have several advantages over other internal combustion engines:

They burn less fuel than a petrol engine performing the same work, due to the engine's higher temperature of combustion and greater expansion ratio.[1] Gasoline engines are typically 30% efficient while diesel engines can convert over 45% of the fuel energy into mechanical energy[44] (see Carnot cycle for further explanation).
They have no high voltage electrical ignition system, resulting in high reliability and easy adaptation to damp environments. The absence of coils, spark plug wires, etc., also eliminates a source of radio frequency emissions which can interfere with navigation and communication equipment, which is especially important in marine and aircraft applications, and for preventing interference with radio telescopes.
The longevity of a diesel engine is generally about twice that of a petrol engine[45] [46] due to the increased strength of parts used. Diesel fuel has better lubrication properties than petrol as well. Indeed, in unit injectors, the fuel is employed for three distinct purposes: injector lubrication, injector cooling and injection for combustion.