What is the difference between direct injection and precombustion-chamber injection in diesel engines?

In a diesel engine, the primary difference between direct injection and precombustion-chamber injection lies in where the fuel is introduced relative to the main cylinder space.

• Direct Injection: Fuel is sprayed directly into the main piston-cylinder combustion chamber. This method is used by the vast majority of diesel engines, with the exception of some small, high-speed systems. Because the fuel and air are not premixed, this design places significant emphasis on the injector nozzle design to ensure rapid vaporization and thorough mixing of the fuel within the compressed air.1
• Precombustion-Chamber Injection: Fuel is introduced into a separate, smaller chamber that is connected to the main cylinder. This design is typically reserved for specific applications, such as certain small, high-speed engines.1

Regardless of the injection method, the diesel engine relies on the heat generated by compressing air to ignite the fuel spontaneously, as the combustion process is heterogeneous and requires efficient mixing to ensure complete burning.12