What is the role of a swirl chamber in the combustion process of a diesel engine?

In a diesel engine, a swirl chamber's primary role is to improve air-fuel mixing and promote more complete combustion. A swirl chamber is a small, separate chamber connected to the main combustion chamber via a narrow passage. During the compression stroke, air is forced through this passage into the swirl chamber, creating a swirling motion of the air within the chamber. Fuel is then injected into this swirling air. The high turbulence created by the swirling air promotes rapid and thorough mixing of the fuel and air. This improved mixing leads to more complete combustion, reducing particulate matter (PM) and unburnt hydrocarbon emissions. The swirl chamber also serves to pre-heat the air-fuel mixture. As the air is compressed into the small swirl chamber, its temperature increases. This higher temperature aids in the vaporization of the fuel, making it easier to ignite and burn. By promoting better mixing and vaporization, the swirl chamber allows for the use of simpler, lower-pressure fuel injection systems. Direct injection systems, in contrast, inject fuel directly into the main combustion chamber and typically require much higher injection pressures to achieve adequate mixing. However, engines with swirl chambers tend to have slightly lower thermal efficiency compared to direct injection engines due to heat losses to the swirl chamber walls. An example is older diesel tractor engines, which often used swirl chambers to achieve acceptable emissions levels with relatively simple injection systems.