Exam Question

How Fuel Oil is Injected and Ignited in a Heavy-Oil Two-Stroke Engine
In a heavy-oil two-stroke internal combustion engine, such as a MAN B&W or Sulzer engine , fuel oil (FO) is injected into the cylinder by a fuel injection pump . There is one pump for each cylinder. The pump's plunger (or ram) is driven on its pumping stroke by a cam and returned by a spring. This system works at a constant stroke. The amount of fuel delivered is controlled by varying the point at which the pressure side of the plunger is put into communication with the suction side. When this communication is established, the pressure drops suddenly, and injection stops.
The fuel is then delivered to a fuel injector in the cylinder head. The injector contains a spring-loaded needle valve. When the pressure of the fuel oil overcomes the spring pressure, the needle valve lifts, and fuel is forced through tiny nozzle holes into the cylinder. These holes are designed to create a fine spray pattern, which is crucial for atomization and penetration .
Atomization is the process of breaking the fuel into very fine droplets, increasing their surface area for better mixing with the air. It is directly proportional to the pressure difference between the fuel and the cylinder. The fuel-air mixture auto-ignites due to the high temperature of the air, which has been heated by compression. This is how ignition occurs in a compression-ignition engine; no spark plug is needed.