Fuel Injectors Cooled by Recirculation
These fuel injectors are the preferred type for use in the modern marine diesel engine, that along with common rail fuel supply and engine management systems add to the engines efficiency.
This modern injector does not have any of the normal cooling water passages to keep it cool. Instead it relies on the recirculation of the HFO to maintain injector temperature, along with the cylinder head cooling water that passes close to the injector pocket..
The cylinder head design is modified to accommodate numerous cooling water drillings around the fuel injector’s pocket and this assists in the cooling of the injector body.
So these two methods combine to keep the injector cool without the use of an external fuel valve cooling system. The resulting reduction in power through not using this system improves the engine efficiency.
The injector itself consists of a steel body and nozzle, the nozzle containing the needle valve, its seat and atomizer holes; the body containing the spring and actuating rod.
Instead of the usual drillings in the injector body to direct the HFO to the nozzle chamber, there are two chambers; an upper and lower one. The upper chamber is continuously supplied with HFO when the fuel pump cam is at the bottom of its stroke, in this stage the fuel in this chamber is constantly recirculated.
When the cam in the fuel pumps rotates to the top, the increase in pressure from the fuel pump operates a relief valve, supplying high pressure fuel from the upper chamber to the lower chamber. The high pressure fuel acts on the shoulder of the needle valve lifting it and injecting atomized fuel through the nozzle holes into the combustion chamber.
A simplified flow diagram of a typical recirculating oil cooled fuel injector is shown below.