How Does a Marine Fuel System Work?

In a vehicle with a marine diesel engine, the fuel system maintains the quality of fuel through reliance on a fuel pump and a fuel injector. Ideally, the fuel within the engine has high combustion efficiency, which means that the particles of fuel quickly go through atomization, making fuel mix with air in the correct proportion. The engine relies on the proper timing and pressure of fuel injection in order to allow for proper atomization in the combustion chamber. This process relies on two main parts: the fuel pump and the fuel injector.

Fuel pumps function to supply the correct amount of pressure to the fuel injectors, which pump the correct amount of atomized fuel into each cylinder. In marine fuel systems, the most common pumps are the bosch jerk pump and the common rail injection system. The main difference between the two is that the bosch jerk pump system allots a specific pump to each cylinder while in the common rail system, the cylinders share a common pump. The common rail provides a single fuel pressure, while there are constantly varying pressures in the cylinders reliant on the bosch jerk system.

The bosch jerk pump contains a piston, or plunger, attached to a spring within a cylinder resting on a cam profile. A helix on top of the cylinder’s barrel controls the amount of fuel taken into the cylinder. When the plunger moves down, suction and spill ports open to fill up the space with fuel. When the plunger then moves up, pressure builds until the injector fuel discharge valves are open and fuel is injected until the spill ports are no longer covered. The amount of fuel being measured and injection timing can be altered manually with a few adjustments to the pump structure.

The common rail injection system works by maintaining the correct fuel pressure within the rail above the cylinders, and it leaks excessive pressure through a pressure limiter. This method is better for reducing both fuel consumption and pollution, while optimizing combustion. A fuel transfer pump forces the fuel through a pressure regulating valve to ensure the correct pressure in the high pressure common rail. Solenoid valves operated by E.C.U. open and close based on signals from the crank angle sensor, using data such as temperature or engine speed to make adjustments.

While the fuel pumps are pushing and measuring fuel, the fuel injectors aim to insert fuel into the combustion tank at the exact pressure needed. The injector has a body and a nozzle that fit together tightly to prevent oil leakage. Pressure within each cylinder can reach 500 bar, and at the desired pressure, a needle within the cylinder lifts against the tension created by the spring above it and injects fuel to the combustion chamber through the nozzle at the proper pressure.

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1. mitchel stark
2. Posted on April 25, 2022
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