How it’s made your boat’s diesel engine

diesel engine


The diesel engine is more common among pleasure boats. Knowing how it works helps you understand how to keep it efficient and prevent breakdowns. And the present is more and more Common Rail even at sea.

The diesel engine, but every engine in general, is the organ within which a transformation of energy is carried out. In this case from thermal to mechanical and is used for propulsion. This energy is generated through a process of combustion inside the cylinders. In diesel engines, the combustion of the fuel takes place through the air (the combustive) that enters a cylinder and is compressed by a piston that increases the temperature. The injectors introduce into the cylinder the diesel fuel which, being in an overheated environment, ignites. Its combustion generates gases that push to restrained the piston activating the transmission organs for propulsion.

Diesel engine is the most common inboard engine

An engine generally consists of four pistons that rise and fall into their respective cylinders. A connecting rod acts as a link between the piston and the engine shaft to allow for rotary movement. A four-stroke 4-cylinder engine then manages the movement of four pistons. The movement of each piston is offset by half a turn with respect to the neighbouring piston. While the first is in the suction phase, the second is in compression, the third in the burst phase and the fourth finally in the phase of discharge. Each piston rotates the shaft by half a turn and two rotations are required to have a complete cycle. The rotary movement thus obtained allows to control the camshaft which in turn controls the intake and exhaust valves that allow the entry of the air necessary for combustion. In this article the combustion cycle a diesel engine.

Diesel engines are equipped with injectors, systems that allow the correct amount of diesel fuel to flow into the cylinder once the air has reached maximum compression and has warmed up to exceed the temperature of flammability of the fuel.

The Common Rail diesel engine

diesel engine common rail


The Common Rail is an injection system that provides a very high fuel pressure inside a single duct (which is translated into English as Common Rail). The difference from traditional systems is the pressure management entrusted to an electronic control unit. It is the heart of the system, it controls the electric pump and allows the pressure of the injection system to be released from the number of engine revolutions, which instead characterises the normal supercharging systems, with the advantage of a constant and optimal pressure at all engine revolutions.

The injectors are electronically controlled and allow highly pulverized fuel injections thanks to the small size of the nozzles. The Common Rail therefore has the ability to adjust the fuel injection even at low rpm, with the direct advantage of a lower noise level, and especially with a low fuel consumption.

The Common Rail system in its structure. The high pressure injection pump is controlled by an electronic control unit and allows to regulate the flow of diesel fuel sent to the injectors for combustion.



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