Sailing: how does the endothermic engine work?

The engine and propeller provide propulsion for a boat.

The types of engines

The main difference between engines is between two-stroke engines or four-stroke engines. We can also talk about gasoline-powered or diesel-powered engines.

Gasoline engine (internal combustion engine)

The cycle of a four-stroke internal combustion engine can be divided into four stages:

1) Suction

A pump feeds the carburetor where air and gasoline are mixed.

The piston adheres tightly to the inner walls of the cylinder and as it descends into the cylinder it sucks the mixture of air and gasoline out of the intake valve, which is open at this stage.

Meanwhile, the crankshaft controls the valves on the cylinder head.

2) Compression

Once the right amount of air and gasoline mixture is inside the carburetor, the intake valve closes and the piston moves upward compressing the air and gasoline mixture.

At this stage all the valves are closed.

3) Bursting

At this point the spark plug, powered by the electrical system, generates a spark that causes a burst, aided by the fact that the mixture is extremely compressed.

The sudden increase in pressure pushes outward, resulting in a lightning-fast increase in the piston’s kinetic energy.

4) Unloading

When the piston stroke is over, the exhaust valve opens and the residue of the burst is expelled.

A complete cycle of the four-stroke engine involves four piston strokes and two 360° revolutions of the crankshaft.

The two-stroke internal combustion engine

For the two-stroke internal combustion engine, however, there are two stages:

1) closed-valve compression and bursting;

2) exhaust and intake.

Each cycle is completed in two strokes of the piston in one 360° turn of the crankshaft

Diesel engine

The only difference with the internal combustion engine is precisely the absence of the burst, which here is replaced by combustion.

Combustion is generated by glow plugs that are placed diagonally in the cylinder head and heat the air inside the cylinder.

This is precisely why if outside temperatures are low you need to check that the glow plugs are working, in a diesel-powered boat.

Another major difference from the gasoline-powered internal combustion engine is that only air from the intake valve is fed in during the intake phase.

Also, it should be remembered that in the classic Diesel engine, air is fed in by simple intake.

In the Turbodiesel, instead, air is forced into the cylinders by the turbocharger.

Another difference is in the diesel fuel pump: a specific circuit a allows unused diesel fuel from the injectors to return to the tank.

Be careful: diesel fuel has a higher flash point than gasoline and burns at temperatures above 60 degrees.

That is why an aeration system is not mandatory in Diesel engines, unlike gasoline engines.