Engine room ventilation

[Magnus W]

From a more practical viewpoint I've found that the recommended (by the manufacturer, in my case Volvo) intake areas are quite excessive and in many cases never met by the boat builder. Another example is from my own fleet where the engine compartment has no intake at all aside from natural leaks. Although clearly a bad design there are no other easily determinable gains when running with the engine room hatch open than a 3 degree C lower indicated engine temperature.

Also, especially in boats with small engine compartments somewhere deep down in the hull (such as many sailboats), there can be a distinct benefit in reducing the intake area and thus increasing the intake air velocity.
This airflow can be directed and used to cool certain items in the engine compartment such as the alternator which in many sailboats run at a high load during few running hours (charging the often large battery bank).

 

[Magnus W]

And a comment on the simulation. I would recommend that the air inlet is positioned higher. Consider a situation with lots of water in the bilge (due to some kind of severe problem) where the engine might suffocate at the worst possible time.
Myself I wouldn't want a design that could lead to an earlier loss of propulsion than absolutely necessary and most diesels (even modern ones) will run completely submerged as long as the intake (and fancy computers) stay in the dry.

 

[an2reir]

Hi Magnus,
thank you ( and all others who were answering my thread);
your messages are being given thought and consideration.
My CFD air flow simulation was done in Solidworks FloExpress that is just a basic Solidworks simulation ; only giving the velocity of the flow at various points on the flow trajectory. There is an inlet that is positioned low on the CAD model but that is a simplification I did for the ease of modeling the CAD model and the Solidworks Flow simulation. In the real engine room the inlet comes via pipes that are routed from the upper part of the engine room with the opening to the lower part of the engine room. There is as well an outlet where the exhaust blower is.
The simulation may be of use by the fact that it does give the velocity of the fluid at the inlet.
The Venturi effect says: in fluid dynamics a fluid's velocity must increase as it passes through a constriction in accord with the principle of the mass continuity, while its static pressure must decrease in accordance with the principle of conservation of mechanical energy. BY measuring the change in pressure the flow rate may be determined ; using Bernoulli's equation for incompressible fluids . By knowing the change in flow rate the pressure may be determined.

 

[gonzo]

It is a bit more complicated for compressible fluids