Ship Diesel Engine: Intake Manifold Modification - Question

I would like to ask a question here, which has unfortunately received very different answers from the various engine technicians I have consulted so far.

I have a very old BUKH DV20 ME diesel engine in our boat. It's a 2-cylinder pre-combustion engine that actually runs very smoothly because it's equipped with various counterweights.
Unlike many modern engines, this motor doesn't produce any smoke, fumes, or unpleasant smells. At most, it might emit a puff of black smoke during extreme load changes, but that's all. And it starts up immediately even in the coldest winter, despite the fact that this engine type doesn't even have glow plugs. But that's probably what this type of engine is known for...

Then a friend came along who knows a lot about old, conventional internal combustion engines. He casually glanced at the engine and suggested several modifications 'for improvement.'

The engine is, of course, mounted in the hull of the ship, and so far it has used the surrounding air for intake through an air filter. However, air can enter through small ventilation openings from the outside.
My friend then told me that it's not good for the engine to use the heated air from the surroundings, which supposedly contains less oxygen, for intake – it's much better to supply the engine directly with fresh air from the outside.
Done and dusted - I built an air intake system using drain pipes, which is about 3-4 meters long, and it brings fresh air directly from the back to the air filter.

Question:
Does this make sense for such an engine, and if so, what is the purpose?
Since I connected the PE pipe directly to the air filter using rubber couplings and adapters, the engine can draw air from the outside without any restrictions. I also installed a small, high-speed fan that forces air to the air filter even without the engine running. Unfortunately, this fan is made of plastic, and the alternating airflow during the intake process significantly affects it.
'I'm now considering improving this fan to push even more air towards the engine. However, we can't really call it a 'supercharger' yet. The idea is to use a heavy metal fan that provides a higher airflow and more 'pressure,' and that isn't easily affected by the backflow of air in the intake manifold. The piping is quite long, after all...'
'Another engine technician told me that this doesn't really make sense for diesel engines. In fact, pre-heated air from the environment is actually better for combustion, because this mixture ignites more easily and quickly... at least in this power class. We're talking about an engine that currently only has 20 horsepower (in a steel boat that is about 7.5 meters long and weighs 5 tons).'
Well, what now?
You certainly can't compare this engine to a modern turbocharged direct injection engine... but does anyone know for sure if these modifications to the intake system are worthwhile?

What is the diameter of your intake manifold?
DN40 might be a bit too small if it's 4 meters .
Simply beautiful and thick, with no fan.

Every engine needs air, and specifically, the oxygen within it.
There is less oxygen in warm air than in cold air.
Therefore, the question of whether cold air is better does not even arise.

m;

Hi,

Regarding the question of cold or warm air: I think warm air would be most helpful for a cold start, but based on your description, you don't seem to be having any problems with cold starts anyway.
Otherwise, cold air provides a slightly greater excess of air, which therefore reduces the thermal load at full load.

Regarding the "electric supercharger": Calculate the maximum intake air volume flow of the engine based on displacement and speed, and compare this value with the fan. If the fan provides less airflow, it will likely cause the diesel engine to struggle for air rather than providing any benefit - as I believe is the case with all these TÜV-free, unnecessary electric boosters .

That sounds very logical...

The pipes should be approximately 60mm in diameter, but they are reduced to about 40mm because the actual air intake from the original air filter is also only 40mm... and that's what I had to reduce to.

For me, the question remains whether the long tube doesn't rather hinder the airflow and prevent the engine from drawing in enough air without obstruction?
It's cold, fresh air with a higher oxygen content, but the intake path is long – and it's not straight, but has several bends and curves... I had to go around corners.

The new fan supposedly has an airflow of 71 liters per second and 255 square meters per hour. The displacement volume will be around 0.96 liters, but I need to double-check that.
The maximum speed should be 3000 RPM, but due to the steeper pitch of the screw, it is not currently reaching that speed.
I'll calculate that later... good point.

Leave out the fan. Make sure your piping is sealed properly to prevent water from entering. A long intake path won't reduce performance in your case. If the air filter were located at the beginning of the piping, it would be slightly better, but you would never notice any difference in performance.

I think you've achieved the optimum result; you're giving the engine fresh air. More power probably wouldn't be worth it in your case, because even your chassis is designed for a certain level of power, and it wouldn't be able to handle much more .

Ensure that the motor cannot suck in any water, under any circumstances, by using an (open-ended) cap or at least a 90-degree pipe bend on deck. Not even a single drop! Also, it must prevent excessive moisture from entering during the storage of the boat.

...you're probably right, at least that's what I was thinking too. I actually wanted to use the fan to compensate for the long cable runs, because I thought that about 4 meters of piping was simply too long, and the motor would need too much power to draw air through it quickly.

I calculated this once, and if my calculations are correct, the engine takes in 48.5 liters of air per second at its maximum RPM (3000 RPM) with a displacement of 0.97 liters. (???)
That's equivalent to 2910 liters per minute and 174600 liters per hour... so that should actually be correct, since the fan is supposedly capable of moving 255 cubic meters per hour.
'The engine itself doesn't reach that RPM... I think the actual speed is probably around 2500 RPM.'

Yes, there's a drain hole directly on the intake, and the air intake is additionally protected by metal plates, located well above the splash zone. Furthermore, the pipe is lower than the air intake on the engine itself. However, I will also add another drain hole at the lowest point. And boats of this size will no longer be stored; they will remain permanently in the water.

Unfortunately, the boat's propeller is not optimally designed. This is unfortunately due to the limited space within the propeller tunnel. As an alternative, Propeller-Gröver suggested increasing the pitch, which we have done.

A 4-stroke diesel engine without a turbocharger, with an approximate displacement of 1 liter, requires about 1500 liters per minute at 3000 RPM, which translates to 90,000 liters per hour .

A fan also needs electricity to develop its power. It will probably draw that power from the same machine you're using. So, it becomes a question of whether it's worthwhile, because putting a load on the generator also means less power available for the screw drive.

Now you need to understand the geometry of your screws (this will allow you to determine the power required based on the speed).

However, all of these measures will not significantly increase the engine's performance.

The cold intake air slightly increases efficiency but also protects the engine somewhat. To achieve more power, a multi-point injection system is also necessary. And whether it makes sense to modify an existing engine for just 1 horsepower... I highly doubt it.

Hi,
I would leave it as it is. The performance gain is more of a theoretical nature, not reliably measurable, and certainly not noticeable.
The problem is related to water. Remember that the engine compartment in a boat stays cooler than in a car because the waste heat is dissipated through the water, not into the air that flows into the engine compartment.

Sure, thanks for the tips. The fan only uses 30 watts.
But I also think that this additional compressed air doesn't really achieve anything, and it's not really advisable to change the injection amount.
Since the engine itself is running well, I think I can probably skip the fan replacement...

Tobaran wrote:

If my calculations are correct, the engine takes in 48.5 liters of air per second at its maximum speed (3000 RPM).

This is for an engine with a displacement of 0.97 liters. (???)

Quote:

This would be "geometrically correct" for a 2-stroke engine. If it's a 4-stroke engine, you can halve that value.

That corresponds to 2910 liters per minute and 174600 liters per hour... so that should actually work, since the fan is supposedly capable of 255 cubic meters per hour.} This would be the first fan-boosted engine I've read about where the fan doesn't restrict airflow at maximum power. But given the low maximum power, that might still be possible.