Engine Room Fans. Suck or Blow. ?

[BartW]

@mapism, yep +1 re return fuel coolers. I have them, integral in c32 and I think they're importnat. My brother didn't have them on his new John Deere 6068s and got a v hot e/room (he has side fuel tanks and a keel tank, all in e/room). He therefore fitted return fuel coolers last winter, and it is much better. DougH also retrofitted coolers to his sskr 66, and got a big improvement

care to point me a adress for such fuel cooler that can be retrofitted ?
we might consider such a upgrade in the future.

we are used to the long cooling down times of our E/R, crew likes it for quickly drying towels...

the "colder" fuel, what advantage does it have for the engine / combustion ?
is it a big difference, or just for the purists ;-) ?
This has been working ok for 25 years in our boat,...

FWIW
our E/R fans are sucking out,
2 suck air in the rear part of the E/R, above the genny's,
2 suck air (via a hose) above the engines,

the engines take air directly through the large side vent openings along the engines.

so I now realise / can conclude ? that I don't need to run the engine room fans when the engines are running,
they are only functional for cooling the E/R, after shut down ?

 

[jfm]

Bowman is perhaps the most well known manufacturer
http://www.ejbowman.co.uk/products/fuelcoolers.htm. In UK, asap-supplies.com sell them

Ref benefits of cool fuel, cue latestarter. AFAIK most/many modern cars have coolers to meet emissions laws

so I now realise / can conclude ? that I don't need to run the engine room fans when the engines are running, they are only functional for cooling the E/R, after shut down ?

I don't think it will make much difference unless they are big fans, but leaving aside quantums I don't think that is right BartW. Having engines sucking air plus fans sucking in an e/room means you have 2 things lowering the e/room air pressure, ie two suckers. AOTBE more air will get sucked in thru the e/r vents, ie more changes of air per minute in the e/room, than if you had one sucker. That will lower the e/room temp during navigation. But maybe only by a tiny amount - that depends on how much extra airflow is created by the fans

 

[TwoHooter]

so I now realise / can conclude ? that I don't need to run the engine room fans when the engines are running,
they are only functional for cooling the E/R, after shut down ?

Doesn't that depend on the engine maunfacturer's specifications? For example, on most Nordhavn boats the engine room fans are usually a requirement because otherwise the engine room ambient temperature exceeds the engine manufacturer's limits. For example:- 'We also ran a bunch of tests to check the engine room temp relative to Deere's specs. On earlier sea trials it seems much hotter than expected, so the boat had been rigged with gauges and we were tasked with producing a lab report. Sure enough, the temps were too hot and drew Jeff Leishman down to the dock on our return who in about 5 minutes spotted the problem. The wrong fan had been used when the boat was built. Once corrected, things looked much better.'

 

[Portofino]

Chiming in with my 0.02 p ,s worth .
I have no E/R fans at all or I think no fuel coolers ( need to check that ?)
So in theory and indeed practice my E/R is ideal to dry wet clothes and towels etc in when all shut down
I have charge air temp guages and pressure guages ,so can see the air being cooled before it enters the cylinders 16 - 17 o Irrespective of the ambient .
Yup fuel coolers -never really thought much about it TBH -would have thought its gonna get hot v soon any how as it's approoaching the injector and starting its path through to the injector tip -it's then atomised into hot compressed air for combustion any how .
So yup without googling the subject -why bother fuel cooling ?
Built to a RINA classification ,perhaps due to the ability to seal /close the E/R during a fire is more important than having shed loads of fan , fanning the flames or put another way fans fanning out the inert gas as well or fanning fresh air in or both .Even with interlocks alledgedly fitted to shut down these fans when you detect an E/R fire, it's another thing to go wrong and give the MAIB guy something to earn his fee about
We do get at the ends of the season a lovely "underfloor " heated cockpit sole , when sat outside enjoying a bottle on an evening -with the heat soak .
There's gotta be a sensible reason why Mario Amarti omitted E/R fans .

Above applies to diesels -can fully buy into fanning air /fumes out of a petrol from 10 mins before start up .

 

[jfm]

why bother fuel cooling ?

Even with interlocks alledgedly fitted to shut down these fans when you detect an E/R fire, it's another thing to go wrong and give the MAIB guy something to earn his fee about

There's gotta be a sensible reason why Mario Amarti omitted E/R fans .

Ref reason for fuel coolers, the benefit that a user feels is that there is much less heat soak into the accom from the hot fuel. After a decent run you can have many tonnes of pretty hot fuel in your tanks, and the specific heat capacity of diesel oil will surprise you - it is much higher than water's, for example. So that's a heck of a lot of heat energy to lose, and plenty of it might get into the accom

Ref e/room fire, on a properly specced boat you have automatic closing louvres that can close without electrical power to seal up the engine room ventilation in case of fire. That's a failsafe even if the fire system interlock that should automatically turn the fans off happens to go wrong

Ref Amati, he might have just figured that he doesn't care about heat soak into accommodation on a non passagemaking open sports boat with a pretty small fuel tank, and banked the cost saving. Pretty reasonable choice I'd say.

 

[michaf]

Interesting one because I learned everything on our setup not so long ago. Ours sucks and signed off by Cummins. Boat is a bit more then two year old. I think there is two school of thoughts and it's probably a matter of what pros and cons you favour. Anyway I wanted to add an observation on our setup. The pipe that sucks the air is located on the sealing between the two engines. It has one advantage and that is it is extracting hot air more precisely since it sucks from the top. As a result you can be sure the hottest air is indeed replaced by cool air. If you blow air in, you don't really know how the flow looks like, there can be pockets of air or even fresh air founding a way out right away.

And then there's the possible fumes etc. There the negative pressure system clearly is winning against the positive one. Intuitively I'd be in favour of sucking air out, but that's only because ours is like that!

 

[Hurricane]

Interesting one because I learned everything on our setup not so long ago. Ours sucks and signed off by Cummins. Boat is a bit more then two year old. I think there is two school of thoughts and it's probably a matter of what pros and cons you favour. Anyway I wanted to add an observation on our setup. The pipe that sucks the air is located on the sealing between the two engines. It has one advantage and that is it is extracting hot air more precisely since it sucks from the top. As a result you can be sure the hottest air is indeed replaced by cool air. If you blow air in, you don't really know how the flow looks like, there can be pockets of air or even fresh air founding a way out right away.

And then there's the possible fumes etc. There the negative pressure system clearly is winning against the positive one. Intuitively I'd be in favour of sucking air out, but that's only because ours is like that!

You are probably correct and I do agree that extract makes more sense.
But a consideration - I remember from my air flow days that the velocity at a grille drops off far quicker on an extract grille than a supply grille (I remember a figure of 70% difference).
In your case, it seems that the extract grille is well placed to get the heat out of the engine but any air in the bilges might be stagnant - whereas if a supply air grille "aimed" at the right areas would reach further into the engine room than an extract grille.
Perhaps this is why some boat builders do both supply and extract.

 

[Portofino]

Not convinced
The engines (diesels compression ratio 16-20 to 1 ) from 5 to 32 Litres ,from 6 to 16 cylinders will suck more air in than any
Fan on a boat E/R can deal with .
98 % of air movement is from the induction stroke .
If you want to fit some Micky mouse 12 or 24 v fans -go ahead .
Do you believe in the SWCAC sea water charge air cooler ?
Do you believes in the Turbo,s ?
They don,t give a dam about the Micky mouse fans .
As long as the E/R is adequately vented to allow air in ,to feed the lumps at full tilt ---- arh hang on a minute --- is it ?

 

[MapisM]

diesels compression ratio 16-20 to 1

I agree with your suggestion that in a boat with big engines spinning fast the air exchange is pretty high also without fans, though only WHILE CRUISING, obviously.
But I'm completely missing the relevance of compression ratio in this debate...

 

[Latestarter1]

I stayed out of the last technical discussion as it wandered totally off course by the time I looked in.

However can I just point out a few facts.

#1 Most manufacturers apply a general rule that the engine air inlet temperature must not exceed 15/17 Degrees C above ambient at rated speed/load.

#2 Forced ventilation if required, must be wired to run continuously at all times when engine is running.

#3 Ventilation must be designed is such a way that no seawater, exhaust gases or blow-by vapour is allowed to enter the air inlet.

To meet the above standards ER ventilation is often a matter style over substance, and in order to achieve the required combustion air flow rate laid down by the engine manufacturer forced ventilation is resorted to.

If the these basic requirements are not met the engine will not make the published power output and the evil of engine overloading rears its head, but a second serious issue arises, excessive turbine inlet temperature.
Once T.I.T. rises above the prescribed maximum combustion temperatures go through the roof resulting in severe distress is exhaust valves and seats.

How we wandered on to fuel cooling I have no clue.

Manufacturers provide engine output numbers to recognised International standards which specify the gravity of the fuel and the test temperature of the fuel to achieve the stated output. The slightly more more marketing led manufacturers use a 25 Degree C test temperature others use the more realistic 40 Degree C test fuel. One manufacturer switched to the more realistic test standard claiming that they had come into line, but when I looked at the spec sheet they had then switched to a dodgy density!

Apart from the fact that engines are sold on the basis of $ per Hp why the difference?

Diesel engine injection systems are volumetric and with just a few exceptions on some electronic engines they do not have fuel fuel temperature compensation. Therefore as the fuel temperature rises the density of the fuel falls and the calorific value of a given volume of fuel falls.

Also remember, dependent on the type of fuel system employed over 70% of fuel is returned to the tank. Certain types of injector use the return fuel to cool the injector. On a vessel with small day tanks and high volume return it is possible to see tank temperatures reaching 50 even 70 C which results in a significant drop in engine power output.

Some engines have integral fuel coolers, and in cases where the installation creates an issue due to hot fuel, fuel coolers can be specified.

Good luck

 

[MapisM]

How we wandered on to fuel cooling I have no clue.

Thanks P, interesting summary as always.

Just to clarify your doubt above, since I'm guilty as charged for starting the o/t on fuel cooling: it was just in reply to TwoHooter, who mentioned that his e/r was running hot.
In this respect, trust me, having 4 steel tanks of one cubic meter each constantly refilled with that 70% of returning fuel COOLED made a huge difference in my boat, vs. the initial installation with neither integral nor separate fuel coolers.
No e/r ventilation on earth could have improved the situation as much as fuel coolers did, in order to meet your point #1.
In fact, I'm never seeing now more than 10/12 degrees above the ambient temp in my e/r, while I used to have close to 20.

 

[Latestarter1]

Thanks P, interesting summary as always.

Just to clarify your doubt above, since I'm guilty as charged for starting the o/t on fuel cooling: it was just in reply to TwoHooter, who mentioned that his e/r was running hot.
In this respect, trust me, having 4 steel tanks of one cubic meter each constantly refilled with that 70% of returning fuel COOLED made a huge difference in my boat, vs. the initial installation with neither integral nor separate fuel coolers.
No e/r ventilation on earth could have improved the situation as much as fuel coolers did, in order to meet your point #1.
In fact, I'm never seeing now more than 10/12 degrees above the ambient temp in my e/r, while I used to have close to 20.

Your engines have injectors which employ a degree of fuel cooling and a very high return rate, you were probably radiating a lot of heat into your engine compartment from the tanks if they are located in the E/R.

 

[Portofino]

I agree with your suggestion that in a boat with big engines spinning fast the air exchange is pretty high also without fans, though only WHILE CRUISING, obviously.
But I'm completely missing the relevance of compression ratio in this debate...

With forced induction -turbo and or compressors (smaller VP stuff ) the relevance of me mentioning the C/R was to illustrate that the swept vol calc,c that you and JFM have used in earlier posts are pretty ,in fact totally irrelivent , cos air is forced in not sucked in .Furthermore undergoes another density consolidation when it passes through the SWCAC .
More relevant would be a mass air flow meter on the inlet manifold just before the inlet -and the density of the ambient air in the ER .
Turbo diesels consume a helluva load more air than simple swept vol x rpm calcs.

So my inference was that in a proper engineered thought out E/R with adequate designed air intakes - ie big enough
There's no need for fans or any fans being tiny air vol movers compared to the diesels -willbe vertually useless in the grand scheeme of airflow

As I said MAN fit air inlet temps on the SWCAC it's Allways 16-17 oC come winter ,come restart afer a run - ambient is 90oc outside temp (who knows inside the E/R ?) - so high E/R temp seems to make no or little detectable difference -to performance - in real the world , remember we also have % load and charge air pressure of air in the SWCAC.
So the turbo,s SWCAC seem to nullify any " problem that needs fans " "perceived rise in E/R temp .

 

[MapisM]

With forced induction -turbo and or compressors (smaller VP stuff ) the relevance of me mentioning the C/R was to illustrate that the swept vol calc,c that you and JFM have used in earlier posts are pretty ,in fact totally irrelivent , cos air is forced in not sucked in.

Actually jfm allowed for 1bar boost in his calculation. Regardless, I still can't see why and how the C/R should affect the math...?

 

[MapisM]

Your engines have injectors which employ a degree of fuel cooling and a very high return rate, you were probably radiating a lot of heat into your engine compartment from the tanks if they are located in the E/R.

Precisely.
I reckon it ain't such a rare occurrence btw, considering that also Silverdee had the same problem also with modern JD engines.

 

[Portofino]

Actually jfm allowed for 1bar boost in his calculation. Regardless, I still can't see why and how the C/R should affect the math...?

Effects your maths in a big way cos that's the true vol TDC with valves closed -not swept VOL of substance like air AIr which is compressed -forced in . so the ref to C/R eludes to that -Its not sucked in .
AIr mass is a better calc .
basically the density is variable with air .
these are not liquid punps where by your swept vol of the pump chamber is just about right given tiny changes in liquid density with temp -

by the way we have boost pressure guage too along with SWCAC pressure
just writing what I see / observations and trying to make sense -not looking for an argument
real world high ambient temps in the E/R seem to make no noticeable diff to any of that stuff when I scroll through the screens ~ 1850 rpm .
I have no fans at all

 

[jfm]

Precisely.
I reckon it ain't such a rare occurrence btw, considering that also Silverdee had the same problem also with modern JD engines.

Yup. Return fuel cooling is all round good: reduces the supply fuel temperature, helps manage the e/room temp, and reduces heat soak into the accom

 

[jfm]

Effects your maths in a big way cos that's the true vol TDC with valves closed

. I'm with MapisM: the engine's compression ratio is a complete red herring. The turbocharger's "compression ratio" is relevant but I already included it in the calculations above

 

[Bazzer]

I had a G/F who could suck a golf ball through a 15mm hose pipe

My Yanmar 75 engine compartment has a vent with a blower - the hot air in the compartment is expelled via the vent

what was her name I think I may know her