Cooler in diesel return tank ?

[kds]

During a recent chat with another forumite, he mentioned that he had been advised to put a water-cooled section into his diesel fuel return pipe, because it was ging back into a plastic fuel tank.
I don't have one in my system. /forums/images/graemlins/confused.gif
The engine is 13.5 hp. and the tank is a plastic 45 litre TEK TANK.
The boat is a 29' yacht.
Any experts able to comment ?

 

[steve28]

The Amount of fuel that will be leaving the return pipe is so small, combined with the hp being only 13 i doubt it will ever be above skin temprature when it gets to the tank.


steve

 

[tcm]

hm, i wd not haev thort so. imho

The returned fuel is small in comparison with volume of fuel there and temp likley approximates to temp of water which in uk is 20-30 degrees cooler than some places. I wd imagine tek tank good enough to easy 50 centigrade anyway, or possibly loads loads more - it has to be decent gear to be able to stand holding fuel?

Garbage, imho. But i wd like to hear from Tek Tanks.

 

[vyv_cox]

After a hard day's motoring my 25 gallon fuel tank increases in temperature to luke warm, I would estimate no more than 35C. My engine is a Yanmar 3GM30F. High or low-density polyethylene plastic is certainly good for 100C so I don't think you need to be concerned.

 

[David2452]

One thing to remember though, exept in modern ECU controled diesels which will allow for fluctuations in fuel temperature a rise in fuel temp to around those you quote can result in a loss of HP and that could be a more valid reason for using a cooler

David

 

[BobnLesley]

Spring Fever has the same set-up as your own, though only a 30 litre tank. Nothing's gone boom! in the six years we've had her, so I wouldn't worry.

 

[Talbot]

I have a plastic (custom) tek tank (note that the custom are thicker plastic than a stock tank) I have a 27 hp diesel engine.

Last year after motoring all the way to cherbourg from Portsmouth, the tank was pretty warm! no warm enough for me to get worried though!

 

[tcm]

fuel temp v hp

hm really. Even if there were a variatioon it would be in kelvin, not centigrade. Sepretly of coursws the luke arm fuel is again heated by runing down the inlet pipes, so cooling retun makes utterly marginal diffeence. Finally of course the inlet density is mostly air, not mostly fuel.

 

[pheran]

Not an expert in these matters but wonder whether warm fuel would, in fact, adversely affect performance. I was watching a program the other night about big ship diesels (93000hp and 104rpm max.) and they use a fuel pre-heat stage that warms the fuel up massively.

 

[philip_stevens]

Diesel was preheated, though I cannot remember the temperature, but MFO and HFO was massively preheated to something like 120C. Again, it is quite a few years ago, and the figure I have given may well be wrong, but I do know it was bluddy 'ot.

HFO had the cold consistency of tar! We spent about 6 hours in one port after a shutdown, trying to get the oil temp up enough to get the boilers lit. The Auxy boiler threw a wobbler over night, and we spent most of the day trying to get enough heat into the service tank.

So yes, the fuel had to be heated to quite an extent - diesel as well as MFO and HFO. Therefore, warm diesel will not lose power, more the opposite, as you use preheaters to warm the fuel or inlet air when the engine is stone cold

 

[tcm]

preheat reduced viscosity and improves spraying, hence combustion

 

[pheran]

Thank you m'lud. I would have guessed at something like that but am glad to have it confirmed. The program I was watching (on Discovery) was about the biggest container ship in the world, 1000 feet long and its 12 cylinder diesel engine was said to be six stories high. Bloody amazing!

 

[TheBoatman]

I have just installed a new Yanmar 3YM30 and according to the manual the Hp loss between fuel @ 25C and 40C, thats at the injector pump, is 0.4hp.

Somehow I don't thing I'm gonna loose any sleep over it!

Peter.

 

[jimi]

Could it be that the loss of power is simply down to less calories in a given volume as the diesel liquid expands when warmer?

 

[Oen]

It might be worth bearing in mind that temperature alters the ability of some types of plastic to cope with stress... That is, depending on the material from which your tank is constructed, it may deform more readily when warm than when cold. Have you checked to ensure that deformation would not allow it to come into contact with anything rough or sharp, which through continued wear might cause a puncture?

[engage boring irrelevant information mode] Some GRP aircraft have a maximum static temperature and wouldn't, for example, withstand being flown after a day parked in the Arizona sun... This is one reason, too, why they're almost invariably white. Sticking with aircraft, where low temperature (cold-soaked) fuel is a consequence of prolonged flight at altitude, it's common for engine and hydraulic oil to be cooled in heat exchangers mounted in the fuel tanks to assist in warming the fuel, for much the reasons that tcm mentions. There's a minimum fuel temperature, and in extreme cases, it's necessary to descend into warmer air to avoid reaching it.

 

[kds]

Thanks very much for all the answers - I found them interesting, as well as helpful.
Ken

 

[reeac]

With respect to small aircraft, you're probably talking petrol/piston engines. With them, power output decreases with increasing temperature as the engine is sucking in a smaller mass of air if the air is hot - hence problems with take off when max. power is required. Once aloft, however, there is the possibility of carb. icing especially when descending. Pre-heating the fuel is probably done in order to minimise the likelyhood of this icing. We're getting off the subject, however... .

 

[Oen]

You're right - we're well off topic.

But, I was talking about jets. I'm not aware of any fuel heating used on piston aircraft - though I haven't (yet) flown the diesel-engined ones. Avgas is a lot lighter than Avtur, so presents fewer problems in this regard.

Pre-heating of fuel is not, to my knowledge, used anywhere as a means of preventing carb icing - the much more significant gain from heating the intake air (usually by passing it through a shroud around the exhaust) provides a much greater potential temperature rise, as the mass and volume of air going into the carburettor is much greater than the mass and volume of fuel going in, and the air is simpler to heat.