weecough
New Member
Next daft question is on the engine cooling. From what I can gather, boat engines seem to draw in coolant from the water they are sailing in. Is this right?
Engine cooling
- Thread starter weecough
- Start date
carlton
Well-Known Member
Er...yes...some of them are 'direct'-cooled by simply pumping raw water around various parts of the engine.
Others have a separate, closed cooling system (like a car engine has) but, instead of a radiator, have a heat-exchanger which the raw water passes through to absorb the heat from the coolant.
Others have a separate, closed cooling system (like a car engine has) but, instead of a radiator, have a heat-exchanger which the raw water passes through to absorb the heat from the coolant.
Cliveshep
Well-Known Member
Correct - top marks there for Key Stage one question
Revision for Key Stage two: engines if not aircooled (some are) can be either raw water cooled or indirect cooled.
Raw water - sucked up from what you float in, pumped around engine, or via by-pass if stat is closed, injected into exhaust elbow to cool and muffle exhaust. That's why boat exhausts spit water and gas.
Indirect - water around engine is pumped through a heat exchanger and back to engine. Water you float in is pumped through heat exchanger (doesn't mix with engine coolant water) and then injected into exhaust after cooling the engine coolant.
Key Stage 3 - If your engine is indirect cooled you can fit a calorifier piped to engine coolant take-offs on engine. This is a hot water cylinder with the coil in the centre having engine coolant running through it but not mixing with domestic water in the cylinder. This heats the water giving hot water for shower/sink etc. More effective on diesels which have greater waste heat to dispose of but still ok on petrol engines.
Next?
Was that a troll? (Week off?)
Revision for Key Stage two: engines if not aircooled (some are) can be either raw water cooled or indirect cooled.
Raw water - sucked up from what you float in, pumped around engine, or via by-pass if stat is closed, injected into exhaust elbow to cool and muffle exhaust. That's why boat exhausts spit water and gas.
Indirect - water around engine is pumped through a heat exchanger and back to engine. Water you float in is pumped through heat exchanger (doesn't mix with engine coolant water) and then injected into exhaust after cooling the engine coolant.
Key Stage 3 - If your engine is indirect cooled you can fit a calorifier piped to engine coolant take-offs on engine. This is a hot water cylinder with the coil in the centre having engine coolant running through it but not mixing with domestic water in the cylinder. This heats the water giving hot water for shower/sink etc. More effective on diesels which have greater waste heat to dispose of but still ok on petrol engines.
Next?
Was that a troll? (Week off?)
sailorman
Well-Known Member
[Next? Was that a troll? ] /forums/images/graemlins/shocked.gif
thats a bit ott /forums/images/graemlins/confused.gif, he might be a very nice NuBee /forums/images/graemlins/laugh.gif
thats a bit ott /forums/images/graemlins/confused.gif, he might be a very nice NuBee /forums/images/graemlins/laugh.gif
Cliveshep
Well-Known Member
Oi you, be nice to me or oill set me missus on ter yer!
He might be a newbie, and I answered his question fully and honestly, as I did his other post.
Tolerant, that's me!
There have been a lot of newbies about lately, all joining up in the last week or so. OK, it's that time of year when englishmen want to explore their historical heritage and get afloat, but when their bios are completely devoid of any info at all one is perhaps entitled to suspect a possible troll!
He might be a newbie, and I answered his question fully and honestly, as I did his other post.
Tolerant, that's me!
There have been a lot of newbies about lately, all joining up in the last week or so. OK, it's that time of year when englishmen want to explore their historical heritage and get afloat, but when their bios are completely devoid of any info at all one is perhaps entitled to suspect a possible troll!
Wiggo
Well-Known Member
[ QUOTE ]
More effective on diesels which have greater waste heat to dispose of but still ok on petrol engines.
[/ QUOTE ]
Methinks not, Clive. Diseasel engines are more thermally efficient than petrol - about 33% vs 25%, meaning they extract more useful energy from the fuel and hence wastes less as heat.
The scary bit is working out how much heat they actually dump. We have a pair of KAMD43s, so 460 shaft hp between them. If they are 33% efficient, then they are generating over 900hp of heat or almost 700kW. Which explains why they leave a plume of steam from the exhausts...
More effective on diesels which have greater waste heat to dispose of but still ok on petrol engines.
[/ QUOTE ]
Methinks not, Clive. Diseasel engines are more thermally efficient than petrol - about 33% vs 25%, meaning they extract more useful energy from the fuel and hence wastes less as heat.
The scary bit is working out how much heat they actually dump. We have a pair of KAMD43s, so 460 shaft hp between them. If they are 33% efficient, then they are generating over 900hp of heat or almost 700kW. Which explains why they leave a plume of steam from the exhausts...
Cliveshep
Well-Known Member
Quote: "The efficiency of any cycle, be it a gasoline or diesel cycle, is equal to the output divided by the input. The efficiency of the diesel cycle is higher than the gasoline cycle because of higher compression ratio, and because the temperature of combustion in a diesel engine is much higher. Therefore, the heat input in a diesel engine is at a higher average temperature. The higher temperature is outweighed by the increased heat output at that same temperature. A gasoline engine cannot have the same compression ratio as a diesel engine, because fuel and air are mixed before they reach the cylinder, and they would explode before the piston reached the correct firing position, causing the engine to “knock” and not exploit the most efficient use of energy. It is true then that a diesel engine is more cycle efficient."
Where I'm coming from is that the diesel produces heat greater than petrol engines and that this can be used rather than losing it in cooling. The principle in a diesel is that the air is compressed causing it to heat right up to the point at which injected fuel will ignite, Petrol engines take in cold fuel and cold air and the power stroke is derived from spark combustion of the explosive mix of the two.
Where I'm coming from is that the diesel produces heat greater than petrol engines and that this can be used rather than losing it in cooling. The principle in a diesel is that the air is compressed causing it to heat right up to the point at which injected fuel will ignite, Petrol engines take in cold fuel and cold air and the power stroke is derived from spark combustion of the explosive mix of the two.
Wiggo
Well-Known Member
I can accept that.
jfm
Well-Known Member
Cliveshep, I don't know who you're quoting but he /she is no engineer and needs to study some more thermo. The bit "Therefore, the heat input in a diesel engine is at a higher average temperature. The higher temperature is outweighed by the increased heat output at that same temperature" is just garbage and commits the cardinal sin of mixing up heat and temperature which of course are two different things.
Getting back to Wiggo's point, a diesel engine gets more energy out of a given amount (in energy content terms) of hydrocarbon fuel than a petrol engine, hence the greater efficiency of diesel engines. However the extra energy conversion that the diesel gets manifests itself in more kinetic energy to the crankshaft AND more heat. Wiggo, the greater efficiency of a diesel engine is a matter of extracting more energy from the hydrocarbon fuel, and is NOT a matter of extracting a similar amount of total energy from the fuel but converting more of it to kinetic energy and less to thermal.
Hence, the higher efficiency of a diesel means it has more spare heat energy available.
Getting back to Wiggo's point, a diesel engine gets more energy out of a given amount (in energy content terms) of hydrocarbon fuel than a petrol engine, hence the greater efficiency of diesel engines. However the extra energy conversion that the diesel gets manifests itself in more kinetic energy to the crankshaft AND more heat. Wiggo, the greater efficiency of a diesel engine is a matter of extracting more energy from the hydrocarbon fuel, and is NOT a matter of extracting a similar amount of total energy from the fuel but converting more of it to kinetic energy and less to thermal.
Hence, the higher efficiency of a diesel means it has more spare heat energy available.
Wiggo
Well-Known Member
Now is that 'extra' energy a result of diesel oil storing more Joules/litre than petrol, or is it something else? I understand that the big ship, slow revving 2 stroke diesels can get efficiencies over 50%, so that implies a process efficiency gain rather than/as well as an 'energy density' gain...
jfm
Well-Known Member
Glad you're following the logic!
It's all process gain. Back at the good ole refinery petrol is actually higher up the distillation chain than diesel and has about 10% more energy density in terms of Joules per unit of weight or volume. And the sludgy oil that ships burn when they're up to temperature is even further down that chain. So it's all process efficiency, specifically the fact the combustion chamber temp is much higher so more fule burns fully.
Incidentally, as a matter of presentation, when engineers say a diesel engine is X% efficient and a gasoline engine is Y%, they normally back out the difference in energy density of the fuel. To leave it in would be kinda cheating. So when you compare x/y % efficiencies you are looking at pure process efficiency - chemical joules in versus kinetic joules out
It's all process gain. Back at the good ole refinery petrol is actually higher up the distillation chain than diesel and has about 10% more energy density in terms of Joules per unit of weight or volume. And the sludgy oil that ships burn when they're up to temperature is even further down that chain. So it's all process efficiency, specifically the fact the combustion chamber temp is much higher so more fule burns fully.
Incidentally, as a matter of presentation, when engineers say a diesel engine is X% efficient and a gasoline engine is Y%, they normally back out the difference in energy density of the fuel. To leave it in would be kinda cheating. So when you compare x/y % efficiencies you are looking at pure process efficiency - chemical joules in versus kinetic joules out
Wiggo
Well-Known Member
Are we now down the point that diesel burns versus petrol exploding? A longer combustion time thus allowing more complete combustion?
jfm
Well-Known Member
Basically yes. We could get all technical on burn vs explode but that aspect isn't my speciality and Lateboater or someone would know that better (in both cases the burn time is milliseconds so neither is slow burn and both are much faster than a grenade. Diesel engine has a longer burn time and that's part of the reason why fuel burns better)
Point is, diesel and petrol fuels aren't that different. Basic hydrocarbons with a few detailed differences. Both came out of same hole in the ground. But, the diesel engine cycle just burns the fuel better and more thoroughly, and spits less unburnt fuel down the exhaust pipe. Simple as that. That's why diesel cycle prduces more kinetic engery output per joule of fuel energy squirted into it. (And more heat energy output, to get back to the original point in this thread)
Point is, diesel and petrol fuels aren't that different. Basic hydrocarbons with a few detailed differences. Both came out of same hole in the ground. But, the diesel engine cycle just burns the fuel better and more thoroughly, and spits less unburnt fuel down the exhaust pipe. Simple as that. That's why diesel cycle prduces more kinetic engery output per joule of fuel energy squirted into it. (And more heat energy output, to get back to the original point in this thread)
burgundyben
Well-Known Member
All very interesting, I think we may have gone far beyond the point for the chap that asked the question!
Cliveshep
Well-Known Member
Ah iss not an injuneer sah, just a bodgie person like what sum oh yoo mite bee!
I did have an education though!
My Quote: "More effective on diesels which have greater waste heat to dispose of but still ok on petrol engines."
JFM's quote: "Hence, the higher efficiency of a diesel means it has more spare heat energy available. "
Don't actually give a toss about whether my source is an engineer or not (he was an engineering student actually), I was and am making the point that there's generally more heat energy available for a calorifier with a diesel lump than with a petrol. What's to argue about? Why do we have to get all techie? The man might just want to fit a hot/cold shower later on! He asked a question about cooling, I answered fairly accurately I thought. I didn't expect to have to duck and run!
I did have an education though!
My Quote: "More effective on diesels which have greater waste heat to dispose of but still ok on petrol engines."
JFM's quote: "Hence, the higher efficiency of a diesel means it has more spare heat energy available. "
Don't actually give a toss about whether my source is an engineer or not (he was an engineering student actually), I was and am making the point that there's generally more heat energy available for a calorifier with a diesel lump than with a petrol. What's to argue about? Why do we have to get all techie? The man might just want to fit a hot/cold shower later on! He asked a question about cooling, I answered fairly accurately I thought. I didn't expect to have to duck and run!
jfm
Well-Known Member
Calm down. It's just a forum and it's bad form to criticise other posters just because their posts cover ground (still relvant to the thread's subject) that you'd prefer wasn't covered
No-one said anything you said was wrong. No-one even slightly disagreed with you. I criticised the student you quoted, but you were clearly citing his views and not your own, so my "garbage" label was clearly stuck on him not you. Indeed, all the posts in this thread merely added to what you originally wrote, and didn't diasgree with it. As for "why do we have to get techie", as i say that's bad form. You started it in any case, but you do not own the agenda here matey and posters here are free to get as techie (or non techie) as they like thanks, and you don't have to read it.
No-one said anything you said was wrong. No-one even slightly disagreed with you. I criticised the student you quoted, but you were clearly citing his views and not your own, so my "garbage" label was clearly stuck on him not you. Indeed, all the posts in this thread merely added to what you originally wrote, and didn't diasgree with it. As for "why do we have to get techie", as i say that's bad form. You started it in any case, but you do not own the agenda here matey and posters here are free to get as techie (or non techie) as they like thanks, and you don't have to read it.
Cliveshep
Well-Known Member
Ooooh...........I'm all hurt.
Sorry mate, didn't mean to offend you - ok?
Week-Off was asking a very basic question, got a very basic answer with a little fat on the lean. It then wandered into the exotic black arts of fuels and combustion and other black magic concerned with techie stuff. But, you're right, I don't own the forum or the thread and I stand suitably chastened.
Can I have my cocoa now with a biccie please?
Sorry mate, didn't mean to offend you - ok?
Week-Off was asking a very basic question, got a very basic answer with a little fat on the lean. It then wandered into the exotic black arts of fuels and combustion and other black magic concerned with techie stuff. But, you're right, I don't own the forum or the thread and I stand suitably chastened.
Can I have my cocoa now with a biccie please?
weecough
New Member
Thanks chaps, I only asked as it goes against everything I know about engines. Especially salt water. I was also wondering why I couldn't take the engine out of a BMW turbodiesel, put it in a boat and run the heating of the rad just like a car. I am a dumbass newbi and as such, don't know what a Troll refers to.
Cliveshep
Well-Known Member
I withdraw the "Troll" bit which refers to those who only post as a wind-up for the rest, often I gather long-time members re-registering under assumed names.
Pretty sure a Beemer engine can be marinised at huge cost, not to mention everything else you would need, gearbox (totally different to cars) etc, but won't you sensibly be looking for a boat with either an inboard engine (inside the boat under the floor or a box) already fitted or an outboard (hung on the back) engine?
What sort of boat are you hoping for anyway, sports type boat, speedboat, cabin cruiser? Where are you wanting to use it? Inland waterways/rivers, coastal/tidal waters? Your choice of "where" will influence your choice of "what", and the "what" by your budget. Boats can be pretty expensive. Give it some more thought and ask some more questions when you figure out where you're heading with this. Good luck.
Pretty sure a Beemer engine can be marinised at huge cost, not to mention everything else you would need, gearbox (totally different to cars) etc, but won't you sensibly be looking for a boat with either an inboard engine (inside the boat under the floor or a box) already fitted or an outboard (hung on the back) engine?
What sort of boat are you hoping for anyway, sports type boat, speedboat, cabin cruiser? Where are you wanting to use it? Inland waterways/rivers, coastal/tidal waters? Your choice of "where" will influence your choice of "what", and the "what" by your budget. Boats can be pretty expensive. Give it some more thought and ask some more questions when you figure out where you're heading with this. Good luck.
Wiggo
Well-Known Member
In principle, you can do just what you suggested. In practice, it wouldn't work very well: you'd need a truck load of custom made parts to adapt the cooling system, you'd need a custom exhaust, because boat exhausts are 'wet' and have the waste cooling water injected just after the manifold. That would drown the cat, and removing a cat would mean reworking the ECU. Finally, an automotive diesel engine is expecting to run through a 5 or even 6 speed gearbox and its power and torque curves are optimised for this environment, but in a boat, you have a single speed box so you need massive low down torque of the sort that's not usually available in car engines.
