air-seawater vs air-coolant

[phillippeterson]

Would you mind giving pros and cons of engine cooling by seawater vs engine cooling by radiator.

 

[DDW]

The main con of a marine engine cooled by an air radiator is there aren't any.

 

[rslifkin]

I think this is referring to aftercoolers. Seawater aftercoolers aren't as streaks durable as one in the coolant loop and need more maintenance. But they can get the air colder, enabling higher performance.

 

[BruceK]

Perhaps the OP will clarify. I`m thinking its about on engine heat exchanger cooling vs more remote keel cooling. Most of us understand heat exchanger, the most helpful responses could be from someone with keel cooling experience.

 

[phillippeterson]

I think this is referring to aftercoolers. Seawater aftercoolers aren't as streaks durable as one in the coolant loop and need more maintenance. But they can get the air colder, enabling higher performance.

Perhaps the OP will clarify. I`m thinking its about on engine heat exchanger cooling vs more remote keel cooling. Most of us understand heat exchanger, the most helpful responses could be from someone with keel cooling experience.

Actually, I guess don't really know what I'm asking. I was looking at Deere marine diesels and some are A and some are S - the aforementioned air to coolant and air to seawater after coolers. These options are mentioned under the heading of aspiration. Revisiting the Deere page, I now surmise they are talking about the air charge cooling after the turbocharger and not the engine cooling.

 

[phillippeterson]

The main con of a marine engine cooled by an air radiator is there aren't any.

If a marine diesel wasn't cooled by seawater I guess the engine rooms would be unbearably uninhabitable hot. And everything in the engine room would suffer heat soaking.

 

[rslifkin]

Actually, I guess don't really know what I'm asking. I was looking at Deere marine diesels and some are A and some are S - the aforementioned air to coolant and air to seawater after coolers. These options are mentioned under the heading of aspiration. Revisiting the Deere page, I now surmise they are talking about the air charge cooling after the turbocharger and not the engine cooling.

Yes, on the JD engines they're referring to the intake charge aftercoolers.

 

[BruceK]

Actually, I guess don't really know what I'm asking. I was looking at Deere marine diesels.... Revisiting the Deere page, I now surmise they are talking about the air charge cooling after the turbocharger and not the engine cooling.

Got it. My Cummins 210s don`t have/need aftercooling,unlike higher output versions of the 5.9 block. Less servicing/less to go wrong.

 

[C lectric]

phillippeterson

It sounds like you are asking about the aftercoolers only.

A coolant cooled aftercooler can only cool the intake air after the turbo to the temperature level of the coolant, approx. 180oF.

The seawater cooled aftercooler can cool the intake air after the turbo to the temp of the seawater which is a lot less than the coolant. That air is then denser and can support a higher , much higher, level of power output from the engine.

There are engines about that don't use an aftercooler at all even though they have a turbo. THose are lower output engines yet again BUT higher output than a naturally aspirated engine.

The aftercooler has very little to do with the engine heat radiated into the ER.

The primary function is to cool the incoming air after the turbo heats it so the engine can produce more power than would otherwise be possible.

Engine heat is mostly handled by the coolant system itself although it will help and the water cooled exhaust system.

 

[DDW]

Ok, aftercoolers. I presume the coolant - air aftercooler takes coolant from the cool end of the engine heat exchanger, which could (and should) be running well below regulated engine coolant temperature, in fact nearer seawater temp. I'm not sure there would be a huge difference in performance. It should be lower maintenance, not being steeped in seawater.

 

[socalrider]

Here's a rough guess: assume coolant is 90C and seawater is 20C, density of air goes from 1.2 to just under 1.0 (kg/m^3), so you get about 16% more oxygen for the fuel to react with in a given cylinder volume, which will translate to 16% more torque or HP if there aren't other constraints.

So it's the difference between a 500hp engine and a 580hp engine. Material for a planing boat I'd say, given no weight penalty.

 

[sunchaser]

The nomenclature that's been around for over half a century for cooling marine after cooler charge air is raw water Vs jacket water.

 

[Lepke]

Some people have installed land engines in boats and small ships. Usually generators with radiator cooling. It makes the engineroom unbearably hot. Others have used air cooled diesels with the same result.

 

[CharlieO.]

Worked on a boat that had an air cooled diesel gen on board. Yes, the engine room was hot and loud. It was a landing craft so the idea was to be able to have power when we were on the beach. Also came in handy to assist a vessel in distress on the beach, was able to pull up next to them, they tied off to us for stability as the tide went out and were able to use our generator and welder to repair their hull before the next tide.

 

[DDW]

Here's a rough guess: assume coolant is 90C and seawater is 20C, density of air goes from 1.2 to just under 1.0 (kg/m^3), so you get about 16% more oxygen for the fuel to react with in a given cylinder volume, which will translate to 16% more torque or HP if there aren't other constraints.

So it's the difference between a 500hp engine and a 580hp engine. Material for a planing boat I'd say, given no weight penalty.

But again, that is the coolant temp exiting the hot engine. Certainly any engineer worthy of his degree would use the coolant after it has been through the seawater heat exchanger and is close to seawater temperature. Only the coolant exiting the block is at 90 °C, the coolant entering the block should be only a little elevated above seawater. If it is also 90° then your engine is about to overheat.

 

[rslifkin]

But again, that is the coolant temp exiting the hot engine. Certainly any engineer worthy of his degree would use the coolant after it has been through the seawater heat exchanger and is close to seawater temperature. Only the coolant exiting the block is at 90 °C, the coolant entering the block should be only a little elevated above seawater. If it is also 90° then your engine is about to overheat.

The temperature drop across the heat exchanger won't be that much under the worst-case conditions (high seawater temperature and heavy engine load). And heavy engine load is when intake charge cooling matters most. It wouldn't be abnormal to only have a 20 - 40* F drop across the heat exchanger (and therefore a similar rise from engine inlet to the return to the heat exchanger). If it's more than that, your coolant flow rate is likely too low or the heat exchanger is very oversized.