Marinising BMW 3.0 Turbo diesel

[Rokraider]

Originally Posted by captnjack

I have never heard of an air cooled marine engine of that size, hp, and heat production. Not having any cooling water I'm guessing you'll have dry exhaust too? That would be a bit odd on a trailered boat around here.

My intention is to have a conventional water cooled system as used in a car with the cooling for the radiator, intercooler and oil coolers supplied by electric and hydraulic fans, rather than a separate heat exchanger and pumping sea water round via a heat exchanger to cool the engines coolant.
The exhaust will be short and dry with lagging around the turbo and pipe to contain the heat. The engine box will be well ventilated with double blind air ducts, so plenty of air will be passing through with any water splash dealt with by the blinds. I dont believe the heat is going to be a problem.

[chewy]

Originally Posted by Rokraider

I dont believe the heat is going to be a problem.

Hmm, I think your engine box will be toasty.

[Leapy]

Originally Posted by Rokraider

My intention is to have a conventional water cooled system as used in a car with the cooling for the radiator, intercooler and oil coolers supplied by electric and hydraulic fans...I dont believe the heat is going to be a problem.

At full chat - and I'm assuming that having taken the trouble and expense to uprate the engine to 275hp you intend to use it - then you'll be looking to dissipate something like 200kw heat to coolant through a coolant to air radiator and 200kw heat down the exhaust.

I suspect the cooling is going to need careful thought to avoid thermal runaway. Electric and hydraulic fans may well do a good low speed, low heat job as they do in a car...but 200kw heat to coolant to air at boat speeds using ram air only? That's a very big ask.

[chewy]

Its gonna be noisey too, if you do get enough circulation to cool the engine then you'll end up with pretty big vents too.
The turbos gonna throw out a shed load of heat, if its on load for any period of time its prob gonna end up glowing red.

[captnjack]

Agree with Leapy and Chewy here.

You have a big heat dissipation problem and in opening up the engine compartment to create the air flow while using dry exhaust you are creating a big noise problem.

One of the huge benefits of wet exhaust in the massive reduction in volume you get via cooling the gas. That volume reduction with water alone muffles sound quite well compared to a dry muffler.

I would look again at a water-water heat exchanger and wet exhaust. There's a reason 99+% of inboard RIBs have gone the wet exhaust route. As far as air cooling with a radiator, I don't think its feasible unless you have a essentially open engine like a car - and a big radiator. There are no low work downhills at sea.

[Rokraider]

All good points to consider. Nothing is set in stone at this point. One of my biggest headaches is there is a lot of surface weed where I intend to spend a lot of my time we have had several boats cook their engines due to weed blockage in the seawater circuit. I am interested in exploring alternatives. The mud pluggers I have built in the past with radiotors in the back and fans have worked fine even when under heavy loads with no airflow to help.

More to think about on the subject..

[Erin]

With the right kind of strainer, a good filter basket and an exhaust overheat alarm I think I'd be going down the raw water cooled route.

[captnjack]

Originally Posted by Erin

With the right kind of strainer, a good filter basket and an exhaust overheat alarm I think I'd be going down the raw water cooled route.

In an auto engine? I don't have any data, but having salt in there just gives me the hebie jebies. If I ever get a inboard powered boat again I will be getting a sea chest/raw water strainer with a macerator to chop up any offending weeds.

Keel coolers are nice but never seen one on a planing boat. Being partial to wet exhaust myself the keel cooler seems like excess risk of corrosion or impact when you need to bring water into the boat for exhaust anyway.

[Rokraider]

Originally Posted by captnjack

In an auto engine? I don't have any data, but having salt in there just gives me the hebie jebies. If I ever get a inboard powered boat again I will be getting a sea chest/raw water strainer with a macerator to chop up any offending weeds.

Keel coolers are nice but never seen one on a planing boat. Being partial to wet exhaust myself the keel cooler seems like excess risk of corrosion or impact when you need to bring water into the boat for exhaust anyway.

I wouldn't run salt water through the engine cooling system. That would just have a sealed system with the usual anti freeze / water mix circulating. The engine coolant would pass through a heat exchanger which is essentially a radiator that uses sea water to cool it, rather than air. The heat is drawn out of the engine coolant and transferred to the sea water via the heat exchanger.

I agree about keel coolers, they would seem very vulnerable, especially as it is likely to spend time in very shallow water with a high risk of going aground. At speed a large area of the hull will not be in the water much of the time.

The castoldi jet unit has a take off pipe that will pump sea water round a circuit when the jet is pumping, but will do nothing when the jet is in neutral, it will still need a second pump to circulate the sea water if the engine is idling with the jet in neutral.
To complicate the exhaust further, I am going to run a particulate filter to clean up the emissions. It is not very pleasant being towed in a dinghy behind a diesel. It would not be possible to allow salt water to pass through the filter, so if it ws to be exited via the exhaust, it would have to be down stream. At the moment, the planned exhaust is only going to be probably 4 feet long from the turbo, with the particulate filter taking up at least 2 feet of that, so the benefit of water cooling the last 2 feet is almost negligible.
My plan is to wrap the entire exhaust including the manifold, turbo and filter using the upper end of the product range:
Thermo-Tec : Latest exhaust insulating and heat protection technology
My theory being that the exhaust is so short with little backpressure, that the gas will pass through quickly and the wrap will contain what does hang around, hopefully limiting much radiation.
In an ideal world it would be good to have a water jacket around the exhaust manifold, but it will be a very high dollar option and difficult to manufacture reliably unless cast.

[chewy]

I'd scrap the particle filter straight away, having it mapped and leaving the DPF is a backward step.
Does the jetdrive have neutral?
A guard around the keel cooler would sort the ground problem.

[captnjack]

Yes I know what freshwater cooled is. I was responding to Erin's idea of using raw water cooling. I wouldn't on an engine of this origin and value.

Not sure about that exhaust filter idea.
Given:
the volume of dry exhaust in an engine of this HP range,
the need to have near zero backpressure, and
the particulate size range (~2 um)that you need remove to accomplish your objective...

That filter is going to have a cross sectional area measure in many many square meters. And its going to clog up fast.

[chewy]

Originally Posted by captnjack

Yes I know what freshwater cooled is. I was responding to Erin's idea of using raw water cooling. I wouldn't on an engine of this origin and value.

Not sure about that exhaust filter idea.
Given:
the volume of dry exhaust in an engine of this HP range,
the need to have near zero backpressure, and
the particulate size range (~2 um)that you need remove to accomplish your objective...

That filter is going to have a cross sectional area measure in many many square meters. And its going to clog up fast.

The DPF was probably fitted as standard by BMW which is why he's looking at reusing it.

[Leapy]

Originally Posted by Rokraider

To complicate the exhaust further, I am going to run a particulate filter to clean up the emissions...
My theory being that the exhaust is so short with little backpressure, that the gas will pass through quickly and the wrap will contain what does hang around, hopefully limiting much radiation.

A DPF is a difficult programming task...hope you've got the experience or have access to it. What are going to do with the trapped particulates?

Exhaust heat - sounds like you're planning re-writing thermodynamic law. In simple terms, 200kw is 200kw, regardless of gas velocity and back pressure. Consider this...if you've got boiling water flowing down a metal pipe are you saying the shorter the pipe the less hot the pipe gets?

[Rokraider]

Originally Posted by Leapy

A DPF is a difficult programming task...hope you've got the experience or have access to it. What are going to do with the trapped particulates?

Exhaust heat - sounds like you're planning re-writing thermodynamic law. In simple terms, 200kw is 200kw, regardless of gas velocity and back pressure. Consider this...if you've got boiling water flowing down a metal pipe are you saying the shorter the pipe the less hot the pipe gets?

I am not expecting the exhaust temperature to be lower, if anything it will probably be higher. I was working on the basis the shorter the exhaust length, would equate to less metal to radiate the heat into the engine box and the thermal wrap would also help reduce the heat radiation, hopefully leading to lower temperatures in the box.

I am still looking at the diesel particulate filter idea, my initial thoughts are to mount the filter on the transom above the Castoldi, as it is dead space. This would also get another very hot item outside of the engine box.

There is a system made by Dinex that has a removable core that you take out and clean and refit once in a while. The crap coming out of it is toxic and has to be disposed of properly. This system is designed to cope with traffic use in cars. the more stop start use will clog the filter quite quickly, requiring it to be cleaned annually. If it is used in mostly middle to high speed situations, it may only need cleaning every couple of years. 4' from the turbo is a good distance for the filter as it will burn a lot of the crap off, but will get very hot doing it. The other option is as mentioned above, to use the original car unit and mapping. The other big problem is that the ceramic based core does not like thermal shocks, such as getting dunked in a wave whilst red hot, so this will need some thought as well.

I realise that this project is all sounding a bit Heath Robinson, but I enjoy exploring options and alternatives to the norm. Most companies stick to tried and tested as it is the most economical route to go with least risk. As this is a private project for my own use, I am happy to explore an apparently dumb route on the offchance that something worthwhile can come out of it. The speed that technology jumps these days often means that what wasn't possible 5 years ago is common place now.

Thanks for your input.

[Leapy]

Nice answer

You'll have great fun doing it. There's hurdles to over-come but I like your can-do attitude. Good luck :thumbs

[Erin]

Originally Posted by captnjack

I was responding to Erin's idea of using raw water cooling. I wouldn't on an engine of this origin and value.

Poor explanation on my part. I was referring to raw water cooling of the heat exchanger, not the engine block. I'd agree that it would be mad to send brine through the engine.

[chewy]

I'm with Leapy, like your attitude, no doubt you will sort something.
Still not convinced on the DPF though...

[captnjack]

Good attitude.
I actually like the filter idea the more I hear about it. The heat and an air radiator is still concerning me though.

[captnjack]

Originally Posted by Erin

Poor explanation on my part. I was referring to raw water cooling of the heat exchanger, not the engine block. I'd agree that it would be mad to send brine through the engine.

At least on this side of the pond
"raw water cooled" = sending salt water through the engine block
"freshwater cooled" = using a heat exchanger.

I don't know what to call an air radiator on a boat.

[Leapy]

Originally Posted by captnjack

I don't know what to call an air radiator on a boat.

Unique?

Going to make a good build-a-boat thread though