Engine performance in varying ambient temperatures

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J-N
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Engine performance in varying ambient temperatures

Postby J-N » Wed Sep 20, 2017 6:07 am

Hi all,

I am a mechanical engineering student in Delft, the Netherlands and I'm conducting a research on ship performance in different ambient temperatures.

So far I'm mainly focusing on finding reduction factors or formulas which can tell me how a engine performs in different climates. A ship (and it's engine) seem to perform better in cold (atlantic) water compared to warm (tropical) water. However, I can't find exact data or literature.

Factors I'm looking into:
- Seawater temperature -> primary affects the engine cooling and secondary density of the water
- Air temperature -> intake temperature for the engine -> oxygen decreases with higher temperature

I'm not taking fouling of the hull/propeller into consideration right now, so I'm consider the ship & it's engine as new.

Anyone able to help me out with literature studies, calculations or any other information?

Thanks in advance!

Kind regards,

Jeroen

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Big Pete
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Re: Engine performance in varying ambient temperatures

Postby Big Pete » Thu Sep 21, 2017 12:09 am

Hi Jeroen,

Welcome t the site.
I am not an Academic so I can't point you in the direction of Academic papers on this.
However, the main factor for the engine is the air temperature at the air intake to the engine. The colder and drier the air and the higher the air pressure the better.

I remember reading about a Railway line, I think it was in Peru, South America, that was running 100 year old wood fired steam locomotives over the Andes. They decided to modernise and bought new Sulzer powered Railway Locomotives. Everything was fine down at sea Level but the engines lost power and died as they climbed up the mountains because of the drop in air pressure/Density. Had to go back to the steam locos while the diesels were modified. You will usually see in makers Literature that the performance of engines is quoted at Sea level with a note that you should contact the makers for specific advice if operating the engine either above or, in the case of the Dead Sea and some other locations, below Sea Level, where the air would be denser and the engine could be overloaded.

JK has written on this site about problems with ice breaking ships engines caused by very cold air inlet temperatures making the air much denser than the engine makers had designed for.

It should be obvious to you that in hot humid climates the turbochargers compress their normal volume of ambient air but when it is cooled by the inter coolers to the correct temperature, and all the water condenses out and the remaining air has "shrunk" much more than it would if it had started out colder, there is less mass flow of air going into the engine than there should be, so the exhaust gas temperature will be higher for any given power output, simply because the heat energy added by the fuel is spread over a smaller mass of air. This will limit the maximum power output.

For propeller calculations, water is always assumed to be "in elastic" and "in compressible", however, if air is dissolved into it, the air bubbles will make it elastic and compressible to some extent, cold water can hold more air in solution that hot water so this problem can be worse in areas with low Sea Temperatures. In some parts of the World, including the Persian Gulf, perforated pipes are laid on the Sea Bed and compressed air is blown through them during storms, the wall of air bubbles created, makes the Sea elastic and stops the propagation of waves, creating a calm area at Port entrances much more cheaply than a Concrete and stone Breakwater.

The other problems are to do with designing the cooling system.
Obviously the hotter the Sea water the more volume flow is required to transfer the same amount of heat, and the bigger the heat exchanger area required to keep the engine cooling water lubricating oil and charge air temperatures within specification. There have recently been widely reported problems with the British Daring Class Destroyers, because there cooling system is inadequate for warm waters and they repeated have total electrical failures. This has also been discussed on this site.

Hope this helps.
It is always better to ask a stupid question than to do a stupid thing.

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Re: Engine performance in varying ambient temperatures

Postby J-N » Thu Sep 21, 2017 1:42 am

Hi Big Pete,

Thanks for the welcome and the thorough reply. Most of the information was roughly known, however I didn't know about the propeller calculations and the perforated pipe system plus bubbles in the water etc. Any more information on the system and it's calculations?

Of course the engine design specifics are very important to this matter. Ships designed for hot humid climates will actually perform properly, a lot can be done with today's knowledge. Given the fact that the ship's working area is being taken into account when designing the ship, they still have to move through different climates from time to time. Either because the ship is simply moving all of the world or the ship is changing jobs. This doesn't make my research any easier, unfortunately.

Any more information/questions/suggestions/discussion is more than welcome! Thanks.

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Re: Engine performance in varying ambient temperatures

Postby D Winsor » Thu Sep 21, 2017 3:58 am

One particular calculation that can sometimes tell a lot with respecet to propeller and mechanical effiency in a wide variety of air and water temperature conditions is Propeller Slip. Slip is the difference the theoretical speed the propeller is capable of producing at a given pitch, or the distance the propeller will move in one revolution in a solid material, to the actual speed of the vessel.
There are may factors that will affect Propeller Slip and ultimately vessel efficency such as Water Density (Salt,Fresh & Brackish Water) Water Temperature, Depth of water, Currents & Tides. Even on vessels where the propulsion machinery is operationg at peak efficency factors affecting propeller slip can produce major variations on vessel and fuel efficency.

One particular zone of operation you could look at for further insight, is into the design and construction of vessels specifically designed to work in the Great Lakes. These vessels are designed to operate from sea level to 183 meters above sea level, in Fresh Salt & Barackish water, in very shallow waters sometimes within a meter of the bottom in canals and rivers, extreme arctic type conditions in winter to almost tropical conditions in summer, and contend with strong river and tidal currents.
Troubleshooting 101 "Don't over think it - K.I.S.S. it"

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Re: Engine performance in varying ambient temperatures

Postby J-N » Fri Sep 22, 2017 5:14 am

Will look into those vessels as well as the slip, see if I can get some theoretical and practical values and calculations on that.

Additional question to all; is there a way to calculate engine shaft power/torque without a meter on the shaft? By calculation on input/output temperatures or whatever?

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Big Pete
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Re: Engine performance in varying ambient temperatures

Postby Big Pete » Fri Sep 22, 2017 10:13 am

Hi J-N,
The Old way was to calculate Indicated Horsepower, by using a mechanical indicator card, this worked like a recording barograph to record cylinder pressure for each individual cylinder, and the drum was rotated by a piece of string linked to the camshaft so that the Indicator card drew a graph of pressure against piston stroke. A mechanical integrator was used to calculate the area under the curve which represented Horse Power or kw.
The Indicated Power, less frictional losses inside the engine is equal to the shaft power.
Nowadays electronic strain gauges can be screwed onto the indicator cocks on each cylinder of larger engines and crankshaft angle measured electronically and a computer does all the hard work.

Engine makers usually produce graphs of the principal engine parameters against power, measured during test bed trials. However the results are often different when the engine is installed in a ship, for example the exhaust pipe will be much longer in a ship than on the test bed and greater exhaust back pressure will increase the exhaust temperature.
Comparison of charge air pressure and Turbocharger RPM will usually give a good approximation of power output.
BP
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JK
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Re: Engine performance in varying ambient temperatures

Postby JK » Tue Sep 26, 2017 4:42 am

Just asa BTW:
Ships that regularly work in colder waters will recirculate the discharge back into the seabays. The engines don't see the colder temperatures.

Fascinating topic

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Re: Engine performance in varying ambient temperatures

Postby J-N » Wed Sep 27, 2017 11:44 pm

Thanks for your input again all.
I've established a model based on ISO 15550 (Internal combustion engines - Determination and method for the measurement of engine power) which should give somewhat of a correction based on the performance of the engine. Going to check this model with engine makers. On turbo-charged engines the ambient variances don't have a lot of effect. The sea water cooling systems (HT/LT) is still something I am unsure about.

I will continue researching on other parameters, like ship propulsion/hull performance vs. density in water.

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Big Pete
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Re: Engine performance in varying ambient temperatures

Postby Big Pete » Thu Sep 28, 2017 3:09 am

I think the latest generation of engines with precise control of charge air pressure through 2 stage turbo charging with waste gates to precisely control charge air pressure and 2 stage charge air coolers to precisely control charge air temperature can almost completely compensate for changes in ambient air temperature. However, there are still relatively few of them in service Globally.
Modern marine Engines tend to have an HT (High Temperature) or JW (Jacket Water) enclosed Fresh Water cooling system, treated with corrosion inhibitors. This circulates through the cylinder Blocks (Entablatures), cylinder Heads and Turbocharger casings, in some cases it is also circulated through heat exchangers immediately after the Turbo charger in the charge air manifold. This will pre- heat the charge air at low engine loads (low scavenge (charge air) pressures and temperatures, in order to improve combustion. At high loads when the air temperature leaving the turbocharger compressor are much higher, the same heat exchanger acts as a first stage air cooler.

Older engines used a S.W. (Sea Water system to cool the H.T. or J.W. and the Lubricating oil and charge air.

Newer engines use an LT (Low Temperature) enclosed Fresh water cooling system, treated with corrosion inhibitor, to cool the charge air and Lubricating Oil and (usually by mixing through a Thermostatic valve) the HT coolant. This means that the heat exchangers used for this do not suffer from corrosion, Bio Fouling and blockage by mud, shells and other debris in the Sea Water.
However the LT Water still has to be cooled by Sea Water so all these problems still occur at this point.
The LT water can cooled by Tubular heat exchangers, plate heat exchangers, keel coolers, or Box coolers, but they all, except the keel coolers suffer from these problems.

Many modern ships use a single LT cooling system to cool the main propulsion engines, Electrical Generating sets,condense steam from the steam plant, Bow and Stern Thrusters, Air conditioning, and Refrigeration systems. Traditionally there would be separate SW systems for the main Engines and for the Generator sets, and probably a General Service SW pump providing cooling for the Refrigeration and Air Conditioning Plant, steam condenser, as well as Toilet Flushing water.

Hope that clears up your understanding of HT/LT!

With regard to propulsion efficiency wave action continually aerates the Sea. As I said before the dissolved and suspended Gases make Sea Water slightly elastic and compressible, and can come out of suspension and solution at low pressures, creating gas bubbles or even sheets. Cavitation is often thought of as the Sea Water boiling at low pressure, but just as with bottled beer, reducing the pressure above the aerated liquid causes it to foam. The obvious low pressure points are the at the propellers and the afterbody of the vessel, where the water that has been divided and pushed aside by the Bows is being pulled back towards the hull of the ship.
Good luck with your research, and I would like to congratulate you on your English..
It is always better to ask a stupid question than to do a stupid thing.


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