Frosty
Previous Member
Yellowjacket While a variable prop can improve efficiency in some cases said:
The Boat Design & Boatbuilding Site
Continuously Variable Transmissions
- Thread starter Fanie
- Start date
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apex1
Guest
Thats right Frosty, interesting. But wrong.
MattZ
Junior Member
Snowmobiles use a rubber belt with 100+ HP, but they are very high maintenance.
For a diesel engine there`s really little to no difference in efficiency at various engine loads. Gasoline engines have terrible efficiency at part loads, so there is some benefit in this case.
You can very easily achieve continuously variable transmission with a variable displacement hydraulic pump and hydraulic motor. The cost is very prohibitive though.
For a diesel engine there`s really little to no difference in efficiency at various engine loads. Gasoline engines have terrible efficiency at part loads, so there is some benefit in this case.
You can very easily achieve continuously variable transmission with a variable displacement hydraulic pump and hydraulic motor. The cost is very prohibitive though.
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apex1
Guest
Quite the opposite is true Matt, sorry.
And as mentioned a thousand times, the cheapest solution is a CPP!
MattZ
Junior Member
I'm afraid it's true.
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apex1
Guest
Do you call a difference of 100% between underload and full load conditions "no difference"?
I thought all the world knows about Diesel efficiency, obviously not so.
this shows a variety from 210 to 340g/kWh "only"
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MattZ
Junior Member
Now find a similar plot from a gasoline engine and see if you can spot the difference.
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apex1
Guest
No no, I will not do any effort to make your wrong statement look better!
And I know what I am talking, your statement shows you do not, sorry.
Regards
Richard
MattZ
Junior Member
I'm afraid that I'm right and you're wrong. If you looked at similar data for a gasoline engine you would see that the specific fuel consumption doesn't decrease nearly as rapidly as the load is increased.
Even then, the data you posted isn't the correct data to discuss the point I was trying to make, or the concerns of the original poster of the thread.
Even then, the data you posted isn't the correct data to discuss the point I was trying to make, or the concerns of the original poster of the thread.
A
apex1
Guest
What are you trying to tell us here? Please rethink your statement and / or formulation, you are wrong! And everybody knows you are.
Here you contradict yourself! Yes petrol engines have no big difference in specific consumption at different rpm or load. Diesels have!
We know a continously variable transmission, a CPP. That is the easiest and cheapest way to achieve the requirement. And when you read the thread that becomes quite clear. Though not all know exactly what a CPP is, that´s quite clear too, when one reads the more recent comments.
The concerns of the original poster were not related to diesel efficiency at various loads, as the first post shows, but your comment was, and it was wrong! And remains wrong!
A Diesel engines efficiency varies >extremely< under different load conditions, like it or not!
Regards
Richard
Last edited by a moderator:
MattZ
Junior Member
Here's some enormous change in fuel consumption for a diesel engine between part and full loads.
http://www.manbw.com/files/news/filesof2054/p387_0201.pdf Scroll to page four.
Kind of makes a CPP somewhat insignificant from a fuel consumption point of view.
http://www.manbw.com/files/news/filesof2054/p387_0201.pdf Scroll to page four.
Kind of makes a CPP somewhat insignificant from a fuel consumption point of view.
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TeddyDiver
Gollywobbler
I'm not sure where your logic comes from but..... that pretty much is the point of the advantages of a CPP.
MattZ
Junior Member
CPP is typically used to maintain a constant engine RPM for generators, hydraulic pumps, refridgeration plants, or to improve maneuverability, or in gas turbine and steam powered military ships so that they can avoid a reversing gear.
Also in RORO's where quick acceleration and high cruising speed are needed, icebreakers where you need high thrust for breaking ice and still achieve a high speed in open water.
They are used to give you high thrust when needed without over-revving the engine at high cruising speeds, or to allow you high thrust without overloading a smaller engine.
For the most part diesel engines don't vary in specific fuel consumption between different loads. Obvious at 0% load they are 0% efficient, but the difference in specific fuel consumption between say 30% load and 90% load is less than 10% (for a commercial engine. With that and the fact that a CPP is only optimum at one pitch angle, you erase the benefit of a CPP.
Look at the Caterpillar website for some engines and you see the relative flatness of the specific fuel consumption curves.
You won't often see a CPP on an ocean going crude carrier, even the smaller ones with 25,000HP (well within CPP territory) even though they see wide changes in loads running with or into the wind/sea, and fully loaded or minimum ballast.
Also in RORO's where quick acceleration and high cruising speed are needed, icebreakers where you need high thrust for breaking ice and still achieve a high speed in open water.
They are used to give you high thrust when needed without over-revving the engine at high cruising speeds, or to allow you high thrust without overloading a smaller engine.
For the most part diesel engines don't vary in specific fuel consumption between different loads. Obvious at 0% load they are 0% efficient, but the difference in specific fuel consumption between say 30% load and 90% load is less than 10% (for a commercial engine. With that and the fact that a CPP is only optimum at one pitch angle, you erase the benefit of a CPP.
Look at the Caterpillar website for some engines and you see the relative flatness of the specific fuel consumption curves.
You won't often see a CPP on an ocean going crude carrier, even the smaller ones with 25,000HP (well within CPP territory) even though they see wide changes in loads running with or into the wind/sea, and fully loaded or minimum ballast.
TeddyDiver
Gollywobbler
Sorry but why you don't study something about the subject instead of mixing up partial knowledge with irrelevant. Whatever anyone else states here won't help you .. or maybe you just Troll or smth..
Teddy
MattZ
Junior Member
No offense, but I think I'm a little more studied on the topic than you.
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