Technology and Operations
This forum is for discussing technological & operational matters pertaining to U-boats.
Re: U-boat diesel fuel consumption
Posted by:
Theo Horsten
()
Date: August 22, 2006 04:27PM
That is 165gram/hp/hr for the MAN which is about normal for a 4 stroke diesel. Depending on the type of engine it will always be somewhere between 165 and 180. In those days, that is. Nowadays diesels are running more economical.
It doesn't make any difference if the engine is used for propulsion or battery charging. If the engine is giving you 1400 hp, it needs so much fuel, no more no less. If the load is increasing, the consumption will change, which doesn't necessarily mean that the consumption will increase. A diesel may be using 180 grammes at 50% load and 165 at full load. When you want to run or have to run economical, you're not so much interested in the consumption per hour, what you want to know is the consumption per mile.
Jukka is looking for a figure that is accurate plus or minus 1 gram and I'm afraid that will be almost impossible. If you find it, it will be purely theoretical anyway. The curve the builder of the engine will supply, is the consumption they found on the testbed. Sufficient to calculate how much fuel you will need and good for comparing it with other engines, but the actual consumption will always be different. That's why the accuracy of plus/minus 1 gram is not realistic - not for practical purposes.
How do you calculate your actual fuel consumption at sea? How accurate are your calculations? Nowadays it will probably be easier to place electronic flow meters and let the computer do the calculations for you, but before the digital age a flow meter would never give you an accurate figure. Where do you measure the flow? Before the fuelpump? In that case you'll find a very high consumption because part of the fuel the pumps are receiving is going back to the day tank. After the fuelpump? That's difficult to measure. I'm sure it can and will be done nowadays: measuring the flow to every seperate cylinder, but not in the U-boat days.
So calculating the fuelconsumption was a matter of reading the level of the day tank. Accurate enough for everyday use, but never as accurate as Jukka would like to know.
Fuelconsumption is a very interesting subject. I can talk about it for days. With a nice cold beer, if possible. :-))
.
It doesn't make any difference if the engine is used for propulsion or battery charging. If the engine is giving you 1400 hp, it needs so much fuel, no more no less. If the load is increasing, the consumption will change, which doesn't necessarily mean that the consumption will increase. A diesel may be using 180 grammes at 50% load and 165 at full load. When you want to run or have to run economical, you're not so much interested in the consumption per hour, what you want to know is the consumption per mile.
Jukka is looking for a figure that is accurate plus or minus 1 gram and I'm afraid that will be almost impossible. If you find it, it will be purely theoretical anyway. The curve the builder of the engine will supply, is the consumption they found on the testbed. Sufficient to calculate how much fuel you will need and good for comparing it with other engines, but the actual consumption will always be different. That's why the accuracy of plus/minus 1 gram is not realistic - not for practical purposes.
How do you calculate your actual fuel consumption at sea? How accurate are your calculations? Nowadays it will probably be easier to place electronic flow meters and let the computer do the calculations for you, but before the digital age a flow meter would never give you an accurate figure. Where do you measure the flow? Before the fuelpump? In that case you'll find a very high consumption because part of the fuel the pumps are receiving is going back to the day tank. After the fuelpump? That's difficult to measure. I'm sure it can and will be done nowadays: measuring the flow to every seperate cylinder, but not in the U-boat days.
So calculating the fuelconsumption was a matter of reading the level of the day tank. Accurate enough for everyday use, but never as accurate as Jukka would like to know.
Fuelconsumption is a very interesting subject. I can talk about it for days. With a nice cold beer, if possible. :-))
.
