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Can anyone give me a heads up on how these diesel fuel consumption charts work?

We kept very precise engine records during our six months on the canals and after 300 hours engine running we know for sure that our fuel consumption is 3.1 litres/hour.

The engine is a 60hp Lombardini. Max RPM is 3600 and we normally cruise at 2300rpm. From the engine curves at this rpm the engine is producing 27hp.

We are using a diesel consumption chart produced by the Barrington Diesel Club for a naturally aspirated engine which ours is. I have seen other charts but the info is all the same. So at our 27hp the chart says we should be burning about 6 litres/hour instead of the 3.1 litres that we actually are.

I don't understand it at all.

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It's a 4 cylinder diesel. At 2300 rpm we are pushing a 9 tonne canal boat with very bluff bows at 6 knots with 30 -80 cm of water under us. Shallow water is a big impediment to speed. we have lots of dangly bits under the boat related to the engine keel cooling so i think our performance from a 60hp engine is pretty ok. From what I have read these consumption charts are compiled on a formula of so many grams of fuel per horsepower. I'm not complaining that I'm only using 3.1 litres/hour instead of 6, i just like to know why the huge discrepancy.

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At 3.1l/h you aren't producing 27hp.

A good rule of thumb for non turbo is 20hphours/gallon. 3.1/4.5*20 is around 14hp.

In other words your prop doesn't have much pitch.

As well, and I know that this is a bit rough and ready, but our rev counter is accurate and we max out at about 3550 rpm with the engine puffing black smoke so the prop pitch must be ok for the engine.
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you are probably spending alot more time at low revs than you realise which will pull your average consumption down

Yep, thought about that which is why we were interested in our consumption once we left France and entered Holland - No locks which did involve slow speed running. In Holland our average daily runs were 3 hours. Start up in the morning and immediately get underway,no warm up but gradually increasing rpm as the engine warmed over a few minutes until we reached 2300rpm. And there we sat for the days run, reducing speed for a few minutes at the end to berth the boat and then "finished with engines'. Our fuel calculations were based on the holland part of the cruise.
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A consumption of about 250grams of diesel a kilowatt hour is a common figure for industrial diesel engines.  If you give Wheels the model number and he finds the figures it likely show a more precise figure.   Anyway,  so if you are using 3.1 litres and we use specific gravity of the fuel of 0.90 [this varies] we get 2.790kg of fuel or 2790 grams.  Divide this by 250......2790/250=11.16kw or 14.95hp.   Which is pretty close to Darkside's calculation of 14hp. 

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Lombardini LDW 2204M. 2014 model.

I've gone back through the figures and it gets worse (or better.)

Our fuel consumption figures are from Holland - No locks to mess up the engine run time with idling or slow speed running. Start, run for a few hours at 2300 rpm, stop. Since we start and stop from the canal back there is no slow speed maneuvering. And I confirm 3.1 litres/hour. What makes it better or worse is that it was getting cold by the time we got to Holland and we were running the central heating for an hour or two most evenings. I don't know how much diesel a Webasto unit uses. Not much I expect.

I take the point about not using the all the hp produced at 2300rpm but our boat is a barge - we have full beam 2 metres back from the so called pointy end so it's a bow in name only. So, we are pushing 9kt of barge at 6 knots using only 14hp?

Possible I suppose. We are turning a large 4 bladed prop, size and pitch unknown, through a 2.8 : 1 reduction. Also of course there are no wind or waves and only minimal current to contend with on the canals.

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The product manual for that engine shows about 255 gm / kWh at 2,300 rpm, so very close to what mcp said.

There is a bunch of caveats for being at sea level at 20 deg C etc... and a theoretical perfect propeller curve as well.

 

Page 8 on the below link

https://www.transdiesel.com/app_docs/lombardini%20focs%20series%20ldw2204.pdf

 

I looked closely at these engines for our repower, mainly cause they were cheap. Since then, they have been re-branded as Kohler, and painted black and gold instead of silver. BUT, the big thing was they were all rated at a very high Hp rating for the size and weight of the engine. They are all advertised as having lower Hp ratings now, in comparison to the engine size.

For example, the LDW 1404 M was being sold as a 40 Hp engine, but is only 1,372 cc. The engine we got is 35 Hp at 1,500 cc, i.e. less Hp at greater displacement (lower revving though 2,800 rpm instead of 3,600). I was always concerned that the engines just had the sh*t rung out of them to achieve the Hp rating. The rep basically agreed that was the case, after they started advertising them at the lower Hp ratings. That doesn't have much to do with fuel consumption though. My limited understanding is that it isn't revving that high at 2,300 rm compared to max revs, and its probably not consuming all the available power at the prop at those revs, if the prop is properly sized for max revs.

 

That LDW 2404 M is now advertised as 50 Hp. (Max revs appears to have dropped from 3,600 to 3,000 as well, but same displacement, engine weight etc)

https://www.lombardinimarine.com/en/product/ldw-2204-m/

 

PS, a 2 kW Webasto unit uses between 120 ml and 240 ml diesel per hr, depending on its heat setting. I'd say such a small amount, its hard to measure.

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In the old World, Engines used come with more realistic power figures. Today, there seems to be less of a range of power figures published and yet far greater range of uses for each industrial engine. We can have shafgt Hp, Brake Hp, SAE Hp, DIN Hp, Continuous, Max, Intermittent and I am sure I have forgotten some. So it comes down to what figure is used on the glossy brochure. Because manufactueres want to produce the smallest yet most powerful engine possible, they all tend to use the figure that gives them the best glossy publication figure they can get away with.

Also, as said above in a couple of posts, there are some variants that are set when bechn tested. Air temperature, How the air is devlivered, The exhaust restriction and the Fuel temp and viscosity during the lab test. All are variables in our real world installation. All have an affect on Hp and what an engine will burn.

 

mcp has some important figures and I will copy and past them once again below. The only difference between most modern Diesels and thew older ones is the high pressure fuel line with computer controlled injection. These newer engines are more efficient because they have greater fuel control delivery via the injector and the Torque curve canbe controlled more.

 

mcp "A consumption of about 250grams of diesel a kilowatt hour is a common figure for industrial diesel engines. Anyway, so if you are using 3.1 litres and we use specific gravity of the fuel of 0.90 [this varies] we get 2.790kg of fuel or 2790 grams. Divide this by 250......2790/250=11.16kw or 14.95hp. Which is pretty close to Darkside's calculation of 14hp".

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Firstly, thank you for all the replies. As a result I know quite a bit more now about engines, revs vs hp vs consumption etc so that's good.

So to summarise, I have an engine of indeterminate horsepower pushing a bath tub shaped boat at 6 knots in flat water for 3.1 litres of diesel per hour. I think that's pretty good, too.

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Yes absolutely be happy with that. Perhaps the prop being way under pitched is also the "clutch" to get your big heavy bathtub moving.

Thinking about this, you are correct. Opening up the throttle we don't so much accelerate as slowly increase speed. I have a few lightbulbs illuminating upstairs..

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Thinking about this, you are correct. Opening up the throttle we don't so much accelerate as slowly increase speed. I have a few lightbulbs illuminating upstairs..

If there are speed restrictions on the canals (i.e. 5 or 6 knts), then you'd be bonkers to fit a prop sized and pitched for max revs. As you've already stated, you've done several countries at 2,300 rpm. It is common for various boats to size and pitch their prop for max power / max speed at cruising revs, not full revs. The upshot means you can't make max revs. The only time where being able to make max revs is really important is when the engine is still under warranty (I'm sure others on here will say its a bad thing to do though). The converse arguement to the need to achieve max revs, is ensuring the engine is suitably loaded at the revs you do 95% of the time, i.e. cruising revs. This is focused on getting the propeller power curve closer to the engine power curve at the revs you use most of the time.

 

That said, I'm not sure that would explain your fuel consumption, and from a few posts in appears the opposite is true, your prop is under pitched?

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