Cummins Onan genset - how to measure fuel burn - Q for ARE?

jfm

jfm

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This may be a question for ARE but if anyone else knows the answer I'd be interested to hear please

I'd like to get Cummins-Onan genset fuel burn data onto N2k network. Does anyone know how? My gensets are model code MDKBT, 23kva, though I do not think this Q is specific to a particular genset.

My research so far comes up with following possibilities:

1. Fit maretron J2K100s . These take the gensets' j1939 data and put it onto the boat's N2k network. Perfect, you'd think, but Maretron tell me this wont deliver fuel data onto the network, presumably because the Onan electronics don't "talk" this data http://www.maretron.com/support/know...000+network?. ARE is it really true that so little data can be grabbed off the genset's j1939 network? Is there a way to get fuel data?

2. Fit Maretron flow meters into the fuel flow and return lines. These then create the correct data for N2k network. These would work well, but cost is about £1000 per genset and I'd like to see if #1 above can be made to work before installing these. http://www.maretron.com/products/ffm100.php

3. Fit floscan metering. Very expensive, and impossible to calibrate for a genset, so this one is a non starter.

Any better ideas?
 
Being devils advocate, why do you want to know?

A genset on a leisure mobo is going to be very low fuel burn compared with main engines and will be relatively insignificant.

You can mitigate genset fuel burn by turning down or off all equipment including the genset if you want to be absolute and run on shore power where you have the choice.

I am anal about my fuel burn and I use a spread sheet for every fueling over 7 years, into which tank ie port or starb, against engine hours by each engine and miles through the water.

If the reason is to know how much is left in the tank go for the Hart system Tank Tender air gauges they are not electronic but very accurate providing you calibrate them against a fill up.

http://thetanktender.com/
 
Bandit said:
Being devils advocate, why do you want to know?
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On some trips it can be significant to me. I have virtually perfect data on fuel consumed by the engines and the fuel I had in the tanks when full, but if I go somewhere and anchor for a week the genset burn becomes significant and so I have to put a figure for genset burn into my calculation on whether I can get back to base without refuelling

Eg my outbound trip might be 40% of my tank, and return might be 40%, and then the question of whether my genset has used 5% or 15% becomes a big deal. (I work on a 10% reserve in most calculations, not 20%, in view of large tanks and a less weather-sensitive boat). Sure, I can estimate the genset burn, but I'd like to know a real figure especially if it only takes a little black box to grab it from the j1939 network that is already sitting right there on each genset
 
I know it is not directly what you want, but how about a Kw hour meter for the leccy, there are figs for the kw/hr fuel burn , then add a base amount for the fuel consumption on no load x no of hours run?

would give a reasonable idea perhaps
 
jfm said:
Fit floscan metering. Very expensive, and impossible to calibrate for a genset, so this one is a non starter.
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Why? I'm pretty sure that they also build sensors specific for gensets, and they also make a N2K interface, so probably you don't need to buy their gauge, just the flow sensor and the interface.
Tbh, I'm not sure about Onan compatibility, but they do make sensors for small(ish) Northern Lights gensets - 15kW or so, IIRC.
Can't see why they shouldn't work on Cummins engines...

That said, is the load/fuel burn so hugely variable?
I'd expect just a plain vanilla hours check to give a good enough ballpark number...
...particularly with a couple of C32 to feed, for which you surely don't want to count on the last 100 litres or so! :)
 
david_bagshaw said:
I know it is not directly what you want, but how about a Kw hour meter for the leccy, there are figs for the kw/hr fuel burn , then add a base amount for the fuel consumption on no load x no of hours run?

would give a reasonable idea perhaps
Click to expand...
Yup that makes sense as a second order of accuracy thanks, but I'd love to crack the problem at its root and know the actual number of diesel molecules that have been squirted through the injectors, if I can :-)
 
I understand your desire to predict what you will have after a week at anchor.

The important thing is to know you have enough for the return leg or whether you need to divert to an alternative port to fill.

I have the Hart/Tank tender system and I run a spread sheet to aid prediction.

I use 20% as the absolute minimum.

When I say calibrate as above I have two identical tanks just mirror image.

My tanks are shaped for the side of the hull to follow the hull/bilge shape. Ie 20mm of fuel on the gauge at the top of the tank is far more in litres than near the bottom of the tank.

I transferred all the fuel to the starboard tank, I then fuelled 50 litres at a time and took a reading which is in mm of each 50 litres until the tank was full .

From that I drew a graph and read the litres in the tank against the mm on the gauge. This is accurate to less than 15 litres per tank of 1250 litres each.

I don't trust electric fuel gauges and I am concerned as to how ell electronic ones are calibrated.

In my mind a dip stick would be ideal if a little agricultural.

With my system I can be accurate to within 30 litres out of 2500.
 
I understand jfm's wish to have an accurate fuel usage, but assuming the ave fuel burn of 4lt/hr, say 10 hrs/day, over 10 days, that's 400lt used. Can't remember the fuel capacity of Match 2, but assuming 6,000lt that is only 7%. For me I wouldn't want to plan a distance voyage using 10% reserve, 20% gives enough to cover the genny burn… but the OP is very experienced & well capable of his own voyage planning.
 
MapisM said:
Why? I'm pretty sure that they also build sensors specific for gensets, and they also make a N2K interface, so probably you don't need to buy their gauge, just the flow sensor and the interface.
Tbh, I'm not sure about Onan compatibility, but they do make sensors for small(ish) Northern Lights gensets - 15kW or so, IIRC.
Can't see why they shouldn't work on Cummins engines...

That said, is the load/fuel burn so hugely variable?
I'd expect just a plain vanilla hours check to give a good enough ballpark number...
...particularly with a couple of C32 to feed, for which you surely don't want to count on the last 100 litres or so! :)
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Yup but I'm trying to do better than an estimate. The comparison with C32 is, with respect, meaningless. If I do Antibes-Bonifacio return, I'll know for 100% sure that I had 7500 litres at the start and that the C32s have used and will use say 6000 litres. Assume I never want to go below 500litres due to tank sloshing and risk of air in fuel. At this point in the maths, the fuel burn of the C32s is meaningless. I just have 1000 litres that I'm happy for the gensets to burn and I want to know if they have burnt 800 or 1200 litres during my week at anchor say, and if there is a back box that just tells me that then alleluia. Otherwise it is all down to estimation.
 
pan said:
I understand jfm's wish to have an accurate fuel usage, but assuming the ave fuel burn of 4lt/hr, say 10 hrs/day, over 10 days, that's 400lt used. Can't remember the fuel capacity of Match 2, but assuming 6,000lt that is only 7%. For me I wouldn't want to plan a distance voyage using 10% reserve, 20% gives enough to cover the genny burn… but the OP is very experienced & well capable of his own voyage planning.
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I often plan based on 10% reserve and burn 90% of my fuel. Tanks are 7500 so keeping the traditional 20% as reserve, ie 1500 litres, is nuts imho. 1500 is a heck of a lot of fuel!
 
Bandit said:
I don't trust electric fuel gauges and I am concerned as to how ell electronic ones are calibrated.
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They are not gauges as such, on my boat, though I do have gauges as well. The electronic fuel metering that you get by drawing ifo from the j1939 network is is done by adding up the fuel that the ECU tells the injectors to squirt into each engine cycle
 
jfm said:
I often plan based on 10% reserve and burn 90% of my fuel. Tanks are 7500 so keeping the traditional 20% as reserve, ie 1500 litres, is nuts imho. 1500 is a heck of a lot of fuel!
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Out of curiosity, doesnt sea state account for more than 10 pct? I mean, if A to B will use 1000 litres, are you happy to go with 1100 litres ?
Or is a bit of a sliding scale 10pct on 7000 litres but maybe 30pct when the gauges read minus ;)
I admit I am bit uber cautious, but then the mechanical gauges have a mind of their own ...
 
jfm said:
Yup but I'm trying to do better than an estimate. The comparison with C32 is, with respect, meaningless. If I do Antibes-Bonifacio return, I'll know for 100% sure that I had 7500 litres at the start and that the C32s have used and will use say 6000 litres. Assume I never want to go below 500litres due to tank sloshing and risk of air in fuel. At this point in the maths, the fuel burn of the C32s is meaningless. I just have 1000 litres that I'm happy for the gensets to burn and I want to know if they have burnt 800 or 1200 litres during my week at anchor say, and if there is a back box that just tells me that then alleluia. Otherwise it is all down to estimation.
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Also playing devils advocate here, if your C32s use 3000 litres on the way from Antibes to Bonifacio, how do you know they will use the same on the way back given that fuel consumption is going to be dependent on sea state? Is it not more prudent to buy say 1000 litres of fuel in Bonifacio to be on the safe side and not worry about your gennie fuel burn?
 
a raggie speaks...

If the baffling in the tank is good, then the level will not surge (much). Would an ultrasonic or optical meter give you a precise enough output after calibration ?

And even small aircraft need fuel flow system monitors with the kind of precision jfm is seeking, with a greater impact if they get the figures wrong. Perhaps something here ?

http://www.aircraftspruce.com/menus/in/fuelinstrumentation_fuelflow.html

The Microflo device (other totalizers are available :) ) gives fuel flow, fuel used, fuel remaining, and endurance, though whether the output can be integrated into one of the big Match screens is a known unknown.
 
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My litres per mile ( though the water) vary from 5.5 to 7.6 , temperature, speed , sea state, hull fouling etc. so a 38% variation.

I keep 20% up my sleeve as a minimum, running in bad weather and pulling air instead of fuel on a roll, adverse tides and coming to port and there is a real emergency where I could make a difference are considerations.

20% gives me a theoretical 5.8 hrs, I don't want to run low or run out.

A lot of people rely on electronic equipment which gives you three decimal places of accuracy but on flawed date. Miles run and fuel burnt per NM is the only real data worth looking at. Work back from tank fill/miles run (through the water) data.
 
jfm said:
Yup but I'm trying to do better than an estimate. The comparison with C32 is, with respect, meaningless. If I do Antibes-Bonifacio return, I'll know for 100% sure that I had 7500 litres at the start and that the C32s have used and will use say 6000 litres. Assume I never want to go below 500litres due to tank sloshing and risk of air in fuel. At this point in the maths, the fuel burn of the C32s is meaningless. I just have 1000 litres that I'm happy for the gensets to burn and I want to know if they have burnt 800 or 1200 litres during my week at anchor say, and if there is a back box that just tells me that then alleluia. Otherwise it is all down to estimation.
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Well, I wasn't suggesting that the mains had anything to see with the genset fuel burn math.
I was just trying to put the overall relevance of the genset fuel burn in perspective.
Let's see: the 4l/hr pan suggested sound as a reasonable average to me. It's probably more at full load, but using the genset at full load 100% of the time is pretty unlikely. Anyhow, let's assume 5 l/hr, just to stay on the safe side.
Now, to burn the 400 litres of difference that you mention (and which I fully accept it'is not trivial!), it takes no less than 80 hours - hardly something that goes unnoticed.
And even then, with your two monsters spinning at planing speed, the 400 litres only mean a difference of what, a tad more than one hour, probably?
Not something I'd be happy to rely on, in a long(ish) passage. Though the difference would be more critical at D speed, of course.

Anyhow, all that aside, I did understand that you're after something better than an estimate - my comment re. the Floscan was in that direction.
Maybe worth a look, if you can't get the "real" numbers out of the Onan ECUs. Which I agree would be the easier/better way, if feasible.
 
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