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Brake Specific Fuel Consumpiton and Listeroid Slow Speed Diesels


On the group today this topic arose. I started a reply, ended up researching things a bit more, doing some math and decided that a blog entry was necessary. I learned a few things in the process.

First off, what we’re talking about. The Listeroid engine, here built into a very nice genset by Rocketboy

RocketBoy's Lister 12/2 genny setA very nice setup by Rocketboy

Yep, a very nice OLD technology engine that’s as reliable as a box of rocks.

Next, a definition. Brake Specific Fuel Consumption or BSFC. This is the standard way of measuring an engine’s fuel efficiency and is expressed in units of lbs/HP-Hr. or pounds of fuel consumed per horsepower-hour produced. (You folks who are shackled to the SI system of measure will just have to figure out the conversions for yourselves.) This is an energy-in, energy-out calculation with a whole bunch of normalizing thrown in to make it easy to wrap your arms around. BSFC varies from about 1 for low efficiency engines to about 0.25 for the largest and most efficient.

The Post

>>Listeroids come in 6hp to 24hp, but I wouldn’t call the 6hp “small”. They
>>work great on everything from veggie to motor oil and tranny fluid.
>This link
>cites a claim of .3 gallons per hour @8,000 watts.

My Analysis

I have a serious problem with that claim. The accepted expression of fuel economy is pounds of fuel per horsepower-hour. Pounds can be converted to gallons for a specific fuel, of course. I’d consider 0.5 lbs/hp-hour to be a very good figure for a small engine.

Brake specific fuel consumption (BSFC) generally gets better with engine size. The very largest engine, the Sultzer, is also the most fuel efficient. See the Table below.

Engine Description Disp, Cu In HP RPM BSFC
Sultzer marine, max power 1,300,000 90,000 100 0.278
Sultzer Marine, max econ. 1,300,000 53,244 90 0.260
Stultzer Marine, overspeed 1,300,000 100,000 101.5 0.280 est
Caterpillar C18 1007 600 1600 0.352
Caterpillar 3126B-200 439 200 1550 0.340
Yanmar LV100 26.5 8.3 3600 0.459
MEP-531A 2 KW genny (yanmar) 12.9 4.2 3600 0.480
Lister 12/2 175 12 650 0.714 to 1.0 *

All the numbers are taken from the manufacturer’s specifications and normalized to English units.

(Damn, do you have any idea how lot it took to rustle up those numbers? Engine makers are kinda sparse with BSFC data.)

Of particular interest is this graph of BSFC vs RPM. This is taken from the data sheet for the Cat C18 engine. It’s remarkable to see the BSFC drop to its lowest (best) point at very high speed. Exactly counter “conventional wisdom.

Cat C80 BSFC graph Compliments of Caterpillar

* Let’s take a closer look at the Lister. It has a rep for good economy but I’m not so sure. Here a user of the 6/1 has measured 0.125 gal/kw-h. Let’s do some normalizing. Using 6.2 lbs/gal for diesel fuel, that is

0.125 * 6.2 lbs = 0.763 lbs/kw-hr.

One KW is 1.34hp so converting kw-hr to hp-hr

0.763 lbs/kw-h * 1.34 hp/kw = 1.02 lbs/hp-hr

The BSFC was measured on a 6/1 but it should be the same on a 12/2 since a 12/2 is really just 2 6/1s on the same crankshaft.

This is figured at the generator terminals (presumably). If we assume the generator is about 70% efficient then the engine BSFC comes to

1.02 * .70 = 0.714.

I think that number may be a bit high, based on perhaps some errors in measuring the original 0.125 gal/kw-h value. Problem is, after several hours at the Altar of Google, I can’t find anything else to base a calculation on.

Looking at the situation from the gallons-per-hour angle, that 4.2hp, 2kw army generator uses 0.333 gal/hr. Straight scaling from the army generator to a 12/2 is:

0.333 * 12/4.2 = 0.943 GPH.

A gallon per hour seems about right for a 12 hp engine and is quite similar to my 10KW high speed diesel running at maybe 3/4 load. Accounting for the low speed and water cooling, I might buy 0.8 GPH but not much lower, at least not without a turbocharger.

Generac QuietPack 55G generator Click for a larger image.

It’s interesting to note that with these small engines, there’s not a major economy advantage between diesel vs gas. From the manual of my QuietPack (photo above) 5.5kw generator, the full load fuel consumption is 0.97 gal/hr. Scaling from the army diesel generator,

0.333 GPH * 5.5/2 kw = 0.907 gal/hr.

Close enough to the same. My QuietPack’s engine is a Vanguard 27 HP engine being run at only 2200 RPM which, from the published power curve, is only about 11 HP. I doubt that Generac did anything to optimize the engine for this lower speed (cam and cylinder head part numbers are the same as for the regular 3600 RPM engine) so I bet the BSFC could be made a LOT better with some optimization.

I wish someone would actually measure a Listeroid’s BSFC sometime. Google didn’t turn up anything useful. Google hit the Lister engine forum where some people were slinging some pretty non-credible numbers around. Someone needs to do some actual measuring. (my numbers above are all from manufacturers’ spec sheets.) I’d like to have some more data to work with before I took that rather poor BSFC number “to the bank”.

While I’m at it, is there a Listeroid mailing list (NOT forum) somewhere? I’d like to get on it.


Posted by neonjohn on June 13th, 2007 under Power Generation

13 Responses to “Brake Specific Fuel Consumpiton and Listeroid Slow Speed Diesels”

  1. briankk Says:

    There is a VegOil engine mailingl list, which sometimes sounds like a Lister support group ;-), I think it’s hosted out of the UK..

  2. echarters Says:

    The lister 12/2 consumes 255 grams of fuel per kw. A 12 HP engine is 8.952 kw. That is 2282 grams of fuel per hour at full output.

    That Equals 1.028 lbs fuel per hour. A US gallon weighs about 7 lbs winter/summer average, so that is 0.718 gallons per hour. This is slightly worse than the 7% rule which states consumption should be 7% of the KW load.

    The Lister 12/2 puts out 100 foot lbs, so it wins over a gas engine on gen start up which goes to triple the HP load rating. This means that if you want to put a starting inducitive (motor) load across a generator, it had better be 3 times the electric motor’s rating. So a 4 HP motor attached to a load will need a 12 hp/ 9 KW genset. Gensets can be different unless they are connected to batteries direct, so start up should be decoupled and the batteries kicked in gradually if your gen is not over the load by three times. Twice is dicey.

    Don’t try to run a gas engine 24-7 for a year running any sort of load. It will last about 4 months unless it is long stroke with stellite valves. Few of them around anymore. B & S used to make one for pumps.

  3. neonjohn Says:

    Thanks for the comments, guys. A couple of things.
    The engine torque doesn’t matter much for motor starting since the torque is proportionally reduced as the RPM is stepped up to 1800 (or 3600) at the generator. What DOES matter is the stored energy in the rotating parts’ inertia and the ability of the generator to supply the overload without saturating.

    Obviously the Lister has inertia out the ying-yang. Those “old school” ST alternators like many people use with Listers has plenty of iron in the magnetic path and so saturation isn’t a problem.
    The trade-off is, of course, weight. I couldn’t very well move 1500 lbs of Lister and ST around like I can, say, my Generac 7000XLT.

    Inertia can be easily added to a belt-driven generator. I have a 10KW genset that I built using I Riggorini twin cylinder high speed air cooled diesel engine. I built it to run a concession stand which is mostly resistive loads. I needed it to be quite light so that I could move it around easily.

    A second use was as the backup generator for my restaurant’s refrigeration. In that capacity it needed LOTS of surge power. To provide that surge power I fabricated an approx 30 lb flywheel made from a piece of 1″ thick cold rolled plate. I machined it to accept a TaperLoc hub which enables it to be easily attached and removed from the generator’s shaft. This is the best of both worlds – a lightweight generator for easy portability and surge capacity when it’s needed.

    Speaking of, I used my Generac to power a concession stand 12 hours a day, 6 days a week for over a year. It quit at the end of that time but only because it had collapsed the aluminum pushrods. I replaced them and the generator resumed service. The engine is still tight and it uses no oil. I suspect that the pushrod problem was my fault for not keeping the valve clearance adjusted.

    It certainly wasn’t my first choice – the noise is almost intolerable – but it’s what I had on hand and it did the job. You really can’t plaster all high speed generators with the bad rep that the throw-away generators sold by the big box stores have rightly earned.


  4. Jason dinAlt Says:

    The Indian Listeroid manufacturer, Power Engineering, has fairly extensive test data on their 8-1 Lister clone at their website.

    Their data shows a peak efficiency of 250 g/kWh @ 4.8 kW output. That’s 0.410 lbs/HP h for those who actually find these units useful. This is not too shabby, if it proves accurate.

    For what it’s worth, I recently measured the fuel consumption of my 2-71 Detroit Diesel from Affordable Power. The numbers are not good and I will probably be replacing it with a Lister 8-1.

    The following data was collected with a fuel temperature of 15 degrees F and has been volumetrically normalized for 60 degrees F. The test fuel was #1 diesel. Test loads were provided by electric heaters, measured with a Watts-Up meter.

    Load: 0 kW
    Fuel Consumption: 0.90 gallons/hour

    Load: 1.76 kW
    Fuel Consumption: 1.02 gallons/hour
    Est. BSFC: 2.68 lbs/HP h

    Load 3.52 Kw
    Fuel Consumption: 1.13 gallons/hour
    Est. BSFC: 1.49 lbs/HP h

    I did not have a larger load to test, but if these numbers are extrapolated (0.90 gal/hour + 0.0653*LOAD gal/hour), I would expect the full rated capacity of 12.5 kW to consume about 1.68 gallons/hours. This would have a BSFC of 0.622 lbs/HP h. Absolutely terrible! Get a lister 8-1 instead.

  5. nutreite Says:

    hmmm….very interesting!
    thanks google

  6. Curtis Shipp Says:

    That is ok. I still like the fact they run on anything and live with the KISS rule.

  7. mike sherwin Says:

    what nobody takes into account is the fact that you can only get gas petrol from the gas station and costs whatever it costs fuel for a lister you can buy from whereever sells veg oil etc and can cost next to squat

  8. Dale Wiggins Says:

    I have read recently that 1 gallon of diesel should produce about 16 hp for an hour. Assuming that the UK site I read this on was using the bigger UK gallons then the figures achieved by you John are sort of in the ball park. I have seen BSFC figures for some older engines but they seem to be used more on engines destined for marine work. Probably more for the builder of the boat to match prop size and hull shape to engine outputs and revs.

  9. Gunney Says:

    Hi everybody! I have a lister-type 6-1 GTC engine running pump diesel at 632 revs pulling about 2 kw about 10-12 hours per day. Three gallons sucked up per day is the rough usage – and I’ve got almost 4000 hours of run time to back that up. The factory tank is about enough to run 12 hours at modest load – (that makes sense!)I really ought to get scientific about it, but so far anyway, the fuel has not been a biggie for us and I’ve got other fish to fry.

  10. Edward van natta Says:

    I lam looking for detail about your product place leave a message

  11. cujet Says:

    I have a 20/2 Listeroid diesel driving a 15KW ST generator head. I’ve reduced the RPM to 800 and accept the slight loss of HP. I can run my home off-grid with ease. It will run my 5 ton AC. I also run off-grid with an 11HP Subaru 1 cylinder 5500W generator (which will not run my 5 ton AC) .

    Interestingly, the smaller gasoline generator consumes 15 gallons per day. The Listeroid consumes about 8 gallons per day. Don’t forget the Listeroid is doing more work too.

    So, while the listeroid may not have superb efficiency, the typical small gasoline generator is absolutely horrible.

  12. Hardial Chand Says:

    I have 8hp ( w.cooled ) lister diesel engine & it consumes only( less than ) 1 liter of diesel per hour at 750 rpm and runs very nicely on 3″x3″size of water pump by underload !Please guide me its capacity for electric Generator.

  13. Hardial Chand Says:

    your effort is praisable for energy

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