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Onan: Interesting Gas Vs Diesel consumption comparison on Youtube

K-Tron

Registered
Nice video Mike, I enjoyed watching it. I was thinking about load banking my Lister SR1 Kohler 3500watt generator head to compare to yours, but my neighbors would call the cops on me. There is nothing quiet about it with its factory muffler. Under normal operation it has run over six hours on a gallon of fuel, so it is likely a lot more efficient than your Onan diesel. One day I hope to record the fuel consumption of both my four cylinder Waukesha FC powered 10kw 1200rpm generator and my 1-71 GM diesel 10kw 1200rpm generator under varying load and full load. I am sure the difference between gasoline and diesel fuel consumption is going to be a factor of five or more.

Chris
 

BigBlockChev

Subscriber
Last Subscription Date
07/06/2019
What are you thinking is wrong with his conclusions?
I am not sure the adjustments made To the spreadsheet regarding the displacement is a valid concept. At no load it may be but at higher loads I think it is less of a factor. I am unable to quantify things like pumping losses, friction losses , thermal losses etc between the two types of engines. The compression ratio difference is a much greater factor as is the fuel/air ratio in my opinion. It would be interesting to do a comparison between a JC and a DJC with the same displacement and genset rating so more of the differences could be ruled out. I thought this was a good well thought out test but I think the results are skewed in ways which I am not able to define. Cheers Dan
 

Jim McIntyre

Subscriber
Last Subscription Date
07/10/2019
Yeah - he made adjustments based on rated capacity, as I understood it - one set was a 3kW and the other a 3.5 kW.

Still, his bottom line is not outrageous - the Diesel bested the gasser by about 2:1.
 

Horse Power at 511

Registered
Last Subscription Date
10/02/2016
Thanks for the input. My thoughts behind the “corrected” gas unit numbers was just as you thought Dan. I was guessing that the reason for the lesser rating on the diesel was due to the engine itself having less overall capacity at 1800 rpm compared to the gas engine. The issue is I don’t know that for sure, it may be that the Diesel engine is equally matched to the gas engine and the limiting factor is the generator end itself. If that was the case the correction factor would not be required. I think that a correction factor may be necessary when doing any comparison of units of different load capacities if the difference it engine based.
 

turtmaster

Subscriber
Last Subscription Date
07/01/2020
I could do a test between a 12 DJC and a 15 JC, I have both, I just have to put the sx460 regulator in the djc, and I have to locate a scale. Not too sure when I'll get around to it though.
 

Sooty Jim

Registered
Thanks for the input. My thoughts behind the “corrected” gas unit numbers was just as you thought Dan. I was guessing that the reason for the lesser rating on the diesel was due to the engine itself having less overall capacity at 1800 rpm compared to the gas engine. The issue is I don’t know that for sure, it may be that the Diesel engine is equally matched to the gas engine and the limiting factor is the generator end itself. If that was the case the correction factor would not be required. I think that a correction factor may be necessary when doing any comparison of units of different load capacities if the difference it engine based.
I agree with how you did it. Only so far you could go with an exact apples-to-apples test and fuel consumption tests at specific loads that were well within reach of both units made it a fair comparison. Might have been fun to see them both tested at their maximum loads, just to see, but you spent enough time as it was and stayed well focused on the stated subject.

That was one of the most enjoyably geeky videos I've seen in quite a while. You earned my subscription from it!
 

Vanman

Subscriber
Last Subscription Date
06/10/2020
In some cases the actual engine hp is published. I know it is for many of the Kohlers. That would be the ideal data to use for a correction factor. :brows:

Would be interesting to see if the hp data for these two engines could be found.

Is a CK a smaller engine than a CCK?

Keith
 

Sooty Jim

Registered
CK is 38 ci. I couldn't find it just now but I remember 10 hp @ 1800 on the CK... but don't hold me to that. The hp isn't in either of my two CK manuals. One of them lists up to a 2400 rpm model for the basic engine. These are manuals concurrent with the era of Mike's set.
 

Sooty Jim

Registered
Just found info from 1965 and the CCK was a bigger engine than the CK. It's shown with a 3.25x3" bore and stroke (49.7 ci) vs the CK with a 3x2.75" B&S (38.8 ci). The CCK is shown at 12.9 hp @ 2700/ 30 lbs-ft@1800. There is a Super CCK listed and it's shown making 16.5 hp @ 3600 and 29.5 lbs-ft @1800 (same B&S).
 

Horse Power at 511

Registered
Last Subscription Date
10/02/2016
Thank you for the info on the CK unit Jim!
I pulled the manual that I received with the 3DSP to check out the engine specs.
The 3DSP has a 3.5" bore and stroke, a displacement of 33.7 CI.
It has a compression ratio of 17.3 to 1 and is rated at 5.5 HP at 1800 RPM.
 

Sooty Jim

Registered
FWIW, 30 lbs-ft@1800= 10.3 HP, and 29.5 lbs-ft @1800 = 10.1 HP.
Yeah, all this makes me think that I have misremembered the "10 hp @ 1800" figure for the 38 ci CK. Probably nearer 6-7 hp. If so, that would even up Mikes test a lot more. I could swear I have seen the CK numbers somewhere, though.
 
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