# Natural Gas Conversion: Power Penalty?



## PeteCress (Feb 9, 2014)

I am assuming that a gasoline engine that has been converted to run on natural gas does not put out as much horsepower running on natural gas as it does on gasoline.

True so far? 

If so, and I want 4KW from a gas generator that has been converted to run on natural gas, what size generator am I shopping for? 5KW? 6.5KW?...?

*Edit 2014 02-11 21:17:*
I thought I had answered my own question. Browsing power.cummins.com, I come away with the impression that 4kw gas will get you 3.6kw on propane... so, I thought, can natural gas be much different?

The answer seems to be "Yes", and a *lot* different: http://www.propane101.com/propanevsnaturalgas.htm

Can anybody who knows something about this stuff put a finer point on it?


----------



## aandpdan (Oct 8, 2012)

I can't answer on the natural gas issue but I can on the propane.

I have two generators which I've converted using US Carbs kits. One of the steps you have to do to properly set them up is load it up to max load.

Both generators, a Tecumseh HM-100 5000 watt and a 3000 watt 7 hp Briggs easily ran at full output. 

While propane and natural gas may have less BTU's than gasoline, remember, the carbs on these engines are "low tech." The mixtures are often far from optimal. The gaseous fuels likely burn more completely so you better utilize the fuel. As I've said in other threads, my generators run MUCH more smoothly on propane than they ever did on gasoline.


----------



## ajnuzzi (12 mo ago)

aandpdan said:


> I can't answer on the natural gas issue but I can on the propane.
> 
> I have two generators which I've converted using US Carbs kits. One of the steps you have to do to properly set them up is load it up to max load.
> 
> ...


Interesting - I feel the same way about my natural gas converted generator. I know technically it's supposed to be significantly less power on natural gas than gasoline but I was able to fine tune the fuel mixture with the load block on the regulator to where it sounds like its running so smooth and doesn't bog down as much as it seems to on propane. I have not actually load tested this to see exactly how many watts it can push mind you, this is all going by ear test and how the motor sounds under load. For all I know it could be putting out 3000 watts less than gasoline but I wouldn't be surprised if it didn't lose as much power as people tend to think.


----------



## OrlyP (Oct 19, 2021)

It’s not a simple comparison.... gasoline vs propane or NG. Aside from the differences in energy content between these fuels, fuel delivery is also vastly different.

There’s nothing ‘simple’ about the carburetor. Every hole, orifice, passageway, vent, and their measurements has a critical purpose. Tolerances are pretty tight and usually, it takes very little to go wrong that can spell the difference between an engine running or not runnng, and everything in between.

Gasoline has to go through hoops inside this carb and as mentioned above, anything wrong with how the fuel and air is metered and the engine will run poorly, if it runs at all.

Propane and NG bypasses 90% of the carb’s function. It doesn’t care about jettings, the emulsion tube, float valve, clogged passages, etc. All it needs in a carb is a venturi and the throttle valve... that’s about it. Most of the work has already been done by the regulator(s). You can literally put the end of the propane hose into the air box and it will run.

That said, you may feel that your generator runs better on propane/NG compared to gas or that the generator produces more power on propane/NG than on gas and conclude that you’ve cracked the holy grail of load block tweaking. While that may be true, it may also mean that the carb isn’t setup right to run gasoline, hence the perception that gas is worse than propane/NG.

It’s just easier to get things right when running on gaseous fuels. The opposite is true for gasoline.


----------



## drmerdp (Apr 10, 2018)

I did gasoline/natural gas load tests on a champion 41532 7000/9000 generator with 439cc engine. It was a uscarb snorkel kit. It was able to produce 7000 watts on natural gas but needed to make the fuel mixture extremely rich. That much fuel on NG creates very high EGTs and would be detrimental to the longevity of the engine. That’s Why it’s better to just make a mental note of derating the output wattage, setting the fuel at the 80% mark and leaving it at that.


----------



## Browse Deweb (Jan 16, 2021)

drmerdp said:


> I did gasoline/natural gas load tests on a champion 41532 7000/9000 generator with 439cc engine. It was a uscarb snorkel kit. It was able to produce 7000 watts on natural gas but needed to make the fuel mixture extremely rich. That much fuel on NG creates very high EGTs and would be detrimental to the longevity of the engine. That’s Why it’s better to just make a mental note of derating the output wattage, setting the fuel at the 80% mark and leaving it at that.


I agree with this. Unless you have a diesel engine, you probably want to run a generator at lower loads anyway, especially for longer periods of time. For gens with eco mode, this means lower fuel use, lower temps and less engine stress...prolonging engine life.


----------



## OrlyP (Oct 19, 2021)

drmerdp said:


> I did gasoline/natural gas load tests on a champion 41532 7000/9000 generator with 439cc engine. It was a uscarb snorkel kit. It was able to produce 7000 watts on natural gas but needed to make the fuel mixture extremely rich. That much fuel on NG creates very high EGTs and would be detrimental to the longevity of the engine. That’s Why it’s better to just make a mental note of derating the output wattage, setting the fuel at the 80% mark and leaving it at that.


That's right. You can go particularly rich on LP/NG and the engine will still run smooth and will more than likely carry the rated load. It's easy to mistake this as a good thing but those extra fuel that's taking a longer time to burn will eventually reach the exhaust system and combust there, raising the EGT.

Right now, running on LP with half a load, I'm measuring 450°C at the exhaust pipe immediately after the cylinder. I believe this was around 425°C when I ran gasoline on it a few months ago. Ambient temp is around 30°C.


----------



## GenKnot (Dec 20, 2021)

OrlyP said:


> I'm measuring 450°C at the exhaust pipe immediately after the cylinder


OMG that's hot!
450°C is 842°F.
I am able to run full load on NG with my 3KW Champion using the carb-regulator combo from eBay.


----------



## OrlyP (Oct 19, 2021)

GenKnot said:


> OMG that's hot!
> 450°C is 842°F.
> I am able to run full load on NG with my 3KW Champion using the carb-regulator combo from eBay.


What temp reading do you get?

I find that the exhaust surface temp I measured is pretty close to the temperature they got in this study.

Engine out exhaust temp: ave. 720°C (1,328°F)
Muffler surface temp: ave. 520°C (932°F)


----------



## GenKnot (Dec 20, 2021)

OrlyP said:


> What temp reading do you get?


I don't know now. It seems that I have lost my readings. The FLIR shot that I found earlier was not the correct one (it was after shutdown) and now I can't find my other shots. I will have to make new readings when I drag the gen out again.


----------

