Gas vs propane 'peak' wattage? - Power Equipment Forum : Power Equipment Forums
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post #1 of 8 (permalink) Old 09-08-2019, 11:24 AM Thread Starter
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Gas vs propane 'peak' wattage?

I'm trying to understand a little about the starting vs running Watts when on propane with a dual fuel generator.

For instance, the Champion 100263 3400/3100 Inverter generator.
https://www.championpowerequipment.c...fuel-inverter/

I understand that on gasoline, 3400W is as high as it goes, whereas 3100W is for running normally. But what sets those limits? The engine specs? The inverter board? Something else?

The reason I ask is, if propane on that model peaks at 3060W, why couldn't that also be the running wattage as well? We already know it can handle up to 3400W if needed. So what is the limiting factor? Does it simply not suck propane fast enough?

I can see their running vs peak numbers on propane is a ratio compared to gas, but why aren't those two numbers much closer on propane?

Thanks
Robert
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post #2 of 8 (permalink) Old 09-08-2019, 11:49 AM
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I've always assumed the limits were due to the inverter boards getting too hot when outputting above the running wattage.

My EU2000i can put out the starting (2000W) for up to 30 minutes before overloading, vs the 1600W running wattage. Whereas, from what I've read, the Yamaha 2000W inverter can only produce the 2000W for about a minute before overloading, vs the 1600W running.

That, to me, implies it's an inverter limitation. FWIW, my starting rating is about 25% above the running, vs the Champion at 10% above running.

But your point is a good one. The engine will produce less power on propane, as I understand it. But if it was just the inverter getting too hot >3100W, then perhaps the starting watts could be the same as running, if both were under 3100W. Since that's not the way they rate it, maybe it does also have to do with engine limitations?

It may depend on more subtle aspects. If the inverter gets lower voltage from the alternator, on propane (due to less torque, perhaps), then maybe it's because the input amps to the inverter are the same as at full output on gas. And electronics heat often relates more to amps, vs actual power.
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post #3 of 8 (permalink) Old 09-08-2019, 12:06 PM Thread Starter
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I was just using the Champion generator as an example because it's a commercial product, but I'm also curious on propane conversions to Hondas, Yamahas, etc. Most of those conversion companies state the same reduction in power, but I wonder if it was ever tested, or if they are just theorizing it based on energy density differences.
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post #4 of 8 (permalink) Old 09-08-2019, 07:10 PM
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Originally Posted by Robh View Post
I was just using the Champion generator as an example because it's a commercial product, but I'm also curious on propane conversions to Hondas, Yamahas, etc. Most of those conversion companies state the same reduction in power, but I wonder if it was ever tested, or if they are just theorizing it based on energy density differences.
It's not theory; it's based on the difference in available HP between gas and propane due to the lesser energy available in the fuel. Conventional gasoline has an energy content of 116,090 BTUs per gallon, while propane has an energy content of 84,250 BTUs per gallon. 1.38 gallons of propane has the same amount of energy as one gallon of gasoline.
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post #5 of 8 (permalink) Old 09-08-2019, 07:30 PM Thread Starter
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But it can still take in more propane if needed, right? The difference between gas and propane wattage on these generations is not 38%.

Last edited by Robh; 09-09-2019 at 05:26 PM.
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post #6 of 8 (permalink) Old 09-09-2019, 03:55 PM
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But it can still taken in more propane if needed, right? The difference between gas and propane wattage on these generations is not 38%.
An internal combustion engine is essentially an air pump. There's only so much air that cylinders of a given size can pump through at up to 3,600 RPM. The fuel must be supplied close to the stoichiometric ratio. This is 14.7:1 by mass for gasoline and 15.5:1 by mass for propane. This has all been calculated into the carburetor jets for gas and the 2nd stage regulator settings for propane. You can play with it a bit to make it richer/leaner, especially with respect to varying altitude, but you can never get a given engine to make as much power with propane as you can with gasoline. It's even worse with natural gas where the ratio is 17.2:1.
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Last edited by tabora; 09-09-2019 at 09:02 PM.
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post #7 of 8 (permalink) Old 09-09-2019, 05:29 PM Thread Starter
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Originally Posted by tabora View Post
An internal combustion engine is essentially an air pump. There's only so much air that cylinders of a given size can pump through at up to 3,600 RPM. The fuel must be supplied close to the stoichiometric ratio. This is 14.7:1 by mass for gasoline and 15.5:1 by mass for propane. This has all been calculated into the carburetor jets for gas and the 2nd stage regulator settings for propane. You can play with it a bit to make it richer/leaner, especially with respect to varying altitude, but you can never get a given engine to make as much power with propane as you can with gasoline. It's even worst with natural gas where the ratio is 17.2:1.
Great answer. Thank you sir. That helps a lot.
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post #8 of 8 (permalink) Old Today, 08:50 PM
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Mod the engine

if the engine will be run on a dedicated propane line and never again on gasoline, I suggest you simply lightly port your intake tracts as well as your exhaust. then adance the timing on the engine by about 2-3 degrees this should be enough to bring the HP back up to above the level as it was getting with gasoline.



this is not as hard as you would think. find where the magneto, or coil is attached on the unit. if it use a hall effect cell, or magnetic pickup to an remote triggered ignition then you need to find the sensor.



pull covers so you can see the pickup or coil. use a simple inductive timing light and fire the engine up without covers and you should see that it fires just as the magnet section runs across the pickup or coil. this will be your actual Zero for our purposes (not degrees timing; but your personnel reference mark) stop engine, scribe/stamp/engrave a mark that allows you to return to this zero point. pull coil or pickup and using a small hand file slot out the holes in the opposite direction of rotation by 2 millimeters or about 1/8 inch. Now reinstall your coil/pickup, set your gap according to the manufactures instructions and you have just advance your timing by a couple of degrees (this is safe as propane needs the extra timing) . this adds HP.



next



open up your intake and exhaust. this may require you to pull the heads on the engine. if you are not comfortable with this then find someone who regularly pulls small engines apart. simply smoothing the transitions and the passages on BOTH intake and exhaust will net you gains. with gasoline you only want to polish the exhaust as a slightly rough wall helps the intake to prevent puddling of gasoline. with propane this is not an issue so the more flow you get, the more air and hence fuel can enter making more HP



You can add a whole HP on a 5HP engine especially when slight polishing of the ports is coupled with timing advance.



many years ago when we used to build racing lawn mowers, this was generally considered the bare minimum just to get started. there are many more involved methods of making more HP out of a small engine, but that would make this post take up a metric ton of bandwidth so email me for questions.


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