Q&A: I was told propane and natural gas produces less power than gasoline. Is this true?

Question: I was told propane and natural gas produces less power than gasoline. Is this true?

Answer: Both yes and no. Yes, propane and natural gas have lower BTU's than gasoline, but there shouldn’t be much loss in power.

Propane is 80% efficient compared to gasoline. This just means propane uses 20% more fuel by volume to generate the same horsepower.

But a reduction in horsepower is simply caused by mechanical limitations in the propane fuel system. Having the correct setup should maintain power output.

What is the difference between propane and natural gas? One of the difference is in octane rating.

  • Gasoline w/ Ethanol: 85~98 Octane Rating
  • Propane: 104~110 Octane Rating
  • Natural Gas: 130 Octane Rating

This higher octane allows for increased engine compression and combustion efficiency = increased horsepower. A typical gasoline engine would need to be either modified or reengineered to take full advantage of the high octane rating of either LP or NG. 

E85 Ethanol is a classic example of low BTU / high octane fuel being used in the aftermarket car community. If ethanol content is truly 85% ethanol, the octane rating would be close to 108. There are many videos on YouTube showcasing race cars producing over 1000hp with E85, and are street driven. The high octane fuel reduces engine detonation and pre-ignition under high loads. Especially in turbocharged or supercharged applications. 

We can get into more detail about this, but that would not pertain to what's really important. Which is how these fuels behave when being used on a typical generator. 

Not all generators are built the same. You can not generalize propane or natural gas to be bad, when it may have ran poorly on one generator, and then classify every other generator to likely be the same. People speak from experiences, but many have not taken the time to investigate why this is happening. 

Honda® has done a very good job manufacturing and engineering, efficient, quality, high output engines for several years. Both inside and out, Honda® really put a lot of R&D towards their generators in both engine efficiency and performance.

The only other manufacture that comes close to Honda® is Yamaha®. These small engine designs are so good, there are many Chinese copy's of these engines running rampant in the market. 

Because of the high standard in engine design from Honda®, we were able to match both factory specified surge and continuous power output rating when running on alternative fuel. How we were able to achieve this was though several visits to the emission testing station, analyzing engine performance on specialized test equipment.

We wanted to look at the numbers to make sure the engine was getting the correct amount of fuel, and running at the correct engine temperature while the generator was under varying loads. All of this was done while fine tuning the demand regulator. Once the demand regulator was perfectly dialed in for both low and high idle. The generator surge and continuous wattage power rating held up very well, and this concluded our findings. 

The most interesting discovery we ran into during the test was how particular the demand regulator can be when dialing in the adjustments. It dawned upon us on why folks may have trouble running alternative fuels, which resulted in some loss of power or engine surging when eco mode is on.

If the demand regulator is not dialed in perfectly, too much fuel or too little fuel will drastically affect either low end, or top end power of the engine. Too much fuel and you will loose power + over heat the engine, but too little fuel will result in engine surges and stalling or starting issues. Everything needs to be in perfect harmony to get the most out of your engine. 

The demand regulator acts similar to the float bowel in the carburetor. This regulator releases vapor fuel when the engine pulls vacuum through the intake, much like how air passes though the carburetor to pull in gasoline from the float bowl. 

The demand regulator needs to see good vacuum "low pressure" for its internal diaphragm to steadily open and regulate itself. To achieve reliable operation, this required a completely new design of the spacer plate adapter that installs over the opening of the carburetor. 

During low idle (eco mode on) less vacuum is produced in the intake. If the vacuum is not enough, the demand regulator diaphragm will not regulate properly when the engine is running. Resulting in engine surges or poor idle. The venturi design of the adapter allows for air to increase speed when passing through the adapter, resulting in a much better vacuum signal during low idle. Which helps the demand regulator function at both high and low idle. 

To summarize this concern, we will have upcoming videos to showcase the generator running on propane without issues. 

As for the design of the venturi adapter and doubts of its design. Please stay tuned for our next article. 


*Updated 11/4/2020