Best Of

There are 3 main advantages to Propane. 

1. Higher octane than gasoline, meaning it burns cooler and more controlled, less influenced by hot spots (think detonation), which also can reduce NOx
2. Boils at -40 F, so it is introduced as a gas instead of a vaporized liquid, which means it mixes with the incoming atmosphere better to create a more consistent mixture throughout the cylinder
3. Higher BTU per pound, so it provides more energy per pound than gasoline

Side benefit, since it isn't a vaporized liquid, there isn't any that runs down the cylinder walls into the crankcase, so the oil stays cleaner.


On the inlet side of all engines, you introduce atmospheric air (78% NO2, 21% O2, and 1% trace gasses) and fuel (Hydrocarbons)

In perfect combustion, there are 3 by products, CO2, Water, and Nitrogen (inert - meaning it doesn't support combustion) Since nothing is perfect, there are additional gasses.

CO - Carbon Monoxide - which is created when fuel is burnt but not completely due to either too much fuel or not enough oxygen. This is colorless, odorless, tasteless, but very deadly

O2 - Oxygen - which is passed through unburnt when there isn't enough fuel to burn all of the air

NOx - Oxides of Nitrogen, which is created when combustion chamber temperatures are in excess of 2500 degrees F, where O2 molecules bond with Nitrogen to convert NO2 to NOx.

In addition, there is usually a small amount of unburnt raw fuel that passes through, measured in PPM (Parts per Million)

HC - Hydrocarbons - raw unburnt fuel that is not to be confused with CO which is partially burnt fuel

Where the real problem comes in (as it did 50 plus years ago) is that people don't take care of things properly and regular maintenance is not performed. You can take a late 60's car (non-performance) and the tailpipe emissions will rival a modern vehicle under most normal operating conditions. The major problems were caused by people not taking care of things.

The exception is the NOx, which can be produced by ANY vehicle that is operated under a load but again is caused most often by combustion chamber deposits or a leaner than desired Air-Fuel ratio. The EPA fix was to install a catalytic convertor that could treat the NOx. NOx is blamed for low level smog in the larger cities. Today the concern has moved to CO2 (aka the greenhouse gas).

So, the bottom line with small engines comes down to keeping things like air filters clean, regular replacement of the sparkplug(s), and using clean fresh fuel (preferably without any ethanol added), along with a stabilizer, such as Stabil. 

Most people who wish to have a dual fuel or propane powered generator are wanting to get away from carrying gasoline in a can or dealing with the smell of gasoline that is in the generator. If you have use a SUV for a TV, I wouldn't ever carry a gasoline container inside the vehicle.

Brad

Yes, yes it does.  Glad we both survived our towing incidents.  
Cheers

Yes, but a firefighter or other first responder, has no way of knowing if the gas valve is open or shut, without looking first.  A locked tank access area makes that hard to do.