Generator LPG conversions

[agentrfr]

Gasoline energy density = 9 500 Wh/L
* 25 L = 237.5 kWh

LPG specific energy = 13 778 Wh/kg
* 9 kg = 124 kWh

And 124/237 = 0.52
R 250 / R 450 = 0.55

So the price difference makes sense, unsuprisingly, because as I said above, price is based on energy content. The caloric value of 25 L of petrol is about twice that of 9 kg of LPG.

So the question is how are you getting the same runtime out of both fuels at these volumes? Is the engine twice as efficient on LPG? Or are you running half the load?




Clearly marketing speak. What about the physics though?

How would LPG offer superior efficiency? Does it burn much hotter? How?

How would LPG generate less CO? The only reason any hydrocarbon combustion produces CO is shortage of oxygen. Why would oxygen supply be different?

Same for hydrocarbon emissions. That's just unburned fuel. It's only going to be unburned if you're choking the engine or running it rich. Why would you do that? We are able to get stochiometrically near-ideal combustion ratios thanks to modern fuel injection and oxygen metering. Even without electronic control it defies belief that the OEM can get the design so wrong that an aftermarket conversion can work this kind of magic.

Ja so I have a lot of questions. Bottom line is this comes across as borderline perpetual-motion-machine-level bulls*it.

You're forgetting latent heat vapourization for the liquid fuel - afaik that is the difference in effective crankshaft output power.

With liquid fuel the latent energy is provided itself by the burning of the fuel in the combusiton chamber, with LPG the latent heat is provided by atmosphere heating the storage bottle as it cools/vapourises to maintain the vapour pressure

 

[Tomtomtom]

You're forgetting latent heat vapourization for the liquid fuel - afaik that is the difference in effective crankshaft output power.

With liquid fuel the latent energy is provided itself by the burning of the fuel in the combusiton chamber, with LPG the latent heat is provided by atmosphere heating the storage bottle as it cools/vapourises to maintain the vapour pressure

There's two orders of magnitude between the latent heat of vaporization, and the energy density, for both fuels.

So it's a rounding error, unless I'm completely misunderstanding something.

 

[lkswan747]

@lkswan747, how's yours going?

Still going strong and definitely more economical. I have run 60 hours so far on a 48Kg gas bottle.
I have absolutely no regrets. I service the gennie every 100 hours.

 

[Jean-Jacque]

In South Africa gasoline is taxed by the government. There is claims that 50% of the price is tax. So based on that LPG is already cheaper as you cut out the taxation.

 

[wingnut771]

In South Africa gasoline is taxed by the government. There is claims that 50% of the price is tax. So based on that LPG is already cheaper as you cut out the taxation.

In South Africa we don't call it gasoline.