Viability of a gaseous propane powered engine?

[DanTrentfield]

OK so I've been working this out in another thread http://www.scienceforums.net/topic/93574-propane-versus-gasoline/and I've come up with the following facts for propane when compared to gasoline: Propane is ~900% cheaper than gasoline (with a 5-7 times greater consumption factored in) given it's average market value in gaseous form is $0.02 compared to $1.80 for Gasoline. Propane only produces 15/16th's of the Co ₂ that a 5o₂+2C₈H₁₈->16Co₂+18H₂o gasoline combustion reaction does, as propane only produces 3Co₂ in a C₃H₈+5o₂ reaction (Times 5 for the consumption rate), so it is slightly more environmentally friendly. Now I know that buses and larger industrial and commercial vehicles use propane, but what would be the viability of say a midsize sedan using a gaseous propane engine and still being able to achieve at least 80 mph from an engineering standpoint?

Edited February 17, 2016 by DanTrentfield

[John Cuthber]

The price of petrol is mainly tax.

Also, the cost per gallon isn't the right metric. How much per kilometre?

[Phi for All]

Now I know that buses and larger industrial and commercial vehicles use propane, but what would be the viability of say a midsize sedan using a gaseous propane engine and still being able to achieve at least 80 mph from an engineering standpoint?

 

Can you link us to information regarding buses using gaseous propane? Everything I see is using LPG.

[DanTrentfield]

 

Can you link us to information regarding buses using gaseous propane? Everything I see is using LPG.

Excuse me, thanks for pointing that out..... *LPG Buses*

 

The price of petrol is mainly tax.

Also, the cost per gallon isn't the right metric. How much per kilometre?

Gasoline is ~$0.07/mile, and with propane falling 4/5 short of gas on efficiency we get about $0.008 for a gaseous propane powered vehicle with an MPG of 10 versus a gasoline powered vehicle with an MPG of 25. As I said. MUCH cheaper. The problem is getting a gaseous propane engine to work.....

[Phi for All]

Gasoline is ~$0.07/mile, and with propane falling 4/5 short of gas on efficiency we get about $0.008 for a gaseous propane powered vehicle

 

Can you link to these "gaseous propane powered vehicles" you're getting these figures from?

[EdEarl]

I think technologies besides electronics are about to change quickly. The next 25 years are crucial to minimize climate change, and transportation must become cleaner. I think there will be many experiments towards that goal, before one technology becomes dominant again, maybe. If fuel wins, I expect several will service different market segments, including hydrogen, methane, methanol, ethanol and biodiesel. If electrics win, I expect some form of supercapacitor instead of chemical batteries. But, there are no clear winners at this time. Propane has a role to play.,

Edited February 17, 2016 by EdEarl

[DanTrentfield]

 

Can you link to these "gaseous propane powered vehicles" you're getting these figures from?

Excuse me *cough* *cough* Theoretical vehicles running on gaseous propane..... Not real vehicles.... I'm beginning to think that this won't go anywhere.... Surprised?

[Moontanman]

Excuse me *cough* *cough* Theoretical vehicles running on gaseous propane..... Not real vehicles.... I'm beginning to think that this won't go anywhere.... Surprised?

 

LP powered vehicles do run on LP gas, the liquid turns into a gas via a carburetor type device, the LP is only a liquid while in storage on the vehicle..

[John Cuthber]

Excuse me, thanks for pointing that out..... *LPG Buses*

 

Gasoline is ~$0.07/mile, and with propane falling 4/5 short of gas on efficiency we get about $0.008 for a gaseous propane powered vehicle with an MPG of 10 versus a gasoline powered vehicle with an MPG of 25. As I said. MUCH cheaper. The problem is getting a gaseous propane engine to work.....

The problem here is that you are ignoring the fact that a litre of propane weighs about 2 grams and litre of petrol weighs about 700 grams.

 

Since the energy per gram is roughly the same you are getting hundreds of times less energy for ten times less cash.

On a mile per mile basis the propane is roughly ten times as expensive.

[DanTrentfield]

 

LP powered vehicles do run on LP gas, the liquid turns into a gas via a carburetor type device, the LP is only a liquid while in storage on the vehicle..

Exactly the concept, I'm not an engineer, I'm studying chemistry in college (If you couldn't tell)

The problem here is that you are ignoring the fact that a litre of propane weighs about 2 grams and litre of petrol weighs about 700 grams.

 

Since the energy per gram is roughly the same you are getting hundreds of times less energy for ten times less cash.

On a mile per mile basis the propane is roughly ten times as expensive.

And there went my BTU calcuations...... Sorry everyone, my brain has officially had it's first fart of the day...... Disregard my first calculations.....

[Sensei]

You're calculating it incorrectly.

 

What user is interested in is how much energy fuel will release while burning.

1 L of gaseous propane with density around 2 g/L, has very little energy, in comparison to 1 L of liquid gasoline.

As it's 0.0446 mol/L (*44.1 g/mol= 1.96686 g/L) at 0 C,101325 Pa (or so).

According to energy density table:

https://en.wikipedia.org/wiki/Energy_density

LPG propane has 49.6 MJ/kg = 49.6 kJ/g

so 2 grams (let's ignore liquid/gas state) = ~100,000 J

 

Gasoline 1 L has energy density 34.2 MJ/L = 34200000 J/L

That's 342 times more energy in same volume.

 

1 L of C8H18 with density ~700 g/L has mass 700 g (some materials say 719 g/L),

divide by 114.232 g/mol = 6.13 mol/L.

At the same time gaseous propane has 0.0446 mol/L.

That's 137 times more molecules.

 

You cannot compare price of 1 L gaseous propane, with price of 1 L of liquid gasoline.

 

You should calculate price of fuel based on energy they release while burning.

Compare engine that has f.e. 1000 W using one fuel, with engine that has 1000 W, using other fuel (with different energy density).

Edited February 17, 2016 by Sensei

[Moontanman]

Exactly the concept, I'm not an engineer, I'm studying chemistry in college (If you couldn't tell)

 

 

Again, I do not understand your assertions, since vehicles already run off gaseous propane...

[John Cuthber]

When you see mpg figures for LPG engines they are calculated as miles per gallon of liquid.

So the price of a gallon of the gas is irrelevant.

[J.C.MacSwell]

Back in the seventies I drove a truck that ran on gaseous propane...that was (of course) stored as LPG. It would also run on gasoline.

[Enthalpy]

The combustion heat released per kilogram is about the same. The engine using a gas must be somewhat less efficient because of the compression work, but let's neglect it.

 

So the comparison, in a first approach, would be between the prices per kilogram. Or slightly better, the price per produced heat, which is available online: per Btu, per kWh, per what you want provided it's heat.

 

And as JC mentioned, the comparison is essentially a matter of tax. If you run your own car, taxes won't change, but if you sell a million vehicles, expect the government to raise taxes on propane aligned to gasoline.

 

For instance, a simpler way to save fuel money is to run a Diesel car with heating oil. It's the same fraction of crude oil, only the use differs, and heating oil is much cheaper because of taxes - but this is forbidden by law in the countries I know, and heatig oil carries additives to smell and look distinct. What's legal in Germany (but not France) is to run a Diesel with kerosene (slightly lighter cut from crude oil); provided you find some, it's much cheaper because governments tax airliners less than cars.

 

What I do like with propane is that it's a zero-emission fuel. Well, not directly: it does emit dioxide, sure. But if you don't run a vehicle with it, it will be burnt at the oil or gas well because its value it too low to transport to the customer.

 

I wish someone would develop a small chemical plant to convert propane to polypropylene granules directly at the well. And convert butane too, to alkylate or polypropylene. My guess is that such a plant must be bigger to earn money.

[EdEarl]

Butane is heavier than air; thus, it can pool in low places, which makes it dangerous. It is no longer available in bulk, only small amounts useful for lighters and torches.

[John Cuthber]

Butane is heavier than air; thus, it can pool in low places, which makes it dangerous. It is no longer available in bulk, only small amounts useful for lighters and torches.

Have you met octane?

[EdEarl]

octane family C8H18 or octane rating of gasoline?

 

At one time I bought butane to heat my house, and the state prohibited that use. Now I use propane.

[John Cuthber]

Octane that "is heavier than air; thus, it can pool in low places, which makes it dangerous. "

[EdEarl]

Pure octane isn't generally available, AFAIK. Gasoline contains octane and is a liquid at room temperature; although, it does evaporate rather quickly and can be dangerous.

 

I didn't make the law that eliminated butane as a heating fuel, didn't even know it was being done. One day I tried to order a few hundred gallons, and learned I had to buy a propane tank and convert my appliances.

[Enthalpy]

Propane too is heavier than air. 44g/mol versus mean 29g/mol. Is that much better than butane with 58g/mol?

[EdEarl]

Shh, they'll ban propane, too.

[John Cuthber]

Pure octane isn't generally available, AFAIK. Gasoline contains octane and is a liquid at room temperature; although, it does evaporate rather quickly and can be dangerous.

 

I didn't make the law that eliminated butane as a heating fuel, didn't even know it was being done. One day I tried to order a few hundred gallons, and learned I had to buy a propane tank and convert my appliances.

All the components of gasoline are heavier than air, and flammable.

Was this law put in place to try to promote the use of hydrogen?

[EdEarl]

IDK, the people who once sold butane, and switched me to propane, said it was for safety as I said before. I didn't investigate. It was many years ago.

 

I just looked, and Butane is still sold in bulk, in Texas. Maybe it was a city ordinance, or maybe the company wanted to sell propane instead of butane.

Edited April 5, 2016 by EdEarl

[DanTrentfield]

I'd like to clear one thing up, My idea of using gaseous propane as a possible fuel did not go as well as planned, I ran an experiment with a small lawn mower engine and with the data from the experiment, figured that propane is in no form much more advantageous than gasoline, the original question of my original thread on this, 15/16's of the emissions, Better tank capacity but similar price because of the 5x greater consumption with taxes factored in, and finally horrible combustion efficiency.