# gas powered planes?

Discussion in 'General Experimental Aviation Questions' started by cheapracer, Feb 18, 2014.

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1. Feb 19, 2014

### saini flyer

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From this side of the pond, it seems like Diesel is the main guy there.... I had no idea that you folks also use LNG....So much for general knowledge of americans:depressed

2. Feb 19, 2014

### BBerson

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LNG= Liquid Natural Gas
LPG= Liquid Propane Gas
CNG= Compressed Natural Gas.

I haven't heard of LNG in use for cars, is this a misprint?

3. Feb 19, 2014

### Dan Thomas

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4. Feb 19, 2014

### Dana

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But it also has to be at cryogenic temperatures, no? So the tank needs to be insulated and/or continuously venting vapor so it auto-refrigerates. This shouldn't be a problem for a vehicle driven frequently, but it's less suitable for an aircraft that sits for a long time between flights.

And even 8 bar means a cylindrical/sherical tank, much harder to fill an odd shaped volume like airplane tanks can.

Dana

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5. Feb 19, 2014

### berridos

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In spain until the eighties cabs drove on lpg.

6. Feb 20, 2014

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Yes, apologies. I was talking about LPG, not LNG.

7. Feb 20, 2014

### akwrencher

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Not sure where that info comes from. LPG, or Propane, as we usually call it, just gets pumped into a pressure tank, then used, for engines, stoves, BBQ's, etc. Do not need, or want, to cool it down, it just looses pressure. As was stated though, really spendy here in the States right now.

8. Feb 20, 2014

### Dana

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That was LNG I was talking about, not LPG. LPG, as you say, only needs a pressure tank.

Dana

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9. Feb 21, 2014

### Brian Clayton

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If it helps, natural gas is a mix of several gasses (like butane, propane, etc). Propane is rather pure. Because of that, natural gas will only store as a liquid when cooled/refrigerated (its the only real commercial use of stirling engines I know of), vs propane/butane that store as a liquid simply under pressure. CNG as a stored fuel has the same issue as say, compressed air. You can only pressurize it so much in a storage tank, volume limited by cubic feet. Unlike propane and butane that you can have in gallons. Using a gas as a fuel also has other issues, like poor fuel economy compared to gasoline, not just from stored BTU's, but from displacing air in the intake charge. Reminds me of batteries. Nice idea, but not really practical for most applications. Gasses do burn clean, and rather cheap (nat gas anyway) compared to gasoline. In the end, you pay the pretty much the same thing for BTU's and voltage to create the same amount of power, if you include the supporting equipment. Fuels (wood included) are commodities, and unless you get the fuel for free or unreasonable discount, there is no free lunch.

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10. Feb 21, 2014

### BBerson

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11. Feb 21, 2014

### Pops

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NG/oil well about 300' from my house. I use the well head NG in my house and hanger. 2 of my neighbors have NG auto's. The BTU's of the NG from this well is almost as high as propane. You have to use propane orifices in the NG furnaces, etc to use the well head NG from this well. Told my neighbors if Gasoline gets much higher in cost, I might convert the engine in my little Cub to NG and use their pumps. Dan

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12. Feb 21, 2014

### floridapilot1

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I followed the discussion with interest, for at least in Europe LPG cuts fuel cost in half. At present, this is influenced by tax politics (as with Diesel fuel, too), on the long run it is abundant and will have advantages for long term availability.
Converting an AC to Diesel requires complete new-designing the engine (and has been done though), whereas in comparison changing an existing engine to gaseous fuel is a piece of cake. You should however be aware that there is no residual lubrication effect from gaseous fuel and that combustion is somewhat slower resulting in higher temperatures at the end of the combustion stroke: Outlet valve seatings have to be steel reinforced – which is generally granted in modern automobile type engines.
The belly pod application for the Husky has demonstrated feasibility even for CNG, but the real advantage of LPG lies in the lower tank pressure which is not more than about twice the pressure we have in our tires. Energy content per mass (volume does not count here) and octane specifications are better than AVGAS or MOGAS. For local AC operations, the only disadvantage that remains is tank weight. BTW, statistically some 80% of AC movements belong to this category, especially when it comes to glider towing with powerful engines.
Up to now the only certified airworthy tanks are used by the balloonists. They are made of stainless steel holding some 40liters weighing somewhat about 20kg. Admittedly this is rather bulky, but there are already GFC cylinders for general use on the market as mass products demonstrating economic feasibility. At our airfield we have a filling station (balloon fuel gas not identical, but closely related to LPG) for our balloonists J
During operation of the burner the LPG leaves the tank in the liquid state. At low environment temperatures it has to be forced out by pressurizing the tank with Nitrogen they carry along –LPG intrinsic pressure is so low that it is not sufficient!
When we consider a suitable AC engine, injection would be a must. Inevitably we will get an electrically dependent engine which need not be a problem if accurately planned. You might need a second battery, the Rotax injection engine as an example even has a second power generator already built in.
I’m not an automobile or LPG fuel expert, but I will outline my understanding of present technology:
Up to five years ago LPG injection was accomplished by injecting gaseous (=vaporized) LPG into the intake tract at moderate pressure (type tire, see above): usually 1 additional LPG injector per cylinder, thus cooling the intake valve. Obviously the LPG - liquid at tank pressure – has to be transferred in the gaseous state before, needing evaporation heat e.g. from the cooling water circuit while the engine runs in AVGAS/MOGAS operation the first minutes. That is impractical for aircraft use with highly varying environmental temperature conditions.
Modern automobile engines use direct injection however (like Diesel engines). The high pressure allows a finer distribution of the fuel - thus improving economy. The injection can be directed the piston crown, thus cooling the piston. When you convert such an engine to LPG, the clue it that you need not change anything except for the reservoir: AFAIK, the converting kits use the same hardware (pump, lining, injectors) and replace only the contents: liquid MOGAS by liquid LPG. No need to care for evaporation heat, vapor lock etc. The slight differences resulting from stoichiometry are compensated by trimming the manufacturer’s engine’s central unit with modified parameters to keep the results of the lambda probe in the desired range.
This seems a very elegant solution. I am sure that if General Aviation industry would have only 1% of the budget cell phone manufacturers use for new models every 6 months, we could have a flat four or six operating with suitable GFC tanks operating cheaply and efficiently on LPG. AFAIK, the design of a direct injection engine is not trivial, however: You get easily holes burnt into your piston crown.
Up to now the only workaround I see is using a proven automobile direct injection engine already (factory) converted to LPG use without making much changes and gearing it for AC use. Perhaps one could design a suitable GFC / CFC cylinder tank appropriate for AC use compensate for the weight disadvantage, fill up at the ballooners’ filling station and go for glider towing or local flights for half fuel cost…

13. Feb 21, 2014

### bcguide

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Do a google search for fiberglass tanks for LPG and 1 for LNG they have been around sine the 80s

14. Feb 21, 2014

### Dana

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Natural gas is a mixture, yes, that varies, but it's mostly methane with smaller amounts of other gases including propane and butane. It's not that propane is "rather pure"; propane is, by definition, well, propane. As the molecular weight increases, the boiling point (or the pressure required to liquefy the gas at room temperature) goes down. Methane has to be cooled to -263°F to liquefy, propane to -44°F, butane to +23°F, while octane (gasoline) boils at 257°F. At 60°F, gasoline stays liquid, a tank of propane would be at 100 psi, a tank of butane would be at 60 psi, and methane wouldn't be liquid at all (but if a tank was filled with LNG at cryogenic temperatures and allowed to warm, it would be somewhere in excess of 15,000 psi!)

It doesn't matter how you measure it. Gallons are typically used for convenience for liquid fuels, cubic feet for gases. No is "displacing air" an issue; all fuels (including gasoline) need to vaporize and mix with air before they burn.

Dana

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15. Feb 21, 2014

### Brian Clayton

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My point was that you cannot store as much Nat gas in a given area (under normal conditions) compared to propane or gasoline, because it is a compressed gas not a liquid. Your usable stored fuel is much less with a gas than a liquid.

My understanding is that since gaseous fuels displace air for combustion, power output is also lowered. Liquid fuels (gas/diesel/methanol) are not a vapor, but more suspended droplets in a running engine. You cant get the same density in a intake charge with gaseous fuels as you can with liquid fuels. This is the reason you cant make high power with say propane. The lower BTU doesnt account for it either, since some of the highest HP engines are methanol fueled.

16. Feb 21, 2014

### BBerson

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Good point, I understand better now. So propane direct injection is almost ideal.
Jack Roush is selling direct injection propane converted Ford trucks at Airventure.
http://www.roushcleantech.com/content/propane

17. Feb 21, 2014

### Pops

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A lot of the land in my area has free NG from well drilled on the land. I grew up on a farm with my grandfather and he owned 1/16 th of the well that was about 600' from the farm house that was drilled in the mid 50's. A lot was just sold on the runway where I live that had free gas for the same reason.
My electric bill runs about $30-$40 a month due to the solar system that I have put up. Hope to be off the grid sometime latter in this year. I converted a B&S engine to NG and use it to power a large GM alternator to charge my batteries if several days of low light. The engine starts and runs better on NG than gasoline. Don't know about the power because the engine just has to run at a fast idle to turn the alternator. My highest grid electrical use is the air compressor and welder in my hanger/workshop. To go completely off the grid and still be able to power the high usage items, I have a 10k generator that will be powered by a VW engine on NG. Getting ready to put the engine together now.

You do know that all the coal fired power plants that supply almost 50% of our production are starting to be closed down this year. Several in my area that I help build. Your future will be smart meters at your home that the power co. controls, with electric rationing and very high electric bills.
Dan

18. Feb 21, 2014

### Brian Clayton

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Sort of. I looked at some "multi-port" propane injectors a while back, when propane was still cheap vs gasoline. Part of the draw for me was that you got away from the vaporizer and the stock ecms could be reprogrammed and used with a piggyback unit to drive the new injectors. It still has some of the same issues. In the end, I just felt there was no gain for me converting to propane from gasoline, because of all the extra problems. I am by no means a propane/nat gas guy, but it didnt take but a little looking to see that it was not practical for me (I was trying to save money on my 400 mile one way commute). A lot of the same reasons to me like where a hybrid car is great in town and no advantage on long interstate trips.

19. Feb 21, 2014

### Brian Clayton

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I wish I lived in a area like you for NG. Where I live (middle ga), you really dont have any choice but the power company. Well, until solar comes down to make it not so cost prohibitive. In TN they are wanting to tax solar installs, to regain the lost revenue. My boss has already had the county (TN) visit several times to his house, where he has a large solar array and we have been working on hydro power (springs that originate on his property). Same reasons you are supposed to pay the fuel taxes if you make your own fuel like biodiesel/ethanol. But.....back to airplanes.....

20. Feb 21, 2014

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