Atomising Liquid Propane

Propane, Butane, LPG, GPL, C3H8, C4H10
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amish25
Posts: 2
Joined: Tue Oct 18, 2016 10:42 am

Atomising Liquid Propane

Post by amish25 »

Hi everyone, I'm currently progressing through my masters project based on the redesign of the fuel injection system for a pulse detonation engine (aerospace application). I am looking into taking technology used in the automotive industry, for example fuel injection systems, and implementing them in my project. The engine is currently run on gaseous form of propane but I would like to design a system whereby either liquid or gaseous propane can be used.

I'd be really appreciative if the community can help me answer the following questions:
  • Would it be possible to use diesel injectors for propane or would I have to buy LPG specific injectors?
  • What pressure would I need to inject liquid propane at to ensure proper atomisation and mixing of the fuel?
Cheers!

C3H8
Posts: 1129
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Atomising Liquid Propane

Post by C3H8 »

To answer this question you just really need to understand the Properties of Propane. I inserted a link for you to look at below but the basics are this.

1. Propane remains a liquid if it is enclosed in a sealed container strong enough to withstand the pressure generated as it tries to return to a gaseous state.
2. Propane boils at -44 degrees F. So basically at -44 you can carry it around in a pail. At -43 and warmer it will turn to a gas/vapour with the pressure increasing as it gets warmer if it is in a sealed container.
3. The warmer the temperature the higher the pressure. At -44 it is 0 PSI. At 100 F it is 172 PSI.
4. Liquid expands 270 times as it turns to a vapour.
5. Releasing it to atmosphere will cause it to vapourize. This will react like AC materials drawing heat from the surrounding area when it vapourizes.
6. Any injector will control propane keeping in mind that some materials (seals) can be affected by the fuel. Depending on design the possibility exists that the tip may frost up as the liquid is released and expands sucking heat out of the metals around the area to vapourize.
7. The diesel injector will work depending on what heat value you want to achieve.
8. The value will change with temperature because the tank pressure will change.
9. The value can remain constant if the pressure is controlled with a delivery pump and a return line with a regulator on it that returns excess fuel to the tank.
10. An ECU is required to pulse the injector in most cases.
11. Heat may be required to keep an injector from freezing up (icing up at the outlet tip).

http://www.propane101.com/aboutpropane.htm

Ask some more specific questions and I or another member may be able to answer them but first do all you can to educate yourself on the basic properties.

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Atomising Liquid Propane

Post by storm »

I had never thought about diesel injectors delivering propane.

To add to C3H8's thoughts.
I doubt a mechanical injection system would be able to do it and if it could the fuel lines (at the very least) would need to be replaced for much stronger units.
Common rail diesels run extremely high pressure so in theory could do it as long as the system was sealed properly. The advantage with common rail diesel is in some cases it can be tuned using after market tools (from memory both HP Tuners and EFI Live can be used to tune the Chev Duramax), other engines (e.g. Toyota V8) need a piggy back chip.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

bumpstart
Posts: 133
Joined: Wed Jan 20, 2010 9:09 pm

Re: Atomising Liquid Propane

Post by bumpstart »

im thinking comprex pressure wave supercharging on a 2 stroke or miller cycle compression ignition engine at a whole new level of efficiency//
using the expansion ratio of liquid propane/butane to both a mechanical and adiabatic advantage inside the comprex supercharger//,
also acting as the primary fuel expansion/mixing timing chamber

eg. amplify the comprex pressure wave inlet charging effect by utilising the timed expansion of LPG liquid fuel and also using the exhaust pressure wave to effect heat cycling effect required at the injector tip .
the huge gas expansion works to provide layer separation of exhaust and inlet air, preventing inlet charge dilution by the exhaust while providing boost charging and increased exhaust scavenge

this could be done using common rail injection components at a point where they would be exposed to the exhaust cycle heat within the comprex to keep them from freezing
and a miller cycle could be utilised using late fuel timing at high pressure during elongated inlet stroke
when the going is hard, don't retard, remember your lubrication

fpvmustang
Posts: 33
Joined: Thu May 05, 2016 3:28 pm
Location: Quincy Ca. USA

Re: Atomising Liquid Propane

Post by fpvmustang »

Nitrous foggers would be the rout I would take.
I know roush and cleanfuel use a gasoline fuelpump.
but in the propane tank then run around 45 psi over tank pressure to keep lpg from vaporizing in lines.

amish25
Posts: 2
Joined: Tue Oct 18, 2016 10:42 am

Re: Atomising Liquid Propane

Post by amish25 »

Thanks for the responses everyone, I really appreciate your help!

Do you think there would be any other problems apart from seal performance/icing of tips that would arise from using diesel injectors for propane?

And do you think diesel injectors could cope with injecting both liquid and gaseous propane (as separate events)?

With regards to the icing of the tips due to the flash-vaporisation process drawing heat away from the tips, I think that this would not be a problem for my application, as the tips would be subject to very high momentary heat during detonation of the fuel, with flash temperatures reaching around 2600F. Icing protection tips could also be used; a previous research study titled 'Experimental study on the icing characteristics of LPLi injectors under various injection conditions' suggested this.

storm
Posts: 796
Joined: Wed Jan 10, 2007 10:10 pm
Location: NSW, Australia

Re: Atomising Liquid Propane

Post by storm »

if the tips of the injectors, or any surface in the combustion chamber/cylinder for that matter, got to that temperature you would have melting parts. There is a boundary layer of gas on all surfaces that stops melting and that includes direct injection injectors. The high temperatures you mention won't stop tip icing simply because the tips, and other metal surfaces, don't actually see/feel the high temperatures.
Fuel flow requirements calculations
Engine air flow requirement calculation: CFM = Cubic Inches x RPM x Volumetric Efficiency (VE) ÷ 3456

bumpstart
Posts: 133
Joined: Wed Jan 20, 2010 9:09 pm

Re: Atomising Liquid Propane

Post by bumpstart »

there would be an issue with fidelity if using one injector tor for both liquid and vapour
even with pressure and temperature compensation /fuel density map the injector needs very finite control and tiny injection period with liquid, but outrageously long duration required with vapour

as mentioned to a scale at least 200 : 1..

i would suggest that you could try a common rail but several staged injector approach. using only one in liquid phase but several larger ones , staging secondary and tertiary for vapour
when the going is hard, don't retard, remember your lubrication

C3H8
Posts: 1129
Joined: Fri Sep 09, 2005 11:23 pm
Location: Winnipeg, Canada

Re: Atomising Liquid Propane

Post by C3H8 »

There is some basic principles to keep in mind here. When gasoline or diesel pass through an injector they are only atomized. Therefore the BTU content remains stable. The amount of fuel being delivered is done under a constant pressure on gasoline and an ECU controls the length of time the injector opens in MS. A diesel injects into the cylinder under very high pressure and flow was usually changed by injecting at a higher pressure or volume to increase fuel flow. I am not 100% up to date on the newest diesels but they may use the gasoline principle of an ECU controlling the duty cycle.

On propane there are two challenges. The first is to supply propane at a constant pressure. This usually means using a pump that delivers a fixed pressure of somewhere between 35 to 75 PSI. It requires recirculating liquid propane through a pressure regulator which will cause the tank to heat up and increase it's pressure. These systems actually exist already with Vialle, Clean Fuels Inc., Rousch and even the Liquid injected Dodge vans manufactured in the 90's. The downside was the longevity of the pumps. Dodge tried using two standard gasoline pumps in each tank but the life was quite short in most cases. Vialle and others designed their own pumps with much better results.

The second issue is the liquid being injected through the injectors. As the liquid leaves the injector it flashes to a vapour (not atomizing) expanding 270 times. In theory this could be done but under normal circumstances the engine is going to flood. In this case he is not talking about an engine so it is possible to use an electronic diesel or gasoline injector to deliver the fuel. Two issues have to be addressed. A programmable duty cycle compatible with the desired fuel flow. The second is tip freezing however this could be a mute point if the environment the injector is operating in is warm enough to prevent freezing as long as the injector can handle the heat. A company in Minnesota, USA actually installed redesigned liquid injectors in Ford Crown Vic 4.6L engines and E350 V10 engines and utilized the existing injector opening and Ford ECU. The injectors were designed to match the BTU delivery of the gasoline. This of course meant that the fuel openings were much smaller on propane.

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