oxygen cleaning for nitrox (partial pressure) fills

[JeffG]

I was taught in my welding class that high pressure can change the temperature needed for some materials to burn. A diesel engine is a pretty good example of how this works.

Mark Vlahos

You still need a ignition source even though the flash point has been lowered.

 

[bnelson]

so, DA, what you are saying is that if you pressurize, but very slowly, oxygen into a regulator lubricated with petroleum oil, for example, if you increase the pressure very slowly to avoid any increase in temperature (you're referring to adiabatic processes) that the oxygen will not combust? it still needs an ignition source?

incorrect, lighting your fireplace needs an ignition source, because at room temperature, and ambient temperature, and 20.9% concentration, oxygen will not combust with the wood or paper. Nor will it react with a lot of things out there combustively unless they are already combusting. (including oils and petroleum products and fun things of that nature).

Say, you put a newspaper in your oven. At 400 degrees in your oven, the oxygen is no more apt to start a fire. Increasing the temperature to, say, around 451 degrees F (230somethingish C, incidentally, there's a book by that tempertature in Fahrenheit), which, also, coincidentally is the (pilotless) ignition point of paper, that paper has reached the point where the temperature provides the energy needed (the activation energy) to begin combustion.

Two scenarios, one outcome: the fuel combusting. You applied fire (a pilot combustion) in the first one, you applied heat (energy) in the second. There needs to be no ignition, just sufficient energy to achive activation energy.

imagine how low the activation energy for 100% oxygen under pressure at room (or slightly elevated) temperature for is?

oxygen will combust with petroleum lubricants under pressure. without ignition. the adiabatic process might provide some energy in the form of heat, but that's not an ignition, and there's already plenty of energy available...

 

[JeffG]

so, DA, what you are saying is that if you pressurize, but very slowly, oxygen into a regulator lubricated with petroleum oil, for example, if you increase the pressure very slowly to avoid any increase in temperature (you're referring to adiabatic processes) that the oxygen will not combust? it still needs an ignition source?

Here's the Coles Notes version

http://ehs.sc.edu/modules/Fire/01_triangle.htm

 

[WarmWaterDiver]

Hydrocarbons do have a property called 'autoignition temperature' - you can find the value on a material safety data sheet. See section 5 of this MSDS for diesel fuel.

http://www.petrocard.com/Products/MSDS-ULS.pdf

The 'fire triangle' model has been replaced by the 'fire tetraherdon' model in recent years.

http://www.firesafe.org.uk/html/miscellaneous/firetria.htm

This site gives a decent explanation on the difference between 'flash point' (external ignition source required) and (auto)'ignition temperature' (no external ignition source required). The graphic representation of a tetraherdon however is if you cut the seams and laid it flat (2D instead of 3D).

http://www.firefightercentral.com/public/what_is_fire.htm

I don't own diesel powered vehicles, but I have rented and driven a few. Here's my understanding. The glow plugs are heated to the diesel fuel autoignition temperature when you turn the key to the 'run' position. Once the glow plug indicator light goes out, the glow plugs have reached the autoignition temperature and the key can be turned to the 'start' position to start the engine. Once the engine starts (and the glow plugs are off), you are relying on autoignition temperature to keep the diesel engine running - some is supplied by the heat of compression, some is supplied by residual heat from the previous cycle.

I have some experience with industrial diesel engines without glow plugs - such as oil barge liquid transfer pumps. These had a lever where the engine operator had to 'pump up' a reservoir to enough pressure to get the engine to start. This isn't really user-friendly, but can save you some health club fees!

If you are looking at what temperature a puddle of diesel has to reach before you can light the evolved vapors with an ignition source, that is the flash point temperature. Much lower than the autoignition temperature.

Cetane rating for diesel fuel is somewhat directionally opposite octane rating for gasoline fuel (used in spark ignition engines). Higher octane rating indicates greater resistance to ignition before the spark plug fires - engine 'knock' results when the fuel ignites prematurely in the cylinder - during the compression stroke instead of close to TDC to deliver the combustion energy in the power stroke. Higher diesel fuel cetane rating indicates lesser resistance to ignition and increased ease of use in a diesel engine.

http://www.procarcare.com/icarumba/...a/icar_resourcecenter_encyclopedia_fuels1.asp

http://www.familycar.com/Classroom/fuel.htm

http://www.itow.org/fuelguide.htm

 

[bnelson]

exactly

Hydrocarbons do have a property called 'autoignition temperature' - you can find the value on a material safety data sheet. See section 5 of this MSDS for diesel fuel.

http://www.petrocard.com/Products/MSDS-ULS.pdf

The 'fire triangle' model has been replaced by the 'fire tetraherdon' model in recent years.

http://www.firesafe.org.uk/html/miscellaneous/firetria.htm

This site gives a decent explanation on the difference between 'flash point' (external ignition source required) and (auto)'ignition temperature' (no external ignition source required). The graphic representation of a tetraherdon however is if you cut the seams and laid it flat (2D instead of 3D).

http://www.firefightercentral.com/public/what_is_fire.htm

I don't own diesel powered vehicles, but I have rented and driven a few. Here's my understanding. The glow plugs are heated to the diesel fuel autoignition temperature when you turn the key to the 'run' position. Once the glow plug indicator light goes out, the glow plugs have reached the autoignition temperature and the key can be turned to the 'start' position to start the engine. Once the engine starts (and the glow plugs are off), you are relying on autoignition temperature to keep the diesel engine running - some is supplied by the heat of compression, some is supplied by residual heat from the previous cycle.

I have some experience with industrial diesel engines without glow plugs - such as oil barge liquid transfer pumps. These had a lever where the engine operator had to 'pump up' a reservoir to enough pressure to get the engine to start. This isn't really user-friendly, but can save you some health club fees!

If you are looking at what temperature a puddle of diesel has to reach before you can light the evolved vapors with an ignition source, that is the flash point temperature. Much lower than the autoignition temperature.

Cetane rating for diesel fuel is somewhat directionally opposite octane rating for gasoline fuel (used in spark ignition engines). Higher octane rating indicates greater resistance to ignition before the spark plug fires - engine 'knock' results when the fuel ignites prematurely in the cylinder - during the compression stroke instead of close to TDC to deliver the combustion energy in the power stroke. Higher diesel fuel cetane rating indicates lesser resistance to ignition and increased ease of use in a diesel engine.

http://www.procarcare.com/icarumba/...a/icar_resourcecenter_encyclopedia_fuels1.asp

http://www.familycar.com/Classroom/fuel.htm

http://www.itow.org/fuelguide.htm

 

[bnelson]

the fire triangle merely states fuel, 02, and heat (energy)

just how much energy (heat) is required varies, with lots of things, but it's really low when working with pressurized 100% oxygen and some oxygen-unsafe compounds...

Here's the Coles Notes version

http://ehs.sc.edu/modules/Fire/01_triangle.htm

 

[Leadking]

My diesel boat engine got hydrolocked (water on top of the pistons) while I was diving last year-40 miles offshore in Lake Superior. As I tore down the engine my fellow divers, all tri-mix rebreather trained, asked about the sparkplugs. I explained that there are none and that the diesel fuel ignites by the heat of compression and the "spark plug" was the timing of the fuel into the cylinder. I took that as an opportunity to explain about oxygen clean. If diesel fuel will ignite at 20:1 compression (300 lbs) what do you think hydrocarbons, or any other combustible material will do when the compression ratio, when you open the tank valve, can be 230:1?

Lee
www.seapearls.com

 

[froginmgl]

JUST YO LET YOU KNOW!I puchased a luxifer from Scuba Toys & it is nitrox up to 40% ready to go. I also called many dive shops to see if they would fill it. Some wanted to F.... me others didn't I am sick of LDS taking advantages of those who need their services. Just tell the truth! Maybe that way you would get more business. BY THE WAY THEY WILL WANT TO PUT THAT 6" NITROX STICKER ON YOUR TANK.

 

[Mark Vlahos]

JUST YO LET YOU KNOW!I puchased a luxifer from Scuba Toys & it is nitrox up to 40% ready to go. I also called many dive shops to see if they would fill it. Some wanted to F.... me others didn't I am sick of LDS taking advantages of those who need their services. Just tell the truth! Maybe that way you would get more business. BY THE WAY THEY WILL WANT TO PUT THAT 6" NITROX STICKER ON YOUR TANK.

Does the Luxfer cylinder you bought have a GREEN or RED border around the Luxfer sticker?

If that sticker has a red border your cylinder IS NOT properly prepared for partial pressure Nitrox blending.

If that sticker has a green border your cylinder IS properly prepared for partial pressure Nitrox blending, unless the valve has been replaced with a valve that is not clean.

Your post says the cylinder is ready for 40%, is this based on information from Scuba Toys website, or the cylinder? If the two places provide contradictory information the cylinder is the one that matters.

As far as the big NITROX tank band, some shops do require them, some do not. I have not needed them in Florida or Southern California. Of course my experience is limited to the shops where I have gone to get fills, and not every shop in those areas. In Virginia I have needed the tank band. I don't really care that much about the whole tank band thing, I would rather not have one, but when they were required I had them.

Mark Vlahos

 

[dflipp]

JUST YO LET YOU KNOW!I puchased a luxifer from Scuba Toys & it is nitrox up to 40% ready to go. I also called many dive shops to see if they would fill it. Some wanted to F.... me others didn't I am sick of LDS taking advantages of those who need their services. Just tell the truth! Maybe that way you would get more business. BY THE WAY THEY WILL WANT TO PUT THAT 6" NITROX STICKER ON YOUR TANK.

That's interesting... I exchanged emails with Larry at ScubaToys and he told me that none of their cylinders come from Luxfer cleaned for partial pressure blending.

-Dan