Talk:Flash point

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This page shoud start with a definition of what a flashpoint is not a discussion of petrol and diesel. Theresa knott 21:30, 2 Aug 2003 (UTC)


Contents

[edit] Other Uses of Flash point

Flashpoint is also an event that starts a war. (IE: Hitler invading Poland was the flashpoint of WW2). We should fit this in some where. CaptainAmerica 15:46, 20 Jun 2005 (UTC)

Done. (211.31.177.90 14:16, 15 October 2005 (UTC))


Flash point (in the safety/hazards consideration area) also corresponds to approximately the lower flammable limit (LFL) otherwise known as the Lower explosive limit (LEL).

Should mention open cup (such as Cleveland) and closed cup testers (automated such as pensky Martens or non-automated Seta). there are ASTM and DIN standards.

some quirky materials - such as halogenated hydrocarbons have flammable limits, but no flash point - they often ignite outside the cup.

flash point and materials (transport classification)

Influence of environment - eg pressure

stoichiometric concentration - estimate LFL as approx 50% stoich.

context of upper flammable limit too? mixture flash points.

[edit] Greater Than / Less Than symbols

At the end, instead of > or < for the flashpoints of supstances, it should say "greater than" and "less than" So it is less confusing.

Can someone please do this?

You can if you think it desireable. Personally I don't this it necessary. Pzavon 00:45, 12 July 2006 (UTC)
To be honest I'm slightly confused. In Flash point: >-45 °C Is 45 °C less than the flash point, or is the flash point greater than 45 °C? --70.29.196.200 01:58, 15 July 2006 (UTC)
Both! Saying that A is less than B is the same as saying B is greater than A.
And that is minus 45°C (below zero) not 45°C.
But the above may be nitpicking. Let me try to address the meaning of the ">" (greater than) and "<" (less than) symbols.
Read a line from left to right. If the symbol is open on the left and closed on the right (>), read "greater than". If the symbol is closed on the left and open on the right (<), read "less than." So Flash point: >-45 °C reads as Flash point: greater than -45°C (You could think of the two symbols as graphically showing the realtive size of the items on each side. Bigger is next to the side of the symbol that is open or covers more space, smaller is next to the side of the symbol that is closed or covers less space.)
Pzavon 23:20, 15 July 2006 (UTC)
Ah thanks for clearing that up for me. Now I understand. So would this mean that petrol won't ignite if it is -45 C or lower? And would it also mean diesel won't ignite if the temperature is below 50 C, since the flashpoint is above 50 C? Not even a spark or flame could ignite diesel if the temperature wasn't 50 C or over?
Sort of. Sometimes flames are also sources of heat as well as being sources of ignition. A spark that is merely a source of ignition will not ignite a flammable liquid when it and its environment is below its flashpoint. A flame that is also a source of heat (a blow torch, for example) may locally raise the temperature above the flashpoint and cause ignition. If the blowtorch is then removed, whether the liquid will continue burning depends on whether the fire is able to maintain the local environment above the flashpoint.
What is being ignited is the vapor immediately above the liquid surface, not the liquid itself, so you are also looking at enough energy to vaporize the liquid sufficiently to make a combustible mixture with air. Pzavon 17:16, 17 July 2006 (UTC)

[edit] Mechanism - involves heat of combustion?

Pzavon, I guess you could give some sort of answer to this and possibly include it somewhere (in short): is the fact that different vapour concentrations are needed to sustain the burning of the vapour related to the heat being released from the burning vapour? So that a substance with a high enthalpy of combustion would require less vapour concentration, because the heat evolved will sustain the fire even at low concentrations? Or have I not really understood the concept of flash point, proposing this? Question posted 25 July 2007 by 130.238.197.120

This is far from my specialty, but I would think that is not the case. The minimum concentration needed to sustain combustion relates to the ease with which the vapor oxidizes, and that is not, I think, directly dependent on temperature (although all chemical reactions are faster at higer temperatures). The flash point is simply the liquid temperature at which the vapor concentration just above the liquid surface reaches a sufficient concentration to be able to flash, or be ignighted. Sustained combustion is not a requirement of Flash Point, only that what is there will flash over. Generally a higher temperature (or vapor concentration) is required to sustain combustion. Once sustained combustion is established, it is likely that the heat from the combustion reaction will contribute to the continued evaporation of the combustible liquid. (The is how a candle works.) Pzavon 01:09, 26 July 2007 (UTC)

[edit] Question Regarding Diesel vs. Gasoline Section

The question I have refers to this caption of the article:

"Diesel is designed for use in a high-compression engine. Air is compressed until it has been heated above the autoignition temperature of diesel; then the fuel is injected as a high-pressure spray, keeping the fuel-air mix within the flammable limits of diesel. There is no ignition source. Therefore, diesel is required to have a high flash point and a low autoignition temperature."

I understand why a diesel engine needs a low autoignition temperature (no sparkplug & unscavenged, unburnt fuel is imcompressible), but why does it have a higher flashpoint? Once diesel fuel is introduced into the cylinder the intention is for it to burn, rapidly. Doesn't the atomisation of the fuel spray encourage evaporation anyways? I could understand if it is just a byproduct of the manufacturing process (i.e., no consideration due its irrelevance on the operation of the engine), but if it was intentional the reasoning has lost me. Apart from compression and the ignition source, I don't know of any differences between a diesel or a gasoline engine...

I hope someone could clear up the issue here, and if need be on the article itself. LostCause 09:08, 16 August 2007 (UTC)