The geek in me just has to jump in here with some technical information. So here goes:
Yes, Rick, vaporized diesel will blow up like vaporized gasoline. And Yes, Patrick, diesel does not vaporize easily. And is a lot less likely to support a flame than Gasoline as well. The flash point (lowest temperature at which a liquid starts to evaporate) of Gasoline is -45 to -50 degrees F (-60 C, I think). The flash point of #2 diesel is 126 F (52 C). Biodiesel, BTW, is about 225 F so if you use B10 or B15 in your boat the flash point of the fuel would be higher. The ignition concentration of a fuel vapor is the percent of fuel vs air that will support ignition. Too low a concentration or too high a concentration and you get no fire. That is why (if you are very lucky and not too bright, you can throw a lit match into a bowl of gasoline and nothing happens. For gasoline the range is 1.4% to 7.6%. Diesel is pretty similar at 0.6% to 7.5%. The ignition point (temperature at which it will start burning) of gas and diesel are also very similar. Gas is 475 F, and diesel is 494 F. But gasoline is much more volatile, and at much lower temperatures. So you are likely to find gasoline vapor vs. diesel vapor. Any fuel leak at above -45 F will result in gasoline vapor. A diesel leak will just make a puddle unless the temperature is above 126 F. Yes, it would be a smelly puddle, but your nose can sense vapor concentrations far below the concentration that would support ignition. Since the density of the gasoline vapor is about 2.0 (air is by definition 1.0) at standard temperature and pressure (70 F and sea level), the combustible vapor sinks to the bottom of your bilge. Diesel vapor would do the same thing, except a measurable concentration of diesel vapor could not exist at STP. Even high pressure diesel forced out of a pinhole leak in one of your injector lines is more likely to result in a smelly mist (too high a concentration to support ignition) than in a combustible fuel vapor. The flash point indicates when a liquid starts to evaporate. But there is another specification called the fire point that is probably a better illustration of the relative risk from gasoline vs. diesel. The fire point is the temperature at which a liquid fuel will generate a vapor concentration high enough to support a flame for 5 seconds – which is enough time to cause significant evaporation of the liquid and start a real fire (as opposed to a momentary flash). Liquid gasoline has a fire point of 30 F (-1 C), while liquid diesel is 154 F (68 C). So unless you are boating in some really ridiculous heat, you are unlikely to get a fire from diesel fuel. Lots of smell – which may make a blower to ventilate the engine spaces very desirable – but a fire is not a high probablility event. Rick Brass Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Patrick Davin via CnC-List Sent: Monday, December 28, 2015 10:43 AM To: cnc-list@cnc-list.com Cc: Patrick Davin <jda...@gmail.com> Subject: Re: Stus-List Proper Blower Installation - 30 mki Diesel doesn't vaporize easily, unlike gasoline. That's one of its big advantages on boats, that it's non-volatile. It's good practice to shut down the engine at the fuel dock anyway, but they're probably asking that more as a general policy due to the gasoline boats they fill (or in case some gasoline vapors wafted over to your boat). The flash point (vaporization temp) of diesel is 126 F: https://en.wikipedia.org/wiki/Flash_point#Examples There's a good writeup on engine blowers here: http://www.unitedmarine.net/blog/index.php/2013/01/30/who-needs-engine-room-blowers/ On Mon, Dec 28, 2015 at 6:09 AM, <cnc-list-requ...@cnc-list.com <mailto:cnc-list-requ...@cnc-list.com> > wrote: ---------- Forwarded message ---------- From: Rick Rohwer <rickroh...@gmail.com <mailto:rickroh...@gmail.com> > To: cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com> Cc: Date: Sun, 27 Dec 2015 22:16:22 -0800 Subject: Re: Stus-List Proper Blower Installation - 30 mki I am pretty sure vaporized diesel will blow up like gasoline vapor. I know vaporized cooking fat will. Don’t most of the fuel docks ask you to shut down the engine and run the fan while fueling? I had never thought of it as an air supply for the engine. Rick Paikea 37+ Poulsbo, WA
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