Diesel Polishing

[s/v Jedi]

Originally Posted by Wotname

Quiet day here in the deep south of Australia so it was time for some hillbilly pyromania.

Will diesel readily ignite?

Noelex77 reports small amounts are easy to light with a match.

a64pilot suggests any amount is easy to light with a match even if it is floating on water.

s/v Jedi believes the thermal mass is an important consideration.

Wottie is skeptical about igniting floating diesel with a match.

So...what does happen??? A quick and dirty experiment was carried out using a small metal lid as the test container with a diameter of 70mm (2.75"). It was resting on mesh so effectively it was surrounded by air with a temperature of 15C (60F). Cloudy and no wind. All numbers are approximate.

20ml diesel was used for the test and this was about 0.5mm (0.020") deep in the lid.

This was fairly easy to ignite with a match!


Next step was 100ml of water added to the container and 20ml of diesel. The water depth was 2.5mm (0.1"). The match would not ignite the diesel before the match burnt out. Maybe a pocket gas lighter would provide enough heat but not having one, I brought out the big gun - the MAPP gas torch.

This readily ignited the diesel but it would not remain alight once the MAPP torch was removed. It would burn for 2 or 3 seconds before self extinguishing. I presumed the water was keeping the diesel too cool for it to maintain the vapour above the flash point regardless of the heat of the small flame of the burning diesel. This is in keeping with the fire triangle where heat, oxygen and fuel must be present for combustion to occur. There simply wasn't enough heat to maintain the combustion.

Now I recharged the lid with water and diesel in same ratio as before but this time, I heated the mix from underneath with the MAPP torch until is was fairly hot. I can't be sure what the temperature was except to say it certainly above 50C (122F) but well less than 100C (212F).

This time the match ignited the diesel floating on the hot water and the diesel remained alight.

Finally I recharged the lid with 120 ml diesel only, no water. This diesel was about 3mm (1/8") deep. The match would not ignite the diesel. The MAPP torch would ignite it but it went out as soon as the torch flame was removed. The diesel was then heated to above 50C (122F) and it remained alight when the MAPP flame was removed.

All in all, the results suggest to me that the thermal mass is an important consideration as well as the ambient temperature fuel and the air. Again, this conforms to the fire triangle of heat, air and fuel. See https://en.wikipedia.org/wiki/Fire_triangle

Thank you laws of nature have stood the test of time so are applicable here as well. The fire triangle dictates that all three must be present and thermal mass, thermal conductivity / heat sinks are all facts based in science

[Wotname]

Originally Posted by noelex 77

...........
The other caution I would suggest after observing my diesel heater is that even a small quantity of burning diesel produces a serious fire.

I would suggest, for example, that in many cases the small amount of diesel released when bleeding the fuel system would be enough to produce a fire (if ignited) severe enough that it could well eventually set alight other materials and destroy the boat unless rapid firefighting measures were taken.

.........

These guys don't use very much diesel to a decent sized fire going. Around here the drip torches used for back burning etc typically use a 75/25 diesel petrol mix. If the ambient temperature is high, then more diesel less petrol is used.

https://www.youtube.com/watch?v=1MWCpZdfS0s

[Wotname]

Regarding my quick and dirty diesel test, I would like to remind folk that the ambient temperature was much lower (15C / 60F) than what one might expect around your average sail boat engine bay.

However it isn't going to be 30C (86F) anytime soon around here so I won't be testing again at a higher ambient. Unsurprisingly I have been banned from repeating the test on our kitchen bench .

[Anders]

How about using the daytank by pumping from the main tank to the day tank through a filter or two and plumbing the breather back to the tank so that disel can circulate from main tank to day tank and back to main tank again?
Would it still need a separate breather? The day tank would be above the main tank.

[noelex 77]

Originally Posted by Anders

How about using the daytank by pumping from the main tank to the day tank through a filter or two and plumbing the breather back to the tank so that disel can circulate from main tank to day tank and back to main tank again?

A fuel day tank is a very helpful system for maintaining a clean and reliable fuel supply for the main engine. Many cruising powerboats have this system although it is perhaps overkill for yachts where the sails provide an alternative power source.

However, one of the main goals of the day tank is to provide super clean fuel for the main engine. If you polish the main diesel tanks by feeding the fuel through the day tank any deposits that escape through the filter from the polishing process will to sink to the bottom of the day tank defeating the major purpose of this system.

Polishing means circulating the same fuel many times through a filter.

Polish the fuel from the main tank back into the main tank rather than the day tank. The day tank should have cleaner fuel than the main tank.

[RaymondR]

Good work Wotty.

[Q Xopa]

Who woulda thought mis spent youth could have become so useful?

Good effort.

[Steve DAntonio]

When I managed a boat yard the vast majority of our customers were diesel-powered sail and power vessels. A vessel with a diesel leak was a nuisance to be sure. On one occasion we had a trawler in the paint shed. The owner came in over the weekend to do some work in the engine room, when he was leaving he inadvertently bumped the drain cock on the Racor turbine filter. The filter was located at the lower half of the saddle tanks. It slowly drained the fuel out of the tanks into the bilge, until the fuel level in the tank reached the level of the filter drain, about 250 gallons (ABYC Standards call for these valves to be plugged or capped). Thankfully, the electrical system was also being worked on and was thus disabled, so the bilge pumps did not pump the fuel into the shed. Never the less it was a mess. At no time was I concerned (or maybe only mildly so) about a fire or explosion. The cleanup took a couple of days, the waste fuel as easily collected and disposed of by our waste oil collection firm.

On another occasion, a customer dropped off a small cabin cruiser, gasoline powered, for routine maintenance. He left it at the dock over the weekend. When we came in Monday morning a mechanic went aboard but quickly exited, as the smell of gasoline was overpowering. I went aboard to shut the battery switches (all were ignition protected) open hatches, and I have to say my heart was in my mouth. We set up a ventilation fan on deck and eventually dropped a duct into the bilge and ventilated it using a ignition protected bilge blower, and then pumped the gasoline out using a portable fuel pump. It was nerve wracking. Disposing of the waste fuel was far more complex and costly.

In the US, the rules for fuel and electrical systems on gasoline powered vessels are codified as federal law, while rules for these systems on diesel powered vessels are voluntary. I once asked a US Coast Guard Marine Safety Officer why that was the case. He said, "Statistically, because diesel boats don't blow up".

While diesel burns (I routinely use it to safely help ignite brush burn piles), I would never use gasoline for this purpose, as its burn characteristics are essentially explosive. Diesel powered vessels do catch fire and burn, but in my experience it's rarely the fuel that is the source of the fire. Having said that, atomized diesel will burn readily if sprayed onto an ignition source (but again it will not explode per se). Diesel vessels are not required to have ignition protected components or bilge extraction blowers. Gasoline vessels, on the other hand, explode, often the result of fuel leaked into a bilge and the vapors ignited by a non-ignition-protected source.

[BigAl.NZ]

Just reviving this thread as we have recently had a fuel problem. Twice in 10 years we have had small contaminant in the fuel which was large enough to block the fuel line/pickup.
When we inspected our tank the pickup is a piece of metal tube that goes almost all the way to the bottom of the tank.
Because the blockage is occuring before our dual racors they dont get the chance to do there filtering.
I am wondering if a small mesh cage fitted to the end of the pickup (think of a mesh box bigger than the head of the pickup) would stop larger items blocking the fuel system before it gets to the racors in the engine room.

What do other peoples pickups look like?

[s/v Jedi]

Originally Posted by BigAl.NZ

Just reviving this thread as we have recently had a fuel problem. Twice in 10 years we have had small contaminant in the fuel which was large enough to block the fuel line/pickup.
When we inspected our tank the pickup is a piece of metal tube that goes almost all the way to the bottom of the tank.
Because the blockage is occuring before our dual racors they dont get the chance to do there filtering.
I am wondering if a small mesh cage fitted to the end of the pickup (think of a mesh box bigger than the head of the pickup) would stop larger items blocking the fuel system before it gets to the racors in the engine room.

What do other peoples pickups look like?

What you need to do is not allow this to happen at all by building a fuel polishing system that removes fuel from the bottom of the tank (either a bottom connection or a draw pipe all the way down… both preferably in a sump), pull it through a Racor and pumps it back in via the fuel return. We run it using a timer.

Also, in case of blockage, we have a feed manifold between tanks and the racor, with a spare connection and little stop valves on each connection. This allows you to close all valves, connect an air compressor to the spare port, run it to pressure, open the valve to the clogged tank, the slowly open the pressurized valve until you hear the “whoosh” sound that clear the blockage.

[skipgundlach]

All of the above are good ideas but I LOOOOOVE my fuel polisher.

Total parts around $500, two metal canister-type fuel filters in series 30/10 micron, with suction pump, with vac gauge to indicate if I need to change, tees into both supply and return lines on my engine.

All parts from McMaster-Carr in Atlanta. I'm not at my computer, which has the links to its installation in my photo gallery, but the short story is that I've not changed a Racor, other than once by mistake (loose fuel line = air in supply), in over 3000 hours.

I run it any time I have the engine on, and in any lumpy seas (the better to dislodge grunge); since our wreck (first voyage, ~1/2 full tank, 3-5000 impacts on dry-at-low-water shelf in 3-day storm likely loosened everything), when I changed, and then changed again after lumpy trip back to yard to finish refit, and once in between then and the sale of our boat; the fuel is pristine.

(Buyer was curious about the tank/s. I showed him location of all 4 total. He asked if he could see in the fuel. I told him it was full, but he was welcome to; I pulled the bung and shone my big flashlight down it.

He said, "I've never seen the bottom of a fuel tank reflecting back up at me! I need to find a surveyor!!" I presume that meant he figured I took care of Flying Pig )

My canisters have a drain valve; I take out a bit to allow my canister some security against spill when I change the filters, and take out (and, in this case, catch/retain) a relative-lot of it from the 10-micron one to wash the canisters before inserting the new filters. The dirty fuel I put into my "used" oil (Honda oil changes) empty jug for discard later.

Running the pump fills the canisters (filtered fuel is returned to the tank via the return line from the engine), and I don't usually even have to bleed the engine afterward (my norm is to start it and let it run a bit).

I have never, in my 15 years of ownership, changed the fuel filter on the engine. I presume my filtration works