Fuel gunge attractor?

meandraft

meandraft

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I've just fitted an inspection hatch to my diesel tank after suffering from fuel starvation. I was pleasantly surprised to find very little gunge in the tank. However both copper pick up pipes were heavily coated inside and out. Is anyone aware something I could leave in the tank to attract this gunge better than the pick up pipes? I keep the fuel dosed with additive so I guess that the gunge is merely dead microbes.
 
copper tends to be fatal to biological entities. I'd think about killing any bugs in the main body of the tank, rather than letting the copper pickup pipes become blocked. That way bugs pass through your newly cleaned pipes and get collected in the filter(s).

I can't think of anything that will collect gunge better than a filter in the fuel delivery pipes. Unless you build a small polishing system as Little Ship has demonstrated.
 
sarabande said:
I can't think of anything that will collect gunge better than a filter in the fuel delivery pipes. Unless you build a small polishing system as Little Ship has demonstrated.
Click to expand...

Having your tank fitted with a small drainable dirt sump, is even better. Works 24/7, cost zilch.
 
meandraft said:
...I guess that the gunge is merely dead microbes.
Click to expand...

It could be, but gunge forms in tanks and pipes due to chemical processes anyway. Diesel is not completely stable1 and tar-like substances (aka Asphaltene) will precipitate out, and may even form in the diesel itself over time. Whichever, you'd still want to get rid of it anyway, but the dreaded bug is something of a bogeyman.

These http://fuelschool.blogspot.co.uk/2009/02/asphaltenes-and-plugged-fuel-filters.html and http://fuelschool.blogspot.co.uk/2009/02/black-fuel-filters-asphaltene.html aren't the most scholarly of articles, but give some current thinking.

(1) The diesel from an individual source may well be reasonably stable, but normal practice in boats is as bad as possible to imagine:
i. We tend to top up tanks. This mixes fuel from multiple sources, and in more or less equal proportions (ie fill up if down to maybe 1/3 of a tank left). A road vehicle tends to let the tank get emptier before re-filling.
ii. Our engines usually differ from cars'. On a car, the usual injection system does not return fuel to the tank (hence the mpg display is possible and accurate), whereas many or most boat engines (mine certainly) returns warmed diesel to the tank, sometimes nicely oxygenated by splashing. As I understand the articles I've read, warmth, Oxygen and agitation are the ideal conditions for re-forming the heavier fractions which were 'cracked' in the crude-oil diesel refining process.
iii. We frequently, in fact almost always I think, have some copper or brass pipework or unions. Copper is implicated in promoting de-stabilisation of diesel fuel
iv. The fuel is then left alone for sometimes months on end which allows precipitation, and frequently with a small amount of water present which creates the gungy paste we all fear and loathe!
 
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meandraft said:
I've looked for a drain tap but Tek Tanks say there isn't one fitted to this tank. It's very low down so space would be a problem.
Click to expand...

If it has a Tek Tanks label on it, there will not be a direct drain from the sump. They don't approve of them, believing them to be an unnecessary leakage risk. The guy I dealt with told me they will fit one if the customer absolutely insists, but then they won't put their name on the tank!

(They will happily fit a sump-emptying tube that emerges through the top of the tank, to be operated by suction rather than gravity.)

Pete
 
jdc said:
ii. Our engines usually differ from cars'. On a car, the usual injection system does not return fuel to the tank (hence the mpg display is possible and accurate), whereas many or most boat engines (mine certainly) returns warmed diesel to the tank, sometimes nicely oxygenated by splashing. As I understand the articles I've read, warmth, Oxygen and agitation are the ideal conditions for re-forming the heavier fractions which were 'cracked' in the crude-oil diesel refining process.
Click to expand...

This is a subject on which I am currently trying to find information. It seems there are various designs but if anyone can point me at definitive information I would be very pleased.
1. Several small marine engines including Yanmar, Volvo and Bukh. Fuel from the injection pump arrives at the injector in metered amounts. The valve in the injector is not perfect and a small amount leaks from it, which is returned to the tank via the spillback line. I recently measured mine, Yanmar 3GM30F, at 2000 rpm I collected no more than 1 ml per minute. There is no other spillback with these engines.
2. Other mechanical injection systems have a weir before the injection pump, which returns fuel unwanted by the injection pump back to the tank. Flow rate can be much higher. My book 'Introduction to internal combustion engines' by Richard Stone shows a schematic of this without naming the engine type.
3. Common rail fuel systems, as on most modern cars, have a spillback valve at the end of the manifold, again returning fuel to the tank constantly. I found figures on a 4x4 website suggesting quite high spillback rates of the order of litres per minute with a 2 litre engine.

Clearly if there is an appreciable spillback rate it will act to some extent as a polishing system. I would be grateful for any info.
 
vyv_cox said:
This is a subject on which I am currently trying to find information. It seems there are various designs but if anyone can point me at definitive information I would be very pleased.
Click to expand...

I have a small nugget of first-hand information which may or may not be useful. My engine is a Volvo D1-30, and I have a squeeze-bulb priming pump which, if pumped with the filter bleed screws closed, will push fuel into the engine. Doing this with the engine stopped, little resistance is felt and the fuel gushes audibly back into the tank through the return line. It feels and sounds as if the engine were simply a longish loop of fuel hose. I guess that corresponds most closely with your "weir" description.

Pete
 
prv said:
I have a small nugget of first-hand information which may or may not be useful. My engine is a Volvo D1-30, and I have a squeeze-bulb priming pump which, if pumped with the filter bleed screws closed, will push fuel into the engine. Doing this with the engine stopped, little resistance is felt and the fuel gushes audibly back into the tank through the return line. It feels and sounds as if the engine were simply a longish loop of fuel hose. I guess that corresponds most closely with your "weir" description.

Pete
Click to expand...

That's an interesting one, thanks. I'll try to find a diagram of the piping layout for that engine. I have felt my fuel tank distinctly warm after a period of motoring but I suspect that may have been when I had a Bukh engine. Recently I have not detected any warmth with the Yanmar. An explanation could be that my fuel flow rate is low due to faulty pump or blocked primary filter but there are no symptoms that suggest this.
 
vyv_cox said:
This is a subject on which I am currently trying to find information. It seems there are various designs but if anyone can point me at definitive information I would be very pleased.
1. Several small marine engines including Yanmar, Volvo and Bukh. Fuel from the injection pump arrives at the injector in metered amounts. The valve in the injector is not perfect and a small amount leaks from it, which is returned to the tank via the spillback line. I recently measured mine, Yanmar 3GM30F, at 2000 rpm I collected no more than 1 ml per minute. There is no other spillback with these engines.
2. Other mechanical injection systems have a weir before the injection pump, which returns fuel unwanted by the injection pump back to the tank. Flow rate can be much higher. My book 'Introduction to internal combustion engines' by Richard Stone shows a schematic of this without naming the engine type.
3. Common rail fuel systems, as on most modern cars, have a spillback valve at the end of the manifold, again returning fuel to the tank constantly. I found figures on a 4x4 website suggesting quite high spillback rates of the order of litres per minute with a 2 litre engine.

Clearly if there is an appreciable spillback rate it will act to some extent as a polishing system. I would be grateful for any info.
Click to expand...

It's certainly unclear about the pros and cons of the effect of spillback. As you note, it acts as a sort of polishing system, which is presumably good, but also returns warmed and possibly oxygenated diesel to the tank, which the articles I posted earlier say are bad (and I found an article by BP also saying the same, so it's at least corroborated by a company who ought to know what they are talking about!).

As far as real knowledge of engines, I only have my own ones to observe.

The Bukh DV20ME on my old boat did return appreciable amounts; I could hear the splashing and the tank got appreciably warm to the touch, but of course I never measured it!
My generator uses a Kubota OC60, and this returns lots. I know this because I actually use the return line, which has a join in a very convenient place, to fill a small jerry can with diesel whenever I need some - it's easier than trying to pump it from the tank. I estimate it at a litre a minute or so - huge compared to that burnt.
My main engine is a Kubota 2203, and that also returns diesel, but I haven't actually measured the volume - I must do so.
My car (VW 1.9 litre turbo) is an electronic injection system and as far as I can tell (way too complicated to service myself) returns nothing.

But whichever design of engine one has, the (in)stability of diesel fuel genuinely seems to be becoming a real issue. I was amazed to find out that copper or brass pipework or unions are, according to BP and to Cummins engines to name just two sources, very much frowned upon.

I conducted an experiment almost 12 months ago now: I took about 250cm3 of clean red diesel, added to it the black scrapings from my Racor primary filter when changing that, and shook this contaminated diesel up with 70cm3 of tap water. I then left this in a jam jar in the house, so quite warm compared to my boat's tanks. As I say, that was nearly 12 months ago. It did nothing for about 4 months, then it grew a small amount of grey stuff in the water, which, after another 5 months sank leaving a gritty looking deposit, but of much more interest a really solid varnish like substance on the bottom of the diesel and above the water. So solid that when I invert the jar the water stays put, trapped by the 'varnish'. I know it's a layer and the water hasn't gone to jelly as I then punctured the varnish layer. By the way, the red colour has faded entirely, and the diesel is now a pale brown. I don't think we need blame microbial activity for any of this - the diesel just isn't stable.
 
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hmm, I suspect we are on to something serious about the inter-action of biodiesel (in its widest terms) with


1 some of the metals commonly used in engines and fuel systems (e.g. copper pipe)

2 air and water , especially at the temperature ranges found in tankage and return pipes.


A quick paper....

Comparative corrosive characteristics of petroleum diesel and palm biodiesel for automotive materials
Abstract
http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.elsevier-11553072-50f6-38e4-84ef-a566a69b8cb5

Text from another paper
https://www.google.co.uk/url?sa=t&r...Gz4z233MFQYFwmA&bvm=bv.78677474,d.cWc&cad=rja

The latter has some good diagrams...


Indications are that biodiesel plus warmth, plus air, plus water is not good for a number of metals....
 
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I don't have a lot of experience with fuels but quite a lot with lubricants. It is well known (by us, at least!) that copper should be avoided in lub oil systems because it promotes foaming. Not normally a problem in a once-through system such as fuels. There is no doubt that copper is very widely used in yacht fuel systems, mostly without problems, but I guess that if there is significant spillback it could be a factor. Some of the lubricants used in machinery are very simple with tiny proportions of additives, which leads one to suppose that it is the hydrocarbons themselves that are at the root of the problem.
 
vyv_cox said:
This is a subject on which I am currently trying to find information. It seems there are various designs but if anyone can point me at definitive information I would be very pleased....
Click to expand...

Vyv, I have a Nanni 4.150, based on a Kubota V1505ES. The fuel system on that can act as a quite effective fuel transfer system or polishing setup. I've never measured the flow rate (probably couldnt with the metering available) but my feeling is that I've shifted a noticeable proportion of fuel from one tank to another by inadvertently feeding from one side and returning to the other (separate taps control both sides in and out, 2x200l tanks). We're talking perhaps 30l (1/8-1/4 on the guage but thats an inaccurate float and the feedin tank was low anyway) over a period of several hours for an engine that 'uses' about 2.5l/hr.

I recently used the 'feature' to drain the port tank when it developed a weep - now all I have to do is figure out how to fix that :(
 
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sarabande said:
hmm, I suspect we are on to something serious about the inter-action of biodiesel (in its widest terms) with


1 some of the metals commonly used in engines and fuel systems (e.g. copper pipe)

2 air and water , especially at the temperature ranges found in tankage and return pipes.


A quick paper....

Comparative corrosive characteristics of petroleum diesel and palm biodiesel for automotive materials
Abstract
http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.elsevier-11553072-50f6-38e4-84ef-a566a69b8cb5

Text from another paper
https://www.google.co.uk/url?sa=t&r...Gz4z233MFQYFwmA&bvm=bv.78677474,d.cWc&cad=rja

The latter has some good diagrams...


Indications are that biodiesel plus warmth, plus air, plus water is not good for a number of metals....
Click to expand...

Many thanks for this (and the other) links.

As I understand it, the problem is not due to biodiesel per se, but due to the manufacturing techniques for ultra-low sulphur diesel. I admit it's hard to distinguish then two as the changes came about more or less simultaneously, but the red diesel I experimented with (and which created the varnish like layer) is supposed to have been ULSD, but to have zero FAME.
 
RobbieW said:
Vyv, I have a Nanni 4.150, based on a Kubota V1505ES. The fuel system on that can act as a quite effective fuel transfer system or polishing setup. I've never measured the flow rate (probably couldnt with the metering available) but my feeling is that I've shifted a noticeable proportion of fuel from one tank to another by inadvertently feeding from one side and returning to the other (separate taps control both sides in and out, 2x200l tanks). We're talking perhaps 30l (1/8-1/4 on the guage but thats an inaccurate float and the feedin tank was low anyway) over a period of several hours for an engine that 'uses' about 2.5l/hr.

I recently used the 'feature' to drain the port tank when it developed a weep - now all I have to do is figure out how to fix that :(
Click to expand...

Thanks for that. Do you know how it is piped, particularly whether there is a return from the injection pump to the tank? I find it difficult to understand how high flow rates can occur from the injectors back to the tank when the flow to them is metered with great accuracy.

I have seen those kind of flow rates reported for 4x4 cars with common rail arrangements but I assume your Nanni is mechanical with point to point piping?
 
The Kubota 2203 (50 HP Beta) is, according to my workshop manual, a Bosch injector pump with metered quantity of fuel distributed to each injector, so the spillage from the individual injectors themselves is likely to be tiny. But the injector and metering pump works, according to this source http://www.cs.rochester.edu/~jag/vw/engine/fi/injpump.html as follows:

The cam disk is rigidly attached to the plunger. The drive shaft rotates the cam disk. The cam disk rides on four rollers (only one shown in this picture), and has four lobes. Thus for each revolution the plunger will pump four times. Note that with this arrangement the plunger stroke is constant. The metering (regulation of how much fuel is delivered) is done not by changing the mechanical stroke, but by spilling some of the fuel through spill ports, and thus changing the effective stroke . This is done by uncovering a spill port under the control sleeve at a particular angle of rotation. The other purpose of the rotation is to deliver the fuel to the correct cylinder. This is done by having four four delivery valves (only one shown in the figure), one for every 90 degrees of rotation. During a full revolution the plunger makes four strokes, one at 0, 90, 180 and 270 degrees. During each stroke the delivery port in the middle of the plunger is connected to a particular delivery valve.
...
When the desired amount of fuel has been injected the spill port opens (located under the control sleeve in the figure), and the pressure quickly drops. This causes the delivery valve to close. During the rest of the stroke fuel is "spilled" through the spill port instead of being injected into the cylinder.
 
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vyv_cox said:
This is a subject on which I am currently trying to find information. It seems there are various designs but if anyone can point me at definitive information I would be very pleased.
1. Several small marine engines including Yanmar, Volvo and Bukh. Fuel from the injection pump arrives at the injector in metered amounts. The valve in the injector is not perfect and a small amount leaks from it, which is returned to the tank via the spillback line. I recently measured mine, Yanmar 3GM30F, at 2000 rpm I collected no more than 1 ml per minute. There is no other spillback with these engines.
2. Other mechanical injection systems have a weir before the injection pump, which returns fuel unwanted by the injection pump back to the tank. Flow rate can be much higher. My book 'Introduction to internal combustion engines' by Richard Stone shows a schematic of this without naming the engine type.
3. Common rail fuel systems, as on most modern cars, have a spillback valve at the end of the manifold, again returning fuel to the tank constantly. I found figures on a 4x4 website suggesting quite high spillback rates of the order of litres per minute with a 2 litre engine.

Clearly if there is an appreciable spillback rate it will act to some extent as a polishing system. I would be grateful for any info.
Click to expand...

On my 3YM20, at about 2000rpm, about half the delivered fuel is being returned to the tank. I had thought of fitting a filter on the line, but was advised by Racor that such a filter would be totally wasted. Understandable if you consider that it's been though the settling bowl and a coarse and fine filter before going past the injection pump.
It was suggested that I fitted an inverted funnel with wire gauze over the large entrance at the pickup.
The returned diesel is hot - soon getting the whole tank to 35-45C.
I've never had blocked filters - always found little billets of tar-like substance blocking the pick-up, on the 4 occasions I've had fuel-feed interruptions.
That's in about 14k hours of motoring, with two engines.
On two occasions I've had the tank out and steam-cleaned - about 4 litres of un-named, murky liquid at the bottom of the tank.
 
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