Injector line residual pressure

[Roark]

Wierd question for the Oldsters in the group.

Between injection pulses, what is the residual pressure in the high-pressure line between the injection pump and the injector on a 'Roid?  Is this residual pressure fairly constant or does it vary with speed/load?

The reason I'm asking is this:  If there is a standard "residual" pressure in the lines between pulses, I can calculate the max pre-heat on the fuel in that line before it flashes to vapor.  Seems to me that heating it to just somewhat under the vapor-flash pressure would do great things for the atomization of heavy fuels.

Any comments from the Illuminati?

Roark

[Stan]

The only people that I have ever read about that heat fuel in the injector line are people running fuel like wvo that might be too thick to pump or atomize properly at cooler temps.  I understand what you are trying to do, but have no experience with trying it.  It also give me the willies!  Diesel is a fairly safe fuel, but any fuel that is heated to "just under the vapor flash pressure" isn't!  Especially with some of the Indian fuel lines that we have all read about. 
Stan

[oliver90owner]

 I will say that I have not a clue but here are some things to give food for thought.

The delivery valve isolates the injector line from the IP immediately the governed volume is reached and pumping element is leaked to inlet.  However it also slightly increases the volume in the delivery pipe which allows the injector nozzle to snap closed. 

Now, tiny changes of the volume of the trapped fuel in the line will be accompanied by a huge pressure drop (liquids are not so easily compressed!).  What that drop is, I would have no idea.  The manufactures might have that information but as one only has about a tenth of a second before the next injection event at full speed it would not be easy to measure, unless the initial pressure drop is then maintained for several seconds after injection ceases and allows time to measure after a single injection event. 

In which case you need a T in the injector line and some fairly nifty measuring gear which does not change the volume while transducing(?) pressure changes - so not a normal pressure guage, for sure! 

I would assume that the line pressure will be reduced to near atmospheric, except that the elasticity of the injector pipe and the condition of the nozzle valve may be a factors to address as well.

My view of 'heating v diluting with volatile liquid' is use one or the other, not both together.

Regards, RAB

[Roark]

Thanks for the input, Gents!  Much appreciated!

To clarify what I'm up to:  I've got a never-ending supply of waste motor oil available to me.  I'd like to run a 'Roid on this stuff without adding anything to "cut" it (ie, no gasoline, diesel, etc).  I just want to mechanically filter it down to within an inch of it's life and also get the water out as well. 

For better combustion, I want to tweak a bit and heat the fuel after it leaves the injection pump and before it hits the injector.  The actual temperature I can heat the fuel to should depend largely on the pressure in the line (and to a certain degree on the fuel properties itself).

Looking back on my post I see where I may have confuzified (sic, hehehe) things a bit when I used the phrase "...heating to just under the vapor flash pressure..."  That term gave Stan the willies, and I understand why.  But what I'm really talking about was the point where the fuel will try to convert (non-explosively) to a vapor, aka "vapor lock"... and not about the point where the fuel goes "boom!" in the line.

Anyway, your responses are greatly appreciated.

Roark

[SteveU.]

Hello Roak

This is the third time in a week I've had to say the same thing to three different people about waste motor oil. WMO out of any shop will have had anything other than coolant/antifreeze that the shop generates intentionally dumped in it : powersteering fluids, automatic transmission fluids, chlorinated cleaners like brake clean, laquer thinner, acetone, ect ,ect, ect. No mystery here. There is no other place to Cheaply dump it. You don't have to worry about adding gasoline, diesel or water - it will already be in there too. All of these thing will have a different vaporization points in temperature and pressure. The vapors are not explosive until exposed to oxygen in the air. Nobody intentionally blows up and burns down a refinery, or distribution center.
So use it as is and filter to your hearts content, then try and figure out filter disposal.
If you are going to heat this witches brew the only way to be halfway safe is to keep the temperatures very low below the vaporization point of the lowest unknown.
Or use a sealed off from air enclosed vacuum distillation process like listeriodsusa1/Mike has evolved.
I will use my own 30-50 gallon US self generated stuff as is. Out side stuff I will only use if I can see through it and it smells like new without some type of Safe/Responsible processing.

Remember any vaporized hydrocarbon leaking/exposed to air just needs a static spark or a dropped wrench to light it off.

Please be safe out there
SteveU.

[mobile_bob]

out of all the stuff that can be in waste oil streams "chlorinated" solvents are what worries me the most
when burnt they give off dioxin and other narsty compounds

now if you are an old dude, maybe you figure to die before getting some mutant cancer problem, but i would worry about
my kids or grandkids being around any of that sort of thing for any length of time.

i gave up on the idea of straight waste motor oil, even though my changfa's burn the stuff well
i figure cutting it with pump diesel is the way i will go, if for no other reason than ease of filtering.

cut 50/50 the resultant mixed fuel is thin enough to filter down to whatever micron level you like
cat makes a new filter that will take out virtually all free water and >85% of emmulsified water as well.
and they are made down to 1 micron level.

not a cheap filter, but if it is used as a secondary filter (use a cheaper primary filter following an even cheaper strainer)
they should last for many thousands of gallons of mixed fuel making them reasonable over the long run.

as for the op question, after injection and as the pump follower comes back down off the cam lobe
there is no residual pressure in the injector line, if there were the pump could not pickup fuel for the next stroke.
therefore it must go back to zero and in all likelihood below ambient (and if the filter is starting to get plugged) into the
negative pressure or vacuum catagory.

bob g

[oliver90owner]

it must go back to zero

Bob,

You are ignoring the delivery valve in the Lister IP outlet.

Regards, RAB

[Roark]

Some *really* good stuff here.

Steve: I'm rather fortunate as the source of the waste oil is a private fleet depot.  They know what I'm up-to, and they're sorta interested in playing-along with my mechanical fantasies.  During the winter they have a burner system which heats part of the shop using waste oil, and the owner has figured-out that it's cheaper to have his guys NOT dump "other" (hehehe) stuff into the waste oil tank than it is to keep replacing the pump on the burner.  So while I have no doubt there will always be some "other stuff" in the mix, this source should be about as good as it reasonably gets.   

Bob:  I hadn't thought about the chlorinated solvents.  If these are present in any quantity, I can see your point.  I'm not *that* old, and I'd rather not have elective surgery to remove a second head, third arm, or prehensile tail.  (Tail could come-in handy I guess, having watched cats use them to great effect for balance. Hmmm...)

Maybe I'll see if I can find a source of condemned jet fuel.  If it's out there, and cheap/free, it does sound like a preferred solution.  Thanks for the input, guys!

Roark

[mobile_bob]

RAB:

good catch, i forgot the delivery valve,, so

depending on how well it seals, and how well the injector seals
the residual pressure could be anything up to right at full injection pressure

maybe up to 1 psi less

so for the purposes of calculating something i think there might be a problem
nothing seals perfectly, and the volume in the line is very small
so there might very well be wildly fluctuating residual pressure in the injection line
between cycles in the same engine, and certainly between different engines.

i bet no two engines are alike in this regard

bob g

[nobby]

Hi everyone,
Bob to chime in here
Part of the delivery valves job by design as RAB has already described and pointed out is to create a marked pressure drop in the injector line in order to initiate the definitive instantaneous snap shut of the injector preventing dribble and creating hence a good injection event. A good line pressure drop also lends itself to preventing a leaky/drippy injector between events.  So it is not going to be close to the injection pressure.

Now I spent some time looking through my various texts and nobody gives a figure as to the amount, however words such as 'Considerable' or 'Substantial' are used in the descriptions.

To be honest if you are already pre-heating your oil and the engine and its area is at operating temperature, I tend to see injector line heating as being off a low gain return so to speak and more than likely negligable in the big scheme of things.

I do concur with your thoughts on neat used motor oil and dilution although I tend to keep out of these discussions as I feel it is like the eternal which lube oil discussion somewhat each to his own.

Cheers
Nobby