Two stroke diesel: Build a simple ECU ??? Do-able, or not?

malc9141

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Hi

I know only general stuff about modern DFI. I have Jeff Hartmann's book but it's too specific, "teaching by example", but wrong examples.

I'm using a single Delphi injector from a 2007 Renault Clio 1.5 L diesel turbo in my attempt to build a single cylinder 2 stroke diesel (to test an idea - see earlier posts).

Q1 I presume the Clio is 12 v - what current opens the solenoid? Approx.

Q2 Presumably the HP pump has some sort of by-pass to avoid excess pressure (eg a wannabe rally driver goes down a gear at high road speed and takes his/her foot off the accelerator, meaning no juice needed but pump being driven very fast - does the pump run up to ~1800 bar and then feed back to tank, or what?).

Q3 For my use, idle and full throttle only (let's say), could a simple ECU be built : to sense crank position, inject boluses of fuel, with the control being by altering number of boluses, or timing of boluses. We've got about 7 microseconds to get the fuel in, but we hardly need any (350 cc single, boost, 1 bar gauge).
(Air mass flow would not be worked out - just alter fuel burn empirically for optimums).

Any ideas here???

Malc :lol:
 

HDi fun

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I'm pretty sure most, if not all systems use a return to tank principle. Even our old 96 Seat Ibiza D has returns from the injectors back to the tank. I can't see how a high pressure system (common rail or PD) could work without blowing up otherwise.

Is such a small engine going to have enough angular momentum to keep it spinning, even as a two stroke? During the compression/exhaust phase there's no other cylinder(s) in a power phase.

What you might be able to do is have a double acting piston with an injector either side so that the engine is always in a power phase somewhere.

Theoretically, this could give the same power as a four cylinder 4 stroke unit with just one cylinder bore.
 

malc9141

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Thanks, HDi,

The injector has a return but the pump would need one too, I imagine. I'll check with Keir (who sell them).

You are half right about the potential prob with a single cylinder. But it's taken care of by using a very big flywheel (for this trial engine - weight doesn't matter to test the air-flow/combustion principle).

Any ideas if an ECU - a control system could be built???

Malc
 

malc9141

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The High Press pump has a fuel inlet (plastic) and HP out to injector (steel) and a by-pass (steel). It by-passes at ~1000 bar depending on pump.

Injector current: I tried to estimate this by measuring the resistance through the coil (amps = volts/ohms) but the resistance is ~ zero, so that's no help.

Anyone an electronic expert here? Build a control system?

Malc
 

HDi fun

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The resistance will be very low as you'll need quite a large current to crack open the injector against the massive 1800bar rail pressure.

Something of the order 30 to 40 amps is common. Divide 12 volts into 36 amps and you get 0.3 ohms, which is pretty low so might well read zero on a typical DVM.
 

malc9141

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resistance will be very low as you'll need quite a large current to crack open the injector

Yep, that figures. Sounds right. Thanx ++
Malc
 

HDi fun

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I think that the fuelling is controlled by pulse duration in nearly all cases, although lots of systems now have multiple injection phases. Eg - short pulse early pilot injection to get the fire underway. Then the main phase as close to TDC as possible. Sometimes you get one in the expansion phase as well for emission control systems that burn off soot actively.

(Incidentally, don't fire one of those injectors anywhere near hands or limbs - the delivery rate is so high that I've heard one case where one stuck open in a Peugeot 607 that it bored a hole into the piston crown.)

For experimental purposes I guess that you won't need this level of complexity.

Do you remember those kits you could get in the 1970's / 80's that converted your car with breaker points into one with electronic ignition? OK, the timing was still controlled mechanically but the switching was done solid state electronics (no points etc.)

These things could switch 10amps or so, repeatedly charging the igntion coil and breaking the circuit to fire the plugs. You need the opposite here, so......

If we could find a way to invert the pulse stream and amplify the curent this might give you a means of firing the injector. Timing was/is by means a magnetic reluctance device, so stick the magnet on the crank and the sensor somewhere adjacent; moving it about will let you change the timing.

Also, what are you going to use to supply the fuel under pressure. Even with a big flywheel I don't think a single cylinder motor will stand the compression load and the high pressure pump load. Still, if the flywheel was very very very big......But, then how do you get it spinning in the first place?

Cheers,

Regards,

Paul.
 

malc9141

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Hi Paul, That's a nice post, thanks. I'll have to think about the meat of your message: ie, the switching.
(I do remember the solid state spark controllers - a friend built one successfully. But I did not!).

You say:

Also, (1) what are you going to use to supply the fuel under pressure. Even with a big flywheel I don't think a single cylinder motor will stand the (2) compression load and the high pressure pump load. Still, if the flywheel was very very very big......But, then (3) how do you get it spinning in the first place?

If I understand your questions, (1) the fuel comes off the Renault Clio pressure pump. I've talked to people about this and I might be wrong but I think there's a lot less work to run one injector in a 300 cc cylinder. So the drive load should be OK - after all, a car starts by the battery turning the engine over, and thence the pump. It doesn't seem a problem. Pressure is only one part of the calculation. (Power needed = pressure X volume delivered, and that's very small). But I'm always open to correction.

It's a two stroke, so both valves are open for the lower 120 degrees or so of crank angle, so there's a loss of compression there. I had thought the initial problem might be getting it fired up (tho' the gloplug is there to help) with lack of compression.

Once firing, it will be a tragedy if it self-destructs! I just hope the robust Lister-Petter unit will stand the shortish experimental runs, to test the cylinder head design and overall concept.
(3)I would turn it fast on a starter ring.

But may I say I welcome this chat enormously, so thanks.

Malc
 

malc9141

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If we could find a way to invert the pulse stream and amplify the curent this might give you a means of firing the injector. Timing was/is by means a magnetic reluctance device, so stick the magnet on the crank and the sensor somewhere adjacent; moving it about will let you change the timing.

Moving the coil (to advance/retard) is too crude, I think.
My guess is I'd need some sort of electronic time base which would represent 360 degrees and some way of recognising where to switch the current in. Trouble is, I'm out of my depth.
Any help gratefully received (I never intended getting into this side of things - my expert helpers seem to have lost interest despite being fed beer etc)

Malc
 

malc9141

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What do you by "invert the pulse stream" ?
I'm thinking you might be right about a simple switch.

I'm not sure how to do it, but just switching straight off the flywheel, with some choices (eg 5 BTDC, TDC, % ATDC, 10 ATDC) and any or all, might work.

I'm thinking - when I know a bit more about the injectors - DHi, Help! - I could mount the single injector in a vice, drive the pump from a good electric motor (anyone got one, say 1 kW ? - and see how much fuel comes out with a short opening. (Next, I'll be revising theory of condenser discharge!).

I started out here with a small team. The good guys got jobs and disappeared, the bad ones talked only. May have too much to deal with!

Malc
 

HDi fun

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If you're only planning to run at fixed RPM then the injection timing could be fixed too.

Invert the pulse stream - the LV side of the coil in a spark engine is charging between firing the plugs (this is the dwell angle). When you want to issue a spark the supply it cut.

In your case you want to have 0v, and only issue 12v when the injector needs to fire.
 

HDi fun

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Actually yeah, a 12v battery should be more than up to that. Now all we need to do is switch the juice on and off at the right time. I can see the fuel timing bit is getting fiddly. I really have no idea at this point what the injection duration needs to be.
 

pgarner

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i would have said a normal relay doing it. But im thinking that even if your running 2000 rpm that would be 1000 switches a min or nearly 17 times a second. im hoping im right that the 2 strokes fire every revolution so your talking 34 times. i really think this might fry the relay before its even really got going. as youl only be wanting it open for what, quarter or a rev ?, at 34 times a min gives around 1.7 seconds so a quarter is just under 0.5 of a second

fiddly yeap i can see this becoming quite difficult
 

HDi fun

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1000rpm is 1000/60 per second, so 16.667 recurring per second.

Firing the injector 17 times a second is not going to work with a elecromagnetic relay I don't think. It will probably just bounce about between closed and open.

But then, the solenoid controlled injector is going to have to do 17 cycles per second and that doesn't suffer from bounce. Perhaps because of the enourmous fuel pressure holding it shut.

I think this has to be solid state in operation. Effectively were looking to get control of high current pulses of specific (and adjustable) duration.

The pulse width is as important as the timing of it.

For a single injector engine that's running at fixed speed under fixed load we can standardise the pulse duration. We can also fix the timing relative to TDC for this purpose.
And, err, I need to go away and think a bit more about circuit design.
 

pgarner

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this isnt going to give you much adjustment but would an old style distributor cap not work only thing i can think of is you may have to use the 2 opposite points on it rather than just 1. it would be able to hold the current and you wouldnt have to worry about the "bounce". granted it might not be an ideal set up but it might allow you to test that its working before going into the electronic side of the timing. remember the old KISS saying
 

pgarner

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ok its not allowing me to edit my own post.

had another quick think about what i had said above you could run it off one point of the dizzy cap and have the rotor arm of the cap connected to the flywheel with the point touching where the piston is just as its opening the intake this way the injector comes on while air/fuel mix is going into the combustion chamber ( does this sound ok to you I dont fully understand the 2 stroke engines )

i understand that this will be no good a set up if it works as the gear box will need to be connected up but would it work as a starting point ?
 
Last edited:

malc9141

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Thanks, Guys,

First, this collective thinking is useful. So thanks again.

With a diesel there is no distributor.
It fires each 360 rev, so at 2000 rpm it's firing 33 times a second.

The pulse duration is going to be very short but that's what modern injectors do. The duration might be about 10 degrees total (suspect less) so for each 1/33 seconds (= 30 microsecs), the pulse will last 30*10/360, ie 0.8 ms.

That seems very brief (!)
but let's think what an injector is doing in a 4 stroke four cylinder car at 3000 rpm - motorway cruise.

Each cylinder is firing once, each two revs, ie 1500 times per min or 25 times per sec. So we can see it isn't going to be much different from 33 times per sec. Each rev takes 40 ms.
If we stick to a 10 degree dwell for the injection (pure guess), each pulse is 40*10/360, ie 1.1 ms.

Now at idle in the 4 stroke buzz-bomb, the rev time is longer and the pulse duration shorter, but
that does imply the solenoids can open/shut this fast.

Next, I'm out of phase with you guys!!! You suggest something, I think, No, won't do. Then you reconsider, and meanwhile, I'm coming round to your earlier way of thinking!
So, what about this? ---->>>

The engine has a 16" dia flywheel (very thick but that's another matter). It has convenient mounting points nearby. The circumference allows exactness.

If I built a small structure that bolted onto the crankcase and had an adjustable extension to contact the flywheel face, we could get a pulse off the f/w by adding the other part of the contact (say a piece of silver) to the f/w. If the silver was roughly triangular, by moving the contact back-forward for advance-retard or up-down for dwell, we might have a useful circuit.

But I don't know if the charge would build fast enough to move the inj solenoid. It would probably need a condenser (discharging) to help it. But it might work, ie going analogue when I assumed (out-of-my-depth) digital.

Comments welcome.

It's all at a planning stage at present.

Malc
 

pgarner

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Thanks, Guys,

Next, I'm out of phase with you guys!!! You suggest something, I think, No, won't do. Then you reconsider, and meanwhile, I'm coming round to your earlier way of thinking!
So, what about this? ---->>>

The engine has a 16" dia flywheel (very thick but that's another matter). It has convenient mounting points nearby. The circumference allows exactness.

If I built a small structure that bolted onto the crankcase and had an adjustable extension to contact the flywheel face, we could get a pulse off the f/w by adding the other part of the contact (say a piece of silver) to the f/w. If the silver was roughly triangular, by moving the contact back-forward for advance-retard or up-down for dwell, we might have a useful circuit.

But I don't know if the charge would build fast enough to move the inj solenoid. It would probably need a condenser (discharging) to help it. But it might work, ie going analogue when I assumed (out-of-my-depth) digital.

Comments welcome.

It's all at a planning stage at present.

Malc

i think your thinking the same way as what i was getting at the dizzy cap idea.

i meant it to be used to open the injector rather than the a spark. but it wouldnt have gave you much room for adjustment for timing / duration



HDI the fig came from Vagcom group 122 ( i think ) dont know how accurate it is thou. was 172 ish on standard unleaded
 

malc9141

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For HDi fun,

If you can confirm that my injectors are Coil, not piezo, it would help.

(Note, if the Renault Clio has coils, what will the piezo car be called?)

Malc
 

HDi fun

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I'm not connected with the motor industry so will ask my French car specialist tomorrow.

I think they are electromagnetic though, Renault fitted piezo ones to the 2.0 dCi 175 units and made a big fuss about telling us so, which bears out my thoughts.
 

malc9141

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Hi Guys,

Getting there, going insane slowly, but succeeding marginally faster.
(I have had a nightmare over the cylinder head with no less than 3 experts saying, "Don't let anyone else fit the valve seats - it might be done wrong" then doing nothing for weeks and finally giving it back to me. It is absolutely unbelievable and there are a bunch of - what are they called? - out there. In their spare time, I think they run the baggage system at BAA airport terminals. Otherwise I'd have reported on progress - I'm hoping the 4th guy WILL do it).

[First (gossip), Delphi, who make the advanced diesel parts for Renault and US trucks, is going down the financial gurgler. I wonder if they'd like to do something useful and build a Two-Stroke Turbo diesel aero-engine for me?


As to my project, getting info on the intricacies of the injectors is like doing industrial espionage. Quite amusant. The experts know only that "you attach terminal x to prong Y and it works."

However, contrary to HDi's guess (which was very fair), the solenoid opens on "a few milliamps" (spy zvw/1, picked up at a Dead Letter Box in the Lake District) but "about 80 volts" (source imgSG/G *3, deciphered from an Ad in the Personal Column of the Mirror). This makes sense, because in simple terms, a high voltage will "push faster" than a low one. The current is another matter. So the rapid response we need must come from discharging a capacitor. Next, what size capacitor? I'll work this out and we have a simple circuit (I'm no electronics expert - I'm looking for one) with an impulse from the flywheel switching a transistor to Go for the capacitor to discharge across the injector solenoid (and Stop to cut the battery out of the circuit for the duration).

(Note: the solenoid doesn't work against the hydraulic pressure, as has been suggested).

All the best

Malc::rolleyes:
 

malc9141

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Estimating the capacitance of the capacitor.

The two-stroke engine fires each rev, and revs at 40/sec. Each shot of fuel lasts, say, 6 degrees (maybe less) of crank turn. ie 6/360 X 1/40 secs. [4/10^4]........u

Our current is 4 mAmp (we've been told), [4/10^3].......w

That current flows for the time stated, so it requires a charge of (amp X sec)
=uw or [1.6/10^6] Coulombs.

Charge (known) is proportional to volts (10^2) and capacitance (unknown).

Capacitance (C) in microFarads means multiplying by 10^6.

So, C = 10^6 times 1.6/10^6 divided by 10^2,

ie about 0.02 muF, which is convenient if true!

Conclusion, we use a 0.02 muF capacitor.

Malc:rolleyes:
 

HDi fun

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capacitive discharge will not be anywhere near enough to fire the injector. The fuel rail pressure will dominate and the injector won't open at all.

No electrolytic cap will be able to discharge fast enough for this application. Electrolytic caps are little more than small polarised primary cells.

What you're looking to do is control big current at big levels of amplitude. and do it very precisely.

You can assume that the injector's electrical behaviour when firing is tantamount to a short circuit. For a very short time.

You're already in the digital domain.

Class H amplifiers --- anyone want to lead????
 

malc9141

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Thanks for reply. Welcome, as usual.

I still doubt if the rail pressure is being opposed by the valve. It is enormous, for example if you had 0.5 sq mm area to oppose at 1500 bar, you'd need about 110 kg wt to shift it. Why do that, if you have the lead in of the pressure at the side of the piston-valve, which gives zero net force?

But I'll look at your other suggestions and keep at it.

Malc

PS
It's so funny, I took the cylinder head to experts last Sept. "Don't let a machine shop do it, we'll do it." Nothing happens. Try elsewhere. Exactly the same. Another 12 weeks. Now, a third guy. He says, "Is this the only one you've got?" meaning "Is it Ok if I wreck it?" He also says I've been grossly over-charged by expert No1 for valve guides - which I'd wondered about.
I have to get that back and get my Machine Shop to do it!!

Also, I paid ~£250 for a rare starter motor and starter ring gear, and yesterday, EXACTLY what I'd needed was on eBay for a bid of £40. Oh, it's cruel world.
 

HDi fun

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The compressed air in the cylinder is also only acting on a tiny surface area, that of then injector pintle valve, so it won't in any way help in the process of opening the injector against the huge fuel rail pressure.
 

malc9141

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HDi

We must clear this up. If you imagine a piston in a cylinder, but of very small dia, and the piston is a rod, with a waist machined into it, you can put a large pressure into that space (the waist) and still move the piston up/down because there's no net force. You let the fluid in one side, and then out the other, as the piston moves.
The fluid pressure opens the the pintle and when the pressure falls (almost at once), a spring closes it. The only work is ultra rapid shifting of the piston against its inertia. The rail pressure doesn't come into it.

As for my info about capacitors etc, there are inconsistencies (from different sources) which I'm still trying to resolve.

I emphasise that I'm pleased +++ at the reponses becouse we are slowly moving along.

Malc
 

malc9141

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force of the return spring

The hi-pressure opens that, it shuts when the pressure is "used up"

The tech problem (not mine) is how to get a solenoid to shift the little piston to expose the side hole in an unbelievably short time - about a ten-thousandth of a second. These solenoids are what have allowed Reactive Suspension to work.

I have found a company that knows the voltage, current and inductance used by Delphi (Delphi won't talk) but this company is "too busy" to tell me. I plan to keep at them - the only lead I've had. My other pieces of info might be no use.

Certainly, I'm wrong somewhere with my calculations because the three bits of info can be checked against each other and it suggests I need a VERY high voltage. Still plugging on. ;):)
 

HDi fun

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I'm lost now. The fuel pressure in a common rail diesel system is more or less constant. The pump itself is merely that, unlike the earlier systems where the pump itself controlled the timing of the injection as well. The timing and duration of the injection is controlled by the injector, which in turn is fired by electric current under computer control.

If there are no trigger pulses to the injector then it will never fire and fuel will be returned to the tank.

This is how common rail systems differ from previous systems. And it's a fundamental difference in operating principle, not just a refinement thereof.
 

malc9141

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The fuel pressure in a common rail diesel system is more or less constant. The pump itself is merely that, unlike the earlier systems where the pump itself controlled the timing of the injection as well. The timing and duration of the injection is controlled by the injector, which in turn is fired by electric current under computer control.

We must be misunderstanding each other. (But just to be pernickety, even the pressure in the Hi-Press pump is varied slightly, via the "overspill"valve, by the ECU, according to demand - nothing that is relevant to my problem, however).

I agree entirely with what you have written above. The duration of your pulse is how long the little slide valve in the injector is open, and in practice, it opens and shuts several times per 720 degrees in a four stroke. This (as you know) is to do with burning carbon particles etc. All I was saying was that the pressure opens the pintle, but the solenoid "goes up and down" like a hatch and its piston valve isn't affected by pressure.

But anyway, I have to find a way to control the solenoid in the injector if I am to succeed in making my diesel work. I find those few who know are "too busy" or else the technical guys "just put things together" and only have a very rough idea of details.

A company called Hartridge, Milton Keynes, make a "black box" which will open and shut the injector, so it can be examined on the bench. The flow pattern, timing etc can be checked. I'm hoping they will give me useful info - they won't help materially. Won't modify a box to fire off the crank, for instance.

I plug on.... :)

Malc:cool:
 

HDi fun

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I would be cautious of firing an injector spuriously in open space. If you're supply the 1300 bar plus of fuel pressure then you basically got a hydraulic cutter on the loose if the thing opens. CD diesel systems have been known to bore holes in piston crowns in the unlikely event that an injector does stick open.
 

malc9141

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Yep, of course. The HP pump pressures are terrifying. (They use these pressures for water machining - your hydraulic cutter). What I have to check is that the junctions, before assembvly, are not at all scratched at good magnification. Otherwise, you have jet fuel across the other side of the shop where there just happens to be someone switching on a light...Unless you stand in the way....+

But I'm still trying to get the way of firing it sorted out. That's what is so "secret"it seems. Perhaps for good reason. GHowever, I see I have just had some info from Hartridge (with alot of money mentioned!!!).

I'll keep reporting. This might get interesting. At present, Prozac (is it?) may be the best option....

Malc

:???:

Malc
 

obi_waynne

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Here is a crazyish idea which may help address the problem of the quick pulses required to deliver fuel into a 2 stroke engine. What about an array of injectors 2 or 3 which fire alternately. It would be possible to get these rapidly firing in sequence without a "bounce" effect as they open and close.
 

malc9141

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put 2 injectors in

That's hilarious.
[The Channel Tunnel project was up for tender, 1980. Finnegan Bros put in a low tender.
Interview: "How can you do it so cheaply?"
Pat Finnegan: "I start digging at Dover, Mick starts at Calais, we meet halfway."
Interview: "But what if you don't meet up?"
"You get two tunnels for the price of one."]

Nice idea. Sadly, there is hardly room for one unit. Also the positioning is critical, you can't just slam some fuel in and get it burning optimally. It has to go into a high air pressure zone. The pressure before burn is not uniform in the "combustion chamber."

I am slowly getting somewhere.
It suddenly occurred to me that since I am using a test bench only, and am trying to investigate combustion, I don't have to use a car battery. I think (I took some time to be convinced on this) the Renault has an "inverter" (no, I didn't know what it was, either) which creates AC then boosts the voltage with a transformer working opp to usual. This high voltage is then turned back to DC and can rapidly re-charge a condenser which can then give the rapid pulsing.

Pretty far out - but then as someone said, it's what I'm getting myself into. Keep it coming, guys, I'm helped to think by what you say.

  1. I am Ozymandias, King of kings. Look upon my works, ye mighty. And despair. Just keep taking the tablets.

Malc
 

malc9141

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This is mainly for HDi fun.

I've got the Bosch book, and injector diagrams which explains where we seemed to be saying different things.

In the injector, there is the piston. It has rail pressure above and below (ie no net force). When the armature is activated, it opens a valve A above the piston. The piston goes up. The pintle is attached so it also goes up. Fuel squirts into the cylinder.

What closes the pintle? Your valid point. Answer: there are bleeds (choked passages) which allow fuel at rail pressure back in above the valve. The armature return spring is evidently strong enough to shut the valve A off.

A bleed under the piston allows it to be closed with the rising pressure above plus a small spring.

Hope this doesn't sound like telling "my grandma how to boil eggs" - just trying to help.

Malc
 

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