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

[malc9141]

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

[HDi fun]

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]

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]

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]

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]

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]

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.

[ascaudio]

sounds right paul

[malc9141]

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]

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]

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]

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.

[malc9141]

Gotcha.


All I need now is the current.

[pgarner]

would a car starter / battery charger not do ?? car battery its self should give you enough of a current.

[HDi fun]

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]

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]

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]

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]

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 ?

[HDi fun]

184.6 - that's a very precise number. Where did that come from?

[malc9141]

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]

Originally Posted by malc9141

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]

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]

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]

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: