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

[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:

[malc9141]

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

[HDi fun]

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]

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]

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]

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