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

[HDi fun]

So how do you plan to overcome the force of the return spring?

[malc9141]

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]

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]

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

[HDi fun]

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]

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

[waynne]

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.

[pgarner]

that would make sense put 2 injectors in place this way you could still get them to fire in a 4 stroke way. with each one set 1 rev apart

[malc9141]

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]

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