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