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

[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?