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John Appel

Injection timing

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I have a Link G4 Storm. I am using it on a 1200cc  twin cylinder 4 stroke motorcycle engine of our own construction.This engine has evenly spaced firing intervals (360 degrees apart) which is commonly called an opposite pair. It is like No.1 and No. 4 cylinders of an inlne 4 cylinder engine. So far we have been running it with sequential injection using a cam sensor. We have experimented with injection timing. I have been judging  the results by comparing the response to blipping the throttle off the idle. I have found the best pick up from a closed throttle to be at about 270 degrees BTDC for end of injection timing. This is when the piston is about halfway down the induction stroke and so the air stream thru the port would be getting close to its maximum velocity. It seems to like injection into the moving airstream rather than injecting into static air with the valve closed. I have read different and conflicting opinions about this.

 I would like to try running the engine without the cam sensor.(It gets in the way)  This would mean running in multi point group mode. With this set up it would squirt twice in a 720 degree engine cycle, in other words once every crank turn.

In your section on injector timing it says that it is only possible to vary the timing in sequential mode. When using two squirts per engine cycle is it possible to set the second squirt at the same 270 degree figure I am currently using and then the first squirt would necessarily be one turn prior (630 degrees BTDC). This way the first pulse would go into the port full of static air (valve closed)  and the second pulse would go  into the moving airstream with the valve almost fully open.With a 360 degree twin the timing would be identical on both cylinders. 

If it is not possible to vary the timing in multi point group mode how does the Link set the timing. Is there a default timing that it reverts to.

 Regards, John

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Hi John,

When using multi-group fuel the injection timing is fixed relative to the trigger offset. Here is an image of Inj 1 (Dark blue), Inj 2 (Pink), Ignition 1 (light blue) and Trigger 1 (yellow).

My engine simulator didn't have 16-2, so I'm running 24-1. The ignition timing is set to 0 degrees. The trigger offset is 0 degrees

NewFile3.thumb.png.9e6faab893f1b84996268

When I adjust the trigger offset to 180 degrees I get the following image:

NewFile4.thumb.png.c203e2d916ea9f833aac8

The problem for you is that to adjust your trigger offset you are going to have to physically rotate your crank trigger wheel.

Scott

 

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Thanks for that Scott.It would appear that the injection occurs at the time of the tooth gap because when you shift the offset only the ignition point seems to change. I assume that the pink line that you call cyl 2 is actually cyl 2 of a 4cyl engine because it is displaced by half a revolution from cyl 1.  My second cylinder would be the same as cyl 4 on a 4 cylinder engine which would be one whole turn displaced. Ignition will be by waste spark so will be the same for both my cylinders.  My trigger offset is 164 degrees.

 Can you show me another graph with the following figures

 Trigger offset  164 degrees

Toothed wheel  24 - 3  ( this will give the same angular gap as my 16 - 2)

Pulse width 2 msec     ( which is about what I expect at idle)

 Ignition timing zero degrees.  (this will show me where TDC is)

 Can you show cylinders ! and 4 of a 4cyl engine. (they should be the same)

 Does it time by end of injection or start of injection ( this will tell me in which direction the pulse width will increase at higher throttle openings)

 My aim is  draw a chart showing injection pulse relative to valve movement.

 Thanks for your help , Regards, John

 

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Hi John,

In the previous images I forgot to say I was on an Injection Rate of '1/2 Engine Cycle'.

In the following image I am on '1 Engine Cycle'. I don't have a 24-3 trigger mode, the closest is 24-2, which is what I have used.

  • Yellow is the 24-2 crank trigger (Trig 1)
  • Light blue is the ignition pulse (0 degrees)
  • Dark blue is injection drive 1.
  • Pink is Injection drive 4.
  • Trigger offset is 164 degrees
  • Injection actual pulsewidth (including deadtime) is 2.011 ms

NewFile5.thumb.png.f581d9d234c16bb08f7ea

Scott

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I havent thought this through in great detail and dont fully understand what John is trying to achieve - but I think John might be able to get what he wants (sequential timed injection, but 2 squirts per cycle, no cam sensor), by setting engine type to "2 stroke" or even rotary?

I also have some experience with injector timing which I will share later when I have a bit more time...

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Thanks for your new graph Scott. That's getting closer to what I want. I have taken oscilloscope traces of the trigger pulses and they look nearly the same as yours. The ignition looks right (once per turn) Can you put the injection pulses for injector drives 1 and 4 to 1/2 engine cycle,(once per turn). I think the two will then be the same.I want to see where it injects relative to TDC ( the ignition point with zero spark advance). Can you then do another graph with a longer pulse width, say 10 msec. This will show me if it times by end of injection or start of injection. I understand what you mean when you say that the only way I can shift the injector timing in group fire mode is to shift the trigger wheel relative to the crank and then reset the trigger offset to compensate to bring the spark back to the right point.

 

To Adamw

My engine runs well in sequential mode. This requires the use of a cam sensor to tell the Link if piston 1 is at the top of the compression stroke or the top of the exhaust stroke. I have found that the transient throttle response does change when I change the injector timing. According to the help section on injector timing it is only possible to alter the timing if you are in sequential mode. I am looking for a way to make my engine run just as well without a cam sensor. The only way I can see of doing this is to run in group fire mode,( sparking and injecting every turn instead of every second turn). This way the Link does not need to know what TDC the piston is on and so the cam sensor is not necessary. It may turn out that the engine will not run as well as it does in sequential mode but the Triumph Bonneville engine is a 360 degree parallel twin same as mine and it has no cam sensor. It uses a single twin lead coil for ignition and so it must spark every turn (waste spark system) I can only assume that the injection also fires once per turn. I have ridden this bike and it has nice smooth throttle response.

  John

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John, thanks for confirming.  I'm fairly certain in this case my suggestion from last night will work for you;  Set engine type to 2 stroke, set injection mode to sequential.  You will then have fully programmable injector timing (every 360deg), you wont need to mess with trigger offset and/or shifting the trigger wheel and you wont need the cam sensor.  The only thing you will need to be careful of is don't use fuel cut for any engine limiters as you could possibly get a situation where it cuts one injection event (which would be half your fuel so you could get a lean cycle), if you use ignition cut instead it should be fine.

Edited by Adamw

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I think Adam's idea will work. I think you'll also have to tell the ECU that the engine has direct spark ignition. Ignition 2 will then be used for ignition, but you won't hook anything up to it, you'll just have the wasted spark coil connected to cylinder 1.

Here is some oscilloscope images as requested. Both are the same as the last ones except at 1/2 engine cycle injection rate. The first one is with an actual pulsewidth of 2ms, an the other is with an actual pulsewidth of 10ms.

NewFile7.thumb.png.f9f42aaa392dfc5957335

NewFile8.thumb.png.e8b059a1ec237bfdf60ae

Scott

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Thanks for those images Scott.Hope you are not getting tired of me.Here is what I am aiming for.

 Ignition: A spark to both  cylinders at the same time and every turn.

 Fuel: One half size squirt to both inlet ports at the same time and every turn, with the ability to time the injection. This way you get the full measure of fuel in a complete engine cycle.(2 turns). When you alter the timing both fuel  pulses will shift together and always remain one turn apart.

 This setup requires no cam sensor because all events occur every turn.

 What if I was to call the engine a single cylinder two stroke. This injects and sparks every turn.For ignition I currently have two separate coils with their own built in igniters. What if I divide ignition 1 output into two and put one wire to each coil. They will then both spark every turn. I know this works because I have already tried this setup in 4 stroke mode.

 Can I similarly divide injector 1 output into two and put one wire to each injector. Would there be enough current.

 Can a single cylinder 2 stroke be put into sequential mode. If so then I would have injection timing adjustability.

There may be another alternative. Rotax make a twin cylinder two stroke race engine. This has two crankshafts geared together for balance reasons. The pistons rise and fall together so there is zero crankpin offset. Both pistons fire at the same time so it sounds like a single. It is really two single cylinder engines doing everything together.

Does the Link G4 Storm have provision for adjusting crankpin offset, or does it just assume that a twin cylinder two stroke would have crankpins at 180 degrees which is the normal arrangement.

 Can I call my engine a twin cylinder two stroke with zero crankpin offset and running in sequential mode I would then have a separate ignition output for each cylinder and a separate injector output for each cylinder.

 John

 

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Does the Link G4 Storm have provision for adjusting crankpin offset, or does it just assume that a twin cylinder two stroke would have crankpins at 180 degrees which is the normal arrangement.

 Can I call my engine a twin cylinder two stroke with zero crankpin offset and running in sequential mode I would then have a separate ignition output for each cylinder and a separate injector output for each cylinder.

 John

John,

The link does have the capability to set "custom TDC's".  I have never used this function so I dont know for sure if it will like us commanding 2 cylinders to fire at the same time, but screenshot below is how I think it should be set up.  Scott might be nice enough to run that setup on his sim to confirm it behaves as expected, otherwise you can just try it and see.  Set engine as 2 stroke, 2cyl, injection mode to sequential, ignition mode to direct spark, rest of config as below;

Capture.png

 

If the above method doesnt work there are a couple of other ways you could do it.  One is setting it up as a single cylinder as you have suggested above and driving both coils and both injectors from the Cyl #1 drivers.  Another way you could do it is set it up as a 4cyl, 2 strokke, coil & injector for cyl #1 goes to ECU #1 drivers,  coil & injector for cylinder #2 goes to ECU #4 drivers.  Drivers 2&3 dont get connected.

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It looks like there are a few ways to make this work. In terms of simplicity telling the ECU that the engine is a single cylinder 2 stroke with direct spark ignition (wired to a wasted spark coil) would be good. This would allow you to adjust the injection timing from 0 to 360 degrees. The only concern would be can the injector drive supply sufficient current for the two injectors. Each injector drive can deliver up to 5.0 amps. What is the impedance (Ohms) on your injectors? No problem to split the ECUs ignition 1 output to multiple ignitors.

Here is some screenshots from the ECU being set up like this. I used the trigger offset of 164 degrees still. The first image is with the injection timing set to 0 degrees.. The second image is with the injection timing set to 180 degrees.

NewFile9.thumb.png.06656e0b12899b4e1149f

 

NewFile10.thumb.png.d52540f5db64fc46e7e9

 

Scott

Edited by Scott

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Thanks Scott for that last screen shot. My injector impedance is 12 ohms  so current draw would be 1 amp each giving a total of 2 amps if we use single cylinder 2 stroke mode.  This would be well within the limit of 5 amps.

 Can you do one more simulation. This time in 2 stroke twin cylinder with cranks at 360 degrees or 0 degrees. This would give me  separate drivers for spark and fuel for each cylinder. This way if I want to do quick comparison tests between one or two injection pulses per cycle (that is with or without the cam sensor) I don't have to alter the wiring to the coils and injectors. 

I have previously found the best injector timing to be at 270 degrees before TDC so can you set it to the following figures

 Twin cyl. 2stroke  Cranks at 360 or 0 degrees

 sequential injection at 270 degrees before TDC

 Zero spark advance

 24 - 2 trigger     

 164 degree trigger offset

 If this proves to be OK I think it would be the best setup

 Thanks for all your help, John

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Hi John,

Here is the oscilloscope images when setup as requested. I used direct spark ignition mode (as Adam suggested).

The first image shows same channels as previously. In the second image the yellow waveform has been changed from Trig 1 (24-2) to Ignition output 2. I only have 4 channels, so this was required to show all the 5 waveforms.

NewFile11.thumb.png.f88dad07a74089e86f76

NewFile12.thumb.png.0fe4688115ccc7670641

Scott

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Thanks Scott and Adam,  That's exactly what I was aiming for. Retaining the ability to adjust injection timing but without the cam sensor.  The only downside I can see is the short injector pulsewidth at idle compared with sequential.  Now to put it to the test.

 Regards, John

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