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4sfed
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Joined: 12 Nov 2008
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 Posted: Wed Nov 12, 2008 4:50 pm Post subject: When is the injector fired relative to TDC? |
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| I'm designing a system for an old, slow-turning siamese port engine. This will require injecting the fuel only on an open intake valve . . . after the valve on the leading cylinder has closed. So when does the Electromotive system trigger the injector?
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TimZ
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Joined: 25 Feb 2008
Posts: 120
Location: Dearborn, Michigan
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| Posted: Wed Nov 12, 2008 6:52 pm Post subject: Re: When is the injector fired relative to TDC? |
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| 4sfed wrote: |
| I'm designing a system for an old, slow-turning siamese port engine. This will require injecting the fuel only on an open intake valve . . . after the valve on the leading cylinder has closed. So when does the Electromotive system trigger the injector? |
If you use phased sequential, then you should still get the injectors for that port firing once per 360 degrees, so it should still work regardless of the timing. It should also still work if you use full sequential so long as you have two injectors firing 360 degrees apart in the siamesed port. I _think_ the only thing that would be a problem would be if you had one injector in the port that only fired once per 720 degrees - am I missing something?
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Information is not knowledge
Knowledge is not wisdom
Wisdom is not truth
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4sfed
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| Posted: Wed Nov 12, 2008 7:26 pm Post subject: Re: When is the injector fired relative to TDC? |
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| TimZ wrote: |
| 4sfed wrote: |
| I'm designing a system for an old, slow-turning siamese port engine. This will require injecting the fuel only on an open intake valve . . . after the valve on the leading cylinder has closed. So when does the Electromotive system trigger the injector? |
If you use phased sequential, then you should still get the injectors for that port firing once per 360 degrees, so it should still work regardless of the timing. It should also still work if you use full sequential so long as you have two injectors firing 360 degrees apart in the siamesed port. I _think_ the only thing that would be a problem would be if you had one injector in the port that only fired once per 720 degrees - am I missing something? |
[img]
Look at the charts below . . . typical of a four-cyl with a firing order of 1-3-4-2. In the first instance, you're looking at an idle pulse width that's timed to inject while the #1 cylinder intake valve is open. The opposite pulse is 360° later on closed valves. It doesn't matter much whether these are two separate injectors fired into the same port, or the same injector fired twice. When intake #2 opens, most of the puddle will enter cylinder #2
The second chart shows the maximum pulse width that can be injected during an open valve.
The third chart shows what happens with a longer pulse width. Valve #1 closes before injection is complete and the remaining portion of that pulse plus the entire next pulse puddle . . . to be ingested by cylinder #2 . . . so cylinder #1 gets lean and #2 gets progressively richer.
In the fourth chart, injection timing is changed by 180°. Cylinder #2 gets one pulse while the valve is open, the next pulse happens after cylinder #1 valve closes, so the fuel is puddled and is ingested by cylinder #2 the next time it opens. The result is that cylinder #1 gets no fuel and cylinder #2 gets a double shot.
Jim
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TimZ
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Location: Dearborn, Michigan
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| Posted: Wed Nov 12, 2008 7:57 pm Post subject: Re: When is the injector fired relative to TDC? |
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I guess I was ASSuming that we were talking about cylinders 2 and 3 being siamesed, like on an old MG 4 cylinder. Your charts show the intake port pulses for cylinders 1 and 3, assuming a 1-3-4-2 firing order. Are we talking about siamese-ing (1, 2) and (3,4)?
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Information is not knowledge
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Wisdom is not truth
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Last edited by TimZ on Wed Nov 12, 2008 11:08 pm; edited 1 time in total |
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4sfed
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Joined: 12 Nov 2008
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| Posted: Wed Nov 12, 2008 8:05 pm Post subject: Re: When is the injector fired relative to TDC? |
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| TimZ wrote: |
| I guess I was ASSuming that were were talking about cylinders 2 and 3 being siamesed, like on an old MG 4 cylinder. Your charts show the intake port pulses for cylinders 1 and 3, assuming a 1-3-4-2 firing order. Are we talking about siamese-ing (1, 2) and (3,4)? |
Cylinders #1 and #2 share a port, and cylinders #3 and #4 share another port. The airflow curves are numbered for the cylinders. The injection pulses are just sequential . . . probably should have left them off.
Jim
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4sfed
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| Posted: Thu Nov 13, 2008 4:09 am Post subject: Re: When is the injector fired relative to TDC? |
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| TimZ wrote: |
| I guess I was ASSuming that we were talking about cylinders 2 and 3 being siamesed, like on an old MG 4 cylinder. Your charts show the intake port pulses for cylinders 1 and 3, assuming a 1-3-4-2 firing order. Are we talking about siamese-ing (1, 2) and (3,4)? |
Were you thinking of 3 exhaust ports? I have seen several British engines with that arrangement.
Jim
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TimZ
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Location: Dearborn, Michigan
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| Posted: Thu Nov 13, 2008 5:44 am Post subject: Re: When is the injector fired relative to TDC? |
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| 4sfed wrote: |
| TimZ wrote: |
| I guess I was ASSuming that we were talking about cylinders 2 and 3 being siamesed, like on an old MG 4 cylinder. Your charts show the intake port pulses for cylinders 1 and 3, assuming a 1-3-4-2 firing order. Are we talking about siamese-ing (1, 2) and (3,4)? |
Were you thinking of 3 exhaust ports? I have seen several British engines with that arrangement.
Jim |
Yes, now that you mention it that was my mental picture. It's been a long week...
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Wisdom is not truth
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4SFED4
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| Posted: Thu Nov 13, 2008 9:20 pm Post subject: |
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| Jon, surely you would have this information no?
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Jon@EMI
EMI
Joined: 26 Feb 2008
Posts: 144
Location: Manassas, VA
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| Posted: Fri Nov 14, 2008 3:13 pm Post subject: |
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The Injectors begin firing at TDC of each cylinder. I was a little confused by your chart. I get it now and I think you're forgetting some details that will solve the problem. In phased, you get an injection event every 180deg, not every 360. With sequential, you get an injector event every 180 degrees as well. The difference is that in phased, channels 1 and 2 are alternating while in sequential, channels 1,2,3 and 4 are all firing 180 degrees after the one before it.
So it's like this:
Phased
0 - ch1
180 - ch2
360 - ch1
540 - ch2
720 - ch1
...
Sequential
0 - ch1
180 - ch2
360 - ch3
540 - ch4
720 - ch1
...
Hope this helps.
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Jon
Project Engineer
Electromotive, Inc
jon at emi.cc
www.distributorless.com
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4sfed
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| Posted: Sat Nov 15, 2008 5:01 am Post subject: |
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| Jon@EMI wrote: |
The Injectors begin firing at TDC of each cylinder. I was a little confused by your chart. I get it now and I think you're forgetting some details that will solve the problem. In phased, you get an injection event every 180deg, not every 360. With sequential, you get an injector event every 180 degrees as well. The difference is that in phased, channels 1 and 2 are alternating while in sequential, channels 1,2,3 and 4 are all firing 180 degrees after the one before it.
So it's like this:
Sequential
0 - ch1
180 - ch2
360 - ch3
540 - ch4
720 - ch1
...
Hope this helps. |
Thanks Jon. I can see that sequential will allow a longer maximum pulse . . . but there's still a maximum. I've shown the ch2 pulse on the chart and ch1 below the chart. Red is the fuel that will enter cylinder #1 and blue is the fuel that will enter cylinder #2. Everything is fine until the pulse is longer than the duration of both intake valve events.
Jim
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TimZ
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Posts: 120
Location: Dearborn, Michigan
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| Posted: Sat Nov 15, 2008 4:08 pm Post subject: |
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This is the conclusion that I was coming to also. I think what you need to do is oversize your injectors by a factor of two and make sure that you don't exceed 50% duty cycle (or whatever number this works out to given your cam timing) anywhere on your VE table - make sure to leave some headroom for things like cold start enrichment, IAT enrichment, etc. Idle pulsewidth might be an issue, but if this engine is going to be naturally aspirated, then you should be able to get it to work.
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Knowledge is not wisdom
Wisdom is not truth
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ETM
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| Posted: Tue Nov 18, 2008 5:44 am Post subject: |
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Not sure you can do this. You may be able to balance your injection event over the two intake events and get equal fuel into both cylinders, but that would only work for a given injector pulse width. At any other injector pulse width it would lose balance. To go from 6ms to 8ms it would be necessary to start the event 1ms sooner and stop it 1ms later to maintain cylinder to cylinder balance. I am not aware of any way to achieve this.
I think you will either have to find a way to get one injector per cylinder or pull the injectors back to the point that it is effectively a TBI system.
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4sfed
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Joined: 12 Nov 2008
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| Posted: Tue Nov 18, 2008 6:56 am Post subject: |
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| ETM wrote: |
Not sure you can do this. You may be able to balance your injection event over the two intake events and get equal fuel into both cylinders, but that would only work for a given injector pulse width. At any other injector pulse width it would lose balance. To go from 6ms to 8ms it would be necessary to start the event 1ms sooner and stop it 1ms later to maintain cylinder to cylinder balance. I am not aware of any way to achieve this.
I think you will either have to find a way to get one injector per cylinder or pull the injectors back to the point that it is effectively a TBI system. |
Perhaps the diagram is not self-explanatory . . . the pulse shown below the diagram is a second injector located in the same port. On long pulse widths there will be a period when both injectors will be on. The portions of the injection pulse are color coded as to which cylinder will recieve that fuel. The overlap period will keep the distribution from being perfect, but it should be as workable as a carburetor.
Cylinder #1 will always gets it's fuel through an open valve. For long pulses it will recieve fuel from injector #2 after intake #2 closes and injector #1 until valve #1 closes. The remainder of injector #1 fuel will puddle and enter cylinder #2 when intake #2 opens . . . then injector #2 adds the rest of the fuel.
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TimZ
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Joined: 25 Feb 2008
Posts: 120
Location: Dearborn, Michigan
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| Posted: Tue Nov 18, 2008 12:51 pm Post subject: |
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| 4sfed wrote: |
Perhaps the diagram is not self-explanatory . . . the pulse shown below the diagram is a second injector located in the same port. On long pulse widths there will be a period when both injectors will be on. The portions of the injection pulse are color coded as to which cylinder will recieve that fuel. The overlap period will keep the distribution from being perfect, but it should be as workable as a carburetor.
Cylinder #1 will always gets it's fuel through an open valve. For long pulses it will recieve fuel from injector #2 after intake #2 closes and injector #1 until valve #1 closes. The remainder of injector #1 fuel will puddle and enter cylinder #2 when intake #2 opens . . . then injector #2 adds the rest of the fuel.
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This looks correct to me. As long as the chain of events for the two injector firings starts after the 1st valve opens and before the 2nd valve opens, then it should work. I think you're going to have to run in full sequential, and it will be imperative that you aren't 360 degrees off on the injector timing.
_________________
Information is not knowledge
Knowledge is not wisdom
Wisdom is not truth
-FZ, Joe's Garage
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