Two-stroke aux injectors

[Håvard Karlsen]

I have a 3 cyl two-stroke engine. It have turbo and two injectors for each trottle (3 trottles) I want to drive primary injectors with tps/rpm table and secondary injectors with a map/ rpm table. Is this possible? Is there a better way to control the injectors? The engine have a very weak manifold vacuum.

[cj]

Yes you can do that. main and aux fuel tables are independent and can have different axes.

On the question of *should* you...  If you didnt have secondary injectors, a common way to deal with turbo + ITB's which have the same mad MAP signal is to run 4d fuelling where the main table is TPS /rpm and the 4d fuel correction table is MAP/rpm. As long as you only use the secondary table above 100kpa then I think it would work fine - just start lowering the values in the 4d map/rpm table at the same cells as you start bringing in secondary injectors. If you tried to phase in secondary injectors off boost however I can see it causing issues at the phase-in transition point would move around and you would get inconsistent behaviour

[Håvard Karlsen]

Can you help me setting this up? Do you know any links for «how to»? I have been taking courses for Link ecu, but the staging with tp/rpm base map i can not find. Every example have map insted of tp in the x axys....

[cj]

Open up the table you want to change, press X to open the axis config screen, then click on the value currently used for X or Y axis. Pick a new value, then you have to pick sensible axis points (eg not point using negative values  or >100 for TPS%, but MAP bay go to 2 or 300 kpa depending on expected boost)

 

[Greg W]

We use the link on turbo bikes, dual injectors , big cams , low compression , ITB, 

Using MAP/BAP X over base setting with TPS/rpm fuel table , staged secondary injectors and MAP based secondary staging table 
would this do what your wanting ?

[Adamw]

On 1/23/2020 at 12:35 PM, Håvard Karlsen said:

I have a 3 cyl two-stroke engine. It have turbo and two injectors for each trottle (3 trottles) I want to drive primary injectors with tps/rpm table and secondary injectors with a map/ rpm table. Is this possible? Is there a better way to control the injectors? The engine have a very weak manifold vacuum.

I would probably lean more towards CJ's first suggestion which is to have main fuel control based on alphaN, but with a 4D MAP/RPM overlay added for any adjustment needed due to varying boost levels or the effect the turbo has on the scavenging (on a 4 stroke you often dont even need this 4D table as MAP is taken care of in the background).  This way will make your life easier than your original requested strategy.  With your requested method, anytime you want to change the injector staging or the split between primary/secondary, you would have to almost totally re-tune both fuel tables to get the mixture right again.  With the 4D method you can experiment with injector staging/split after tuning the fuel tables without consequence.

[Håvard Karlsen]

On 1/24/2020 at 9:34 PM, Adamw said:

I would probably lean more towards CJ's first suggestion which is to have main fuel control based on alphaN, but with a 4D MAP/RPM overlay added for any adjustment needed due to varying boost levels or the effect the turbo has on the scavenging (on a 4 stroke you often dont even need this 4D table as MAP is taken care of in the background).  This way will make your life easier than your original requested strategy.  With your requested method, anytime you want to change the injector staging or the split between primary/secondary, you would have to almost totally re-tune both fuel tables to get the mixture right again.  With the 4D method you can experiment with injector staging/split after tuning the fuel tables without consequence.

Do you have a sample file. How it is done? Settings etc?

[Håvard Karlsen]

On 1/24/2020 at 8:59 PM, Greg W said:

We use the link on turbo bikes, dual injectors , big cams , low compression , ITB, 

Using MAP/BAP X over base setting with TPS/rpm fuel table , staged secondary injectors and MAP based secondary staging table 
would this do what your wanting ?

Can you explain this better for me?  I will not use closed loop afr or any afr input at all. Just for gauge and logging. Twostrokes is hard du auto-tune.

[Adamw]

Ok, below is a basic made-up example.

To explain, fuel table 1 is the main VE table, this basically tells the ecu how much air the engine is inhalling (assuming it was naturally aspirated).  If you set the fuel load equation source to "MAP", then this table is multiplied by MAP in the background, so even though it only has TP on the VE table axis, if you double the manifold pressure the ECU already knows there is double the air going in and therefore adds double the fuel.  The calculated fuel pulse width is also further multiplied by the Lambda target table in the background, so this compensates for the fact that you normally want a richer mixture at say 200Kpa and 100%TP, than you would want at 100Kpa and 100%TP.

Since the turbo creates back pressure on the exhaust side and may effect volumetric efficiency, you may find that as you increase boost more and more the fuel mixture will start to drift off target, to fix this you have the 4D fuel table.  The 4D fuel table is an "adder".  So if you have "10" in a cell it adds a further 10% fuel in that region, if you have a "-10" it removes 10% fuel in that region.  You would set up this table with MAP Vs RPM, usually most of this table will be zero and you will only have to tune a few cells in the high RPM/High boost corner to get the fuel mixture right at all boost levels you intend to run.

To tune these two tables, you start with the 4D table all set to zero, run engine on lowest boost possible (wastegate spring only) and tune the main VE table all over.  Then increase boost say 50kpa and run engine, through whole RPM range, adjust the relevant row of the 4D fuel table if it needs some fuel added or removed at the top end.  Repeat at higher boost levels until you are at the maximum you intend to run.

 

 

After the ecu has calculated the correct fuel volume that needs to be added, then you can choose how you want to split that between primary and secondary injectors.  Again this is very flexible, these can be the same size or different sized injectors, you can have both injectors spraying half the fuel each or you can have all fuel going through the secondary inj at high RPM or whatever you like. In the example below I have primary and secondary injectors both the same size.  I have all fuel going through the primary below 100Kpa MAP, then above  100Kpa I fade in the secondaries and by 180Kpa I have half the fuel going through the primary and half through the secondary.

[dx4picco]

thank you for this interesting writing Adam.

In this case of use of the tps fuel table and boost comp how would you set up your ignition table?

also tps vs rpm and boost comp?

how do you take the idle control valve in account in this kind of fueling strategy?

[Adamw]

1 minute ago, dx4picco said:

In this case of use of the tps fuel table and boost comp how would you set up your ignition table?

Typically just RPM/MAP is fine for the ign table on boosted ITB engines with weak vacuum, I havent done a boosted two stroke personally.  You can add 4D ign if you really wanted but I have never needed to.

 

3 minutes ago, dx4picco said:

how do you take the idle control valve in account in this kind of fueling strategy?

The background MAP multiplication usually takes care of the idle valve well enough.  

[Håvard Karlsen]

9 hours ago, Adamw said:

Ok, below is a basic made-up example.

To explain, fuel table 1 is the main VE table, this basically tells the ecu how much air the engine is inhalling (assuming it was naturally aspirated).  If you set the fuel load equation source to "MAP", then this table is multiplied by MAP in the background, so even though it only has TP on the VE table axis, if you double the manifold pressure the ECU already knows there is double the air going in and therefore adds double the fuel.  The calculated fuel pulse width is also further multiplied by the Lambda target table in the background, so this compensates for the fact that you normally want a richer mixture at say 200Kpa and 100%TP, than you would want at 100Kpa and 100%TP.

Since the turbo creates back pressure on the exhaust side and may effect volumetric efficiency, you may find that as you increase boost more and more the fuel mixture will start to drift off target, to fix this you have the 4D fuel table.  The 4D fuel table is an "adder".  So if you have "10" in a cell it adds a further 10% fuel in that region, if you have a "-10" it removes 10% fuel in that region.  You would set up this table with MAP Vs RPM, usually most of this table will be zero and you will only have to tune a few cells in the high RPM/High boost corner to get the fuel mixture right at all boost levels you intend to run.

To tune these two tables, you start with the 4D table all set to zero, run engine on lowest boost possible (wastegate spring only) and tune the main VE table all over.  Then increase boost say 50kpa and run engine, through whole RPM range, adjust the relevant row of the 4D fuel table if it needs some fuel added or removed at the top end.  Repeat at higher boost levels until you are at the maximum you intend to run.

 

 

After the ecu has calculated the correct fuel volume that needs to be added, then you can choose how you want to split that between primary and secondary injectors.  Again this is very flexible, these can be the same size or different sized injectors, you can have both injectors spraying half the fuel each or you can have all fuel going through the secondary inj at high RPM or whatever you like. In the example below I have primary and secondary injectors both the same size.  I have all fuel going through the primary below 100Kpa MAP, then above  100Kpa I fade in the secondaries and by 180Kpa I have half the fuel going through the primary and half through the secondary.

Thanks. I will take my time and try to learn this. This forum is very good!!  

 

[Håvard Karlsen]

13 hours ago, Adamw said:

Ok, below is a basic made-up example.

To explain, fuel table 1 is the main VE table, this basically tells the ecu how much air the engine is inhalling (assuming it was naturally aspirated).  If you set the fuel load equation source to "MAP", then this table is multiplied by MAP in the background, so even though it only has TP on the VE table axis, if you double the manifold pressure the ECU already knows there is double the air going in and therefore adds double the fuel.  The calculated fuel pulse width is also further multiplied by the Lambda target table in the background, so this compensates for the fact that you normally want a richer mixture at say 200Kpa and 100%TP, than you would want at 100Kpa and 100%TP.

Since the turbo creates back pressure on the exhaust side and may effect volumetric efficiency, you may find that as you increase boost more and more the fuel mixture will start to drift off target, to fix this you have the 4D fuel table.  The 4D fuel table is an "adder".  So if you have "10" in a cell it adds a further 10% fuel in that region, if you have a "-10" it removes 10% fuel in that region.  You would set up this table with MAP Vs RPM, usually most of this table will be zero and you will only have to tune a few cells in the high RPM/High boost corner to get the fuel mixture right at all boost levels you intend to run.

To tune these two tables, you start with the 4D table all set to zero, run engine on lowest boost possible (wastegate spring only) and tune the main VE table all over.  Then increase boost say 50kpa and run engine, through whole RPM range, adjust the relevant row of the 4D fuel table if it needs some fuel added or removed at the top end.  Repeat at higher boost levels until you are at the maximum you intend to run.

 

 

After the ecu has calculated the correct fuel volume that needs to be added, then you can choose how you want to split that between primary and secondary injectors.  Again this is very flexible, these can be the same size or different sized injectors, you can have both injectors spraying half the fuel each or you can have all fuel going through the secondary inj at high RPM or whatever you like. In the example below I have primary and secondary injectors both the same size.  I have all fuel going through the primary below 100Kpa MAP, then above  100Kpa I fade in the secondaries and by 180Kpa I have half the fuel going through the primary and half through the secondary.

Do i need the lambda target table. I would like to have no afr sensor controling the map. Can it be done without it?

[Adamw]

10 hours ago, Håvard Karlsen said:

Do i need the lambda target table. I would like to have no afr sensor controling the map. Can it be done without it?

You can turn it off but I suggest you leave the target table on, it doesnot need a AFR sensor, the table multiplication will still work without a sensor connected.  

[Håvard Karlsen]

32 minutes ago, Adamw said:

You can turn it off but I suggest you leave the target table on, it doesnot need a AFR sensor, the table multiplication will still work without a sensor connected.  

I see  Thanks  

[BrentG]

 I know this is an old thread but .

Would there be a problem running against an EGT table instead of AFR it seems a bit more relevant for two strokes

I cant see a problem but might be missing something 

 

 

[Adamw]

3 hours ago, BrentG said:

Would there be a problem running against an EGT table instead of AFR it seems a bit more relevant for two strokes

This thread is about Aux injection?  Are you saying you want to enable a 2nd set of injectors based on EGT?  As a general comment I would say EGT isn't a good indication of mixture and conversely, mixture isn't a good control of EGT either.  EGT peaks at stoich, and from there it lowers regardless of whether you add fuel or remove fuel.  This means if you are sufficiently lean and add fuel then EGT can actually increase.  So it's usefulness really depends if incorrect mixture is higher risk than excessive EGT or CHT.  I know EGT is important for proper expansion chamber effect with a 2 stroke, but it isn't really a good metric for fuel feedback if that is what you are suggesting.   

[BrentG]

Thanks Adam

Yes correct I was thinking a second set of injectors based on EGT.

In a race Kart we run to a EGT limit say 650 celsius and this is what is used for tuning as no AFR measurement can be taken.

What you say is correct but if the fuel was running against an EGT as a maximum limit wouldn't that work ?

For example if the table had 650 c as a maximum , wouldn't the fueling just change to stay at the 650c under full throttle

In the application think ( drag race) it would be run wide open .Or am I still missing something 

Cheers 

 

[Adamw]

13 hours ago, BrentG said:

What you say is correct but if the fuel was running against an EGT as a maximum limit wouldn't that work ?

It would work somewhat, but there are ambiguous scenarios where it wouldnt work as expected.  As an example, say your normal lambda at WOT is 0.9, and your EGT normally sits somewhere near your upper limit,  but lets say on one run your fuel pressure drops and your lambda ends up lean at 1.2 - too lean to make any power so unlikely to cause any damage - but the EGT just crept a touch higher than it normally is at 0.9lambda.  So because your EGT is high, the ecu adds extra fuel, this will increase EGT further and if the fuel supply problem still exists you are possibly now also dangerously lean at the same time too. 

I never like "failsafes" where the corrective action has the potential to make matters worse.  It would be better just to flash a light at the driver or trip a lower RPM limit etc.  

[BrentG]

thanks taken onboard

 

[Håvard Karlsen]

Hello, now i have dynoed it and done some testing. Can you @Adamw take a look at the fuel settings and the other things here, to see if i have done someting wrong? It works good, but im not sure everything is correct setup.  1000ccm twostroke triple with Comp CT4 turbo. 

Siste kjørte på myra alle egt ok..pclr

[Adamw]

Yes, it all looks reasonable to me.  I would suggest you do a test to validate the staged injection sec/pri flow ratio if you havent done so already.  This is important for correct staged injection behaviour.  

A test to validate this ratio would be something like this:

Set the staging table to 0% - this means it is running on only primary injectors.  Hold the engine stable at a fixed RPM and moderate load - you need some load so that inj PW isn't too short, so best to do this on a dyno, but if no access then you have to use a hill or similar.  Take a note of the lambda (or log the test), then change the staging table to 100% (so you are now running only on secondary injectors), take note of lambda again.  If the sec/pri ratio is correct then the lambda should be the same for 0% and 100%, if you see a significant change in lambda when switching from pri to sec then you need to adjust the ratio setting and test again.  

[Håvard Karlsen]

Here is the logfile from my 500 hp dynorun. Can you see if it looks ok from this?  I can not do the test you suggested before i dyno it next time. @Adamw can you take a look at this log? And can you look at the fuel map-4d map, lambda table too?

 

Log 500hp 26psi 2021-09-5 3;38;37 pm.llg