Ion sensing and peak pressure position estimation
Posted: Mon Apr 07, 2008 3:41 am
Hi all
I've had a bit of a dialogue with Wiglaf on the topic over PM, and now we decided to make a public thread out of it. This is for anyones benefit as well as an opportunity for anyone to contribute to the discussion.
Initially, i've asked Wiglaf if he would be willing to help with design/prototyping of the high voltage part of the system since he mentioned he has lots knowledge in that area.
here is a part of Wiglaf's last PM:
To answer the first paragraph, IMO that the amount of processing power needed to do the number crunching for the pressure peak estimation will necessitate another MCU or even a specialized DSP (perhaps FPGA based). So, i'd say that the digital circuitry will need to be separate from the rest of EMS, but have a communication channel to the EMS to constantly update it with the estimated pressure peak information for later decisions by EMS (for example on how to adjust timing advance on the next ignition events). So i would say it is a good idea for it to be modular in this sense (i.e not monolithic with the rest of the EMS)
There are some caveats with that though: the ion sensing module (ISM, just to call it something) will need to know about the angular position/speed of the crank (to be able to reference the ion current data against the crank angle) and the time window when to sample the ion current. So ISM will probably need to get this info from the EMS over some fast interconnect.
In addition, i realize that Wiglaf is building an engine with non-standard valvetrain (to put it lightly ), and his EMS needs may be different from rest of us, but i believe that he can still leverage a lot of stuff from the freeEMS while making an EMS for his project Really, from what my info is about Wiglaf's project, everything is gonna be the same except for the lack of throttle body (i.e TPS) and consequent lack of reference-able vacuum (i am guessing he's gonna use a MAF to estimate load and airflow) and extra control outputs for controlling the valvetrain actuators.
In regards to accuracy of the high-voltage part, i vaguely remember the current being in milliamp range, but please review the references (next post) to verify.
I will pull up my references about IS and post them up here for everyones benefit. Please add more if you have good ones.
There were a few discussions about this on msefi forums, but they've disappeared last time i've checked. (Lance's pruning?)
Cheers
I've had a bit of a dialogue with Wiglaf on the topic over PM, and now we decided to make a public thread out of it. This is for anyones benefit as well as an opportunity for anyone to contribute to the discussion.
Initially, i've asked Wiglaf if he would be willing to help with design/prototyping of the high voltage part of the system since he mentioned he has lots knowledge in that area.
here is a part of Wiglaf's last PM:
Wiglaf wrote: Is the end goal for this to be integrated into the computer, or would it be standalone that just sends out an AFR and spark advance signal? Just curious, as you know my project will demand a different computer than what most of the guys here are working on so if it was somewhat modular then that would help out.
How difficult the circuitry is kind of depends on how accurate it needs to be. Do you know what the actual current range we are looking at is? Also, 400V seems like almost enough to cause it to arc if it's in there with compressed air and gas. Does it only run the measurement during the power and exhaust stroke? Less than .04" spacing across surface will arc at 400V, air is better but obviously not when it's loaded with gas and high temps. This is a bit of a gray area for me.
To answer the first paragraph, IMO that the amount of processing power needed to do the number crunching for the pressure peak estimation will necessitate another MCU or even a specialized DSP (perhaps FPGA based). So, i'd say that the digital circuitry will need to be separate from the rest of EMS, but have a communication channel to the EMS to constantly update it with the estimated pressure peak information for later decisions by EMS (for example on how to adjust timing advance on the next ignition events). So i would say it is a good idea for it to be modular in this sense (i.e not monolithic with the rest of the EMS)
There are some caveats with that though: the ion sensing module (ISM, just to call it something) will need to know about the angular position/speed of the crank (to be able to reference the ion current data against the crank angle) and the time window when to sample the ion current. So ISM will probably need to get this info from the EMS over some fast interconnect.
In addition, i realize that Wiglaf is building an engine with non-standard valvetrain (to put it lightly ), and his EMS needs may be different from rest of us, but i believe that he can still leverage a lot of stuff from the freeEMS while making an EMS for his project Really, from what my info is about Wiglaf's project, everything is gonna be the same except for the lack of throttle body (i.e TPS) and consequent lack of reference-able vacuum (i am guessing he's gonna use a MAF to estimate load and airflow) and extra control outputs for controlling the valvetrain actuators.
In regards to accuracy of the high-voltage part, i vaguely remember the current being in milliamp range, but please review the references (next post) to verify.
I will pull up my references about IS and post them up here for everyones benefit. Please add more if you have good ones.
There were a few discussions about this on msefi forums, but they've disappeared last time i've checked. (Lance's pruning?)
Cheers