This is why I haven't posted/updated my build for a while:

Many moons ago I played with ion sensing, and could never get a good signal from it. Now that I'm older and slightly wiser I think I have the electronics skills and coding skills to make it work.

The short of it is you can use a spark plug to measure in cylinder pressure and detect detonation. Done correctly it should be able to drive real closed loop ignition control. I've been putting off other aspects of my build to get this right, and I think I'm nearly there.

So far I have a piggyback ignition controller that runs to 10k rpm without issue, and can either advance or retard timing on the fly. I also have code that can read an ion sensing signal every 1 deg up to 10krpm. And now i have an ignition coil that I can read an ion sensing signal off of.

I haven't tested it on the car yet, and that is the obvious next step, but everything looks good so far.

 

That's amazing work man! Love the ingenuity!

 

Thanks, I really hope to get this working on the car! Just knowing that I can produce a signal on the bench gives me a lot of hope.

 

You inspire me!

 

Pretty cool idea. How are you going to calibrate your voltage vs pressure measurements? Do you have an independent pressure reference? I suppose you can run for a little while on a single spark plug and use the other plug hole for the pressure transducer.

Or you can build a pressure testing rig using compressed nitrogen and some Schedule 80 NPT pipe fittings. Mechanically it would not be very complicated, and would not even require any machining if you can find an spark-plug to NPT thread adapter.

 

Is this something that has to be calibrated as plugs age or when they are replaced? How about if different plugs are used (i.e. you went with a hotter or cooler plug or switched from one electrode material to another)?

 

So if refence is 100mV and a hot propane flame is 150mV, do you have an idea of the signal to noise ratio at the pressure /temp you expect at TDC?

 

I have no intention of calibrating it in place, because I don't need actual pressure. What I need is relative pressure. My current plan is measuring relative pressure from 40deg to 60deg in 1 deg increments. The signal to noise ratio should be rather low, so I'm averaging over several cycles to get a peak pressure point. I plan on getting peak to peak difference to detect detonation on a single cycle then averaging out over multiple cycles.

I have the data capture working on a teensy up to 10krpm. So I'm hopeful. And I've seen documentation on other older experiments using closed loop ignition control.

The voltages I'm measuring now will not be representative of what I will see on the car. I'm gonna have to tweak the resistors I'm using to measure current until I get the output I want.

Here are some links:
DIY Ion Sensing
SwRI IRD 2003--Using Ion Sensing with O2 Sensor Based Adaptive Calibration to Perform Cold Start Closed Loop A/F Ratio Control to Reduce Engine Cold Start HC Emissions, 03-9305
Much Ado About Knock and Tuning ......

 

Oh and yes spark plug type and health will effect the readings. So I'm going to have to put some fudge factor in the software to make it usable.