Quote:
Originally Posted by monroe74
"There probably is no closed loop for your car."
I think you've got it backwards; it's in closed-loop most of the time (maybe 100% of the time). In other words, since the sensor has a wide band, the ECU can rely on it to produce useful, high-resolution readings even under conditions that are very lean or very rich.
"I would try to record some data on A/F ratio vs throttle opening"
I don't know quite how to translate the voltage readings into AFR. The way I've got the DMM hooked up, it shows 0 volts for stoich. It goes to about -0.8v for very rich, and to about +0.8v for very lean (in other words, I'm essentially using a reference voltage, instead of measuring the L1H1 output directly; I think this makes the numbers more intelligible). I can maintain a lean AFR if I use gentle throttle. Moderate throttle moves AFR towards stoich. Heavy throttle makes it rich. This all happens in a smooth, linear way.
Similarly, when I monitor the injectors I notice that the duty cycle ranges from about 1% (idle) to about 50% (WOT, high RPM). But under low RPM (say, 30 mph in top gear), the duty cycle won't exceed, say, 15%, even with WOT. This surprised me. And the duty cycle responds in a smooth, linear way, as the throttle opening is varied.
So I'm thinking that maybe open-loop is just never happening. And I'm pondering the relative merits of different throttle settings, and thinking that WOT is a very good thing, if used properly in a P&G context.
"find the throttle position that you achieve 14.7:1, you do not want to be richer than that"
I think I've found that large throttle settings are giving me high FE, even though they entail a rich mixture. It seems that pumping losses are expensive.
Anyway, what's magical about stoich (15:1)? If that ratio is good, isn't 17:1 or 20:1 even better? And my car can maintain those ratios, at cruising speed (e.g., 50 mph). But I think I'm learning that the pumping losses overwhelm the benefit of the lean burn. It seems that lean burn is terrific, assuming you're someone who doesn't want to fuss with P&G.
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#1, you caught me editing my post.
#2, I did some searching and learned a bit about wide band sensors myself, here are 2 good links:
http://www.airfuelmeter.com/german/lsu4_ge_sensor.htm
http://www.gmtcny.com/WBO2S.htm
Pull the map off the second link.
I thought you were trying to optimize a P&G scheme to reduce pumping losses? Regardless if you look at a BSFC map of nearly every gasoline engine FE is never at a maximum at WOT, the 80% that Johnny told you would be a good place to try. You do want to be lean of stoich, but if you engine behaves anything like a non-lean burn car there will be a point that it will move into the rich region, that should be after the 80% throttle mark. At stoich there is enough O2 to burn all the fuel if it mixes 100% perfectly (which it doesn’t), once you move into the rich region it is physically impossible to burn all the fuel without even considering mixing and burn characteristics.