Quote:
Originally Posted by puddleglum
I'm learning quite a bit from your posts, but I checked my car tonight. Air and coolant temp. at 32F at startup. Engine was in CL in about a minute and stayed there. Coolant had only come up to 59F. I backed out of the driveway and drove maybe 100 feet. That is long before the engine is warm enough for fuel economy to start coming down and no way was the Cat. hot or condinsation out of the exhaust. What you have said in your post all makes sense, but I still don't see what the advantage is in using the CL guage.
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I must not being clear. Take a step back, and look at my last post. The behavior is exactly what I predicted. The problem is that engine coolant temp is not a very good indicator of head temp in the engine, which is important for combustion.
Let's walk through it a step at a time. Closed loop has a very specific meaning, by legislation. Simply put, the ECU is attempting to hold the fuel mix at lambda 1.0, which is approximately an AFR of 14.7:1 with gasoline. This is generally the ONLY point which it can track because the O2 sensors are what is called 'narrow' band. They detect stoich because they reverse in chemistry on a very steep curve.
Stoich is used because it produces peak EGT, which is not best for power or economy, but is best for emissions. The peak gas temp is needed for the CAT to operate, and it is also a good spot for CO, NOx, and HC to all be relatively low.
If you are burning at stoich, then the ecu is not running cold engine enrichment. Literally, you cannot be running rich and running peak at the same time.
Next, let's look at the question of condensation. If you are closed loop, by law, you must be relying on the O2 measurements. You can't use the O2 sensors until they are at the proper temp. In a heated sensor, this is on the order of 750 degreesC, well above normal EGT. If you heat a sensor in free air, stick it in an exhaust clamp, put it in the tail pipe, and start the car, it will frequently die almost instantly from shock cooling. If the sensor is heated, the pre-cat portion of the exhaust is expected to be clear of *atomized water vaper* and unburnt fuel. That doesn't take ages, and occurs closer to the manifold, where main sensors generally are, long before cat and post cat thermal condensation stops. That is addressed by placing the sensor bungs at the 9 o'clock to 3 o'clock position in the piping.
Now, cat temp. Cat temp will always rise AFTER closed loop. Think about it, cat temp occurs as part of the catalytic reaction. The ECU swings back and forth across stoich, chasing it. Those swings both allow the reaction, and then 'burn offs'. The CAT temp will not rise appreciably until you have been running at stoich awhile. So, cat temp has the same downside as ECT in terms of measuring when flame front temp, etc. is in normal range. It only reaches the target levels AFTER, sometimes appreciably after, 'normal' combustion has been achieved.
I believe that this leaves the question of 'warm enough for fuel economy'. Frankly, you'll have to be more specific. Again, the primary problems with winter driving and economy are: fuel blends and higher density air charge at the intake. The later mean richer mix for stoich at low loads and generally lower VE, since you have to throttle back more for equivelent performance as on warmer days.
-jjf
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