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Hi All,
Just had a quick question regarding cold start target AFR.
Lets say an engine at full operating temperature and at idle where our lambda target is 1.00. Now lets say the engine is stone cold and at the same idle RPM and load. As the engine is cold we are enriching the startup in order to overcome the fuel not vapouring as it hits the inlet port walls, so we will be physically injecting more fuel for this.
So my question is, on cold start whilst we are injecting more fuel, are we still targeting the same lambda of 1.00? Or are we targeting a richer lambda for any reason?
You will find after you start the engine and it goes through the post start enrichment phase, it will be richer, maybe down in area of .75-.82 then slowly tapper leaner. Once in the warm up enrichment table you can determine the mixture you want to run during the warm up process.
There is no set value here and this will be set based on engine response and feel. Some engines you can run at lambda 1 and the car will idle stable and drive/accelerate smoothly. Then other cars you might need to run down at .85 (example) and taper up to your idle target lambda as it comes up to operating temp in order to get a smooth idle and acceleration etc.
This comes down to engine design, injectors/size/placement/angle, fuel used etc.
Thank you for the reply and information Chris!
