SuperFlow article....... Can you a

[MaxRaceSoftware]

SuperFlow article.......
Can you avoid air and fuel flow measurement by using a Lambda sensor?
Lambda sensors are devices that measure the oxygen content of the exhaust gas to determine the Lambda ratio of carbon to oxygen. The first thing you should know about the Lambda sensor is that it must be calibrated by measuring the air flow and fuel flow into the engine. That is the recommendation of the manufacturers. The reason for this is that the Lambda sensor output is nonlinear and affected by the temperature of the sensor. The most expensive sensors have a built-in heating device to ensure that their temperature doesn’t change so much.
The Bosch Lambda sensor instructions recommend that each one be carefully calibrated, on each engine, by measuring the air flow and fuel flow into the system as well as exhaust gas temperature. Then all these factors are combined to give the Lambda. How are you going to accomplish this if you can’t measure air flow?
It is also important to realize that Lambda is not the same as air-fuel ratio. Lambda is the word used to describe the ratio where the air and fuel will burn completely, exhausting the oxygen and the hydrocarbons available in the process. The air-fuel ratio at which this occurs, ranges from about 13.5:1 to 15.0:1, depending on the carbon content of the fuel.
The fuel must be tested in a laboratory to determine the exact carbon content. Then the Lambda can be calculated, and then finally the air-fuel ratio. By measuring the air flow and fuel flow, the air-fuel ratio is determined directly without a need for laboratory tests of the gasoline. As you can see, it is possible to change the Lambda by changing the fuel. It is not possible to change the air-fuel ratio by changing the fuel. If you attended the 1996 SuperFlow AETC conference, you heard the talk by Dr. Dean Hill describing this phenomenon.
Larry Meaux (meauxrace2@aol.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

 

[ivymike]

This article is referring to the fact that the stoich AF ratio varies with fuel composition, which I understand. In regard to the last statement, "it is not possible to change the air-fuel ratio by changing the fuel," I want to restate this in other terms, just to make sure that we have the same understanding of what the author is saying:

Changing to a different fuel while maintaining a fixed AF ratio will result in a change in Lambda, because the stoichiometric AF ratio of the new fuel will be different.

To belabor the point:
If you have fuel A, where the stoich AF ratio for fuel A is "AFS_A," and you have a fuel B, where the stoich AF ratio for fuel B is "AFS_B," and you have an engine setup where the fuel control system is delivering an AF ratio of "AF_D" then:

Lambda when running fuel A is AF_D/AFS_A
Lambda when running fuel B is AF_D/AFS_B

(I always get lambda and equivalence ratio confused as far as which is delivered/stoich and which is stoich/delivered, so correct me if I got the fractions upside down)