In the EU, our gas is supposed to be mixed with 5% alcohol. The stoich ratio is actually more like 14.4 to 1 than 14.7 to 1.David Redszus wrote:A oxygen sensor cannot measure air/fuel ratio.
It can only send a voltage based on the partial pressures of oxygen.
The target a/f ratio of 14.7 is a myth.
It is a convenient generalized target value for discussion purposes. The actual value,
even if the fuel and air mass are unchanged will depend on the composition of
the fuel. Which is why lambda is used for mapping and not a/f ratio.
For emissions and performance testing, a specific certification fuel is used. It does not resemble
the characteristics of most pump gas.
Most catalysts have an operational window of +- 1% from stoich, that is 0.99 to 1.01. Modern
ECU mapping is designed to maintain this value except for starting or warm-up conditions.
This value is often confounded by the presence of lubrication oils in the exhaust stream.
Closed loop mixture control is not often used (except at idle) due to variations produced by
mis-fires and cycle to cycle inconsistencies. It is used to set error codes and alarms.
In a street engine, the objective is to burn all the fuel.
In a race engine, the objective is to burn all the air.
That being said, I had a case involving claims from car owners against a company producing diesel fuel. One of the items being mixed in dieselfuel these days is plantoil of several sources. There are other items as well.
Now until that time the legal requirement was that the company had to mix 10% of biodiesel into the fuel over the entire year of production. What happened ? They bought biodiesel fuel when it was cheaper than regular oil and mixed it in proportions far exceeding the required % of biodiesel. On other times during the year the used almost exclusively dino oil. Then on other times the additives of the fuel were a lot cheaper and they started mixed them in larger quantities...until it went wrong of course. As long as the total % over 1 year was equal to the legal requirements there was not a problem (so to speak)
Recently rules changed : now the biodiesel has to be blended in always in quantities of 10%. However no such rules exist for the additives.
And gasoline is no better.