Opperational characteristics of a vehicle Lambda sensor.

The following describes how the vehicle Lambda sensor responds to oxygenated fules:

First, the value of lambda between a rich mixture and a lean mixture will change only between 0.975 for a rich mixture and 1.025 for a lean mixture. This may vary plus or minus a few hundredths. That value is determined by the lambda sensor housed just ahead of the catalyutic converter in the system exhaust. Part of the lambda sensor is housed within the exhaust system and the other part is exposed to ambient air.

As the sensor heats up to a temperature of approximately 300 degree C, it begins to conduct oxygen ions. There is a certain amount of residual oxygen expelled after combustion. If there is a difference between the electrodes of the sensor (i.e., the one exposed to the exhaust and the one exposed to ambiant air) a voltage jump will occur indicating whether the mixture is richer or leaner than lambda=1. That set point is called the stoichiometric mixture. This window of change is very small, occurring between 1 and 0.001.

That information is used by the vehicle computer to determine whether more or less air is required for combustion. Normal air-fuel mixture is determined by the throttle setting, so the lambda ratio will either add to or take away from the throttle setting.

The reason for adding oxygenates is to reduce carbon monoxide (CO) and hydrocarbons (HC). With oxygenated fuel the engine excess air factor is lambda = .9, so this will remain farily constant because the oxygenates will keep the large excess air factor or change from occurring. Since the engine operation is already in the rich range (lambda < 1) you will get lousy acceleration and poor fuel consumption. On the other side using this method of controlling fuel mixture allows catalytic afterburning to elminate most of the CO and NH3 emissions.