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An engine bench test has been developed to measure the total amount of liquid fuel wetting the intake walls of a S.I. port fuel injected engine under steady-state conditions. A four cylinder engine equipped with a double injection system was been utilized. One injection system was fed with 2-methyl-2-butene, which did not produce liquid fuel deposit on the intake manifold, the other injection system was fed with different types of fuel and both systems were set at the stoichiometric air-fuel ratio. Putting the injection commutation on, the 2-methyl-2-butene is suddenly replaced by the fuel of the second injection system. An oxygen sensor (UEGO type) monitors the air-fuel ratio excursion due to the injection commutation and the test runs until the A/F re-establishment at the stoichiometric level.

The development of the On-Board Diagnostic Systems (OBD) requires the determination of the critical level of the poisoning of the exhaust aftertreatment components. In order to have an accurate analysis, one way is to separate the effect of the poisoning of the two components: oxygen sensor and three way catalyst [ 1 ]. Our experimentation has been concentrated on poisoning of lambda sensor. An apparatus fed with model gases was realized to evaluate the poisoning of oxygen sensors coming from a fleet test of 6 taxis after a mileage of 100000 km. Our apparatus has been able to differentiate the poisoning level of the sensors by measuring their “switchability”. To confirm these measurements the lambda sensor switchability has been verified with a bench test using the Mercedes- Benz M111E engine. Exposing the aged lambda sensor to the engine exhaust gas, its response was coherent with its behavior on the apparatus fed with model gases.