Failure oxygen sensor

One system for measuring catalyst failure is based on two oxygen sensors, one located in the normal control location, the other downstream of the catalyst (102,103). The second O2 sensor indicates relative catalyst performance by measuring the abiUty to respond to a change in air/fuel mixture. Other techniques using temperatures sensors have also been described (104—107). Whereas the dual O2 sensor method is likely to be used initially, a criticism of the two O2 sensors system has been reported (44) showing that properly functioning catalysts would be detected as a failure by the method. 

J. W. Koupal, M. A. Sabourin, and W. V. Qemmens, Detection of Catalyst Failure On-Vehicle Using the Dual Oxygen Sensor Method, SAE 91061, Society of Automotive Engineers, Warrendale, Pa., 1991. 

It was found that before retort the OTR of the pure EVOH multilayer film was 0.40 cc/ (m -day) but the OTR of EVOH/MLS multilayer film was 1.10 cc/ (m -day). The WVTR of the EVOH/MLS was 57% lower than the pure EVOH film. Table 4 shows the OTR and WVTR data for the multilayer films. It was unexpected that the pure EVOH samples would have a lower OTR than the EVOH/MLS samples because the nanocomposites are supposed to create a toturous path which the molecules have to follow in order to permeate the material. After the retort the pure EVOH and EVOH/MLS multilayer films were tested with the Ox-Tran five times for consistency and accuracy, but failed the test all five times. A sample failure is when the OTR exceeds the upper limit of the sensor range which is 2000 cc/ (m -day), although there is some flexibility for the actual failure value. [14] EVOH is primarily used as an oxygen barrier since the OTR failed after retort it was not necessary to test the WVTR after retort. The OTR and WVTR of the multilayer films were not found to meet the military specifications. Although the transmission rates did not meet the military food packaging specifications further experimentation with different materials or a PP nanocomposite outer layer could lead to a structure which meets the required specifications. 

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