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This paper presents experimental data showing unexpected transient behaviour in several production universal exhaust gas oxygen (UEGO) sensors. The spike-like transients occur when passing through the stoichiometric point, and are particularly significant when passing from rich to lean. The paper illustrates how the spikes are affected by exhaust gas flow rate, deviation of air-to-fuel ratio (AFR) from stoichiometry, and rate of change of AFR while passing through stoichiometry. The spikes are most sensitive to the rate at which AFR passes through stoichiometry. Brief discussions on possible causes for the spikes, and on undesirable consequences for feedback control applications, are included.

Two new techniques are introduced for measuring the residual gas fraction in internal combustion engines. Both techniques use a fast chemiluminescent detection (CLD) type NO sensor. The measurement is made in real-time and requires a single misfire of the engine. Development of the techniques revealed several unexpected, but interesting effects; the results obtained show good agreement with existing knowledge.