Resistive Multi-Gas Sensor for Simultaneously Measuring the Oxygen Stoichiometry (λ) and the NOx Concentration in Exhausts: Engine Tests under Dynamic Conditions

Due to increasingly stringent limits for NO_x emissions, there is now more interest than ever in cost-effective, precise, and durable exhaust gas sensor technology for combustion processes. This study presents a novel multi-gas sensor with resistive sensing principles for the determination of oxygen stoichiometry and NO_x concentration in the exhaust gas of a diesel engine (OM 651). A screen-printed porous KMnO₄/La-Al₂O₃ film is used as the NO_x sensitive film, while a dense ceramic BFAT (BaFe_0.74Ta_0.25Al_0.01O_3-δ) film prepared by the PAD method is used for λ-measurement in real exhaust gas. The latter is also used to correct the O₂ cross-sensitivity of the NO_x sensitive film. This study presents results under dynamic conditions during an NEDC (new European driving cycle) based on a prior characterization of the sensor films in an isolated sensor chamber with static engine operation. The low-cost sensor is analyzed in a wide operation field and its potential for real exhaust gas applications is evaluated. The results are promising and, all in all, comparable with established, but usually more expensive, exhaust gas sensors.