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The basic characteristics of the TiO2 sensor were introduced on a previous SAE paper which was submitted by NGK Spark Plug Co., Ltd. and further discussed on several other papers which have also been recently published. This paper will describe the effect of a precious metal catalyst on vehicle emissions. Emphasis is placed on the effect of the distribution of the precious metal catalyst in the titania element which significantly affects the reaction among unburned components in the exhaust gas as well as sensor performance. The relationship between the catalyst distribution in the sensor element, and the closed loop emission results, including test variability, will also be discussed in this paper.

The corelation between flame ion density and engine operating condition, such as air fuel ratio mixture and cylinder pressure peak value, etc., is commonly known. However, due to the difficulty of ion probe installation in the engine and the interruption of the high voltage ignition spark, the ionization current method is not optimally utilized. This paper presents the Spark Plug Voltage-ion method which requires a minor modification to the ignition system and will indirectly detect flame ion density. The voltage sensor is a voltage divider by capacitance which measures the spark plug voltage. The resulting behavior of the voltage wave form is noteworthy. After spark discharge, the stored residual charge of the spark plug starts to discharge by ion in a flame. Therefore, ion density in a flame is detected by the decay time of spark plug voltage.