Measurement of exhaust gas temperatures: Theoretical and experimental analysis

The optimal management of the three-way catalytic converter is today widely recognized as one of the means to further reduce Spark Ignition (SI) engine polluting emissions, and therefore to respect future emission regulations. Its conversion efficiency is strictly dependent on the operating temperature, and most engine control strategies are today either based on mathematical models that determine such temperature as a function of the engine operating conditions, or on its direct measurement. It is therefore useful to investigate the errors that could arise when measuring exhaust gas temperatures, either during model identification tests or on board the vehicle. The paper presents a theoretical and experimental analysis on the phenomena that could lead to relevant measurement errors in such applications. A physical model of the heat transfer phenomena that take place in the exhaust manifold has been developed to estimate both the exhaust gas temperatures and the error that would arise while measuring them with typical sensors such as thermocouples. The exhaust manifold of a 1.2 liter SI engine was equipped with different types of sensors for the model identification and validation phases.