Robust Methodology for Fast Crank Angle Based Temperature Measurement

The paper presents a measurement methodology which combines a fine-wire thermocouple with input reconstruction in order to measure crank angle resolved temperature in an engine air-intake system. Thermocouples that are of practical use in engine experiments tend to have a large time constant which affects measurement accuracy during rapid temperature transients. Input reconstruction methods have previously been applied to thermocouples but have not been specifically used in combination with an ultra-thin uninsulated wire thermocouple to investigate cyclic intake temperature behavior. Accurate measurement results are of interest to improve the validity of many crank-angle resolved engine models. An unshielded thermocouple sensor has been developed which is rigid enough to withstand the aerodynamic forces of the intake air. The nonlinear dependency of the sensor time constant was linearized and characterized at a number of mass flow rates by applying an identification method which uses two thermocouples with different diameters. For this purpose a test rig was designed to generate temperature step inputs at constant mass flow rates. A discrete time model of the sensor is finally directly inverted to reconstruct the true gas temperature. The results presented show how the sensor time constant was identified at several mass flow rates to establish a simple regression model describing the time constant as a function of air mass flow. Cyclic temperature data are finally presented including quick temperature transients caused by throttle tip-in and tip-out. The results are analyzed and compared with simulation results from a 1D engine model. This method simplifies previously demonstrated approaches and also applies, for the first time, the methodology for the purpose of intake-side cyclic temperature measurement.