In-Cylinder Temperature Measurements in a Motored IC Engine using TDLAS

For an improved understanding of the in-cylinder processes in internal combustion (IC) engines, advanced diagnostics are needed to measure the thermodynamic state of the in-cylinder fluid. This is essential to validate numerical simulations which aim at predicting the in-cylinder processes during motored engine operation. Here, knowledge of the in-cylinder temperature is essential, as it strongly influences in-cylinder gas viscosity as well as the in-cylinder mass and thus the peak pressure. This work presents temperature measurements at 2.3 ∘CA resolution of a motored, optically accessible engine by applying tunable diode laser absorption spectroscopy (TDLAS) to in-cylinder water vapor. The temperature was investigated in different heights along the cylinder axis for variations of intake temperature and engine speed. Temperature uncertainties of ± 2.3 K were achieved at various cycle phases, and the absolute temperatures are verified using thermodynamic calculations of simultaneously measured water vapor concentration. The measured temperature dependency is compared to isentropic and polytropic changes of state, the incylinder gas mass is calculated and an estimation of the heat transfer to the walls is given. Based on the in-cylinder mass, different numerical simulations of the engine found in literature are compared.