Development of the first Raman scattering thermometry during the first stage ignition in a rapid compression machine and determination of detection limits for NO-LIF

The interaction of recirculated NO_X with two-stage fuels in the early combustion process is not fully understood, especially at lower temperatures. Recently developed kinetic combustion models try to reproduce these interactions. To validate and improve these new models, accurate quantitative measurements of temperature in the combustion process are necessary. Previous works used Rayleigh or LIF techniques and have not reached an accuracy appropriate for the kinetic models. The present work demonstrates the feasibility of 1D spatially-resolved temperature measurements in a rapid compression machine with Raman scattering for the first time. The temperature data is measured with high precision during the first stage ignition of n-pentane as a two-stage fuel. Additionally, the temperature data is needed to determine possible NO detection limits. Therefore, the influence on combustion temperatures from NO_X-doping are compared with undoped gas mixtures is determined by spontaneous Raman scattering of N₂ excited by a KrF* excimer laser. The results show that spatially resolved N₂-Raman thermometry is feasible with a precision of approximately 3 % by investigating 30 averaged shots. The measured temperature profile in the first stage reveals a remarkable temperature difference between the edges and the inner area of the combustion volume due to differences in the reactivity, which is affected by chemistry and heat loss. Additionally, the NO detection limit is determined to be 30 ppm when averaging 10 single shots during an NO-doped N₂ mixture.