Thermometry by CARS in an automobile engine

Temperature measurements in an automobile engine running in normal operating conditions have been obtained by observing the CARS spectra of molecular nitrogen. Pulsed lasers and a broad-band technique have been used to allow the single-pulse measurements necessary for studying combustion behaviour and cycle-to-cycle fluctuations. A fitting technique has been used to determine temperatures from the experimental data, with an uncertainty of about 50 to 100K. The authors discuss the problems that are still unresolved in order to achieve better accuracy: beside experimental refinements a further knowledge of molecular parameters seems to be required.