Experimental cross-correlation nitrogen Q-branch CARS thermometry in a spark ignition engine

Abstract

This is the accepted version of the paper.This version of the publication may differ from the final published version. order to obviate any errors arising from deficiencies in the spectral scaling laws which are commonly used to represent nitrogen Q-branch CARS spectra at high pressure. Permanent repository linkThe spectra obtained in the engine were compared with spectra obtained in a calibrated high pressure, high temperature cell, using direct cross-correlation in place of the minimisation of sums of squares of residuals.The technique is demonstrated through the measurement of air temperature as a function of crankshaft angle inside the cylinder of a motored single-cylinder Ricardo E6 research engine, followed by the measurement of fuel-air mixture temperatures obtained during the compression stroke in a knocking Ricardo E6 engine. A standard CARS program (SANDIA's CARSFIT) was employed to calibrate the altered nonresonant background contribution to the CARS spectra that was caused by the alteration to the mole fraction of nitrogen in the unburned fuel-air mixture. The compression temperature profiles were extrapolated in order to predict the autoignition temperatures.2

High dynamic range thermometry at 5 kHz in hydrogen–air diffusion flame using chirped‐probe‐pulse femtosecond coherent anti‐stokes Raman scattering

“…More recently, Lockett et al employed N 2 Q-branch ns-CARS thermometry to study the auto-ignition process for various operating conditions of a spark ignition Otto engine. [4] In an effort to improve measurement accuracy, a cross-correlation method was used to match spectra from a specially designed high pressure, high temperature cell with that of the engine. Still, they reported cycle-to-cycle variation in the engine in combination with dye laser mode fluctuations that led to a single-shot uncertainty in the local fuel-air mixture and temperature in the engine of approximately 7%.…”

“…An issue with ns‐CARS is that the power spectrum of broadband dye lasers exhibits shot‐to‐shot fluctuations, which must be accounted for, typically by splitting off a small portion of the beam for direct measurement of the spectrum or recording the non‐resonant CARS spectrum. More recently, Lockett et al employed N 2 Q‐branch ns‐CARS thermometry to study the auto‐ignition process for various operating conditions of a spark ignition Otto engine . In an effort to improve measurement accuracy, a cross‐correlation method was used to match spectra from a specially designed high pressure, high temperature cell with that of the engine.…”