On the use of laser-induced fluorescence for the measurement of in-cylinder air—fuel ratios

Abstract

This paper presents the development of a new strategy for the calibration of air-fuel ratio measurements in engines by laser-induced fluorescence (LIF). After a brief introduction to the LIF technique, the paper highlights the structured approach undertaken to ensure that accurate quantitative measurements were produced. In particular, the new approach to coping with the fluorescence dependency on pressure and temperature, the issues related to the choice of a fluorescence tracer, the careful determination of the optimum tracer concentration and the complete calibration methodology are described, together with the resolution of some of the obstacles encountered. The paper concludes with some examples of calibrated measurements accompanied by a comparison of the results with combustion and emission performances. These results show a very good correlation.

Quantitative planar laser-induced fluorescence imaging of multi-component fuel/air mixing in a firing gasoline-direct-injection engine: Effects of residual exhaust gas on quantitative PLIF

“…This followed the method of Ref. [25] and is similar to that employed in other studies [35]. The method relies upon in situ measurements of fluorescence intensity from homogeneous mixtures, as the charge is compressed during a typical cycle in a motored engine.…”

“…A method to calibrate the effect of temperature and pressure on fluorescence has been introduced that uses a closed loop containing a known concentration of fuel at measured temperature and pressure [25]. The PLIF images obtained from such homogeneous mixtures in the cylinder are used to calibrate images of fuel-air mixtures under motored conditions at the same conditions of temperature and pressure.…”

Development of laser-induced fluorescence to quantify in-cylinder fuel wall films

“…In this case, the minimum concentration was chosen to be 5% by volume because the extinction coefficients of ketones are generally much lower than those of aromatic species. Fitting equation (5) to this data set yielded an extinction coefficient e à = 50:11 dm 3 =(cm mol) and a = 0.61, with a coefficient of determination of 96.57%. This value of e à corresponds to a decadic extinction coefficient of 21.76 dm 3 /(cm mol).…”

“…One option is laser-induced fluorescence (LIF), which is an established diagnostic for determining the local air/fuel ratio in the gas phase. 4–8 This very sensitive method has the potential to detect even small amounts of liquid fuel inside the intake manifold of engines with port fuel injection (PFI) 9,10 or the combustion chamber of engines with GDI. 11–13 However, quantification of the LIF signal at elevated pressures and temperatures still needs improvement.…”

Measurement of exhaust gas recirculation rate by laser-induced fluorescence in engine

“…In IC engines, De Sercey et al [17] have developed a calibration for each crank angle degree (CAD) with different concentrations of tracer in a homogeneous mixture. The calibration number therefore depends on the number of tests made on the studied engine.…”