Real-time measurement of equivalence ratio using laser-induced breakdown spectroscopy

Abstract

This paper demonstrates the use of laser induced breakdown spectroscopy (LIBS) as a diagnostic technique to obtain optical measurements of equivalence ratio in a sparkignited engine. Point measurements were obtained in the exhaust manifold of an automotive engine close to the exhaust port of a cylinder. The experimental apparatus was synchronized with the engine in order to obtain measurements in a fixed position during the cycle. Eighty-shot averaged measurements of equivalence ratio P, obtained in under 10 s, were shown to have ΔP = ±0.05 (95 per cent confidence interval). Single-shot measurements were hindered by noise in the signal, but it is shown that the statistical technique of principal component analysis can significantly improve the precision of the data and allows discrimination between measurements obtained in lean, stoichiometric, and rich conditions. The data presented represent one of the first applications of LIBS to optical measurements of the equivalence ratio in an engine, and considerable improvements are expected with further study.

Fiber-Optic Spark Delivery for Gas-Phase Laser-Induced Breakdown Spectroscopy

“…1 This effort was followed by quantification of the equivalence ratio in open flames and implementation of an in situ application of the measurements in an engine exhaust manifold. 2 The latter work also demonstrated the application of principal component analysis to improve the accuracy of the equivalence ratio calculated from the emitted spectra. Phuoc and White 3 quantified the equivalence ratio in a CH 4 -air mixture in a laboratory combustion chamber with LIBS using the emission ratio of the H a line (656.3 nm) and the O I triplet near 777 nm.…”

“…Applied to open or closed combustion systems, it can measure gaseous elemental composition with high temporal resolution. [1][2][3][4][5][6][7][8] This work describes application of fiber-spark delivery for use in such gas-phase applications.…”

Industrial Applications of Laser-Induced Breakdown Spectroscopy

“…If the fuel composition does not change, the fuel-air ratio can be inferred from the elemental analysis of unburned and burned gases. It is useful to know that the equivalence ratio can be inferred from burned gas measurement because the elemental composition does not change during reactions [78]. LIBS can be also used for the elemental analysis of particles, such as soot, which contain not only carbon but also metallic elements [79,80].…”

Laser-induced breakdown spectroscopy in a partially premixed turbulent jet flame

“…Another experimental method that has been established as a tool for combustion diagnostics over the past years is laserinduced breakdown spectroscopy (LIBS) [26][27][28][29][30][31][32]. A major benefit of LIBS over the aforementioned techniques is its experimental simplicity, as it does not require tunable lasers and intensified detectors.…”