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.