title: Laser-induced breakdown spectroscopy for in-cylinder equivalence ratio measurements in laser-ignited natural gas engines.
abstract: In this contribution we present the first demonstration of simultaneous use of laser sparks for engine ignition and laser-induced breakdown spectroscopy (LIBS) measurements of in-cylinder equivalence ratios. A 1064 nm neodynium yttrium aluminum garnet (Nd:YAG) laser beam is used with an optical spark plug to ignite a single cylinder natural gas engine. The optical emission from the combustion initiating laser spark is collected through the optical spark plug and cycle-by-cycle spectra are analyzed for H(alpha)(656 nm), O(777 nm), and N(742 nm, 744 nm, and 746 nm) neutral atomic lines. The line area ratios of H(alpha)/O(777), H(alpha)/N(746), and H(alpha)/N(tot) (where N(tot) is the sum of areas of the aforementioned N lines) are correlated with equivalence ratios measured by a wide band universal exhaust gas oxygen (UEGO) sensor. Experiments are performed for input laser energy levels of 21 mJ and 26 mJ, compression ratios of 9 and 11, and equivalence ratios between 0.6 and 0.95. The results show a linear correlation (R(2) > 0.99) of line intensity ratio with equivalence ratio, thereby suggesting an engine diagnostic method for cylinder resolved equivalence ratio measurements.
authors.affiliation: Engines and Energy Conversion Laboratory, Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80521, USA.
authors.forename: Sachin
authors.initials: S
authors.lastname: Joshi
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Olsen
authors.forename: Cosmin
authors.initials: C
authors.lastname: Dumitrescu
authors.forename: Paulius V
authors.initials: PV
authors.lastname: Puzinauskas
authors.forename: Azer P
authors.initials: AP
authors.lastname: Yalin