Two-photon nitric oxide laser-induced fluorescence measurements in a diesel engine

Abstract

A two-photon nitric oxide (NO) laser-induced fluorescence (LIF) technique was developed and applied to study in-cylinder diesel combustion. The technique prevents many problems associated with in-cylinder, single-photon NO planar-laser-induced fluorescence measurements, including fluorescence interference from the Schumann-Runge bands of hot O2, absorption of a UV excitation beam by in-cylinder gases, and difficulty in rejecting scattered laser light while simultaneously attempting to maximize fluorescence signal collection. Verification that the signal resulted from NO was provided by tuning of the laser to a vibrational off-resonance wavelength that showed near-zero signal levels, which resulted from either fluorescence or interference at in-cylinder pressures of as much as 20 bar. The two-photon NO LIF signal showed good qualitative agreement with NO exhaust-gas measurements obtained over a wide range of engine loads.

An Experimental Investigation of the Origin of Increased NOxEmissions When Fueling a Heavy-Duty Compression-Ignition Engine with Soy Biodiesel

“…Ideally, it would be possible to quantitatively and non-intrusively measure the incylinder NO x -production rate and NO x distribution with a high degree of spatial and temporal resolution. Unfortunately, such measurements of NO x -relevant species (e.g., NO, NO 2 , N 2 , N, O 2 , O, OH, and H) and charge-gas temperature at typical diesel-engine conditions are not currently possible, and it is not clear when they will be (see e.g., [33,52,53]). In the mean time, it seems justifiable to use existing knowledge combined with thought experiments to help elucidate a "big picture" view of the mechanisms that determine fuel effects on NO x emissions, even though the thought experiments must necessarily contain some unproven assumptions.…”