Fluorescence imaging inside an internal combustion engine using tunable excimer lasers

Abstract

Tunable excimer lasers are used to obtain 2-D images of molecular (and some state-specific) density distributions inside a cylinder of a modified four-cylinder in-line engine that has optical access. Natural fluorescence (i.e., without a laser) is used for some OH pictures, normal laser-induced fluorescence (LIF) for those of NO and of the isooctane fuel, and laser-induced predissociative fluorescence (LIPF) for other OH pictures and for those of O(2). Relevant spectroscopy is done to find the laser and fluorescence frequencies needed to measure isolated species. LIPF works well at high pressures, is state specific, and is ideally suited to follow turbulent processes. No similar measurements in engines have been previously reported. Pictures are taken in succeeding engine cycles. Their sequence is either at a particular point of the engine's cycle to show cyclic fluctuations, or at succeeding portions of the cycle to illustrate the progress of the gasdynamics or of the combustion.

Review of temperature measurement

“…Studies in the near ultraviolet ͑400-10 nm͒ and near infrared ͑700-1215 nm͒ are becoming more common as near-infrared lasers and frequency-doubling methods improve. LIF has been applied extensively to combustion measurements in flames 168 and the density in an engine cylinder at different locations was measured by Andresen et al 169 …”

Universal calibration of quantitative OH-LIPF measurements in hydrocarbon flames at elevated pressures

“…The dissociation is so fast that the collisional quenching rate is negligible compared with the predissociation rate. Andresen and coworkers [6,7] first applied the LIPF technique to observe OH species in Bunsen flames and internal combustion engine using a KrF excimer laser. They concluded that the use of LIPF could greatly reduce the quenching problem and allow quantitative measurements of OH concentrations at elevated pressures.…”

<title>Optical measurement and visualization in high-pressure high-temperature aviation gas turbine combustors</title>

“…PLIF has been well established in industrial systems [4][5][6][7][8] . Mie scattering is used to visualize the liquid fuel and may be combined with fuel PLIF in a variety of ways to image drop size 3 or describe the extent of vaporization 9 .…”