Fluorescence imaging inside an internal combustion engine using tunable excimer lasers

TLDR

No similar measurements in engines have been previously reported. Tunable excimer lasers and fluorescence techniques (natural, LIF, LIPF) are employed to capture 2‑D images of molecular density distributions in a modified four‑cylinder engine with optical access, with spectroscopy used to select appropriate laser and fluorescence frequencies and images acquired over successive engine cycles. LIPF performs well at high pressures, is state‑specific, and effectively tracks turbulent processes, while sequential images reveal cyclic fluctuations and the evolution of gas dynamics and combustion.

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.