Investigation of Nitric Oxide Kinetics in Diffusion Flames with Laser-Induced Fluorescence Spectroscopy and Detailed Modeling

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

The objective of this joint project involving the University of Michigan, Imperial College (London), and Sandia National Laboratory (Livermore) is to improve understanding and predictive capability of nitric oxide (NO) formation from the prompt (Fenimore) pathway favored in diffusion and fuel-rich flames. Chemical species critical to the prompt mechanism are measured and compared to the results from detailed kinetic models. Temperature and concentrations of NO, CH radical, and oxygen atoms are measured in a stable diffusion flame using nonintrusive laser-based diagnostics. The flame studied is a methane/air diffusion flame stabilized on a Tsuji-type counterflow burner. Species measurements are made with nanosecond and picosecond laser-induced fluorescence (LIF). Temperatures are measured with coherent anti-Stokes Raman spectroscopy (CARS) and quenching is measured directly by resolving the temporal decay of the picosecond LIF signal. Calibration is performed using Rayleigh scattering (CH, O-atom) or by measuring known amounts of dopant (NO). Flame strain rates (air and fuel flows) are adjusted to provide various reaction conditions, and nitric oxide is added to the fuel to measure destruction of NO by reaction with hydrocarbons (reburn). Reduction of pollutant emissions, especially nitrogen oxides, is a key issue in the design of energy conversion devices including automobile engines, gas turbines, and home heating furnaces. Depending on flame conditions, formation of nitric oxide can proceed by two different mechanisms: the thermal (Zeldovich) mechanism or the prompt (Fenimore) mechanism. The thermal mechanism, which dominates in fuel-lean, premixed systems, is fairly well characterized. However, the prompt mechanism is poorly understood.