High resolution water emission from nitromethane combustion under high pressure mono- and bipropellant conditions

• Published in: Combustion and flame 2024-10, Vol.268, p.113630, Article 113630
• Main Authors: Sinrud, Joshua B., Schwind, Rachel A., Dean, Brahm N., Yiyen, Galip, Wolff, Oliver M., Goldsmith, C. Franklin, Walker, Robert A.
• Format: Article
• Language: English
• Subjects: Combustion diagnostics; High-pressure combustion; Monopropellant; Water chemiluminescence
• ISSN: 0010-2180
• DOI: 10.1016/j.combustflame.2024.113630

Optical emission spectroscopy was used to measure rovibrationally resolved spectra of water formed during nitromethane combustion at elevated pressures in both oxidizing and inert atmospheres. Complementary kinetic models were used to predict flame temperatures, product distributions, and product formation rates, and results were compared with experimental observations. Experiments were carried out at pressures of 27.4 bar and 34.2 bar in inert atmospheres (referred to as monopropellant conditions) and air (referred to as bipropellant conditions). Dispersed emission shows many rovibrational transitions with the strongest occurring between 13,000 and 14,500 cm−1. These lines are primarily assigned to the relaxation from water's (3,0,1) vibrationally excited state to its vibrational ground state. Weaker progressions in this same region are assigned to water relaxation from the (1,0,3) and (2,2,1) vibrationally excited states. Data collected under mono- and bipropellant conditions showed very similar relative intensities of individual rovibrational lines. The spectra were fit using a simulated temperature of 2,500 K ± 500 K for both mono- and bipropellant conditions. Ex situ FTIR spectra of NM exhaust confirms the presence of H2O in both mono- and bipropellant combustion. Interestingly, analyses of these same spectra also show significant amounts of CO in monopropellant exhaust, but no detected CO in bipropellant exhaust. These latter findings show higher CO/CO2 concentration ratios compared to simulations, motivating the need for refined models describing nitromethane monopropellant combustion.