Operando Optical Studies of High Pressure Monopropellant Combustion
Abstract
Research described in this proposal will build upon recent success developing a combustion assembly capable of burning monopropellant fuels in inert and oxygenated environments at pressures up to 80 bar. This assembly, dubbed #Dreadnought,# consists of a stainless steel chamber with ports for optical access that are rated to 150 bar. The heart of Dreadnought is a quartz straw strand burner connected via a differential pressure manifold to a 300 ml liquid reservoir. With a nitromethane being burned in a 40 bar inert atmosphere, this assembly maintained a continuous burn for as long as 60 minutes with a fuel consumption rate of 2.25 ml/min. While advances in the past funding cycle has identified intermediates and products in the flame, all data have come from dispersing emissiononto a detector. These experiments are necessarily passive in that only those species emitting light can be detected. Nevertheless, these data have been valuable in the mechanistic information they provideabout water formation and hydroxyl radical distribution in monopropellant flames. More importantly, the flame emission allowed us to develop an optical detection assembly capable of measuring rovibrational resolved spectra of molecular species in flames at high pressures. Spectral band accuracy is ±1 cm-1 with a resolution of # 5 cm-1 FWHM.The ultimate goal of this work is to accurately measure properties associated with Otto Fuel II (OF-II) combustion and to test proposed OF-II combustion mechanisms. Scaling up to a complex mixture like OF-II has required extensive testing and development of new tools capable of experimentally probing monopropellant flame properties at elevated pressures. In the proposed work, we will continue our development of optical techniques that can characterize monopropellant flame behavior. This work will focus on active means of identifying products and intermediates. Work will continue to use nitromethane (NM) as well as isopropyl nitrate (IPN), a more complex fuel that resembles propylene glycol dinitrate (PGDN), the oxidizing component of OF-II. Data will be compared to recently reported predictions from relevant models to test proposed NM, IPN and # if possible # PGDN combustion mechanisms. Furthermore, collaboration will continue with colleagues at Brown University and NUWC-Newport.With the unique capability of sustaining monopropellant flames for long periods and being able to measure spectroscopic signatures of flame species with unprecedented resolution, work described in this proposal will develop and optimize laser induced fluorescence (LIF) techniques to actively detect and image intermediates in monopropellant flames. Specifically, we will construct a platform that uses a 438 nm diode laser to probe different spots in the flame for C2 intermediates that are believed to be the first precursors to higher molecular weight carbon and soot emissions. This new capability will enable experiments to test directly conditions that lead to soot formation and, hopefully, to optimize conditions that reduce the soot being formed. The proposed research will have three specific goals that can all be carried out using the Dreadnought assembly. These goals are described in detail in the proposal narrative.1.Develop the LIF experimental assembly and establish limits of detection for C2 in NM and IPN flames at pressures from 30 to 80 bar.2.Determine the conditions necessary for stable IPN monopropellant combustion.3.Develop imaging capabilities to identify where within flames different intermediates and products are distributed.These studies will be a transformative advance for this research project as it will enable active detection of species in flames as well as scale up the complexity of fuels that can be studied in Dreadnought. Findings will be used to optimize conditions and enable more complete conversion of fuel into products and useful power.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 24, 2023
- Source ID
- N000142312606
Entities
People
- Robert A Walker
Organizations
- Montana State University
- Office of Naval Research
- United States Navy