Development of Combustion Models for Propulsion Applications

Dr. Brian Bojko received his PhD in Aerospace Engineering from the University at Buffalo in 2017, where his research focused on modeling multi-phase turbulent spray flames. He then spent four years at the Naval Air Warfare Center in China Lake, CA conducting research on air-breathing propulsion and heterogeneous solid rocket propellants. Dr. Bojko is currently a lead scientist in the Laboratories for Computational Physics & Fluid Dynamics at the Naval Research Laboratory where he is the principal investigator on multiple research efforts investigating the combustion of solid polymeric fuels, group combustion effects of dense metal flames, and high-speed propulsion. Dr. Bojko recently received the Irvin Glassman Early Career Investigator Award from the Eastern States Section of the Combustion Institute and the Presidential Early Career Award for Scientists and Engineers (PECASE) for his work on multiphase combustion modeling. He currently serves as the chair of the Airbreathing Propulsion Subcommittee for JANNAF and is a committee member of the Propellants and Combustion Technical Committee for AIAA.

Abstract:Practical hydrocarbon fuels used in propulsion systems consist of many carbon atoms and require high-fidelity models to accurately capture their combustion characteristics. Solid polymeric fuels for air-breathing propulsion are advantageous because their high energy densities increase the specific impulse and overall range of the flight vehicle. During combustion, these long polymer chains break down and undergo pyrolysis at various rates, devolving into different gaseous chemical compositions depending on the temperature, heat flux, and pressure within the combustor. Additionally, the mass flux of the solid fuel is directly coupled to the heat release from the flame zone and vice-versa. It is therefore necessary to develop accurate models with detailed finite-rate chemistry mechanisms to understand the fundamental combustion dynamics of the fuel. Using this information, reduced order models can then be developed that are capable of incorporating these findings into system-level simulations. This talk will focus on the understanding of fundamental combustion processes of solid fuel burning at various operating conditions. We will explore comparisons of experimental and numerical studies of an opposed flow burner to highlight the fundamental physics. It is intractable to use the same chemical mechanisms in multi-dimensional simulations due to the vast amount of computational power required to solve the increasing number of partial differential equations (PDEs) and the numerically stiff reaction kinetics. Therefore, upon analyzing the small-scale combustion phenomena, the development of a flamelet progress variable (FPV) approach is described to demonstrate the translation of finite-rate kinetic effects to large-scale simulations in a computationally efficient way. Applying the FPV method reduces the total number of PDEs to solve and eliminates the numerical stiffness associated with combustion, enabling combustion simulations of flight vehicles at scale.