Motivation: Emerging detonation-based propulsion concepts rely on stable and sustained detonation propagation controlled by small-scale shock-chemistry-wall interactions. While detonation has been widely studied in the context of cellular structures in idealized laboratory environments, the dynamics observed in practical detonation engines are often dramatically different as influenced by specific thermodynamic, mixing, and boundary conditions, shown in the figure below. There is a clear disconnect from the state of knowledge of detonation largely derived from studies of detonation cells to realistic detonation dynamics in engine applications.

Research goal: To bridge this gap, we explore new mechanistic descriptions of detonation propagation centered around dynamic features such as transverse waves, with the goal to offer a unifying theory for detonation propagation of different structures and modalities.

Motivation: Plasma-based pyrolysis of hydrocarbons to form hydrogen and carbon nanomaterials is becoming a new technological home to alternative, zero-carbon-emission use of fossil fuel resources. The formation of nanocarbon particles inside plasmas follows a two-step process: a high-temperature decomposition phase followed by a particle-forming phase, illustrated in the figure below. The current understanding suggests that the two steps are decoupled, and as a result, particle formation is expected to be independent of hydrocarbon composition. However, experimental measurements have shown otherwise, as variable degrees of carbon crystallinity were observed when different hydrocarbon species were introduced. The mismatch between the theoretical understanding and experiments reveals a fundamental gap in our knowledge about the molecular process of gas-phase carbon nanoparticle formation, which also stymies the practical application of this process using natural gas where a variety of hydrocarbon species are present.

Research goal: We propose a simulation-guided experimental research program to explore the molecular process of nanographene formation in multi-species hydrocarbon plasmas. We will probe the detailed molecular process by microwave plasma experiments fed with hydrocarbon mixtures of different species composition, explore detailed chemical kinetics pathways that are responsible for the experimental observations, and quantify the sensitivity of nanographene formation towards mixture composition variation to identify and design suitable plasma conditions where such sensitivity can be minimized.

Collaboration with Professor William Sirignano

Motivation: Current flamelet models that are used for large eddy simulations (LES) or Reynolds-averaged Navier-Stokes (RANS) methods can handle multi-species, multi-step kinetics without requiring small time steps during the solution of the resolved-scale fluid dynamics. However, one key limitation of the current flamelet theory concerns the omission of shear strain and vorticity at the small scale of the flamelet, rendering its poor performance in predicting limit behaviors such as extinction where high strains and vorticities are expected.

Research goal: We explore a new flamelet concept that incorporates the impact of shear strain and vorticity on local flame behaviors. The new flamelet model, in contrast to traditional, irrotational flamelet models, is three-dimensional and rotational by design, independent of flamelet types (e.g., non-premixed, premixed, or multi-branched), and expected to better capture combustion limit behaviors such as extinction. We will build the new flamelet model using an incompressible, multi-component reacting flow framework with detailed chemical kinetics and transport properties, and examine its performance in LES of rocket and gas turbine combustors.