John W. Bennewitz

• Doctor of Philosophy
• Professor (Assistant) at University of Alabama in Huntsville

This experimental study explored the response of burning liquid fuel droplets to one-dimensional acoustic standing waves created within a closed, atmospheric waveguide. Building upon prior droplet combustion studies quantifying mean and temporal flame response of several alternative fuels to moderate acoustic excitation (Sevilla-Esparza et al., 201...

Stoichiometric mixing length Ls of reacting coaxial jet flames is a critical scaling parameter for liquid rocket engine combustors. Previous studies have shown that Ls for shear coaxial flames can be scaled like their nonreacting counterparts using a nondimensional momentum flux ratio J. In addition, stoichiometric mixing lengths of reacting and no...

An image processing technique is developed to automatically determine both average and instantaneous detonation wave properties within a rotating detonation rocket engine (RDRE) using high-speed imaging. This method entails segmenting the imaged RDRE annulus into 200 azimuthal bins and tracking integrated pixel intensity in each bin. By combining i...

This research investigation encompasses experimental tests demonstrating the control of a high-frequency combustion instability by acoustically modulating the propellant flow. This investigation complements an accompanying theoretical study implementing linear modal analysis [Bennewitz, J. W., Rani, S. L., Cranford, J. T., and Frederick, R. A., Jr....

This paper summarizes the performance of a small-scale rotating detonation rocket engine (RDRE) with various gaseous propellant combinations. Specifically, a 25 mm RDRE with a 5 mm annular width and 31.2 mm length is experimentally evaluated using methane (GCH4) and hydrogen (GH2) as the fuel with oxygen (GO2) as the oxidizer. Various flow conditio...

Rotating detonation rocket engines (RDREs) are propulsion devices that harness circum-ferentially traveling detonation waves that consume propellants through self-regulating axial injection into the combustion chamber. This process provides theoretical benefits of combustion pressure gain and thermodynamic efficiency compared to classical, deflagra...

In this paper, we study the interaction of an H2-O2 detonation colliding with an RP-2 droplet. The Kelvin-Helmholtz Rayleigh-Taylor (KHRT) model is one of the prevalent, semi-analytical Lagrangian models used to simulate liquid droplet secondary atomization. Using standard coefficients from the literature results in droplet lifetimes that are more...

A thermodynamic power cycle rocket engine model is developed in Python using Cantera, with the distributed mode combustor mode closely based on the previous work of Burr and Paulson. The cycle is modeled from the propellant tanks to the nozzle exit and includes the effects of simultaneous pre-detonation deflagration (𝒒1), detonation (𝒒2) and post-r...

Conventional testing of novel contrast agents for magnetic resonance imaging (MRI) involves cell and animal studies. However, 2D cultures lack dynamic flow and in vivo MRI is limited by regulatory approval of long‐term anesthesia use. Microfluidic tumor models (MTMs) offer a cost‐effective, reproducible, and high throughput platform for bridging ce...

Rotating detonation rocket engines (RDREs) are a promising technology for enabling compact combustion and increasing energy density [3] and are potentially suitable for a variety of applications ranging in size from upper-stage main engines and planetary/lunar landers to attitude control thrusters [9, 13]. RDREs typically take an annular configurat...

Characteristic timescales for rotating detonation rocket engines (RDREs) are described in this study. Traveling detonations within RDREs create a complex reacting flow field involving processes spanning a range of timescales. Specifically, characteristic times associated with combustion kinetics (detonation and deflagration), injection (e.g., flow...

Space travel requires high-powered, efficient rocket propulsion systems for controllable launch vehicles and safe planetary entry. Interplanetary travel will rely on energy-dense propellants to produce thrust via combustion as the heat generation process to convert chemical to thermal energy. In propulsion devices, combustion can occur through defl...

A computational fluid dynamics (CFD) simulation via the Eulerian-Lagrangian model is conducted to study the collision and interaction of a kerosene droplet with a detonation in a gaseous hydrogen-oxygen channel. The CFD solver handles combustion and detonation physics modeling. The detonation and combustion are modeled in the Eulerian domain for th...

Detonation-based engines such as Rotating Detonating Engines (RDEs) have been of significant interest for aerospace propulsion. However, most detonation-related studies have focused on gaseous reactants with the majority of investigations focusing on liquid water interactions with gaseous detonations and shocks. This study explores the dynamics of...

View Video Presentation: https://doi.org/10.2514/6.2021-3685.vid Rotating Detonation Rocket Engines (RDREs) have the potential to increase performance and lower the cost of launch vehicles by harnessing the benefits of pressure gain combustion. Thermal management and modelling in RDREs is challenging due to the high heat transfer rates and complex...

Characteristic timescales relevant to rotating detonation rocket engines (RDREs) are described in this study. The existence of traveling detonations within an RDRE create a highly complex reacting flow field that involves processes taking place over a large range of timescales. Specifically, characteristic times associated with various combustion k...

View Video Presentation: https://doi.org/10.2514/6.2021-3686.vid Although many different annulus geometries have been tested in different rotating detonation rocket engine systems worldwide, parametric studies on various annular gap widths are rare. In the presented study, a geometry that has been characterized over 2000 successful hot-fire tests i...

A rotating detonation rocket engine (RDRE) with various convergent nozzles and chamber lengths is investigated. Three hundred hot-fire tests are performed using methane and oxygen ranging from equivalence ratio equaling 0.5–2.5 and total propellant flow up to 0.680 kg/s. For the full-length (76.2 mm) chamber study, three nozzles at contraction rati...

Time-resolved in situ measurements of thermodynamic properties (pressure, temperature and species density) were performed in the annular exhaust of a methane-oxygen rotating detonation rocket engine (RDRE) using high-speed laser absorption spectroscopy. Bias-tee circuitry was coupled with a distributed feedback quantum cascade near 5 μm to spectral...

This experimental study characterized single detonation wave behavior in a linear detonation channel using injector plane oriented imaging. The linear channel geometry is designed to correlate with an analogous AFRL Rotating Detonation Rocket Engine (RDRE) as a means to further study previously observed detonation behavior. Nineteen test firings at...

Rotating detonation rocket engine (RDRE) experiments have so far been limited to injectors with high pressure drop to limit injector-plenum coupling. However, this corresponds to a reduction in the potential performance benefits of RDREs. To investigate this phenomenon, two injection configurations with different total injection areas are compared...

Mid-infrared laser absorption spectroscopy has been used to measure gas properties (pressure, temperature and species density) at MHz measurement rates in the annular exhaust of a methane-oxygen rotating detonation rocket engine. Bias-tee circuitry is used to modulate laser injection current into distributed feedback quantum cascade and interband c...

Mode transitions have been observed in rotating detonation engines at a variety of flow conditions and across many different engine geometries. This is particularly true for rotating detonation rocket engines (RDRE's), where the number of waves in the annulus has shown variation from as few as two waves, to as many as fourteen waves. While instanta...

A mid-infrared laser absorption sensing method has been developed to quantify gas properties (temperature, pressure, and species density) at MHz measurement rates, with application to annular rotating detonation rocket flows. Bias-tee circuitry is integrated with distributed feedback quantum cascade and interband cascade lasers in the \(4{-}5~\mu \...

The paper presents experimental evidence of continuous detonation in a rotating detonation rocket engine (RDRE) powered by H2/O2 propellants. High-speed chemiluminescence imaging is used to characterize the detonation wave dynamics by introducing a tracer in the hydrogen fuel flow. The results show continuous five-wave co-rotating detonations at va...

The burning process of multiple liquid fuels with various nanoenergetic additives is investigated experimentally in the suspended droplet configuration. Specifically, the burning rate constant K and ignition delay τign are measured for two base fuels, rocket grade kerosene (RP-2) and ethanol, with seven energetic additives; the investigated additiv...

Three injection configurations within a modular rotating detonation rocket engine are investigated in order to characterize mixing effects on performance parameters as well as detonation wave modal properties. A high-speed image processing tool is used to automatically extract detonation mode characteristics such as operational frequency fdet, numb...

A rotating detonation rocket engine (RDRE) with various convergent nozzle geometries is investigated in this study. In total, 300 hot-fire tests have been performed using gaseous methane GCH4 and oxygen GO2 as propellants for flow conditions ranging from equivalence ratio phi = 0.5-2.5 and total propellant flow rate m_tot = 0.2-1.5 lbm/s. Performan...

In this experimental study, a new data reduction approach was developed for measuring droplet burning rate constants that automatically finds the most linear part of the d-squared curve for the longest period of time. The approach, here called K_β, was developed in response to the observation that burning rate constants can vary by up to 10%, depen...

Various modal transitions within a rotating detonation rocket engine (RDRE) are investigated in detail within this experimental study. Using direct high-speed visible imaging along with a recently developed processing technique, detonation mode transition events are captured and analyzed with a focus on quantifying the unsteady wave propagation beh...

The effect of nanoscale energetic aluminum (nAl) and inert silicon dioxide (nSiO2) particulate additives on ethanol droplet combustion was studied under atmospheric conditions. Three different types of droplet experiments were performed to study the influence of the experiment itself on combustion behavior. Simultaneous visible and intensified ultr...

This experimental study characterized operability, performance and detonation modes within a model rotating detonation rocket engine (RDRE). Over 500 hot-fire tests were performed using a modular RDRE burning gaseous methane GCH4 and oxygen GO2. In each test, thrust F and mass flow rate measurements were taken along with direct high-speed visible i...

Two new methods for igniting suspended droplets, namely Plasma Arc Ignition (PAI) and Photoignition (PI), were developed which offer relatively short ignition initiation times within 65–110 ms range for all fuels except hexadecane that is about 260 ms. The fuels included ethanol, methanol, n-heptane, n-dodecane, toluene, RP-2, JP-8, Fischer-Tropsch...

This experimental study investigated droplet burning properties of ten common fuels including two alcohols, four simple hydrocarbons and four kerosene blends. Specifically, ignition delays and burning rate constants were quantified for each of these fuels using a combination of high-speed IR and visible imaging. Ignition delays measured using a sho...

Combustion of a wide range of hydrocarbon fuel droplets has been achieved through photoignition (PI) utilizing sub milligram of aluminum nanoparticles (Al NPs). For diesel fuel, a reliable ignition was made possible by mixing a solid oxidizer with the Al NPs. PI offers a fast (<5 ms) gasless reaction, a high ignition temperature (>2000 K), and a re...

Nanoscale particulate additives in liquid fuels have attracted attention because of their suggested benefits for advanced combustion systems. Since the liquid fuels used in both airbreathing and rocket engine systems can be associated with instabilities during combustion, it is of interest to explore the effects of particulate additives on burning...

This experimental study investigates the response of burning liquid fuel droplets exposed to one-dimensional standing waves created within an acoustic waveguide. Building upon prior droplet combustion studies quantifying mean and temporal flame response of several alternative fuels to moderate acoustic excitation, the present work extends recent st...

A linear modal analysis is undertaken to investigate the effects of acoustic modulation at the inlet boundary on the longitudinal instability modes of a dump combustor. This study complements an accompanying experimental investigation that demonstrates combustion instability control through single-frequency acoustic modulation at the inlet [Bennewi...

This research investigation encompasses expanded testing of a high frequency combustion instability suppression technique, in which an instability is able to be controlled by acoustically modulating the incoming oxidizer flow. To test this concept, a single element model rocket combustor (dinner = 10.16 cm and l = 16.51 cm) which burned gaseous oxy...

This research investigation presents a one dimensional acoustically consistent linear modal analysis based analytical method to analyze the stability of a fundamental longitudinal combustion instability mode when acoustic modulation is introduced. This analytical method was developed to qualitatively describe high frequency instability suppression...

A study was conducted to control a high frequency instability mode by applying band-limited white noise within the oxidizer post of an injector through the use of a piezoelectric speaker. A 500 Hz bandpass frequency width white noise signal was swept at various frequency bands, in increments of 100 Hz in the forward and reverse directions was used...

This research investigation demonstrates a new high frequency combustion instability control approach in which the dominant instability mode is able to be suppressed by strategically applying pressure disturbances within the oxidizer post of an injector. By housing a piezoelectric speaker at the base of the injector, the incoming oxidizer flow into...

This study demonstrates a new approach to liquid rocket engine (LRE) design, which permits the suppression of the severe 1-T spinning tangential combustion instability. Presently, control of the spinning tangential wave with a frequency of f ≈ 5000 Hz has been demonstrated in this laboratory reproduced liquid rocket engine combustor using an asymme...