A non-premixed, reformate and methane flame was experimentally and numerically investigated to explore the effect of steam to carbon ratio and reformate gas content on the criteria emissions generated. In order to better isolate the effects, the experiments were run at fixed flow rates and inlet temperatures. The steam to carbon ratio was varied from 2 to 3 while the reformate gas content was varied from 12.5% to 75% on a molar basis. Nitrogen oxide measurements were collected and analyzed to determine trends throughout the design space. Additionally, an OpenFOAM 2D model of the system was created, validated, and used to further investigate the system.

To meet the performance, economic, and environmental goals of the future, aircraft engines need to improve. One way to accomplish this is by enhancing the thermodynamic cycle by using intercooling and/or recuperation such as is employed in the fuel-integrated energy recuperative aircraft (FIERA) engine. The primary goal of this research was to determine if multistage intercooling using only the stator blades of the compressor is sufficient to provide the heat transfer required to obtain appreciable improvements in engine and combustion performance. This was split into three investigations: a small-scale examination of a single airfoil heat exchanger, an analysis of an effectiveness-NTU model for a full-scale, multistage-intercooled, axial compressor, and an investigation of the combustion characteristics of thermally enhanced kerosene. This work helped to identify a few insights, as well as a few failings of the envisioned FIERA engine. First, it is likely that the fuel consumption at cruise is not sufficient to provide adequate heat sink potential to provide substantial compressor intercooling even if high values of heat exchanger effectiveness are achieved. Secondly, the area provided by compressor stators alone appear to be insufficient to realistically approach high effectiveness values. Lastly, cracking of the fuel would likely not take place in a solely intercooled engine unless an engine with a very high overall pressure ratio (>60:1), or an intercooled recuperative engine was used. Therefore, it is of the author’s opinion that using the fuel in a commercial turbofan engine to create a more complex thermodynamic cycle would not be worthwhile.

Interest in the applications of Triboelectric Nanogenerators (TENGs) has grown in the past decade as a means of effective energy harvesting in addition to its applications in powering low powered electronics and sensors especially in the area of Internet of Things (IoT). Majority of the research into TENGs focuses on maximizing the power output through different material combinations, material doping, topography manipulation, and design construction. However, unlike most energy sources common today such as solar, wind, piezoelectric and pyroelectric, the methods of measuring TENG output have not been established or agreed upon in the scientific community. This makes determining how a TENG will perform in a given design space difficult as the amount of variables that can be adjusted are numerous. A systematic approach to understanding the behavior of a TENG is with Design of Experiments (DOE). DOE can provide insight into the behavior of the TENG by adjusting parameters to determine what influences the output the most. The most common parameters that are altered in a TENG outside of material science are contact area, contact force and displacement distance of the two triboelectric materials. The experimental results showed that the different parameters affected output depending on the stage of contact separation that was measured (coming into contact vs separating), and that separation distance had almost no effect on voltage output.

In this work, a hydrogen-oxygen torch igniter was developed and utilized to study the combustion of gaseous oxygen (GOx) and solid acrylonitrile butadiene styrene thermoplastic (ABS) in conjunction with gaseous hydrogen (GH2) in application to hybrid rocket motors. The effects thereof are not presently found in literature. Initial pyrolysis of the ABS fuel grain was accomplished via products of GH2 and GOx combustion from a spark initiated torch igniter. In order to isolate the effects of hydrogen to the overall combustion, the mass flow rate of hydrogen and its duration was varied in a factorial design of experiment. It was found that an increase of the hydrogen mass flow rate at constant GOx mass flow rate led to an increase in the average linear regression rate for lean to stoichiometric operating conditions of the torch igniter. Additionally, extending the duration of hydrogen flow, from 10% to 50% of the total burn time, led to an increase in the regression rate. The author posits that the increases in average linear regression rate are due to the hydrogen-oxygen flame applying high heat and mass flux to the surface of the fuel grain, helping to overcome the rate-limiting, endothermic pyrolysis step. However, an increase in the hydrogen mass flow rate, from stoichiometric to rich operating conditions, led to decreases in the average linear regression rate. It is posited that at the fuel-rich operating condition, the hydrogen consumes most of the available oxidizer molecules. This resulted in a competition between the hydrogen gas and the ABS fuel grain for available oxidizer molecules. This theory is further supported by the turbulent boundary layer combustion model presented by Marxman and Gilbert [1]. These results suggest that the hydrogen-oxygen torch igniter can be used not only as a reliable starter, but also for regression rate enhancement that targets the rate limiting step, pyrolysis, for hybrid rocket combustion at stoichiometric to fuel-lean operating conditions of the torch igniter.

Hybrid rockets have recently become a more and more desirable method for small satellitepropulsion, due to their lack of safety issues compared to their liquid and solid rocket counterparts. A major reason for this is because the fuel and oxidizer are both separated by distance and state when stored in a hybrid rocket. This also makes it relatively more difficult to ignite and start up the rocket. While many igniter systems have been invented, currently no reliable, self-igniting system has been flown. Recently, a Hydrogen-Oxygen torch was designed, built, and tested in UC Davis’ Energy Research Lab. Methane is typically used in torch igniters for lab-scale testing of hybrid rocket motors. A side-by-side comparison on the same igniter system between Hydrogen and Methane as the igniter fuel was done to investigate which, if any, fuel can exhibit better transient and/or steady state performance. Due to the higher heat of combustion, adiabatic flame temperatures and theoretical characteristic exhaust velocities when reacting with Oxygen, Hydrogen was found to have more reliable and repeatable ignition transients. The solid fuel regression rates were also found to be higher when using Hydrogen despite competition to burn with Oxygen between Hydrogen and the solid Nylon-6 fuel. These performance benefits come at the cost of being less volumetrically efficient than Methane as Hydrogen has a significantly smaller density at a given temperature and pressure.

As hybrid rocket propulsion systems continue to be utilized as launch solutions within the small satellite industry, their inherit poor fuel regression rates and low combustion efficiencies possess a notable threat to mission performance. This body of work investigates the practicality of hydrogen co-firing as a novel technique to combat these deficiencies. A hybrid rocket propulsion system of gaseous oxygen (GOx) and nylon 6 thermoplastic fuel grain with a gaseous hydrogen (GH2 ) co-firing configuration was designed and manufactured for preliminary analysis in understanding the internal ballistic effects of hydrogen addition. In order to appropriately characterize the overall combustion event, comprised of both the GOx/nylon 6 and GOx/GH2 burn, NASA CEA (Chemical Equilibrium with Applications) software was utilized. The baseline burning of GOx and nylon 6 yielded a simulated combustion efficiency of 85.67% and an overall system efficiency of 85.95%. The simulated GOx and GH2 burn prompted results of elevated combustion temperatures as well as a surplus of available oxidizing molecules at stochiometric to fuel-lean O/F ratios. No validation experiments were performed; however, it is posited through the analysis that at an optimal O/F ratio of 16, the upstream burn of gaseous oxygen and gaseous hydrogen would expedite the nylon 6 pyrolysis event and supply enough oxidizer for the pyrolyzed thermoplastic hydrocarbons to sustain a healthy flame. This would promote the heat and mass transfer mechanisms that hybrid rocket propulsion systems are limited to and thus improve regression rates and performance efficiencies.

Proceedings of the ASME 4th International Conference on Fuel Cell Science, Engineering and Technology, Irvine, CA, June 19 - 21, 2006

Hydrogen can be produced in a variety of methods including steam-reformation of hydrocarbon fuels. In past studies the quasi non-dimensional space velocity parameter (inverse residence time) has been shown to be insufficient in accurately predicting fuel conversion in hydrocarbon-steam reformation. Heat transfer limitations have been manifest with reactors of different geometries. In order to achieve ideal fuel conversion, the heat transfer limitations and the changes of these limitations with respect to geometry must be considered in the reactor design. In this investigation, axial and radial temperature profiles are presented from reactors of different aspect ratios while holding space velocity constant. Using both the temperature profile information as well as the traditional space velocity limitations one may be able to develop an optimal reactor design.