Research Update from Blunck Group at Oregon State University 2017

Transcription

1 Research Update from Blunck Group at Oregon State University 2017

2 Turbulent Flame Speed of Large Hydrocarbon Fuels Objective: Determine turbulent flame speeds and stability limits of various jet and jet-like fuels when burned at atmospheric and subatmospheric conditions Process chemiluminescence images to determine flame speed Knowledge from this study can be used to help reduce the cost of evaluating jet and jet-like fuels for aviation applications Gaining a greater understanding of turbulence effects on combustion processes of large hydrocarbon fuels Data has application to afterburners and high altitude relight of engines 2

3 Results from Flame Speed Project Top left corner: Comparative study of stability and flame speeds of different fuel types Top/bottom right corners: Comparison of flame speeds of jet and surrogate fuels Bottom left corner: Flame speeds at sub-atmospheric conditions 3

4 Temperatures of Spark Kernels at Sub-atmospheric Press. Identify how changes in pressure affect the temperature of spark kernels. A gas turbine engine igniter will be operated at varying pressures inside a vacuum chamber. Radiation intensity measurements and a deconvolution technique will be used to determine gas temperatures in the kernels that are produced. The knowledge gained can be used to provide insights into the ignition process at high altitudes. This is important for afterburner ignition in military engines, and for reignition after a flameout in a combustor. 4

5 Identifying Physics that Control Ember Generation Determine the key physics governing the generation of embers during wildland fires Quantify the energy of embers upon deposition on a fuel bed Implement experimental findings into a computational tool for predictive modeling (collaboration) Study generation at multiple scales to relate studies from the laboratory and field Laboratory-scale screening study to determine effect of diameter, species, moisture content, fire intensity, and cross flow velocity on generation Field studies will collect embers and infrared images of ember flux Increased population in Wildland Urban Interface (WUI) means more structures at risk during wildland fires Better understanding of physics controlling ember generation can lead to better predictive fire models Better models will help allocate fire personnel and resources more efficiently 5

6 Results from Ember Generation Project Ember collection setup prior to controlled burn. Results from screening study show that diameter has the strongest effect of timeto-generation, followed by species. Average time-to-generation for all species tested. 6

7 Oxy-Coal Pulsed Detonation Engine Design, build and characterize a pulsed detonation engine (PDE) capable of operating on oxygen and coal. Provide boundary conditions and validation data for simulations of a magnetohydrodynamic (MHD) generator Photodiode Ports Main Tube Fuel- Oxidizer Inject ion Pre-Detonator Measure detonation velocities of oxycoal detonations Evaluate electrical conductivity by measuring magnetic field deflection Collaborate with computational efforts to develop more accurate numerical models for multiphase detonation and MHD power extraction Detonations can provide a step increase in overall efficiency of power plants Detonation/MHD systems can be used as topping cycle in power plants Determine electrical conductivity of ionized species in oxy-coal detonations 7

8 Results from Oxy-Coal PDE Propane-Nitrous detonation achieved within 15% of CJ velocity Coal seeder built Conductivity measurement device built Image of exhaust from PDE Example particle cloud ejected from coal seeder

9 Influence of Dilution on Detonations Determine the effects of dilution with combustion products on the cell size and wave speed of detonations Detonate mixtures with different combustion products Measure wave speed with photodiodes Use focusing schlieren method to photograph the detonation front Determine average cell size for each mixture Perform chemical sensitivity analysis to determine cause of cell size sensitivity An increased understanding of the effects of dilution with detonation products on detonation cell sizes and wave speeds can help to enable the practical use of pressure-gain combustor technology, which is more thermodynamically efficient than typical combustion cycles 9

10 Influence of Dilution on Turbulent Flame Speed Identify the effect of combustion product dilution on the turbulent flame speeds of jet fuel Elucidate the influence of specific diluent species on reaction rates Turbulent Flame Burner Jet fuel is burned in a turbulent Bunsen burner with varying levels of diluents present (CO 2, N 2, and NO X ) Turbulent flame speed is determined for each dilution condition, showing the relative effect of each diluent Jet A flame Improved understanding of turbulent combustion in combustor-like environments (high turbulence intensity, combustion products present) is important to help facilitate better modeling of engine performance, fuel efficiency and reduction of harmful emissions 10

11 Influence of Dilution on Ignition Identify the sensitivities of ignition of jet fuels to dilution with combustion products Determine the effect of dilution on ignition energy required to ignite mixtures of jet fuel and exhaust products Spark Tunnel Spark kernels are generated in a flow tunnel containing vaporized jet fuel, air and diluents The ignition probability for each condition is determined Temperature estimates for kernels at each dilution condition are determined using infrared thermography Energy deposited is measured Efficient and dependable ignition is a key factor in guaranteeing engine reliability. This project will provide insight into the effect of exhaust product dilution on ignition, with the goal to provide knowledge to help improve ignition system reliability. 11

12 Results from Dilution Projects Results to Date: Turbulent flame speed measurements show larger reduction in flame speed for CO 2 dilution than N 2, when mixture specific heat is held constant (right) Preliminary data (no dilution, CH 4 /air benchmark case) for spark ignition project demonstrates validity of measurement technique (below) Turbulent flame speed of jet fuel diluted with N 2 and CO 2 High speed infrared images of developing spark kernel 12

13 Combustion of Surrogate Jet Fuels Determine the influence of fuel preheat temperature on the liftoff height of jet fuels in combustion Measure the effects of oxygen concentration on liftoff heights of jet fuels Identify similarities and differences of combustion characteristics for surrogate and jet fuels in or -like combustion Create or -like conditions using a diluted and high temperature coflow around a central fuel jet Introduce preheated vaporized fuel through a central nozzle Measure liftoff heights using an ICCD camera Analyze effects of changing coflow temperature and oxygen concentration Compare liftoff heights Increase in energy demands has generated an increased need for high efficiency and ecologically friendly energy conversion through combustion combustion offers decreased NO x that is prevalent in high temperature combustion combustion also creates a more distributed reaction zone, as well as lowering peak combustion temperature 13

14 Smoldering Combustion in Forests Identify key physics that control ignition, propagation and emissions of smoldering combustion within naturally occurring plant litter. Weather Station IR Mirror Visual Camera Infrared Camera Reactor Box Scale Plant litter samples are smoldered while monitoring smoldering behavior and weather: Samples tested for moisture content, inorganic content, and composition. Weather data records air temperature, wind speed/direction, and humidity. Infrared (IR) camera is used to find surface temperatures and surface propagation rates. Thermocouples are used to find propagation rates. Smoldering within wildfires can be hazardous to humans and the ecosystem: Sterilizing soil Producing toxic pollutants Transitioning to flaming combustion Understanding smoldering characteristics can facilitate models to predict: Smoke and pollutant production Longevity of smoldering fuel Potential area of influence of subsurface 14 smoldering

15 Field Smoldering Research Progress Propagation velocity from June 26, 2017 field burn: The distribution of smoldering propagation speeds. The average propagation speed was (cm/min). This figure shows the propagation velocities as would appear from a top down view of the fuel bed 15

16 Laboratory-Scale Smoldering Research Use lab-scale smoldering experiments to the identify key physical and chemical processes that control ignition, propagation and emissions of smoldering combustion. Please include research pictures which help to illustrate your research. Surrogate fuel samples composed of the main constituents found in plant litter (cellulose, hemicellulose and lignin) are burned in a controlled environment Parameters such as fuel content and density are systematically varied Infrared images and thermocouples are used to measure smoldering propagation velocities. Smoldering combustion of plant litter can destroy vegetation, release harmful pollutants and greenhouse gases, and transition to flaming combustion. By identifying key physics, more accurate and universal models can be developed and used 16

17 Laboratory-Scale Smoldering Research Recent Results The horizontal propagation velocity decreases with density Propagation velocity decreases as cellulose content increases (with proportionally lower hemicellulose content) when density is held constant Samples with 100% cellulose exhibit larger sensitivities to changes in density 17