Peter Therkelsen

Flashback and Turbulent Flame Speed Measurements in Hydrogen/Methane Flames Stabilized by a Low-Swirl Injector at Elevated Pressures and Temperatures

This paper reports flashback limits and turbulent flame local displacement speed measurements in flames stabilized by a low swirl injector operated at elevated pressures and inlet temperatures with hydrogen and methane blended fuels. The goal of this study is to understand the physics that relate turbulent flame speed to flashback events at conditions relevant to gas turbine engines. Testing was conducted in an optically accessible single nozzle combustor rig at pressures ranging from 1 to 8 atm, inlet temperatures from 290 to 600 K, and inlet bulk velocities between 20 and 60 m/s for natural gas and a 90%/10% (by volume) hydrogen/methane blend. The propensity of flashback is dependent upon the proximity of the lifted flame to the nozzle that is itself dependent upon pressure, inlet temperature, and bulk velocity. Flashback occurs when the leading edge of the flame in the core of the flow ingresses within the nozzle, even in cases when the flame is attached to the burner rim. In general the adiabatic flame temperature at flashback is proportional to the bulk velocity and inlet temperature and inversely proportional to the pressure. The unburned reactant velocity field approaching the flame was measured using a laser Doppler velocimeter with water seeding. Turbulent displacement flame speeds were found to be linearly proportional to the root mean square of the velocity fluctuations about the mean velocity. For identical inlet conditions, high-hydrogen flames had a turbulent flame local displacement speed roughly twice that of natural gas flames. Pressure, inlet temperature, and flame temperature had surprisingly little effect on the local displacement turbulent flame speed. However, the flow field is affected by changes in inlet conditions and is the link between turbulent flame speed, flame position, and flashback propensity.

Analysis of NOx Formation in a Hydrogen-Fueled Gas Turbine Engine

A commercially available natural gas fueled gas turbine engine was operated on hydrogen. Three sets of fuel injectors were developed to facilitate stable operation while generating differing levels of fuel/air premixing. One set was designed to produce near uniform mixing while the others have differing degrees of non-uniformity. The emissions performance of the engine over its full range of loads is characterized for each of the injector sets. In addition, the performance is also assessed for the set with near uniform mixing as operated on natural gas. The results show that improved mixing and lower equivalence ratio decreases NO emission levels as expected. However, even with nearly perfect premixing, it is found that the engine, when operated on hydrogen, produces a higher amount of NO than when operated with natural gas. Much of this attributed to the higher equivalence ratios that the engine operates on when firing hydrogen. However, even at the lowest equivalence ratios run at low power conditions, higher NO was observed. Analysis of the potential NO formation effects of residence time, kinetic pathways of NO production via NNH, and the kinetics of the dilute combustion strategy used are evaluated. While no one mechanism appears to explain the reasons for the higher NO, it is concluded that each may be contributing to the higher NO emissions observed with hydrogen. In the present configuration with the commercial control system operating normally, it is evident that system level effects are also contributing to the observed NO emission differences between hydrogen and natural gas. ASME Turbo Expo 2008: Power for Land, Sea, and Air Volume 3: Combustion, Fuels and Emissions, Parts A and B Berlin, Germany, June 9–13, 2008 Conference Sponsors: International Gas Turbine Institute ISBN: 978-0-7918-4313-0 | eISBN: 0-7918-3824-2 Copyright

Assessing the Control Systems Capacity for Demand Response in California Industries

Assessing the Control Systems Capacity for Demand Response in California Industries Girish Ghatikar, Aimee McKane, Sasank Goli, Peter Therkelsen, Daniel Olsen Lawrence Berkeley National Laboratory January 2012

Energy Efficiency Improvement and Cost Saving Opportunities for the Baking Industry: An ENERGY STAR® Guide for Plant and Energy Managers

The U.S. baking industry—defined in this Energy Guide as facilities engaged in the manufacture of commercial bakery products such as breads, rolls, frozen cakes, pies, pastries, and cookies and crackers—consumes over

Parametric Study of Low-Swirl Injector Geometry on its Operability

800 million worth of purchased fuels and electricity per year. Energy efficiency improvement is an important way to reduce these costs and to increase predictable earnings, especially in times of high energy price volatility. There are a variety of opportunities available at individual plants to reduce energy consumption in a cost-effective manner. This Energy Guide discusses energy efficiency practices and energy-efficient technologies that can be implemented at the component, process, facility, and organizational levels. Many measure descriptions include expected savings in energy and energy-related costs, based on case study data from real-world applications in food processing facilities and related industries worldwide. Typical measure payback periods and references to further information in the technical literature are also provided, when available. A summary of basic, proven measures for improving plant-level water efficiency is also provided. The information in this Energy Guide is intended to help energy and plant managers in the U.S. baking industry reduce energy and water consumption in a cost-effective manner while maintaining the quality of products manufactured. Further research on the economics of all measures—as well as on their applicability to different production practices—is needed to assess their cost effectiveness at individual plants.

Small-Scale HCCI Engine Operation

The low swirl injector (LSI) is a combustion technology being developed for low-emissions fuel-flexible gas turbines. The basic LSI configuration consists of an annulus of swirl vanes centered on a non-swirled channel, both of which allow for the passage of premixed reactants. LSIs are typically designed by following a general guidance of achieving a swirl number between 0.4 and 0.55. This paper aims to develop a more specific guideline by investigating the effects of varying geometry, i.e. vane angle, vane shape, and center channel size, on the LSI performance. A well-studied LSI provides a baseline for this investigation. Nine LSI variations from this baseline design have been evaluated. All LSI are tested with CH4 fuel at bulk flow velocity of 8 to 20 m/s firing into the open atmosphere. Performance metrics are the lean blowoff limit, the pressure drop, flowfield characteristics and emissions. Results show that the lean blow-off limit and NOx and CO emissions are insensitive to LSI geometric variations. The flowfields of seven LSIs exhibit self-similarity implying their turndown ranges are similar. Reducing the center channel size and/or the use of thin vanes instead of thickened vanes can reduce pressure drop across the LSI. Additionally, all ten LSI share a common feature in that 70% to 80% the premixture flows through the vane annulus. These findings are used to develop a more specific engineering guidelines for designing the LSI for gas turbines.Copyright

Evaluation of a Low Emission Gas Turbine Operated on Hydrogen

Homogeneous Charge Compression Ignition (HCCI) combustion in a small-scale engine (25 cc) was experimentally examined. Historically, HCCI combustion has been studied in engines sized for passenger vehicles and trucks (approximately 500 cc and larger). HCCI combustion in large-scale engines is characterized by higher efficiency than SI and CI combustion. High rates of heat flux, due to large surface area to volume ratio and engine body material, initially prevented the small-scale engine from operating in HCCI mode. The high level of heat transfer was overcome and sustained small-scale HCCI operation was achieved with n-heptane fuel. Large-scale HCCI engines utilize ultralow equivalence ratios to achieve high efficiencies. The small-scale HCCI engine could not operate with equivalence ratios lower than 0.73. Performance characteristics including power, efficiency, and NOx emissions of the small-scale HCCI engine were poorer than when operated in SI mode. Recommendations to overcome high rates of heat flux and increase small-scale HCCI engine efficiency are presented.

Aircraft Engine Electrical Power Generation With a SOFC Combustor

The ever increasing strain on traditional centralized power generation and distribution systems has led to an increase in the use of distributed generation (DG) technologies. DG technologies are commonly found in urban areas that are sensitive to criteria pollutants, and as a result, they are subject to increasingly stringent emission regulations. Paralleling the growth of installed DG is the ever-increasing interest in hydrogen as an alternative fuel to natural gas. As a hydrogen infrastructure is developed, a desire to use this new fuel for DG applications will evolve. Microturbine generators (MTGs) are one example of DG technology that has emerged in this paradigm and are the technology of interest in the present work. To evaluate the potential role for hydrogen fired MTGs in this paradigm, understanding of what emission levels can be expected from such a system is needed The current study retrofits a natural gas fired MTG for operation on hydrogen and characterizes the resulting operability and emissions performance. The results of implementing design changes to improve emissions performance while maintaining stability and safety of the MTG when operating on hydrogen fuel are presented. The results also show improved stability limits which are utilized to help attain lower emissions of NOx. Further optimization is needed to achieve the NOx levels necessary to meet current regulations.Copyright

Flashback, Blow Out, Emissions, and Turbulent Displacement Flame Speed Measurements in a Hydrogen and Methane Fired Low-Swirl Injector at Elevated Pressures and Temperatures

Next generation aircraft will require more onboard electrical power generation capacity as systems previously powered by engine bleed and hydraulics are electrified and new electricity based technologies are integrated. Increasing the amount of electrical power generated from aircraft main engines reduces thrust capacity and thrust specific fuel consumption (TSFC), but could increase specific fuel consumption (SFC). An alternative cycle with very high conversion efficiencies is proposed for electrical power production on aircraft. The unique cycle, termed a SOFC combustor, integrates a Solid Oxide Fuel Cell (SOFC) with existing onboard combustion based engines. The SOFC combustor produces direct current (DC) electrical power and provides high temperature exhaust for use in the expansion process of the aircraft engine. The SOFC combustor utilizes compressed air from the engine’s compressor and vaporized fuel to produce DC current. Fuel and air not utilized by the fuel cell are converted to thermal products by an aerodynamically stabilized combustion system capable of adapting to fuel/air and pressure variations. Hot products from the combustion system are returned to the main engines for use as thrust or mechanical shaft work. System level results will be presented for overall impact to aircraft engine specific fuel consumption.Copyright

CONCEPTUAL STUDIES OF A FUEL-FLEXIBLE LOW-SWIRL COMBUSTION SYSTEM FOR THE GAS TURBINE IN CLEAN COAL POWER PLANTS

This paper reports on a work in progress study measuring flashback, blow out, emissions and turbulent displacement flame speeds in a low swirl injector operated at elevated pressures and inlet temperatures with hydrogen and methane based fuels in an optically accessible combustor rig. The goal is to extend the knowledge of low-swirl flames at conditions relevant to gas turbine engines. Testing was conducted at pressures ranging from 3 to 6 atm, inlet temperatures from 290 to 600K, and inlet bulk velocities from 20 to 60 m/s for natural gas and a 90%/10% by volume hydrogen/methane blend. Blow out limits for natural gas were found to be independent of pressure and inlet temperature but weakly dependent on velocity. Flashback limits for hydrogen were found to be independent of inlet temperature but strongly dependent on velocity and pressure. Local displacement turbulent flame speeds for methane were measured and appear to coincide with atmospheric pressure data in the literature. NOx emissions for both fuels were found to be exponentially dependent upon firing temperature, but emissions for the high hydrogen content flames were consistently higher than natural gas flames.Copyright