Well-defined Boundary Conditions Research Articles

Multi-parameter diagnostics for high-resolution in-situ measurements of single coal particle combustion

To study volatile combustion processes of single coal particles non-intrusive simultaneous multi-parameter measurements were performed. The experiment was carried out in a fully premixed flat flame burner with well-defined boundary conditions. For flame visualization high-speed luminescence imaging was combined with high-resolution high-speed OH-PLIF. To address particle size and shape a stereoscopic high-resolution backlight-illumination system was set up. Due to simultaneous recording of individual particle events the volatile combustion duration related to particle size, shape and velocity was measured. A comparison of luminescence imaging and OH-PLIF for flame visualization was investigated to define their application areas in coal combustion. The stereoscopic backlight-illumination setup was benchmarked to a well characterized bituminous coal. With a pixel resolution of ∼2.5 µm fine particle contours were resolved. The particle diameter and eccentricity were evaluated by an ellipse approximation. The experimental setup can be used to investigate different coal ranks and biomass in N2/O2 and CO2/O2 atmospheres in future.

Experimental evaluation of a novel solar receiver for a micro gas-turbine based solar dish system in the KTH high-flux solar simulator

This work presents the experimental evaluation of a novel pressurized high-temperature solar air receiver for the integration into a micro gas-turbine solar dish system reaching an air outlet temperature of 800 °C. The experiments are conducted in the controlled environment of the KTH high-flux solar simulator with well-defined radiative boundary conditions. Special focus is placed on providing detailed information to enable the validation of numerical models. The solar receiver performance is evaluated for a range of operating points and monitored using multiple point measurements. The porous absorber front surface temperature is measured continuously as it is one of the most critical components for the receiver performance and model validation. Additionally, pyrometer line measurements of the absorber and glass window are taken for each operating point. The experiments highlight the feasibility of volumetric solar receivers for micro gas-turbine based solar dish systems and no major hurdles were found. A receiver efficiency of 84.8% was reached for an air outlet temperature of 749 °C. When using a lower mass flow, an air outlet temperature of 800 °C is achieved with a receiver efficiency of 69.3%. At the same time, all material temperatures remain below permissible limits and no deterioration of the porous absorber is found.

A Pressurized Vitiated Co-Flow Burner and Its Preliminary Application for a Methane Lifted Flame

A new pressurized vitiated co-flow burner (PVCB) was designed and built for the investigation of lifted flame properties and was supported by a vitiated co-flow of hot combustion products from a lean H2/air flame at a controllable pressure; its preliminary application for a methane lifted flame was tested. The distribution of the co-flow temperature, oxygen mole fraction, flow rate, and pressure of the PVCB was measured and calculated. The research results show that the co-flow temperature range is from 300 to 1300 K, the background pressure range is from 1 to 1.5 bar, the stable temperature field of the PVCB is wider, and the background pressure of the PVCB can be controlled. The simulation results show that the PVCB provides a controllable, pressurized co-flow of hot and vitiated gases, which makes it possible to investigate flame stabilization mechanisms. The PVCB has the advantages of controllable background pressure and a stable temperature field. The well-defined uniform boundary conditions and simplified flow of the PVCB simplify the establishment of a numerical model and decouple the turbulent chemical kinetics from the complex recirculating flow. It can be widely used in the research on lifted flames. A lifted flame of methane was recorded under conditions of a co-flow temperature of 1133 K and pressure from 1 to 1.043 bar. The lift-off height decreased and stabilized with the increase in the background pressure. The laminar flame speed and the autoignition delay time were tested and simulated at the same time by Chemkin; the influence of background pressure on the lift-off height, laminar flame speed, and autoignition delay were analyzed. The results show that the autoignition, as well as the flame propagation, dominated the stabilization mechanism of the lifted flame in the PVCB.

Derivation of an inhalation TTC for the workplace based on DNEL values reported under REACH

The Threshold of Toxicological Concern (TTC) concept defines a generic tolerable exposure for chemicals of unknown toxicity below which the risk of adverse health effects is considered very small. The original concept was refined and extended over the years, based either on differentiated structural classes or on additional information on certain toxicological endpoints. Initially, the focus of the TTC application was only on systemic toxic effects after repeated oral intake and consisted of one value.However, under well-defined boundary conditions, a long-term systemic inhalation TTC could also serve as a cut-off criterion for occupational exposure in those cases where workers are exposed to very low levels of chemicals by inhalation contact and could therefore reduce the need to perform animal tests.Within the scope of the European REACH legislation, several thousand systemic long-term inhalation Derived No Effect Levels (DNELs) for workers have been published. By statistical evaluation of the DNEL distribution of 1876 chemicals and the resulting 99th percentiles, we propose an inhalation workplace TTC for systemic effects in the region of 50 μg/m3 (7 μg/kg body weight/day). Specific exclusion criteria apply for the discussed concept.

Charge and discharge behavior of elemental sulfur in isochoric high temperature thermal energy storage systems

Thermal energy storage with elemental sulfur is a low-cost alternative to molten salts for many medium to high-temperature energy applications (200–600 °C). In this effort, by examining elemental sulfur stored isochorically inside isolated pipes, we find that sulfur provides attractive charge/discharge performance since it operates in the liquid-vapor regime at the temperatures relevant to many important applications, such as combined heat and power (CHP) plants and concentrating solar power (CSP) plants with advanced power cycle systems. The isolated pipe configuration is relevant to shell-and-tube thermal battery applications where the heat transfer fluid flows over the storage pipes through the shell. We analyze the transient charge and discharge behavior of sulfur inside the pipes using detailed computational modeling of the complex conjugate heat transfer and fluid flow phenomena. The computational model is validated against experiments of a single tube with well-defined temperature boundary conditions and internal temperature measurements. The model results evaluate the influence of pipe diameter on charge and discharge times, heat transfer rate, and Nusselt number due to buoyancy driven convection currents. Depending on the Rayleigh number (pipe diameter), the average Nusselt number obtained for discharge is 3–14 times higher than proposed solid-liquid phase change technologies based on molten salt, which are limited in their performance due to conduction based solidification and low thermal conductivity. The results show competing trade-offs between increase in heat transfer coefficient, thermal energy stored in sulfur, and increase in charge and discharge time with increase in pipe diameter. A preferred pipe diameter can be determined for target applications based on their requirements and these competing trade-offs. A validated fundamental correlation for Nusselt number as a function of Rayleigh number for charge and discharge is developed that can be used to design the sulfur-based thermal storage system for transient operation.

Influential factors in volume change measurements for cementitious materials at early ages and in isothermal conditions

Early age deformations, when restrained, lead to an increase of cracking risk of the material, especially in the case of high strength materials to which we apply modern high energy mixing techniques which accelerate initial hydration rate. The experimental campaign aims to investigate and understand the differences not yet explained between several autogenous measurement techniques, such as the initial swelling measured by the linear devices that is not observed in the case of volumetric measurements. The differences between the results obtained by means of devices when values are zeroed at setting time can be imputed to the intrinsic behaviour of the material within the well-defined boundary conditions imposed by the molds, and not only to the measurement artefact.

Quenching of Premixed Flames at Cold Walls: Effects on the Local Flow Field

The presence of a turbulent premixed flame strongly influences the properties of the adjacent velocity boundary layer. This influence is studied here using a generic configuration where at atmospheric pressure turbulent premixed methane/air flames interact with a temperature stabilized wall. The experiment is optimized for well-defined boundary conditions and optical accessibility in the zone where the flame impinges at the wall. Laser based diagnostic methods are used to measure two components of the velocity field by particle image velocimetry simultaneously with the flame front position using laser induced fluorescence of the OH molecule. Two measurement planes are selected that are aligned perpendicularly to the surface of the wall. Based on this data, the flow field near the wall is analyzed by different methodologies using laboratory-fixed and flame-conditioned statistics, a quadrant splitting analysis of the Reynolds stresses and an evaluation of the production term of the turbulent kinetic energy. The results of chemically reactive cases are compared to their corresponding non-reactive flows for otherwise identical inflow conditions. In the zone of flame-wall interactions the boundary layer structure and its turbulence are dominated by the turbulent flame. Important features are that the flame compresses the boundary layer already upstream the location where the flame is finally quenched and that ejection and sweeps are no longer the dominant mechanisms as in non-reactive boundary layers. This experimental data may serve additionally as a database for model development for near wall reactive flows.

Influence of Single-Component Fuels on Gas-Turbine Model Combustor Lean Blowout

The influence of selected single-component hydrocarbons on lean blowout behavior of swirl-stabilized spray flames was investigated. Additional information on the spray characteristics was collected by phase Doppler interferometry and Mie scattering measurements. The measurements were accomplished in a gas-turbine model combustor under atmospheric pressure and at two different air preheat temperatures. The combustor featured a dual-swirl geometry and a prefilming airblast atomizer. The combustion chamber provided good optical access and yielded well-defined boundary conditions. Three single-component hydrocarbons were chosen: one short and one long linear alkane (-hexane and -dodecane) as well as one branched alkane (iso-octane). Kerosene Jet A-1 was used as a reference. Results show noticeable differences in the lean blowout limits of the various fuels, at comparable flow conditions. By using the results of the measurements, of additional modeling, and of an assessment of the fuel properties, it was concluded that fuel differences in lean blowout in this combustor can be due to differences in the physical properties as well as in the chemical properties.

Sidewall quenching of atmospheric laminar premixed flames studied by laser-based diagnostics

Flame-wall interactions (FWI) of laminar premixed methane-air flames at atmospheric pressure are studied using various laser diagnostic methods. Velocity fields and flame front locations are measured simultaneously by two-component particle image velocimetry (PIV) and planar laser induced fluorescence (LIF) of the OH-radical. Coherent anti-Stokes Raman spectroscopy (CARS) and two-photon LIF of the CO molecule are used to determine temperatures and CO concentrations. The FWI process is investigated using a generic burner setup with well-defined boundary conditions, where one branch of a V-shaped flame interacts with a water-cooled stainless steel wall, corresponding to a sidewall quenching (SWQ) geometry. FWI is studied for equivalence ratios of ϕ =0.83, 1.0 and 1.2. The quenching distance of the flames is determined using two different methods. Additionally, the near wall behavior of the flame consumption speed is analyzed and compared with that of a freely propagating laminar flame. Thermochemical properties are analyzed using CO/T-state diagrams. Comparison to one-dimensional laminar flame calculations undisturbed by the presence of a wall highlights the severe impact upon thermochemical states. Comparing characteristic time scales of heat transfer processes to chemical processes indicates that diffusion rather than chemical reaction processes is the reason for these observations.

CFD modelling of hydrogen stratification in enclosures: Model validation and application to PAR performance

Computational Fluid Dynamics (CFD) models are maturing into useful tools for supporting safety analyses. This paper investigates the capabilities of CFD models for predicting hydrogen stratification in a containment vessel using data from the NEA/OECD SETH2 MISTRA experiments. Further simulations are then carried out to illustrate the qualitative effects of hydrogen stratification on the performance of Passive Autocatalytic Recombiner (PAR) units. The MISTRA experiments have well-defined initial and boundary conditions which makes them well suited for use in a validation study. Results are presented for the sensitivity to mesh resolution and mesh type. Whilst the predictions are shown to be largely insensitive to the mesh resolution they are surprisingly sensitive to the mesh type. In particular, tetrahedral meshes are found to induce small unphysical convection currents that result in molecular diffusion and turbulent mixing being under-predicted. This behaviour is not unique to the CFD model used here (ANSYS CFX) and furthermore, it may affect simulations run on other non-aligned meshes (meshes that are not aligned perpendicular to gravity), including non-aligned structured meshes. Following existing best practice guidelines can help to identify potential unphysical predictions, but as an additional precaution consideration should be given to using gravity-aligned meshes for modelling stratified flows. CFD simulations of hydrogen recombination in the Becker Technologies THAI facility are presented with high and low PAR positions and homogeneous and stratified initial hydrogen distributions. For the stratified initial hydrogen distribution, as expected, the high PAR location performs better than the low positioned PAR. However, for the homogeneous initial hydrogen distribution, the low PAR location performs better than the high PAR. The work demonstrates that CFD can be a useful tool to help inform the positioning of PAR units, which may provide a practicable risk-reduction measure for situations where hydrogen releases are possible.

Slat Noise: Aeroacoustic Beamforming in Closed-Section Wind Tunnel with Numerical Comparison

Experiments in closed-section wind tunnels are more suitable for comparisons with numerical results than corresponding experiments in open-section tunnels because well-defined boundary conditions far from the model can be established for the numerics. This paper reports acoustic experimental results on the slat region of a two-dimensional high-lift model. An objective was the production of experimental data to be used in the testing of numerical procedures. Conventional beamforming combined with a deconvolution technique was used. The Reynolds number was approximately 1 million, whereas Mach number and angle of attack ranged from ~0.07 to and 2 to 10 deg, respectively. To prevent interaction between wind-tunnel-wall boundary layers and the model, which causes undesirable three-dimensionality, suction was applied on the wind-tunnel walls, and its effect was investigated. Experimental results for two angles of attack were compared with computational results given by a lattice–Boltzmann solver for the validation of the experimental procedure based on side-wall suction and deconvolved source map computations. The results agreed, in particular regarding the dominant parts of the spectra, and were considered a cross validation of both experimental and numerical approaches. The numerical results were used in the characterization of the flow in the slat cove.

Progress in study of low-energy photoelectron in ultra-fast strong fields-analytical R-matrix theory based semiclassical trajectory method

The semi-classical method based on the recently developed analytical R-matrix theory is reviewed in this work. The method is described with the application to ultra-fast strong-field direct ionization of atoms with one active electron in a linearly polarized field[Torlina L, Smirnova O 2012 Phys. Rev. A 86 043408]. The analytical R-matrix theory separates the space into inner and outer regions, naturally allowing the possibility of an analytical or semi-analytical description of wave function in the outer region, which can be approximated by Eikonal-Volkov solutions while the inner region provides well-defined boundary conditions. Applying the stationary phase method, the calculation of the ionization amplitude is cast into a superposition of components from trajectories and their associated phase factors. The shape of the tunneling wave packets associated with different instants of ionization is presented. It shows the exponential cost of deviating from the optimal tunneling trajectory renders the tunneling wave packet a Gaussian shape surrounding the semi-classical trajectory. The intrinsically non-adiabatic corrections to the sub-cycle ionization amplitude in the presence of both the Coulomb potential and the laser field is shown to have different influences on the probability of ionization. As a specific study case, soft recollisions of the released electron near the ionic core is investigated by using pure light-driven trajectories with Coulomb-corrected phase factor[Pisanty E, Ivanov M 2016 Phys. Rev. A 93 043408]. Incorporating the Coulomb potential, it is found problematic to use the conventional integration contour as chosen in other methods with trajectory-based Coulomb corrections, because the integration contour may run into the Coulomb-induced branch cuts and hence the analyticity of the integrand fails. In order to overcome the problem, the evolution time of the post-tunneling electron is extended into the complex domain which allows a trajectory to have an imaginary component. As the soft recollision occurs, the calculation of the ionization amplitude requires navigating the branch cuts cautiously. The navigating scheme is found based on closest-approach times which are the roots of closest-approach times equations. The appropriately selected closest-approach times that always present in the middle of branch-cut gate may serve to circumvent these branch cuts. The distribution of the closest-approach times presents rich geometrical structures in both the classical and quantum domains, and intriguing features of complex trajectories emerge as the electron returns near the core. Soft recollisions responsible for the low-energy structures are embedded in the geometry, and the underlying emergence of near-zero energy structures is discussed with the prediction of possible observations in experiments.

Characterization of Liquid Water Saturation in Gas Diffusion Layers by X-Ray Tomographic Microscopy

Performance and durability of polymer electrolyte fuel cells are closely related to the water management. In gas diffusion layers (GDL), the presence of liquid water is associated with mass transport losses. For optimization of the materials, mechanisms and parameters influencing the water saturation have to be understood. Ex-situ water injection and withdrawal experiments, allowing for well-defined boundary conditions, have been performed with three different GDL materials, using X-ray tomographic microscopy to image the liquid water phase on the pore scale of the materials. The liquid saturation in the GDLs has been imaged as function of the capillary pressure. The results reveal that, due to the anisotropic structure of the GDLs, transport of water occurs mainly in the through-plane direction via parallel water paths. When the GDL is coated with a microporous layer (MPL), liquid saturation requires higher capillary pressure to overcome the MPL/GDL mixed region where pore and throat sizes are reduced and the water paths are restricted to the crack regions of the MPL.

The flow field in a high aspect ratio cooling duct with and without one heated wall

The flow in a high aspect ratio generic cooling duct is described for different Reynolds numbers and for adiabatic as well as non-adiabatic conditions. The Reynolds number is varied in a range from 39,000 to 111,000. The generic cooling duct facility allows for applying a constant temperature on the duct’s lower wall, and it ensures having well-defined boundary conditions. The high-quality, optical noninvasive measurement methods, namely Particle Image Velocimetry (2C2D-PIV, i.e., two velocity components in a plane), Stereo Particle Image Velocimetry (3C2D-PIV, i.e., three velocity components in a plane) and Volumetric Particle Tracking Velocimetry (3C3D-PTV, i.e., three velocity components in a volume), are used to characterize the flow in detail. Pressure transducers are installed for measuring the pressure losses. The repeatability and the validity of the data are discussed in detail. For that purpose, modifications in the test facility and in the experimental setup as well as comparisons between the different measurement methods are given. A focus lies on the average velocity distribution and on the turbulent statistics. The longitudinal velocity profile is analyzed in detail for Reynolds number variations. Secondary flows are identified with velocities of two orders of magnitude smaller than the longitudinal velocity. Reynolds stress distributions are given for several different cases. The Reynolds number dependency of \(\overline{u'^2}\) and \(\overline{v'^2}\) is shown, and a comparison between the adiabatic and the heated case is given. \(\overline{u'^2}\) changes significantly when the lower wall heat flux is applied, whereas \(\overline{v'^2}\) and \(\overline{u'v'}\) almost stay constant.

A new well-posed vorticity divergence formulation of the shallow water equations

A new vorticity–divergence formulation of the two-dimensional shallow water equations including boundary conditions is derived. The new formulation is necessary since the conventional one does not lead to a well-posed initial boundary value problem for limited-area modelling.The new vorticity–divergence formulation includes four dependent variables instead of three and requires more equations and boundary conditions than the conventional formulation. On the other hand, it forms a hyperbolic set of equations with well-defined boundary conditions that leads to a well-posed problem with bounded energy.

Numerical Solutions By Method of Lines Approach for Fluid Flow in a Modified Rotating Disk Electrode Apparatus

Studying the reaction kinetics of the electrochemical redox reactions on a rotating disk electrode (RDE) is a well-known technique to access kinetic information under various competing levels of kinetic and diffusion dominated conditions. Reactions of flow batteries are typically carried out on graphite felt electrode surfaces at both cell and stack level. But the kinetics of the both positive (VO2 +/VO2+) and negative (V3+/V2+) redox couple reactions are not well understood, as there is no clear agreement of redox kinetics information available in literature1-2for these electrolytes. Porous rotating disk electrode (PRDE) is a commonly used technique to study the kinetics of graphite felt electrodes. A semi-infinite condition is typically used to arrive at well-known Levich profiles for velocity and limiting current analysis for rotating disk electrodes3. However, this type of analysis didn’t account for the data observed for felt electrodes in a RDE set up. To obtain a numerical solution for fluid flow around a rotating disk electrode in a modified RDE setup is proposed in this work as shown in Figure 1. In this setup, the boundary conditions at the stationary walls, rotating walls and axial symmetry are well-defined. This method can be used for obtaining primary and secondary distributions effectively in electrochemical systems efficiently and also for simulating flow problems4. Numerical solutions with well-defined boundary conditions will help in enhancing the reliability of the simulated results. In this 2D fluid flow model, an axially symmetric cylindrical geometry is used and fluid flow was assumed to vary in radial (r) and axial (z) directions, whereas azimuthal (θ) dependence of fluid flow is ignored. Three components of Navier-Stokes equations (r, θ and z) and a continuity equation represent the fluid flow outside the rotating disk electrode. The velocities (ur, u θ and uz ), pressure and radial and axial distances were non-dimensionalized through a method, using fluid properties and angular velocity, as reported in literature5. The 2D model equations were simulated using a new technique in which numerical method is applied in the z-direction and the resulting equations are integrated using efficient Boundary value problem (BVP) solvers in r. Efficiency and accuracy of the proposed method compared with different finite difference and discretization schemes in r will be presented. Acknowledgement: This work was supported by a contract from The American Chemical Society- Petroleum Research Fund (ACS-PRF) Grant PRF# 52588-ND10.

Determination of the fraction of plastic work converted into heat in metals

A new approach for measuring the fraction of plastic work that is converted into heat (also known as the Inelastic Heat Fraction, IHF or the Taylor–Quinney coefficient) during the plastic deformation of metals is proposed in this paper. The method is based on the uniaxial tension of a slender metal rod, with the lateral surface of the rod being under well-defined thermal boundary conditions. The corresponding one-dimensional model of heat transfer during the process is considered in the form that accounts for all major effects. The current approach is based on the fact that the unknown IHF enters this heat equation linearly and therefore can be found explicitly if all the other terms are accounted for experimentally. The experimental procedure developed is based on local measurements of temperature and its gradients and of strain and velocity with the aid of an infrared (IR) camera and a Digital Image Correlation (DIC) system, respectively. A vacuum tube that encloses the specimen was designed to provide control over the heat losses due to convection during the test. A fitting method based on Hermite splines allows us to deal with smooth functions instead of noisy data sets, improving the overall accuracy of the procedure. The IHF is obtained as a function of plastic strain for a set of strain rates for four materials: 303 and 316 stainless steels, commercially-pure titanium (CP Ti) and the alloy Ti–6Al–4V. The findings indicate that the IHF is not constant with the plastic strain and furthermore, it is also sensitive to the strain-rate. Our measurements revealed that depending on the material the IHF was generally between 0.55 and 0.8, but it could also be as low as 0.3.

The Landscape Evolution Observatory: A large-scale controllable infrastructure to study coupled Earth-surface processes

Zero-order drainage basins, and their constituent hillslopes, are the fundamental geomorphic unit comprising much of Earth's uplands. The convergent topography of these landscapes generates spatially variable substrate and moisture content, facilitating biological diversity and influencing how the landscape filters precipitation and sequesters atmospheric carbon dioxide. In light of these significant ecosystem services, refining our understanding of how these functions are affected by landscape evolution, weather variability, and long-term climate change is imperative. In this paper we introduce the Landscape Evolution Observatory (LEO): a large-scale controllable infrastructure consisting of three replicated artificial landscapes (each 330m2 surface area) within the climate-controlled Biosphere 2 facility in Arizona, USA. At LEO, experimental manipulation of rainfall, air temperature, relative humidity, and wind speed are possible at unprecedented scale. The Landscape Evolution Observatory was designed as a community resource to advance understanding of how topography, physical and chemical properties of soil, and biological communities coevolve, and how this coevolution affects water, carbon, and energy cycles at multiple spatial scales. With well-defined boundary conditions and an extensive network of sensors and samplers, LEO enables an iterative scientific approach that includes numerical model development and virtual experimentation, physical experimentation, data analysis, and model refinement. We plan to engage the broader scientific community through public dissemination of data from LEO, collaborative experimental design, and community-based model development.

Assessment of the structural stability of Blockhaus timber log-walls under in-plane compression via full-scale buckling experiments

Blockhaus structural systems are obtained by assembling multiple timber logs able to interact with each other by means of simple mechanisms (e.g. contacts, tongues and grooves, and carpentry joints, also referred to as ‘corner’ joints). Although these systems have ancient origins, the structural behaviour of Blockhaus systems under well-defined loading and boundary conditions is still complex to predict. The paper focuses on the assessment of the typical buckling behaviour and resistance of in-plane compressed timber log-walls. The effects of various mechanical and geometrical aspects such as in-plane rigid inter-storey floors, load eccentricities, different types of lateral restraints, openings (e.g. doors or windows) or additional metal stiffeners, are investigated by means of full-scale buckling experiments. Results are then critically discussed and preliminarily assessed via analytical formulations taken from classical theory of plate buckling and column buckling. Although further advanced studies are required for the development of a generalized buckling design method, it is shown that several mechanical and geometrical aspects should be properly taken into account to correctly predict the structural capacity of Blockhaus systems under in-plane compression.

Global characteristics of non-premixed jet flames of hydrogen–hydrocarbon blended fuels

Blending hydrogen into hydrocarbon fuels can reduce the carbon-intensity of the fuel and extend the lean flammability limit. However, limited information is available of the global performance of attached, non-piloted hydrogen–hydrocarbon jet flames under well-defined boundary conditions. Three groups of blended fuels were investigated in the current study: Natural gas +H2 (with H2 volume fraction varying from 18.6% to 100%), C2H4+H2 (with H2 volume fraction varying from 0% to 100%), and 40% C2H4+41% H2+19% N2. Measurements were performed of flame dimensions, radiant fraction, and emission indices of NOx and CO. For flames with constant exit strain rate, the increase of hydrogen volume fraction was found to decrease the radiant fraction, decrease the global residence time and increase the NOx emission index. For flames of the same fuel composition, a higher strain rate results in a lower radiant fraction. The NOx production rate scales with the reciprocal of non-adiabatic flame temperature, consistent with the thermal NOx mechanism. The CO/CO2 ratio is determined by the competing influences of flame residence time, carbon input rate and mixing rate of the fuel and air.