The experiments were carried out in the mass spectrometry department at the Institute of Combustion Technology, Deutsches Zentrum f&#252;r Luft- und Raumfahrt (DLR) in Stuttgart, Germany. The work was also supported by the Helmholtz Energy-Alliance &#34;Synthetic Liquid Hydrocarbons&#34;, the Center-of-Excellence &#34;Alternative Fuels&#34; and the DLR project &#34;Future Fuels&#34;. The authors wish to thank Patrick Le Clercq and Uwe Riedel for fruitful discussions on jet fuels.

1. Setup of the molecular beam mass spectrometer (MBMS) and flow reactor system
<ol>
	<li>Heat oven to designated start temperature, which is the highest temperature in designated measurement series. For typical conditions of Jet A-1 with &#934;=1, total oxidation is observed below 850 &#176;C (~1,100 K). The choice of proper starting temperatures depends on the chemical nature of the investigated fuel and the stoichiometry (&#934;).</li>
	<li>Prepare Time-of-Flight (TOF) spectrometer for intermediate species detection. The TOF spectrometer is aligned to the molecular beam and thus provides reliable detection of labile species. 
	NOTE: The mass resolution is suitable for the determination of the elemental composition in a C/H/O system. To avoid fragmentation, chose soft ionization conditions. Values of typically 9.5 to 10.5 eV have been proven suitable for a typical investigation of combustion intermediates.</li>
	<li>Prepare quadrupole spectrometer for major species detection. 
	NOTE: Because the quadrupole spectrometer (also called Residual Gas Analyzer, RGA) is placed inside the ionization chamber of the MBMS system nearby the molecular beam, just the wall-scattered background gases are measured. Since major species are stable, the background pressure well reflects their concentration at the sampling tip. For better signal-to-noise ratio, chose a high ionization energy of 70 eV in this case.</li>
</ol>
2. Preparation of the fuel sample
<ol>
	<li>Prepare the metal syringe for fuel supply. 
	Caution: Use proper personal protective equipment for fuel handling.
	<ol>
		<li>Fill 30 mL of the fuel sample to the vaporizers metal syringe.</li>
		<li>Pressurize fuel supply system (metal syringe) up to 5 bar by adding pressurized air to the system though opening the valve.</li>
		<li>Vent fuel lines and Coriolis mass flow meter by opening the valves in the fuel supply lines.</li>
	</ol>
	</li>
	<li>Heat up the vaporizer and gas supply lines. In the given setup, temperatures far below the normal pressure boiling point can be applied due to the high dilution. Ensure that the vapor pressure at the designated temperature of the highest boiling compound of the fuel is higher than its partial pressure in the gas stream. Typically, 200 &#176;C is adequate for Jet A-1.</li>
	<li>Note that the coldest spot in the system is the tempered inlet flange to the oven. Make sure the diluted fuel cannot recondense at this spot. For typical Jet A-1 (99% dilution) setting the water cooling system to 80 &#176;C is adequate.</li>
</ol>
3. Measurement and data acquisition
<ol>
	<li>Place oven to the sampling position. The sampling cone must be placed inside the oven&#39;s ceramic tube. In the present experiment, the sampling location is close to the plateau value of the spatial temperature profile of the oven. 
	NOTE: The picture in Figure 1 shows the cone and the reactor. The heated reactor (blue) is moved on rails towards the quartz cone.</li>
	<li>Start diluent of choice by adding gas through the Coriolis mass flow meter. 
	NOTE: The mass flow meters are controlled by the original software package. Here, mass flow values can be set. Typically, 99% argon is used. In general, for liquid fuels, the diluent flow may be split to vaporizer and oxidizer gas streams by using an additional Coriolis mass flow meter parallel to Cori Flow 2 passing the heated line and connected directly to the oxidizer stream from Cori Flow 3.</li>
	<li>Start continuous data recording (TOF and Quadrupole) by using the designated instrumental software. 
	NOTE: Click Start-Button in Quadrupole software. Click Start-Button in TOF software.
	<ol>
		<li>Add oxidizer O2 by setting the appropriate flow condition of the Coriolis flow meter software. Observe the incoming oxidizer as new peak in mass spectrum.</li>
	</ol>
	</li>
	<li>Add fuel by setting the appropriate flow condition of the Coriolis mass flow meter.
	<ol>
		<li>Check spectra. If complete oxidation in case of lean and stoichiometric conditions is achieved, observe a stable CO2 mass signal.</li>
	</ol>
	</li>
	<li>When signal intensities are stable for 4 to 5 measurements, a stabilization period ends. After the stabilization period, apply the continuous temperature decay ramp of typically -200 K/h to the oven. This leads to typical measurement times of 2 h per measurement run.
	<ol>
		<li>At a specific oven temperature during the ramp, observe a rapid change of the mass spectra. Sole combustion products (H2O, CO2 and CO, H2 in rich cases) start to disappear and small combustion intermediates become detectable. 
		NOTE: With further decreasing temperature, visible intermediates become larger and larger. At cold oven temperatures, only the signal of fuel compounds and oxygen can be observed; no reactions are taking place within the present residence time of the reactor.</li>
	</ol>
	</li>
	<li>When the final temperature is stabilized (typically 500 &#176;C; 10 min), switch off the oxidizer.
	<ol>
		<li>Continue recording measurements. Obtain fuel characterization (composition of fragmentation) measurements at conditions without oxidizer.</li>
	</ol>
	</li>
	<li>Switch off fuel in the Coriolis mass flow meter software by setting the value to 0. Data will be still recorded; use these spectra for background measurement.</li>
	<li>Stop data recording by clicking the stop button in the software.</li>
</ol>
4. Calibration measurements
<ol>
	<li>For calibration issues, mount a closed chamber in front of the sampling cone. 
	NOTE: The closed chamber is a tube, which is placed in front of the nozzle by hand.</li>
	<li>Open valve to pump. The chamber is evacuated.</li>
	<li>Apply binary mixtures (hydrocarbon of interest and Ar) or commercial calibration gasses for calibration. For demonstration, a customized gas mixture with CO and CO2 and argon is used here.</li>
	<li>Adjust the pressure in the calibration chamber by a needle valve to obtain signal intensity above the signal-to-noise ratio and below the saturation limit.</li>
	<li>Start calibration measurements by starting data recording as performed for the individual measurement in 3.5 by clicking the start button in the TOF software.</li>
</ol>
5. Data processing
NOTE: Recoded spectra must be matched to the respective oven temperature they are recorded at.
<ol>
	<li>At each recorded temperature, for each chosen species, calculate its mole fraction from the corresponding signal. Plot the mole fraction profiles vs. oven temperature (Figure 3).</li>
</ol>

<ol>
	<li>Moore, R. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biofuel+blending+reduces+particle+emissions+from+aircraft+engines+at+cruise+conditions.">Biofuel blending reduces particle emissions from aircraft engines at cruise conditions.</a> Nature. 543 (7645), 411-415 (2017).</li><li>Braun-Unkhoff, M., Kathrotia, T., Rauch, B., Riedel, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=About+the+interaction+between+composition+and+performance+of+alternative+jet+fuels.">About the interaction between composition and performance of alternative jet fuels.</a> CEAS Aeronautical Journal. 7 (1), 83-94 (2016).</li><li>Egolfopoulos, F. 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The authors have nothing to disclose.

The presented combination of an atmospheric high-temperature flow reactor with a molecular-beam mass spectrometry detection system enables quantitative speciation data for a range of operating conditions. Several studies21,22,23,27 demonstrated the flexibility of the experiment starting from rich methane conditions relevant for partial oxidation phenomena (&#966; = 2.5), to investigating the co...

Understanding combustion processes in the wake of modern, low-emission fuels from renewable resources is a challenge for today&#39;s societies&#39; ecological and economic topics. They have the potential to reduce our dependence on fossil fuels, offset CO2 emissions, and have a positive impact on harmful pollutant emissions such as soot and its toxic precursors1. Combining this fast growing field with their utilization in modern combustor systems, the demand on a fundamental understanding of the governing chemical and physical processes has increased dramatically2. Even today, the complex chemical reaction networks resulting from the radical chain reactions are still not fully understood. To analyze or even control phenomena like pollutant formation or (auto) ignition processes, the detailed knowledge of chemical reaction networks is a crucial piece of the puzzle3.
To investigate and understand those chemical reaction networks, experimental and numerical approaches are mandatory. Experimentally, the combustion chemistry is typically studied by applying experiments with simplified and well controlled flow environments to target specific questions. The high complexity and dynamics of individual sub processes prevent exact reproduction of the conditions of technical combustors by the fundamental experiments, while allowing the tracking of the designated key features such as temperature, pressure, heat release, or chemical species. Early on, the need for different experimental approaches became apparent, each tackling a specific question and providing a subsequent set of information contributing to the overall global picture of the combustion chemistry. To cover the full range of conditions and gather those subsequent information sets to describe complex conditions occurring in technical systems various approaches were successfully developed. Well established techniques include:
<ul>
	<li>Shock tubes4,5,6 and rapid compression machines7. These devices provide high control of pressure and temperature over a wide range. However, the accessible reaction time and suitable analytical techniques are limited.</li>
	<li>Laminar premixed flames3,8,9,10,11 are ideal to gain high-temperature conditions in combination with a simple flow field. Since the spatial dimension of the reaction zone decreases with increasing pressure, premixed flames are typically investigated at low-pressure conditions for speciation purposes.</li>
	<li>Counterflow diffusion flames12,13,14,15 are ideal for investigating the flamelet regime in turbulent combustion. They mimic the strain due to inhomogeneities in a real turbulent flow, but are, again, highly limited in analytical speciation techniques.</li>
	<li>Various reactor experiments16,17,18 (static, stirred and plug-flow) provide access to high-pressure environments, while temperatures are typically lower compared to flame environments. Common approaches are:
	<ul>
		<li>Static reactors are widely used for e.g. pulse photolysis experiments, but are in general limited by long residence times and low temperatures.</li>
		<li>Jet-stirred reactors, i.e. gas version of a perfectly stirred reactor (PSR), rely on the efficient mixing of the gas phase and can be operated at steady state with constant residence time, temperature and pressure, making it easy to model. However, molecules have time to migrate to the hot surfaces and undergo heterogeneous reactions.</li>
		<li>Numerous flow reactor approaches are known, with the plug flow reactor (PFR) as one of the most popular approaches for describing chemical reactions in continuous, flowing systems of cylindrical geometry. Plug flow conditions at steady state are assumed with fixed residence time of the plug as a function of its position for ideal PFRs.</li>
	</ul>
	</li>
</ul>
Complementary to those valuable techniques in the field of experimental combustion kinetics, a high-temperature laminar flow reactor experiment19,20 employing the molecular beam mass spectrometry (MBMS) technique for tracing species development in detail is presented21,22 herein. Laminar flow conditions, working at atmospheric pressure and accessible temperatures up to 1,800 K are the main characteristics of the flow reactor, while the sensitive MBMS technique allows the detection of almost all chemical species present in the combustion process. This includes highly reactive species such as radicals that are not or hardly traceable with other detection methods. The MBMS technique is widely used for the detailed investigation of reaction networks in flames of conventional and modern alternative fuels, such as alcohols or ethers23,24,25 and has demonstrated to be of great value for modern kinetic model development.
Figure 1 shows the schematic of the high-temperature flow reactor with a zoomed frame of the sampling probe (A) and two pictures highlighting the overall experiment (B) and the probe setup (C). The system can be divided in two segments: first, the high-temperature flow reactor with gas supplies and vaporizer system and second, the MBMS time-of-flight detection system. In operation, the exit of the flow tube is mounted directly to the sampling nozzle of the MBMS system. The gas is sampled directly from the reactor outlet and transferred to the high-vacuum detection system. Here, ionization is performed by electron ionization with subsequent time-of-flight detection.
The reactor has a 40-mm inner diameter ceramic (Al2O3) pipe of 1,497 mm length placed in a high temperature oven (e.g., Gero, Type HTRH 40-1000). The total heated section is 1,000 mm in length. Gases are fed premixed and pre-vaporized into the reactor by a tempered flange (typically tempered to ~80 &#176;C). The highly diluted (ca. 99 vol% in Ar), laminar flowing reactant mixture passes through a known temperature profile (details on temperature characterization will be given below). Detection of the gas composition takes place at the reactor outlet as a function of the oven temperature. Measurements are performed at constant inlet mass flow, while a monotonically decreasing temperature ramp (-200 K/h) is applied to the oven in the range of 1,800 K to 600 K. Note that similar results may be obtained when distinct temperatures are measured at isothermal oven temperatures and thermal inertia is considered properly. The thermal stabilization of the system still takes some time and the temperature ramp is selected as a compromise of averaging time for a (negligible) small temperature increment and total measurement time per series. The averaging time (45 s) of the MBMS corresponds to 2.5 K. The resulting residence times are around 2 s (at 1,000 K) for the given conditions. Finally, due to the temperature reproducibility, a relative precision of the measured temperatures of &#177;5 K or better can be stated for the present reactor experiment.
Figure 2 shows the schematic of the vaporizing system, optimized to investigate even complex hydrocarbon mixtures such as technical jet fuels. All input streams are metered in high precision (accuracy &#177;0.5 %) by Coriolis mass flow meters. Vaporization of the fuel is realized by a commercial vaporizer system at temperatures up to 200 &#176;C. All supply lines with pre-vaporized fuels are preheated with temperatures of typically 150 &#176;C to prevent condensation of the liquid fuels, while avoiding thermal degradation at the same time. Complete and stable vaporization is routinely checked and may even occur at temperatures below the normal boiling point of the respective fuels. Complete evaporation was ensured by the small fuel fraction and the low partial pressure (typically below 100 Pa) needed.
The gases are sampled by a quartz cone at the centerline of the reactor exit at ambient pressures (around 960 hPa) as seen in more detail in the zoomed frame of Figure 1. The nozzle tip has a 50 &#956;m orifice, which is located roughly 30 mm inside the ceramic tube at the end of the reaction zone. Note, that the sampling location is fixed with respect to the inlet. Thermal expansion of the oven tube only takes place at the outlet, which is not mechanically connected to the sampling system resulting in a temperature independent length of the reaction segment. All reactions are immediately quenched due to the formation of a molecular beam, when gasses are expanded into high vacuum (two differential pumping stages; 10-2 and 10-4 Pa)25,26. The sample is guided to the ion source of an electron impact (EI) time-of-flight (TOF) mass spectrometer (mass resolution R = 3,000) capable of determining the exact mass of the present species in suitable precision to determine the elemental composition within a C/H/O system. The electron energy is set to low values (typically 9.5-10.5 eV) in order to minimize fragmentation due to the ionization process. Note that the diluent and reference species argon is still detectable due to the broad energy distribution of the ionizing electrons (1.4 eV FWHM). While Ar can be measured with good S/N, the low electron energy does not allow for sufficient determination of the major species (H2O, CO2, CO, H2, O2, and fuel) profiles, which are present in significant lower concentrations.
In addition to the detection by TOF, a residual gas analyzer (RGA), i.e. a quadrupole mass spectrometer, is placed in the ionization chamber to monitor the six species above with a higher electron energy (70 eV) simultaneously to the MBMS-TOF measurements.

<table><tbody><tr><td>Time-Of-Flight MBMS</td><td>Kaesdorf</td><td>n.a.</td><td>custom design</td></tr><tr><td>Molecular Beam Samling Interface</td><td>self made</td><td>n.a.</td><td>custom design</td></tr><tr><td>Laminar Flow Reactor</td><td>Gero</td><td>Type HTRH 40-1000</td><td>custom design</td></tr><tr><td>Quadrupole MS</td><td>Hiden</td><td>HAL/3F 301</td><td>adapted to ionization chamber</td></tr><tr><td>Vaporizer</td><td>Bronkhorst</td><td>CEM</td><td>Vaporizer</td></tr><tr><td>Mass Flow Meter</td><td>Bronkhorst</td><td>Mini Cori-Flow M12, M13, M14</td><td>Flow Controller</td></tr><tr><td>Jet A-1</td><td>n.a.</td><td>n.a.</td><td>Standard Jet fuel of interest</td></tr><tr><td>Metal syringe</td><td>Hugo Sachs</td><td>70-2252</td><td>Fuel Supply</td></tr><tr><td>Heating Hoses</td><td>Hillesheim</td><td>HMI series</td><td>Gas Preheating</td></tr><tr><td>Gas</td><td>Linde</td><td>Ar, O2</td><td>Diluent, Oxidizer</td></tr></tbody></table>

combustion chemistry of fuels: quantitative speciation data obtained from an atmospheric high-temperature flow reactor with coupled molecular-beam mass spectrometer

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This flexible tool offers a detailed observation of chemical gas-phase kinetics in reacting flows under well-controlled conditions. The vast range of operating conditions available in a laminar flow reactor enables access to extraordinary combustion applications that are typically not achievable by flame experiments. These include rich conditions at high temperatures relevant for gasification processes, the peroxy chemistry governing the low temperature oxidation regime or investigations of complex technical fuels. The presented setup allows measurements of quantitative speciation data for reaction model validation of combustion, gasification and pyrolysis processes, while enabling a systematic general understanding of the reaction chemistry. Validation of kinetic reaction models is generally performed by investigating combustion processes of pure compounds. The flow reactor has been enhanced to be suitable for technical fuels (e.g. multi-component mixtures like Jet A-1) to allow for phenomenological analysis of occurring combustion intermediates like soot precursors or pollutants. The controlled and comparable boundary conditions provided by the experimental design allow for predictions of pollutant formation tendencies. Cold reactants are fed premixed into the reactor that are highly diluted (in around 99 vol% in Ar) in order to suppress self-sustaining combustion reactions. The laminar flowing reactant mixture passes through a known temperature field, while the gas composition is determined at the reactors exhaust as a function of the oven temperature. The flow reactor is operated at atmospheric pressures with temperatures up to 1,800 K. The measurements themselves are performed by decreasing the temperature monotonically at a rate of -200 K/h. With the sensitive MBMS technique, detailed speciation data is acquired and quantified for almost all chemical species in the reactive process, including radical species.

A typical mass spectrum of the sampled gas composition is shown in Figure 3. With the given setup of a mass resolution of approx. 3,000, species up to m/z = 260 u can be detected within the C/H/O system. After a mass calibration procedure, the peaks are integrated for each mass-to-charge (m/z) ratio with deconvolution algorithms for evaluating under-resolved signals. After background and fragmentation corrections, the signal can be quantified using the approp...

Watch this Scientific Journal Video about Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectr

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

An investigation of the oxidative combustion chemistry of novel biofuels, fuel components, or jet fuels by comparison of quantitative speciation data is presented. The data can be used for kinetic model validation and enables fuel assessment strategies.This manuscript describes the atmospheric high-temperature flow reactor and demonstrates its capabilities.

This manuscript describes a high-temperature flow reactor experiment coupled to the powerful molecular beam mass spectrometry (MBMS) technique. This ...

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10.0K Views.  German Aerospace Center (DLR). Een onderzoek van de oxidatieve verbranding chemie van nieuwe biobrandstoffen, brandstof onderdelen, of jet brandstoffen door vergelijking van kwantitatieve soortvorming gegevens worden gepresenteerd. De gegevens kunnen worden gebruikt voor kinetische modelvalidatie en maakt brandstof beoordeling strategieën. Dit manuscript beschrijft de atmosferische stroom van hoge-temperatuur-reactor en demonstreert de mogelijkheden.

Video: Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

Flame Experiments at the Advanced Light Source: New Insights into Soot Formation Processes

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics Beamline of the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory1-4. This video demonstrates how the complex chemical structures of laboratory-based model flames are analyzed using flame-sampling mass spectrometry with tunable synchrotron-generated vacuum-ultraviolet (VUV) radiation. This experimental approach combines isomer-resolving capabilities with high sensitivity and a large dynamic range5,6. The first part of the video describes experiments involving burner-stabilized, reduced-pressure (20-80 mbar) laminar premixed flames. A small hydrocarbon fuel was used for the selected flame to demonstrate the general experimental approach. It is shown how species&#8217; profiles are acquired as a function of distance from the burner surface and how the tunability of the VUV photon energy is used advantageously to identify many combustion intermediates based on their ionization energies. For example, this technique has been used to study gas-phase aspects of the soot-formation processes, and the video shows how the resonance-stabilized radicals, such as C3H3, C3H5, and i-C4H5, are identified as important intermediates7. The work has been focused on soot formation processes, and, from the chemical point of view, this process is very intriguing because chemical structures containing millions of carbon atoms are assembled from a fuel molecule possessing only a few carbon atoms in just milliseconds. The second part of the video highlights a new experiment, in which an opposed-flow diffusion flame and synchrotron-based aerosol mass spectrometry are used to study the chemical composition of the combustion-generated soot particles4. The experimental results indicate that the widely accepted H-abstraction-C2H2-addition (HACA) mechanism is not the sole molecular growth process responsible for the formation of the observed large polycyclic aromatic hydrocarbons (PAHs).

Gas sampling from laboratory-scale flames with online analysis of all species by mass spectrometry is a powerful method to investigate the complex mixture of chemical compounds occurring during combustion processes. Coupled with tunable soft ionization via synchrotron-generated vacuum-ultraviolet radiation, this technique provides isomer-resolved information and potentially fragment-free mass spectra.

The following experimental protocols and the accompanying video are concerned with the flame experiments that are performed at the Chemical Dynamics ...

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Preparation and Reactivity of Gasless Nanostructured Energetic Materials

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the balls. Among other applications, it is a versatile technique that allows for effective preparation of gasless reactive nanostructured materials with high energy density per volume (Ni+Al, Ta+C, Ti+C). The structural transformations of reactive media, which take place during HEBM, define the reaction mechanism in the produced energetic&#160;composites. Varying the processing conditions permits fine tuning of the milling-induced microstructures of the fabricated composite particles. In turn, the reactivity, i.e., self-ignition temperature, ignition delay time, as well as reaction kinetics, of high energy density materials depends on its microstructure. Analysis of the milling-induced microstructures suggests that the formation of fresh oxygen-free intimate high surface area contacts between the reagents is responsible for the enhancement of their reactivity. This manifests itself in a reduction of ignition temperature and delay time, an increased rate of chemical reaction, and an overall decrease of the effective activation energy of the reaction. The protocol provides a detailed description for the preparation of reactive nanocomposites with tailored microstructure using short-term HEBM method. It also describes a high-speed thermal imaging technique to determine the ignition/combustion characteristics of the energetic materials. The protocol can be adapted to preparation and characterization of a variety of nanostructured energetic composites.

This protocol describes the preparation of gasless nanostructured energetic materials (Ni+Al, Ta+C, Ti+C) using the short-term high-energy ball milling (HEBM) technique. It also describes a high-speed thermal imaging method to study the reactivity of mechanically fabricated nanocomposites. These protocols can be extended to other reactive nanostructured energetic materials.

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the ...

Experimental Methodology for Estimation of Local Heat Fluxes and Burning Rates in Steady Laminar Boundary Layer Diffusion Flames

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex interactions occurring at the interface between gas-phase flames and condensed-phase fuels. The current research provides a technique to explore the dynamic relationship between a combustible condensed fuel surface and gas-phase flames in laminar boundary layers. Experiments have previously been conducted in both forced and free convective environments over both solid and liquid fuels. A unique methodology, based on the Reynolds Analogy, was used to estimate local mass burning rates and flame heat fluxes for these laminar boundary layer diffusion flames utilizing local temperature gradients at the fuel surface. Local mass burning rates and convective and radiative heat feedback from the flames were measured in both the pyrolysis and plume regions by using temperature gradients mapped near the wall by a two-axis traverse system. These experiments are time-consuming and can be challenging to design as the condensed fuel surface burns steadily for only a limited period of time following ignition. The temperature profiles near the fuel surface need to be mapped during steady burning of a condensed fuel surface at a very high spatial resolution in order to capture reasonable estimates of local temperature gradients. Careful corrections for radiative heat losses from the thermocouples are also essential for accurate measurements. For these reasons, the whole experimental setup needs to be automated with a computer-controlled traverse mechanism, eliminating most errors due to positioning of a micro-thermocouple. An outline of steps to reproducibly capture near-wall temperature gradients and use them to assess local burning rates and heat fluxes is provided.

We describe the use of micro-thermocouples to estimate local temperature gradients in steady laminar boundary layer diffusion flames. By extension of the Reynolds Analogy, local temperature gradients can be further used to estimate the local mass burning rates and heat fluxes in such flames with high accuracy.

Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve the complex ...

Combustion Characterization and Model Fuel Development for Micro-tubular Flame-assisted Fuel Cells

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power generation and micro combustion as well as development in fuel cell research has created new means of power generation that combine solid oxide fuel cells with open flames and combustion exhaust. Instead of relying upon the heat of combustion, these solid oxide fuel cell systems rely on reforming of the fuel via combustion to generate syngas for electrochemical power generation. Procedures were developed to assess the combustion by-products under a wide range of conditions. While theoretical and computational procedures have been developed for assessing fuel-rich combustion exhaust in these applications, experimental techniques have also emerged. The experimental procedures often rely upon a gas chromatograph or mass spectrometer analysis of the flame and exhaust to assess the combustion process as a fuel reformer and means of heat generation. The experimental techniques developed in these areas have been applied anew for the development of the micro-tubular flame-assisted fuel cell. The protocol discussed in this work builds on past techniques to specify a procedure for characterizing fuel-rich combustion exhaust and developing a model fuel-rich combustion exhaust for use in flame-assisted fuel cell testing. The development of the procedure and its applications and limitations are discussed.

A protocol for creating a model fuel-rich combustion exhaust is developed through combustion characterization and is applied for micro-tubular flame-assisted fuel cell testing and research.

Combustion based power generation has been accomplished for many years through a number of heat engine systems. Recently, a move towards small scale power ...

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated species. The synthesis approach inhibits the topochemical effect promoting rapid hydration when exposed to the relative humidity of ambient air. This stable, amorphous, nano-particle material was analyzed using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) and showed an exothermic energy release at low temperature (i.e., 180 &#176;C) for the transformation of I4O9 into I2O5. This additional exothermic energy release contributes to an increase in overall reactivity of I4O9 when dry mixed with nano-aluminum (Al) powder, resulting in a minimum of 150% increase in flame speed compared to Al + I2O5. This study shows that as an oxidizer, I4O9 has more reactive potential than other forms of iodine(V) oxide when combined with Al, especially if I4O9 can be passivated to inhibit absorption of water from its surrounding environment.

Reaction Kinetics and Combustion Dynamics of I4O9 and Aluminum Mixtures

A protocol for measuring flame speeds of a reactive mixture composed of tetraiodine nonoxide (I4O9) and aluminum (Al) is presented. A method for resolving reaction kinetics using differential scanning calorimetry (DSC) is also presented. It was found that I4O9 is 150% more reactive than other iodine(V) oxides.

Tetraiodine nonoxide (I4O9) has been synthesized using a dry approach that combines elemental oxygen and iodine without the introduction of hydrated ...

Quantitative Analysis by Thermogravimetry-Mass Spectrum Analysis for Reactions with Evolved Gases

During energy conversion, material production, and metallurgy processes, reactions often have the features of unsteadiness, multistep, and multi-intermediates. Thermogravimetry-mass spectrum (TG-MS) is seen as a powerful tool to study reaction features. However, reaction details and reaction mechanics have not been effectively obtained directly from the ion current of TG-MS. Here, we provide a method of an equivalent characteristic spectrum analysis (ECSA) for analyzing the mass spectrum and giving the mass flow rate of reaction gases as precise as possible. The ECSA can effectively separate overlapping ion peaks and then eliminate the mass discrimination and temperature-dependent effect. Two example experiments are presented: (1) the decomposition of CaCO3 with evolved gas of CO2 and the decomposition of hydromagnesite with evolved gas of CO2 and H2O, to evaluate the ECSA on single-component system measurement and (2) the thermal pyrolysis of Zhundong coal with evolved gases of inorganic gases CO, H2, and CO2, and organic gases C2H4, C2H6, C3H8, C6H14, etc., to evaluate the ECSA on multi-component system measurement. Based on the successful calibration of the characteristic spectrum and relative sensitivity of specific gas and the ECSA on mass spectrum, we demonstrate that the ECSA accurately gives the mass flow rates of each evolved gas, including organic or inorganic gases, for not only single but multi-component reactions, which cannot be implemented by the traditional measurements.

Precise determination of the evolved gases&#39; flow rate is key to study the details of reactions. We provide a novel quantitative analysis method of equivalent characteristic spectrum analysis for thermogravimetry-mass spectrum analysis by establishing the calibration system of the characteristic spectrum and relative sensitivity, for obtaining the flow rate.

During energy conversion, material production, and metallurgy processes, reactions often have the features of unsteadiness, multistep, and ...

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species in the ppm-to-single-percent range. The main purpose of the method is the spatially resolved detection of low-concentration species, which have no transitions in the visible or near-IR spectral range that could be used for detection. IR-DFWM is a nonintrusive method, which is a great advantage in combustion research, as inserting a probe into a flame can change it drastically. The IR-DFWM is combined with upconversion detection. This detection scheme uses sum-frequency generation to move the IR-DFWM signal from the mid-IR to the near-IR region, to take advantage of the superior noise characteristics of silicon-based detectors. This process also rejects most of the thermal background radiation. The focus of the protocol presented here is on the proper alignment of the IR-DFWM optics and on how to align an intracavity upconversion detection system.

Here, we present a protocol to perform sensitive, spatially resolved gas spectroscopy in the mid-infrared region, using degenerate four-wave mixing combined with upconversion detection.

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species ...

Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography

Certain nitrogen-containing compounds can contribute to fuel instability during storage. Hence, detection and characterization of these compounds is crucial. There are significant challenges to overcome when measuring trace compounds in a complex matrix such as fuels. Background interferences and matrix effects can create limitations to routine analytical instrumentation, such as GC-MS. In order to facilitate specific and quantitative measurements of trace nitrogen compounds in fuels, a nitrogen-specific detector is ideal. In this method, a nitrogen chemiluminescence detector (NCD) is used to detect nitrogen compounds in fuels. NCD utilizes a nitrogen-specific reaction that does not involve the hydrocarbon background. Two-dimensional (GCxGC) gas chromatography is a powerful characterization technique as it provides superior separation capabilities to one-dimensional gas chromatography methods. When GCxGC is paired with a NCD, the problematic nitrogen compounds found in fuels can be extensively characterized without background interference. The method presented in this manuscript details the process for measuring different nitrogen-containing compound classes in fuels with little sample preparation. Overall, this GCxGC-NCD method has been shown to be a valuable tool to enhance the understanding of the chemical composition of nitrogen-containing compounds in fuels and their impact on fuel stability. The % RSD for this method is &#60;5% for intraday and &#60;10% for interday analyses; the LOD is 1.7 ppm and the LOQ is 5.5 ppm.

Here, we present a method utilizing two-dimensional gas chromatography and nitrogen chemiluminescence detection (GCxGC-NCD) to extensively characterize the different classes of nitrogen-containing compounds in diesel and jet fuels.

Certain nitrogen-containing compounds can contribute to fuel instability during storage. Hence, detection and characterization of these compounds is ...

Carbon and Nitrogen Analysis of Environmental Samples

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University
Elemental Analysis is a method used to determine elemental composition of a material. In environmental samples such as soils, scientists are particularly interested in the amounts of two ecologically important elements, nitrogen and carbon. Elemental analysis by the flash combustion technique works by oxidizing the sample with a catalyst through combustion in a high-temperature chamber. The products of combustion are then reduced to N2 and CO2 and detected with a thermal conductivity detector.
Unlike other methods for total nitrogen determination (Kjeldahl method) and total carbon determination (Walkley-Black, Heanes or Leco methods), the flash combustion technique does not use toxic chemicals and is therefore much safer to use.
This video will demonstrate combustion-based elemental analysis using the Flash EA 1112 instrument from Thermo Fisher Scientific.

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University
Elemental Analysis is a method used to determine elemental composition of a ...

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Atomic Absorption Spectroscopy: Atomization Methods

Atomic Absorption Spectroscopy (AAS) atomizes samples through flame atomization or electrothermal atomization. Flame atomization typically involves a nebulizer and spray chamber assembly to combine the sample with a fuel&#8211;oxidant mixture, creating a fine aerosol mist that enters a burner. Typically, the fuel and oxidant are combined in an approximately stoichiometric ratio. However, for atoms that are easily oxidized, a fuel-rich mixture may be more advantageous. Only about 5% of the aerosol droplets reach the flame, where they undergo desolvation in the primary combustion zone, leaving bare particles atomized in the inner flame. The gaseous atoms, ions, and molecular species quickly pass through the interzonal region for analysis before exiting the flame. Flame atomizers have low atomization efficiency due to large aerosol droplets not reaching the flame and significant sample dilution from combustion gases. However, the flame atomization efficiencies can be enhanced by continuously aspirating the sample, optimizing fuel-to-oxidant ratios, adjusting nebulizer flow rates, and setting the burner height.
Flame atomization is not suitable for samples with low analyte concentrations or limited volumes due to the small number of samples successfully atomized and detected. In contrast, electrothermal atomization, also known as graphite furnace atomization, uses a graphite tube to capture and concentrate the analytes and works well for small, discrete samples. In this technique, the sample is dried and charred before being atomized at high temperatures.
Elements such as As, Se, Sb, Bi, Ge, Sn, Te, and Pb can be atomized under milder conditions by chemically converting them into volatile hydrides before carrying them to the flame. Additionally, mercury determination can utilize a unique cold-vapor method due to its natural volatility.

Atomic Absorption Spectroscopy (AAS) atomizes samples through flame atomization or electrothermal atomization. Flame atomization typically involves a ...

Combustion Chemistry of Fuels: Quantitative Speciation Data Obtained from an Atmospheric High-temperature Flow Reactor with Coupled Molecular-beam Mass Spectrometer

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