Chemical Equilibrium With Applications Research Articles

New Estimates of Nitrogen Fixation on Early Earth.

Fixed nitrogen species generated by the early Earth's atmosphere are thought to be critical to the emergence of life and the sustenance of early metabolisms. A previous study estimated nitrogen fixation in the Hadean Earth's N2/CO2-dominated atmosphere; however, that previous study only considered a limited chemical network that produces NOx species (i.e., no HCN formation) via the thermochemical dissociation of N2 and CO2 in lightning flashes, followed by photochemistry. Here, we present an updated model of nitrogen fixation on Hadean Earth. We use the Chemical Equilibrium with Applications (CEA) thermochemical model to estimate lightning-induced NO and HCN formation and an updated version of KINETICS, the 1-D Caltech/JPL photochemical model, to assess the photochemical production of fixed nitrogen species that rain out into the Earth's early ocean. Our updated photochemical model contains hydrocarbon and nitrile chemistry, and we use a Geant4 simulation platform to consider nitrogen fixation stimulated by solar energetic particle deposition throughout the atmosphere. We study the impact of a novel reaction pathway for generating HCN via HCN2, inspired by the experimental results which suggest that reactions with CH radicals (from CH4 photolysis) may facilitate the incorporation of N into the molecular structure of aerosols. When the HCN2 reactions are added, we find that the HCN rainout rate rises by a factor of five in our 1-bar case and is about the same in our 2- and 12-bar cases. Finally, we estimate the equilibrium concentration of fixed nitrogen species under a kinetic steady state in the Hadean ocean, considering loss by hydrothermal vent circulation, photoreduction, and hydrolysis. These results inform our understanding of environments that may have been relevant to the formation of life on Earth, as well as processes that could lead to the emergence of life elsewhere in the universe.

Experimental investigation of non-equilibrium spectra for nitrogen behind strong shock waves

The non-equilibrium spectra of shock-heated nitrogen in the UV-visible range are investigated in a detonation driven shock tube. Spectral identification indicates that the main contributors to the spectra are molecular radiation of N2(2+) and N2+(1-). Vibrational and rotational temperatures of N2(C) and N2+(B) are determined through spectral fitting. The post-shock spectra of pure nitrogen are obtained for shock velocities ranging from 6.82–9.00 km/s and P0 = 30–200 Pa at the shock arrival time. Differences between vibrational and rotational temperatures of N2(C) and N2+(B) are observed, suggesting that nitrogen is in a non-equilibrium state at shock arrival moment. Time-resolved spectra are obtained within varying delay times of 0–2.0μs at P0 = 200 Pa and shock velocity of Vsw = 6.60 km/s. Time-resolved temperatures are determined to illustrate the time-resolved non-equilibrium characteristics of nitrogen at high temperature. It is observed that the non-equilibrium characteristics of nitrogen gradually weaken with increasing time and the thermal equilibrium was not obtained within 2.0μs. Finally, the time-resolved temperatures are compared with CEA (Chemical Equilibrium with Applications) prediction, revealing that the difference in temperature between the experiment and the CEA equilibrium calculation decreases as time increases.

Solid oxide fuel cells fueled by carbonaceous fuels: A thermodynamics-based approach for safe operation and experimental validation

ABSTRACT Solid Oxide Fuel Cells (SOFCs) can operate with carbonaceous fuels. However, experiments indicate possible carbon deposition or coking on Ni-based anodes. Thermodynamic equilibrium calculations with NASA computer program CEA (Chemical Equilibrium with Applications) for typical SOFC operating temperatures predict graphitic carbon (C(gr)) formation. While fuel humidification eliminates coking, excess steam degrades Ni-based anode, necessitating suitable steam supply for safe operation. Thermodynamic approach is validated using experiments on 25 mm diameter electrolyte-supported NextCell-HP SOFC button cell fueled by H2 and simulated syngas (CO and H2). The use of 1 SLPM H2 (fuel) with 4 SLPM air (oxidant) provides peak power density of ~1000 mW cm−2. With simulated syngas fuel, cell performance drops. In-situ diagnosis with steam supply to anode suggests carbon deposition based on detection of H2 and CO in tail gas. Equilibrium analysis suggests carbon-free operation by humidifying simulated syngas (CO:H2 = 1:3 molar ratio) with ~5% steam by volume, at 973 K and above. Further experiments are conducted on a fresh cell. Simulated syngas (CO:H2 = 1:3 volumetric ratio) with ~5% steam by volume provides safe cell operation. The study provides a pathway to safely utilize carbonaceous fuels in SOFC by suitable humidification, coupling thermodynamic analyses and experiments.

Analytical Assessment of Blended Fuels for Pulse Detonation Engine Performance

A pulse detonation engine (PDE) is possible to be a next-generation high-performance propulsion system in aerospace-related applications. To generate power or thrust, PDE uses repeated detonations. The current study evaluates the PDE performance with alternative and blended fuels in the Zeldovich–von Neumann–Doring (ZND) model. Parameters such as temperature ratio, pressure ratio, detonation velocity, and specific impulse were determined analytically for the fuels. The computed detonation parameters and specific impulse were compared with those available in NASA’s open-source program, Chemical Equilibrium with Applications (CEA), to ensure the results' sufficient validity. It was found that the highest specific impulse was achieved with hydrogen at an equivalence ratio of 1. Analytical values of all the parameters were in an acceptable range as defined by NASA CEA. As compared to pure butane and propane, their blends yielded higher values (1 to 10 percent) of specific impulse. Propane and butane are safe, non-toxic, clean-burning fuels, great energy sources, and can be used as alternative fuels in PDE.

Effect of hexanitroethane (HNE) and hydrazinium nitroformate (HNF) on energy characteristics of composite solid propellants

This work deals with energy performance calculate results of new solid composite propellants based on Hexanitroethane (HNE) and Hydrazinium nitroformate (HNF). The energy characteristics of solid propellants with HNE and HNF are estimated using NASA Chemical Equilibrium with Applications (CEA). The effect of HNE and HNF as energetic oxidizers on the energy characteristics of composite modified double-base (CMDB) propellants, hydroxyl-terminated polybutadiene (HTPB) propellants, nitrate ester plasticized polyether (NEPE) propellants, glycidyl azide polymer (GAP) propellants has been carried out. Characteristics of ingredients and propellant formulations with HNE and HNF are presented together with the calculate results which demonstrate the increased performance compared to conventional high-performance propellants based on Ammonium Perchlorate (AP). The results show that HNE and HNF can improve the standard theoretical specific impulse of the four propellants in different degrees, and HTPB propellant has the most significant improvement, which is 12.26 s for HNE-based propellant and 14.12 s for HNF-based propellant. At the same time, both HNE and HNF reduce the infrared emission of propellant exhaust plumes when they replace AP, and reduce or even completely eliminate HCl gas in exhaust products. Therefore, it is expected that HNE-based and HNF-based propellants may provide a promising chlorine-free alternative to existing AP-based formulations.

Port-Hamiltonian Modeling of Thermofluid Systems and Object-Oriented Implementation With Modelica I: Thermodynamic Part

In this paper, we present the physical foundations and the development of the thermodynamic part of a Modelica library with the fundamental components for modeling thermofluid systems. We have chosen Modelica because it is an object-oriented modeling language that allows an elegant design of the library, with a top-down conception that starts from very general components where we model the thermodynamic properties common to all simple substances and descend by inheritance to model the properties of each particular substance. To model the behavior of each component, we have used: classical thermodynamics to define the equilibrium states, the local equilibrium hypothesis of Classical Irreversible Thermodynamics to model the changes of state, and the port-Hamiltonian approach to obtain the equations of the system dynamics. With this formulation, we implement the thermodynamic behavior of ideal gases (including monatomic gases as a particular case), the 2073 substances defined for the CEA (Chemical Equilibrium with Applications) NASA Glenn computer program, the IAPWS Formulation 1995 for the Thermodynamic Properties of Water Substance for General and Scientific Use, and the Syltherm 800 HTF (Heat Transfer Fluid). We also define graphical symbols for each library component that facilitate modeling complex systems with simple drag-and-drop manipulations, component connection, and parameter selection. These symbols are a slightly modified version of those used in bond graphs to facilitate their reading and the representation of the structure of complex systems. We also show the modeling, simulation, and comparison for accuracy, performance, and scalability of some thermodynamic systems implemented with the Modelica Standard Library (MSL) and the proposed library.

Small-scale production of hydrogen via auto-thermal reforming in an adiabatic packed bed reactor: Parametric study and reactor's optimization through response surface methodology

In this work, a two-dimensional (2-D) heterogeneous reactor model for ATR process is presented. In order to authenticate the developed reactor model outputs, literature results as well as thermodynamic findings produced by employing chemical equilibrium with applications (CEA) software were compared with the model predictions and an excellent agreement was evidenced that corroborates the model's accurate predictive capability. Response surface methodology combined with central composite design was used to investigate the significance of operational parameters on the performance of the ATR process and Parametric optimization was performed to find the optimal operating conditions. Further insights into the ATR process were obtained by studying the effect of temperature, pressure, S/C, oxygen to carbon ratio (O/C) and gas mass flow velocity (Gs) on CH4 conversion, H2 yield (wt. % of CH4) and H2 purity. It was concluded that 973 K, 1.5 bar, S/C of 3.0, O/C of 0.45 and Gs of 0.15 kg/m2s resulted in CH4 conversion and H2 purity up to 97.6% and 71.8%, respectively.

Modelling of one-dimensional heterogeneous catalytic steam methane reforming over various catalysts in an adiabatic packed bed reactor

Kinetic data relevant to steam methane reforming (SMR) are often applied to catalysts and conditions for which they have not been derived. In this work, kinetic rates for the two SMR and water gas shift reactions were derived for 12 commonly used reforming catalysts based on conversion data obtained from the literature. Subsequently, these rates were tested in dynamic operation, steady-state, and equilibrium using a 1-D reactor model developed in-house with gPROMS model builder. Modelling outputs were further validated independently at equilibrium using the software chemical equilibrium with applications (CEA), and the literature. The effect of variables such as temperature, pressure, steam to carbon ratio (S/C), and gas mass flux (Gs) on the performance of the SMR process was then studied in terms of fuel and steam conversion (%), H2 purity (%), H2 yield (wt. % of CH4) and selectivity of the carbon-based products. A comparative study was then performed for the 12 catalysts. Some catalysts showed better activity owing to their fast kinetics when they are tested in mild industrial conditions, while others performed better in more severe industrial conditions, substantiating that the choice of a catalyst ought to depend on the operating conditions.

Predicting the Gurney velocity of chemical high explosives: thermochemical code calculations and studies on the detonation products isentrope

ABSTRACT The simplicity and versatility of the Gurney model has led to its widespread adoption for the calculation of peak fragment velocity of explosively-driven munitions such as fragmentation warheads and artillery projectiles. The Chemical Equilibrium with Applications (CEA) thermochemical code provides several relevant parameters that were found to be important for the construction of a mathematical model for estimating the Gurney velocity of pure and mixed chemical high explosives. Compared to other methods, the proposed model demonstrated its accuracy in predicting the Gurney velocity of sensitive and insensitive explosive compositions. Models based on detonation velocity were found to be particularly inadequate to predict the Gurney velocity of insensitive explosives, which is strong proof that the detonation velocity does not necessarily correlate with the Gurney velocity for all types of high explosives. Results from the cylinder expansion test provide some evidence that the low to moderate metal acceleration ability of insensitive explosives is due to their unique and steep expansion isentropes rather than charge diameter effects or non-ideal detonation behavior.

Theoretical and Experimental Heat of Combustion Analysis of Paraffin-Based Fuels as Preburn Characterization for Hybrid Rocket

The energy characteristics and theoretical performance of the hybrid rocket fuels are discussed in this paper. Aluminum (Al) and boron (B) metal additives were used to increase the energy density of the paraffin-based solid fuels. To predict the energy characteristics, the heat of combustion was evaluated by adiabatic bomb calorimetry. Theoretical performance parameters such as specific impulse (Isp), flame temperature, and characteristic velocity were obtained with NASA Chemical Equilibrium with Applications (CEA) code. Calorimetric test results revealed that paraffin/polyethylene/boron (P/PE/B)-based fuel formulations exhibited the highest heat of combustion among all the tested fuels. The heat of combustion value of the P/PE/B sample at 25 wt% B loading was found to be 9612 ±16 cal/g and 9293±17 cal/g for the P/PE/Al fuel formulation. The CEA results showed that the addition of Al to paraffin is noneffective in improving specific impulse performance. When B loading increased from 5 to 25 wt% in the P/PE/B, the Isp increased by 47 s compared to pure paraffin. A specific impulse increase implies the possible propellant mass saving. The reduction of the oxidizer and fuel masses may yield increased payload performance for given boundary conditions. The P/PE/B25 formulation has reported the highest value of characteristics velocity (C*) compared to other paraffin-based formulation.

Influence of Doped H2O or H2 on Soot Production and Power Capability in the Fuel-rich Gas Generator

ABSTRACT Influence of doped H2O or H2 on both soot production and power capability in the fuel-rich gas generator has been studied together by using the program of chemical equilibrium with applications (CEA). The oxidant is LOX, and the fuel is composed of Jet-A and the additive. The parameters of the gas generator are as follows: the range of combustion temperature is 800–1700 K, combustion pressure is 0.1–5.0 MPa, oxidant/fuel ratio is 0.1–1.2, and the mass percent of the additive in fuel is 0–60%. The results indicate that the addition of either H2O or H2 can obviously reduce the mass percent of soot in combustion products, and the reasons are discussed on the base of the products distributions. Moreover, the minimum amounts of addition to surrender mass percent of soot less than 0.1% are present. The effects of combustion pressure on soot mass percent in combustion products appear turning appoints around 1100 K, no matter the additive is H2O or H2. The addition of H2 can obviously improve the power capacity of combustion products in the whole temperature range. The addition of H2O can also improve slightly the power capacity of combustion products, when the combustion temperature is less than 1400 K. Effective molar weight of combustion products is the main factor affecting power capacity.

Experimental study of using biogas in Pulse Detonation Engine with hydrogen enrichment

Pulse Detonation Engine (PDE) is one of the pressure gain engines that provide prominent features over conventional engines such as higher thermodynamic efficiency, higher thrust, and less design complexity. Biogas is one of the promising alternative energy sources. The aim of this paper is to study the influence of hydrogen addition in biogas on detonation characteristics performance of PDE. The ideal detonation combustion characteristics of biogas are estimated using NASA Chemical Equilibrium with Applications (CEA). The equivalence ratio range is varied from 0.7 to 1.4. It was found that the higher the percentage of methane concentration in biogas increased the detonation characteristics of biogas such as pressure, temperature, and Mach number. However, a reduction in the flame speed, temperature, and pressure of biogas compared to pure methane was stipulated to be due to the presence of CO2 that acts as a dilutant in biogas. It was found also that, the optimal percentage of hydrogen addition into the biogas fuel mixture is 15%. At this percentage, the detonation pressure improved by 23%. The performance of PDE fuelled by biogas is presented experimentally at a frequency of 10 Hz. The results show a successful and stable detonation initiation in PDE by using biogas with 15% and 20% addition of hydrogen.

A non-calorimetric approach for investigating the moisture-induced ageing of a pyrotechnic delay material using spectroscopies

The degradation of thermal properties due to ageing such as burning rate and exothermic heat release are unsolved issues faced during a long-term storage of the pyrotechnic substances. Accordingly, we employed various non-calorimetric methods to investigate the thermal performance of pyrotechnic delay, which is exposed to various moisture-rich conditions at extended durations. The chemical and physical changes in the compositions of a pyrotechnic delay comprised of metal fuel (Zr-Ni alloy) and oxidants (KClO4, BaCrO4) are analysed for four different relative humidity levels using X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope and laser-induced breakdown spectroscopy. The calculations using the NASA Chemical Equilibrium with Applications (CEA) software indicated that the heat of reaction for the components stored under the moisture-rich conditions is reduced by more than 50%. Unlike the conventional calorimetric analysis, the present non-calorimetric approach provided the compositional changes as well as the cause and effect of the relevant ageing process of pyrotechnic delay.

The hygrothermal aging effects of titanium hydride potassium perchlorate for pyrotechnic combustion

Titanium hydride potassium perchlorate (THPP) is a well-known pyrotechnic initiator commonly utilized in the field of aerospace propulsion. The current study experimentally elucidates the effects of hygrothermal aging on the pyrotechnic combustion of THPP and proposes two methodologies for analysis. The first technique implements a two-step isoconversional method to analyse the hygrothermally aged THPP with Differential Scanning Calorimetry (DSC), and the second method offers a novel aging prediction methodology by comparing the experimental heat of reaction values against idealized equilibrium values. As the heat of reaction plays a major role on determining propellant’s performance, NASA Chemical Equilibrium with Applications (CEA) was used to predict its value. The knowledge of the combined aging effects is directly connected to the performance, lifetime, and safety of a pyrotechnic initiator that utilizes the THPP. The values of heat of reactions for different samples with different aging duration were estimated based on their composition extracted from the X-ray Photoelectron Spectroscopy (XPS) study.

Thermodynamic optimization of coal-biomass co-gasification process by using non-stoichiometric equilibrium modeling

Co-gasification of coal and biomass improves the gasification process by reducing the amount of tar generated and also produces a low carbon footprint on the environment. In this study, Chemical Equilibrium with Applications (CEA), a non-stoichiometric equilibrium simulation tool, developed by NASA, based on Gibbs free energy minimization technique has been used to study the thermodynamic optimization of coal-biomass co-gasification process. Simulation of the co-gasification process has been done to evaluate the product gases from gasification process for various coal-biomass mixtures at different equivalence ratios and temperatures. The simulation results show that as the gasification temperature increases, CO molar fraction increases for a particular equivalence ratio and reverse is the trend for CO2. Again, the CO molar fraction increases with a decrease in equivalence ratio for all the gasification temperature and reverse in case of CO2. The study also observed that as the percentage of coal increases in the fuel mixture, mole fraction of CO increases at a particular equivalence ratio with the increase in temperature. However, a reverse trend is observed in case of CO2. The mole fraction of H2 decreases with the increase in coal percentage for all gasification temperature for a particular equivalence ratio.

Experimental and Numerical Study of Low Temperature Methane Steam Reforming for Hydrogen Production

Low temperature methane steam reforming for hydrogen production, using experimental developed Ni/Al2O3 catalysts is studied both experimentally and numerically. The catalytic activity measurements were performed at a temperature range of 500–700 °C with steam to carbon ratio (S/C) of 2 and 3 under atmospheric pressure conditions. A mathematical analysis to evaluate the reaction feasibility at all different conditions that have been applied by using chemical equilibrium with applications (CEA) software and in addition, a mathematical model focused on the kinetics and the thermodynamics of the reforming reaction is introduced and applied using a commercial finite element analysis software (COMSOL Multiphysics 5.0). The experimental results were employed to validate the extracted simulation data based on the yields of the produced H2, CO2 and CO at different temperatures. A maximum hydrogen yield of 2.7 mol/mol-CH4 is achieved at 700 °C and S/C of 2 and 3. The stability of the 10%Ni/Al2O3 catalyst shows that the catalyst is prone to deactivation as supported by Thermogravimetric Analysis TGA results.

Benchmarking of Improved DPAC Transient Deflagration Analysis Code

The deflagration pressure analysis code (DPAC) has been upgraded for use in modeling hydrogen deflagration transients. The upgraded code is benchmarked using data from vented hydrogen deflagration tests conducted at the HYDRO-SC Test Facility at the University of Pisa. DPAC originally was written to calculate peak pressures for deflagrations in radioactive waste storage tanks and process facilities at the Savannah River Site. Upgrades include the addition of a laminar flame speed correlation for hydrogen deflagrations and a mechanistic model for turbulent flame propagation, incorporation of inertial effects during venting, and inclusion of the effect of water vapor condensation on vessel walls. In addition, DPAC has been coupled with chemical equilibrium with applications (CEA), a NASA combustion chemistry code. The deflagration tests are modeled as end-to-end deflagrations. The improved DPAC code successfully predicts both the peak pressures during the deflagration tests and the times at which the pressure peaks.

Effects of Air Vitiation on Scramjet Performance Based on Thermodynamic Cycle Analysis

The influences of air vitiation on scramjet performance were studied in this paper based on thermodynamic cycle analysis. By the aid of NASA Glenn’s computer program Chemical Equilibrium with Applications (CEA), parameters of vitiated air at combustion heater exit could be calculated. Based on thermodynamic cycle analysis, scramjet performance, including internal thrust, specific thrust, and specific impulse, were analyzed with 9 simulation criterions under Mach 4.5 and 6.5 conditions, respectively. The results show that, (1) specific heat and specific heat ratio of vitiated air are mainly affected by combustion heating medium, and also have minor connection with temperature criterions. Moreover, choosing different simulation criterions influences the temperature or pressure between clean air and vitiated air significantly; (2) the internal thrust and specific thrust of scramjet with hydrogen heated airstream are greater than that of scramjet with alcohol and kerosene heated airstream; (3) matching static pressure and dynamic pressure will obtain higher internal thrust compared to total pressure, and the effect of pressure criterions on internal thrust is more remarkable than temperature criterions. On the other hand, these findings proved that the method based on thermodynamic cycle analysis is a simple, dependable, and effective approach to evaluate the scramjet performance affected by air vitiation.

Kinetics Study for the Effect of Alkali Metals on the Homogenous Mercury Oxidation under Isothermal Conditions

This study was mainly focused on the transformation of alkali metals in flue gas, the relationship between mercury oxidation and alkali metals, and the effect of concentrations of Cl2 and SO2 on mercury oxidation. Thermodynamic stability of alkali metals during coal combustion was analyzed with the chemical thermodynamics software, Chemical Equilibrium with Applications (CEA), and so were the interactions among alkali metals and Cl-species or S-species. The analysis results suggested that mercury oxidation in postcombustion gases could be enhanced by alkali metals. Based on the previous studies, a homogeneous Hg/C/H/O/N/S/Cl/K/Na kinetics model under isothermal conditions was established in this paper, and the kinetics calculation and sensitivity analysis were realized by CHEMKIN 4.1. According to the kinetics model, it is concluded that the main products for K and Na are KSO2, KCl, NaSO2, and NaCl at 793 K. Additionally, the impact of alkali metals on mercury oxidation will vary with the concentrations o...

위성 발사체 액체 로켓 엔진의 Pre-burner 성능 모사

다단 연소를 수행하는 위성 발사체 액체 로켓 엔진의 예연소기 성능을 모사한 in-house code가 개발되고 검증되었다. CEA (Chemical Equilibrium with Applications)의 해석 알고리듬을 바탕으로 하여 예연소기의 화학 반응을 모델링 하였고, gas dynamics 모델링과 연동시켜 예연소기의 성능을 모사하였다. CEA와 비교한 결과 아주 높거나 아주 낮은 O/F ratio를 제외하고는 계산 값들이 거의 일치함을 보여 주었다. 또한 실제 엔진 (RD-8)의 성능곡선과 비교한 결과 개발된 in-house code의 계산 값들이 타당한 범위 내에서 모사되었고, 정상상태에서는 거의 비슷한 결과 값을 보였다. In-house code which simulates the performance of pre-burner in staged-combustion liquid-fueled rocket engine was developed and demonstrated. Chemical reaction of pre-burner was modeled based on analytic algorithm of CEA (Chemical Equilibrium with Applications) and gas dynamics model was incorporated with it. Comparison results between in-house code and CEA have shown small relative errors except at very high or very low O/F ratio. Also the performance curve obtained by in-house code revealed that the calculated values follow the overall trend of real engine (RD-8) performance quite well and at steady-state operation, the deviation became very small.