Initial Gas Temperature Research Articles

Technical Note: Lifetime of evaporating droplets in a closed volume

The numerical modeling of heat and mass transfer of droplets within a closed volume containing gas heated in relation to the droplets was conducted. The droplet lifetime at variation of initial values of gas and droplet temperatures and droplet mass fraction has been determined. It was found that droplet lifetime exhibits a weak dependence on the initial droplet temperature and a pronounced dependence on the initial gas temperature. Moreover, it was demonstrated that the droplet lifetime in a closed volume is longer than in infinite space. This is due to the fact that the cooling of the surrounding gas by droplets results in a decrease in the evaporation rate of the droplets. A parameter is proposed which allows for the consideration of the effect of evaporating droplets on the thermal regime of the gas-drop mixture, and which enables the generalization of the results of numerical simulation to obtain an expression for the droplet lifetime in a closed volume. The error in the use of the obtained expression is estimated. It was determined that the margin of error for the calculation results is less than ten percent.

Calculation of the required methanol consumption during the flow of wet hydrocarbon gas in a horizontal pipeline

One of the main problems that have to be solved during the development of hydrocarbon deposits is the formation of gas hydrates in pipelines. In this regard, the article presents a preventive method to struggle against the formation of gas hydrate deposits on the pipes inner walls associated with the supply of a hydrate formation inhibitor to the gas stream. The research was conducted on the basis of a mathematical model of the wet hydrocarbon gas flow in a horizontal pipeline. The research object is to determine the minimum required consumption of methanol, in which there is no formation of gas hydrate deposits on the channel inner walls. The practical significance of this study is that it is aimed at reducing the risks associated with the formation of gas hydrates in pipelines. The numerical implementation of a mathematical model of natural gas flow in a horizontal channel is based on a sequential solution of a system of four differential equations by the Runge-Kutta method of 4 orders of accuracy, followed by a search for sequential approximations of the minimum inhibitor flow rate, in which the "gas + water ↔ gas hydrate phase" transition process does not occur on the inner surface of the channel. The article presents a calculation of the proportion of a hydrate formation inhibitor in the liquid phase by solving a cubic equation using the Cardano method. Based on the computational experiments results, graphs were constructed and interpreted of the dependencies of the minimum inhibitor consumption on the soil temperature, inlet gas pressure, total water concentration in the gas flow, initial gas temperature and total gas flow rate.

Experimental Study of Influence of the Gas Flux on Urotropine Gasification in the Low-Temperature Gas Generator

The experimental study was carried out to investigate the gasification of urotropine (hexamethylenetetramine) in a low-temperature solid fuel gas generator under varying inlet gas flows. Nitrogen was applied as the filter gas. The filter gas flow was varied from 0.6 to 1.4 L/s with a step of 0.2 L/s. The inlet gas's initial temperature was equal to 910 K. It was shown that with an increase in the nitrogen flow, the fuel gasification time decreased. Increasing the flux of inlet nitrogen from 0.6 to 1.4 L/s results in an increase in the average urotropine gasification mass rate from 0.63 to 1.61 g/s. When the initial nitrogen flow is raised, the rate of fuel gasification increases almost linearly. Studies have demonstrated that the proportion of mass flows between urotropine gasification products and nitrogen remains constant regardless of the incoming gas flow. The mass flow ratio remains steady at approximately 0.9 g/g when the incoming gas flow is altered. It has been shown that the gaseous products of urotropine gasification consist of nitrogen with a small amount of hydrogen and hydrocarbons. The content of simple gaseous products does not exceed 4% vol.

Parameters effect and optimization on calciner for treating magnesium salt based on computational fluid dynamics

The magnesium salt Mg(NO3)2·2H2O from laterite nickel ore nitric acid leaching process can be reused by thermal decomposition using calciner. To improve the performance of the calciner, a new numerical model integrating the gas-particle hydrodynamics and the particle pyrolysis reaction was established by Euler-Lagrange approach. In particular, the particle size variation caused by pyrolysis reaction was considered to accurately describe the gas-particle hydrodynamics. The particle pyrolysis model was developed to realize the interphase mass transfer. The P-1 model was modified to realize interphase radiation heat transfer. Then, the influence of different parameters on the thermal decomposition processes was discussed by using the established model. Finally, the optimal conditions for Mg(NO3)2·2H2O thermal decomposition were determined via response surface optimization analysis. The results show that the thermal decomposition of Mg(NO3)2·2H2O can be improved by increasing the initial hot gas temperature, reaction zone height, and decreasing treatment capacity of Mg(NO3)2·2H2O. The degree of influence of each parameter on thermal decomposition follows the order of initial hot gas temperature > treatment capacity of Mg(NO3)2·2H2O > reaction zone height. The decomposition rate of 99.99 % is obtained at optimized conditions of initial hot gas temperature 1111 K, Mg(NO3)2·2H2O treatment capacity 251 kg/h and reaction zone height 9 m.

A Numerical Study on the Ignition and Flame Propagation for Locally Stratified Methanol/n-Heptane Dual-Fuel Mixtures

ABSTRACT Flame propagation under thermal and compositional stratifications is relevant to a wide range of applications in combustion devices. In this work, numerical studies are conducted to investigate the multi-stage ignition process and flame propagation in the stratified methanol/n-heptane-air dual-fuel mixture under engine-like conditions. Firstly, the effects of the initial gas temperature of the oxidizer (TOX) and fuel stream on the ignition process and combustion modes are investigated. The results show that TOX affects the early-stage ignition, and a fuel-rich stabilization mode is observed at low temperatures. For example, at 800 K, both cool and hot flames are initiated at the regions close to the most reactive mixture fraction, . A transition from the fuel-lean to fuel-rich and then back to the fuel-lean regions in the mixture fraction space is observed at higher temperatures. Then, hot flames propagate into the methanol/air premixture, forming quasi-steady hot-flame fronts in the fuel-rich regions at TOX = 800 and 900 K owing to the lack of oxygen and low adiabatic flame temperatures. At 1000 K, another flame front propagates into the n-heptane/air mixtures owing to enhanced reaction rate at higher local temperatures. By increasing TOX, a balance owing to the gas expansion is observed at 1020 K, and a spontaneous ignition mode appears at temperatures above 1050 K owing to the high reactivity and early ignition of the methanol/air premixture. Secondly, the effect of compositional stratification on the ignition and flame structures is investigated. Compared with the double flame structure under thermal and compositional stratification conditions, only a single flame structure is observed for those cases with uniform temperatures. A high temperature in the fuel stream region accelerates the decomposition of n-heptane, resulting in the complete consumption of oxygen.

Experimental study on combustion of H2–CO–air mixtures in closed and vented vessels

Experiments were conducted in two test facilities, a 0.25 m3 spherical vessel and a 60 m3 rectangular vented chamber, to examine the premixed combustion behavior of H2–CO mixtures. The study aims to provide data for the validation of models used for the assessment of combustion risks during postulated nuclear severe accidents and the use of syngas as an alternative fuel. The effects of fuel concentrations, molar ratio of CO/H2, initial gas temperature, steam concentration, and fan-induced turbulence on the flame dynamics are presented in this paper. The measurements are compared with literature data and predictions by empirical correlations. Within the range of the fuel concentration (≤15% in air) examined in this study, the results demonstrate that both the closed and vented combustion dynamics of H2–CO–air mixtures are similar to those of H2 only mixtures. The peak overpressures are always greater with more H2 in the mixture due to slower flame speeds of CO relative to H2. The combustion overpressures of H2–CO mixtures become similar to those of H2 mixtures when the fuel concentration is greater than what is required for downward flame propagation. The effect of fan-induced turbulence is much more pronounced for extremely lean mixtures.

Effect of the variation of oxygen concentration on the laminar burning velocities of hydrogen-enriched methane flames

The combustion properties of hydrogen-containing fuel mixtures and the effect of the variation of the oxygen content of the oxidizer are at the center of recent research interest. Laminar burning velocity measurements with varied oxygen content can help in the validation of reaction mechanisms for better simulations of combustion systems using exhaust gas recirculation (EGR) or oxygen-enriched atmosphere. Such measurements were carried out in hydrogen-enriched methane−air flames using the heat flux method with higher accuracy and a wider range of initial oxygen and hydrogen concentrations compared to the similar studies in the literature. The mole fractions of the hydrogen and oxygen contents of the initial fuel and oxidizer mixtures were varied between xH2 = 0 and 0.20, and xO2 = 0.14 and 0.23, respectively. The initial gas temperature and pressure were 298 K and 1 bar, respectively. It is demonstrated that the increase of combustion rate by the hydrogen enrichment can be compensated with the decrease of the oxygen content. This compensating effect was investigated in detail in a wide range of equivalence ratio (φ). The experimental data were simulated with 11 widely used methane combustion reaction mechanisms. The prediction accuracies of the mechanisms at lean and rich equivalence ratios were significantly different and the important reaction steps were identified using sensitivity analysis for three mechanisms. Mechanisms POLIMI-2014 and Caltech-2015 gave the best overall predictions.

Numerical Studies on Hydrogen Production from Ammonia Thermal Cracking with Catalysts

To explore and optimize the process of hydrogen production from plasma-assisted ammonia-cracking, a tubular ammonia-cracking on-site hydrogen production device with plasma-assisted ammonia combustion flue gas as the heat source was developed. Using the Temkin–Pyzhev kinetic model and the local thermal equilibrium (LTE) hypothesis, the effects of operating conditions, such as combustion flue gas temperature and ammonia flow rates, on ammonia-cracking efficiency were investigated. The numerical results are quantitatively consistent with the experiment. Ammonia cracking efficiency is notably influenced by the initial combustion gas temperature. When the gas velocity of the cracking system is less than or equal to 0.03 m/s, the cracking rate increases by 63% when the inlet temperature of the heat pipe changes from 700 K to 800 K. The cracking rate of ammonia decreased with the increase of ammonia flow rate, and this trend reached the maximum and began to weaken when the flow rate was 0.3 m/s. Longer catalyst bed length does not always mean higher cracking efficiency; the length of the cracking tube over 0.6 m shows little effect on cracking efficiency. Response surface methodology was used to conduct multi-factor analysis of the three main factors affecting the cracking rate of the cracker, namely, the temperature of the heating tube, the flow rate of flue gas in the heating process, and the inlet flow rate of the catalytic bed. It was found that the flow rate of the catalytic bed was the most significant factor affecting the cracking rate, which could be used as the main control method. The numerical results would provide technical guidance for industrial applications of on-site hydrogen production devices from ammonia decomposition.

Measurements of the laminar burning velocities of small alkyl esters using the heat flux method: A comparative study

Consistent datasets of the laminar burning velocity, LBV, for homologous fuels are indispensable for the elucidation of the structure-reactivity trends and the development and validation of pertinent detailed kinetic models. In the present study, all available LBV measurements for small alkyl esters obtained using the heat flux method have been reviewed. New results of the LBV for methyl propionate + air flames employing this method have been acquired at atmospheric pressure and initial gas temperatures from 298 to 348 K over equivalence ratios, ɸ = 0.7–1.5. Earlier experimental data for alkyl esters scattered across non-archival reports were re-examined and corrected when necessary. To prove the validity of the correction, additional LBV measurements for methyl formate and methyl butanoate were performed as well, and successfully demonstrated the consistency of the data obtained using different installations over an extended period of time. Then, the LBV of different families, such as methyl esters of various acids, formates, and acetates, along with isomers, were compared and structure-reactivity trends were assessed. Furthermore, the detailed kinetic mechanism of the authors was expanded by the reactions of methyl propionate and successfully compared with the LBV measurements for methyl formate, methyl acetate, methyl propionate, and ethyl formate. Distinct reactions controlling their flame propagation were revealed using sensitivity analysis and the origin of their rate constants is briefly discussed.

Mapping of operating windows for methane and ethane pyrolysis in the pulsed compression reactor by experiments and modelling

By modelling and experiments optimal operating conditions for methane (between 1000 and 3000 K, 300 bar) and ethane pyrolysis (between 800 and 3200 K, 400 bar) in the pulsed compression reactor (PCR) were evaluated. The PCR is a free piston reactor that can compress a gas from atmospheric pressure up to 600 bar in a single pulse. A differential internal energy balance was used for solving the temperature and pressure during the compression. The GERG-2008 equation of state was used to account for non-idealities. To predict the reaction products, both chemical equilibrium (EQ) and kinetic models available from literature were evaluated. The kinetic models (GRI-mech, Holmen et al., 1995 etc.) did not predict part of the experiments well. The EQ model predicts trends well. Therefore, the EQ model was used to map the operating domains. The aim is to reach a maximum concentration of products (olefins and aromatics) in the product gas and a conversion of 20% or more. For methane pyrolysis at 1600 K and 320 bar with nitrogen as diluent and an initial gas temperature of 588 K, the model analysis led to an experimentally observed factor 5.2 increase in ethylene in the outlet (1.4%mol) compared to a previous optimum point (Slotboom et al., 2021). With ethane pyrolysis 9% of ethylene was obtained at a conversion of 66% with an ethylene selectivity of 61% around 1480 K and 400 bar. Further analysis with the EQ model showed that for the thermal coupling of methane with an initial gas temperature of 773 K, conversion is possible without diluting with nitrogen. For ethane decomposition nitrogen is always needed as a diluent up to 773 K.

SRG/eROSITA discovery of a radio-faint X-ray candidate supernova remnant SRGe J003602.3+605421 = G121.1−1.9

ABSTRACT We report the discovery of a candidate X-ray supernova remnant SRGe J003602.3+605421 = G121.1−1.9 in the course of the SRG/eROSITA all-sky survey. The object is located at (l, b) = (121.1°, −1.9°), is ≈36 arcmin in angular size, and has a nearly circular shape. Clear variations in the spectral shape of the X-ray emission across the object are detected, with the emission from the inner (within 9 arcmin) and outer (9–18 arcmin) parts dominated by iron and oxygen/neon lines, respectively. The non-equilibrium plasma emission model is capable of describing the spectrum of the outer part with an initial gas temperature 0.1 keV, final temperature 0.5 keV, and ionization age ∼2 × 1010 cm−3 s. The observed spectrum of the inner region is more complicated (plausibly due to the contribution of the outer shell) and requires a substantial overabundance of iron for all models that we have tried. The derived X-ray absorption is equal to (4–6) × 1021 cm−2, locating the object at a distance beyond 1.5 kpc, and implying its age ∼(5–30) × 1000 yr. No bright radio, infrared, H α, or gamma-ray counterpart of this object has been found in the publicly available archival data. A model invoking a canonical 1051 erg explosion (either SN Ia or core collapse) in the hot and tenuous medium in the outer region of the Galaxy ∼9 kpc away might explain the bulk of the observed features. This scenario can be tested with future deep X-ray and radio observations.

A numerical investigation of methane pyrolysis in a molten catalyst Bath–A single bubble approach

A dynamic one-dimensional numerical model of methane pyrolysis within a rising and pyrolysing bubble in a column of molten Ni0.27Bi0.73, as a molten catalyst, is presented. The model predicts both the behavior of the rising bubble in the column and the chemical reactions within it, accounting for any variations in bubble diameter and rising velocity, which have previously been assumed to be constant. The conservation equations of energy, mass and momentum are solved simultaneously using the implicit Gauss–Seidel numerical method. The model accounts for the main parameters contributing to the methane pyrolysis reaction. The reliability of the model was assessed by comparison with the available experimental data from the literature and a reasonable agreement was found. Considering the model assumptions, the results show that, for the assessed conditions, more than 97% of the overall conversion occurs at the interface of the bubble and the molten bath, while the reaction within the bubble contributes only <3% of the overall conversion. A sensitivity analysis was also undertaken to the variations in the bubble size, column height, molten bath temperature, pressure, gas composition and temperature. Calculations show that methane conversion is more sensitive to the molten bath temperature than the initial gas temperature. Furthermore, it decreases significantly with any increase in pressure. Also, at pressures of > 2 MPa, the equilibrium condition is achieved within the bottom one-third of the column for the assessed conditions.

The effect of process temperature and powder composition on microstructure and mechanical characteristics of low-pressure cold spraying aluminum-based coatings

The effect of operating gas temperature and powder type on microstructure and mechanical characteristics of cold spraying coatings deposited on EZ33A-T5 magnesium alloy was studied. Three aluminum-based cold spraying powder mixtures Al + Zn, Al + Al2O3 and Al + Zn + Al2O3 were used for the investigation. Deposition was performed using D423 low-pressure cold spray system at operating gas pressure of 1.0 MPa and different temperatures –300 °C, 450 °C, and 600 °C. The coatings microstructure was investigated with optical and scanning electron microscopy. Mechanical properties of the coatings were characterized through standard test methods for adhesion and cohesion strength, and standard test methods for Vickers hardness of thermal spray coatings. The results demonstrate that with increasing initial gas temperature at spraying nozzle inlet from 300 °C to 600 °C, an increase in the porosity of the coatings of all investigated powder mixtures can be observed. Microstructure characterization showed an increase in porosity from 2.3% to 4.1% for Al + Zn powder mixture, from 2.1% to 3.5% for Al + Al2O3 powder mixture, and from 2.5% to 5.6% for Al + Zn + Al2O3 powder mixture. The minimum porosity was obtained at 450 °C for all investigated powder mixtures. Adhesion and cohesion strength and microhardness of coatings were reach their maximum value at 450 °C. The best performance was obtained for Al + Al2O3 powder mixture: coating adhesion—31.9 MPa (was limited by the bonding strength of the glue), cohesion—93.5 MPa, microhardness—81 HV0.15. The influence of Al2O3 particles in the powder mixture on the above-mentioned parameters was also established. The results show that the presence of ceramic particles in powder mixtures can positively effect porosity level and mechanical characteristics.

Cluster growth in binary N2–Kr supersonic jets: Effect of initial gas temperature and krypton gas concentration

An electron diffraction diagnostics of substrate-free clusters formed in N2–Kr binary jets expanding through a supersonic nozzle into a vacuum was carried out. Gas mixtures contained 0.5, 1, and 6 mol % krypton, the measured average sizes of aggregations in the cluster beam varied from 500 to 30000 molecules per cluster. A change in the nucleation mechanism in the jet from homogeneous to heterogeneous was revealed when the temperature of the gas mixture at the nozzle inlet T0 decreased from 120 to 100 K, which had a profound effect on the sizes, phase composition, and component composition of the clusters. The effect of cluster growth suppression by adding impurity with stronger intermolecular forces was revealed for the first time. It is shown that the effect is caused by the kinetics of gas condensation in a supersonic jet and is manifested at T0 = 120 K when the krypton gas content increases to 6 mol %. It was established that the intensification of cluster growth by inserted krypton nucleation centers at T0 = 100 K occurs through an increase in the fraction of the fcc phase compared to the hcp.

Cenosphere Formation and Combustion Characteristics of Single Droplets of Vacuum Residual Oils

ABSTRACT The ignition, combustion characteristics, and cenosphere formation of single droplets combustion of four vacuum residues (VRs) from different refineries with various asphaltene contents were studied experimentally. The single droplets of VRs were suspended at the tip of a silicon carbide fiber and heated in air at temperatures of 973 and 1023 K, respectively, in an electrically heated tube furnace. The ignition and combustion behavior of the VRs were recorded using a CCD camera, which enabled the determination of droplet size, ignition delay time, flame duration, and cenosphere size. The effect of initial droplet size, gas temperature, and asphaltene content on the ignition delay time, flame duration, cenosphere morphology, and particle size were investigated. The whole ignition and combustion process of single droplets of the VRs consisted of five stages in succession: (1) pre-ignition, mainly involving the evaporation of highly volatile components from the droplet surface; (2) steady combustion of fuel vapors evaporated from the droplet surface; (3) splashing combustion of fuel vapors evaporated from droplet interior; (4) disruptive combustion due to thermal decomposition of asphaltene; and (5) solid residue ignition and combustion. A visible and sooty flame was formed upon ignition and lasted during stages 2–4. The droplet size increased sharply in the stage 4 due to the thermal decomposition of asphaltene, which was more profound for VRs with higher asphaltene content and at higher gas temperatures. The ignition delay time increased with increasing initial droplet size and gas temperature but varied little as the asphaltene content in the VRs increased, suggesting that the ignition process of VRs was controlled by the vaporization of high volatile components on the droplet surface. The thermal decomposition of asphaltene produced solid residue, which was in the form of a cenosphere with the shell thickness being ca. 20 μm and a number of blowholes presented in the shell. The VRs with higher asphaltene content had more and bigger blowholes. The ratio of cenosphere particle size to initial droplet size is independent of the initial droplet size but almost increased linearly with the asphaltene content in the VRs.

The effect of mixing and heat transfer on regression rate of TAGN-based fuel in a segregated AP/TAGN solid motor

The effect of mixing and heat transfer on regression rate of TAGN-based fuel of a segregated AP/TAGN solid motor is studied in the present study. A regression rate model of TAGN-based fuel under coupled combustion is developed and validated based on detailed reaction mechanism. The two-dimensional mixing characteristics in boundary layer and the effect on regression rate of TAGN-based fuel are analyzed in detail. The simulation results show that the increase of initial temperature of oxidizer gas leads to better mixing in the axial direction and higher temperature of burning surface. However, the mass concentration of O2 decreases greatly due to the increasing consumption by primary combustion reactions of AP-derived gaseous species. Therefore, the regression rate of burning surface decreases slightly. With inflow Mach number increasing from 0.32 to 0.75, mixing in the boundary layer is greatly enhanced. Therefore, both the temperature and regression rate increase with inflow Mach number. As pressure increases from 4 MPa to 10 MPa, the primary reactions of AP-derived gas species are also enhanced. Therefore, the mass concentration of O2 decreases rapidly, which leads to oxygen-lean combustion in the combustion chamber. Therefore, the temperature of burning surface decreases while the regression hardly varies despite of the better mixing near the burning surface at high pressure. The results show that the coupled combustion reactions between inflow oxidizer gas and fuel gas mainly occur in a narrow belt-like region of the boundary layer. The results show that the regression rate of solid fuel in the segregated solid motor is controlled by the competition between primary combustion and coupled combustion.

Numerical study on transient regression rate and combustion characteristics of segregated AP-based oxidizer/TAGN-based fuel

In the present study, a two-dimensional combustion model is established to simulate transient flow and combustion characteristics of a segregated oxidizer/fuel solid motor (SOFSM). A detailed gas-phase reaction kinetic mechanism with 35 species and 190-step reactions is developed to describe the gas-phase combustion process between AP-based oxidizer and TAGN-based fuel. The effects of mass flux and initial temperature of inflow oxidizer gas on the transient flow and combustion characteristics of the TAGN-based fuel are numerically investigated. With the mass flux of inflow oxidizer gas increasing from 249 kg·m−2·s−1 to 995 kg·m−2·s−1, the maximum spatially averaged regression rate of the burning surface of TAGN-based fuel increases by almost 200 % and the combustion efficiency first increases and then decreases with a maximum combustion efficiency of 94.3 % at the mass flux of 442 kg·m−2·s−1. With the initial temperature of inflow oxidizer gas increasing from 1000 K to 1750 K, the maximum average regression rate of the burning surface of TAGN-based fuel increases by around 10 %. Meanwhile, the combustion efficiency increases from 88.38 % to 95.8 %. During the combustion process (almost 3 s), the spatially averaged regression rate remains basically stable from 0.5 s to 2 s and increases slightly from 2.0 s to 3.0 s for given mass flux and initial temperature, indicating the combustion process is basically stable under the studied conditions. The results also show that during the transient combustion process, a large vortex first appears and then is split into a major vortex and a small one in the post-combustion chamber. With the increase of the mass flux and initial temperature of inflow oxidizer gas, the size of the vortex increases while the center position of the vortex moves towards the burning surface, which significantly enhances the mixing process and increases combustion efficiency.

Investigation on multi-physical field simulations of blade ECM using vertical flow

Electrochemical machining (ECM), an advanced manufacturing technology, is widely used in aero-engine blades machining. In traditional ECM, the electrolyte flows through the inter-electrode gap (IEG), generating hydrogen bubbles and heat, which affect the conductance and thus influence the machining quality. This paper focuses on the effect of bubble movement on the flow field and the machining quality of ECM. A novel vertical flow mode of electrolyte is proposed according to the bubbles dynamics analysis. Multi-physical fields simulations of blade ECM using vertical and horizontal flows were carried out. With an initial gas void fraction, flow rate, and temperature at the inlet of 0, 19.7 m/s, and 302.65 K, respectively, in both flow modes, the vertical flow reduces the gas void fraction, flow rate, and temperature at the outlet by 2.4%, 0.4 m/s, and 0.6 K, and increases the conductance by 0.47 S/m. Thus, the vertical flow of the electrolyte is beneficial in reducing the gas void fraction and controlling the temperature rise, while enhancing the conductance. Then, the corresponding experiments using a vertical flow were carried out. The maximum machining deviation ranges from 3.4 to 75.6 μm and surface roughness Ra < 0.35 μm. The machining quality is high and the variation observed in the experiments is consistent with the simulation results, the validity and correctness of the simulations are verified. Thus, the vertical flow mode proposed in this paper is appropriate, can be used for other complex structures in ECM.

Study on homogeneous charge compression ignition combustion in argon circulated closed cycle hydrogen engine

It is important to improve thermal efficiency and to reduce harmful exhaust gas emissions in internal combustion engines. A closed cycle engine system that uses a monatomic molecular gas as the working fluid can be expected to have high thermal efficiency due to the high specific heat ratio of the gas. Several studies have been reported on closed cycle engines with conventional spark ignition or compression ignition. This research newly proposes an argon circulated closed cycle homogeneous charge compression ignition (HCCI) engine system fueled with hydrogen. In this engine system, effects of in-cylinder gas initial temperature and residual water in recirculated gas on combustion characteristics were investigated. The results show that the system with argon circulation has the wider range of operable conditions and the higher thermal efficiency compared to the case with air as the working fluid.

An improved reduced model for the evaporation and decomposition of urea-water solution (UWS) droplets

Urea-water-solution (UWS) is often used as a source for the reduction agent ammonia for the selective catalytic reduction of nitric oxides in combustion after-treatments systems. In applications, however, some technical problems, for example the formation of solid residuals or incomplete decomposition of urea, appear. To solve these problems complex phenomena must be taken into account which involve turbulent flow, multiple phases, chemical reactions of products of urea decomposition with exhaust gas etc. Hence, in order to understand and optimize the process of nitric oxides reduction, these very complex processes with different temporal and spatial scales need to be addressed with a reasonable computational effort. In this study the influence of the urea decomposition in the liquid phase onto the evaporation and decomposition of UWS droplets is investigated. It is shown that the liquid chemistry model (13 species and 13 reactions) appropriately describes the decomposition. A detailed parametric and comparative study for typical system parameters of the NOx reduction conditions is performed. Moreover, a simple but robust model reduction concept is suggested and employed to describe the process with only 3 parameters. A self-similar behavior of the droplets during the evaporation process is used for the reduced description and applied to the entire droplet evaporation process. The diameter and the species source terms can be represented with a simple polynomial model for the boundary and initial conditions ambient gas temperature, water concentration and initial droplet diameter, by using a fixed number of tabulation parameters.