Reactant Injection Research Articles

Numerical Investigation of the Effect of Equivalent Ratio on Detonation Characteristics and Performance of CH4/O2 Rotating Detonation Rocket Engine

Equivalent ratio (ER) is an important factor affecting detonation characteristics and propulsion performance of rotating detonation rocket engine (RDRE). In this paper, the effects of different equivalent ratios detonation characteristics and thrust performance of methane-oxygen RDRE were studied by 2D numerical simulation. The premixed reactants were injected through the injection holes to simulate the discrete injection of reactants on the injection panel in actual RDRE, the number of injection holes was 60 and 120. The results show that there is hybrid detonation mode (HDM), co-direction multi-wave detonation mode (CMM) and unstable detonation mode (UDM) in detonation combustion due to the influence of equivalent ratio and the number of injection holes, and the co-directional multi-wave detonation mode is beneficial to the thrust stability of RDRE. At the last, the number of detonation waves in RDRE decreases with the increase in the equivalent ratio, and the specific impulse (Isp) increases with the increase of the equivalent ratio.

Enhanced Reaction Kinetics in Stationary Two-Phase Flow through Porous Media.

Understanding the interaction between multiphase flow and reactive transport in porous media is critical for many environmental and industrial applications. When a nonwetting immiscible phase is present within the pore space, it can remain immobile, which we call unsaturated flow, or move, resulting in multiphase flow. Previous studies under unsaturated flow conditions have shown that, for a given flow rate, the product of a mixing-driven reaction increases as wetting phase saturation decreases. Conversely, the opposite effect is observed for a given Péclet number (i.e., the flow rate is adapted depending on the wetting phase saturation). However, the impact of multiphase flow dynamics on mixing-driven reactions is poorly understood due to experimental and numerical challenges. To assess the impact of multiphase flow conditions on product formation, we use an optimized chemiluminescence reaction and an experimental setup that allows the separate injection of reactants along with a stationary two-phase flow. In our experiments, the mass of the reaction product under stationary two-phase flow conditions increases faster than Fickian beyond the diffusive time. The global kinetics initially increase before experiencing a monotonic decrease with significant fluctuations caused by the displacement of the nonwetting phase. For a given flow rate of the wetting phase, product formation depends on the flow rate of the nonwetting immiscible phase.

Flow-field analysis and performance assessment of rotating detonation engines under different number of discrete inlet nozzles

This study explores in depth rotating detonation engines (RDEs) fueled by premixed stoichiometric hydrogen/air mixtures through two-dimensional numerical simulations including a detailed chemical kinetic mechanism. To model the spatial reactant non-uniformities observed in practical RDE combustors, the referred simulations incorporate different numbers of discrete inlet nozzles. The primary focus here is to analyze the influence of reactant non-uniformities on detonation combustion dynamics in RDEs. By systematically varying the number of reactant injection nozzles (from 15 to 240), while maintaining a constant total injection area, the study delves into how this variation influences the behavior of rotating detonation waves (RDWs) and the associated overall flow field structure. The numerical results obtained here reveal significant effects of the number of inlets employed on both RDE stability (self-sustaining detonation wave) and performance. RDE configurations with a lower number of inlets exhibit a detonation front with chaotic behavior (pressure oscillations) due to an increased amount of unburned gas ahead of the detonation wave. This chaotic behavior can lead to the flame extinguishing or decreasing in intensity, ultimately diminishing the engine's overall performance. Conversely, RDE configurations with a higher number of inlets feature smoother detonation propagations without chaotic transients, leading to more stable and reliable performance metrics. This study uses high-fidelity numerical techniques such as adaptive mesh refinement (AMR) and the PeleC compressible reacting flow solver. This comprehensive approach enables a thorough evaluation of critical RDE characteristics including detonation velocity, fuel mass flow rate, impulse, thrust, and reverse pressure waves under varying reactant injection conditions. The insights derived from the numerical simulations carried out here enhance the understanding of the fundamental processes governing the performance of RDE concepts.

Transient-assisted plasma etching (TAPE): Concept, mechanism, and prospects

Atomic layer etching (ALE) schemes are often deemed economically unviable due to their slow pace and are not suited for every material/hard-mask combination. Conversely, plasma etching presents pattern profile challenges because of its inability to independently control ion and neutral flux. In this work, we introduce a new cyclic transient-based process, called transient-assisted plasma etching (TAPE). A cycle of TAPE is a short exposure step to a sustained flow of reactant before the reactant gas injection is stopped in the second step, resulting in a plasma transient. As the plasma ignites and a substantial amount of etchant remains, a chemically driven etching process occurs, akin to conventional etching. Later in the transient, the modified surface is exposed to a reduced etchant quantity and a sustained ion bombardment, in a similar way to ALE. The cointegration of conventional etching and atomic layer etching allows interesting compromises between etch control and processing time. Going for a transient plasma allows to provide the time and conditions needed for the necessary plasma-surface interactions to occur in one step. In this perspective, the mechanisms behind etch rate, profile correction, and conservation of surface composition using amorphous carbon, as a benchmark, are discussed.

An Analysis of Fixed-Bed Catalytic Reactors Performances for One-Stage Butadiene Synthesis from Ethanol

The present study assesses, using a theoretical approach, the performances of two widely used fixed-bed reactors for the ethanol-to-butadiene (ETB) one-stage (Lebedev) process: multibed adiabatic reactors (MBAR) with inter-bed heating and a multitubular reactor (MTR). The mathematical model consists of mass and heat conservation equations at catalyst particle and particle bed scales, coupled with a published kinetic model specific for a modified MgO–SiO2 catalyst. The process simulations at the level of catalyst particle have shown that the inter-phase concentration and temperature gradients are negligible, the only physical step with a limiting influence on process kinetics being the internal diffusion. A simplified version of the reactor model was also formulated, including empirical expressions developed in the study for the calculation of internal effectiveness factors. The reactor simulations highlighted that the MBAR with inter-bed heating by injection of hot reactants provides worse butadiene (BD) yields as a consequence of reduced reaction times (due to reactant by-pass of catalyst beds). The MBAR with inter-bed heating using heat exchangers provides better performances but inferior to those of MTR if the number of catalyst beds is less than six. A preliminary optimization study for the MBAR and MTR is also presented. The results showed that the maximization of BD yield has the drawback of a low BD production rate, whereas the maximization of BD production rate corresponds to a relatively low BD yield and high ethanol and inert recycles. A trade-off between the two extreme cases can be attained by maximizing the income generated by reactor operation.

Reactivity of tert‐butylperoxyl radical with some phenylthiazolidine derivatives and probucol

AbstractThe hybrid molecule phenylthiazolidine derivatives and probucol were kinetically examined as antioxidants (AOs) in scavenging tert‐butylperoxyl radical (t‐BuOO•) with comparable to the reference AO, butylated hydroxytoluene (BHT). The anti‐t‐BuOO• reactivity of phenylthiazolidine derivatives and probucol was established using the direct kinetic electron paramagnetic resonance (EPR) technique with pulse reactant injection. Absolute values of the bimolecular reaction rate constants and antiradical capacities of the studied compounds were measured from −63 to 0°C. The main antiperoxylradical sites of the compounds under study were revealed.High removal ability of t‐BuOO• by (2‐(4‐hydroxyphenyl)thiazolidine), 4‐[thiazolidin‐2‐yl]benzene‐1,2‐diol, 2‐(4‐hydroxyphenyl)thiazolidine‐4‐carboxylic acid and probucol was connected with the reaction of hydrogen atom abstraction from phenolic OH group.Weaker antiperoxylradical reactivity of 2‐phenylthiazolidine was connected with the slower reaction of hydrogen atom abstraction from benzylic C–H bond in reference to nitrogen and sulfur atoms compared with the phenolic OH group. It is found that sulfide groups had much weaker participation in antiperoxylradical reactivity of the studied compounds. It is concluded that removal of alkylperoxyl radicals by oxidizable phenylthiazolidine derivatives and probucol may partially account for biological activity of their compounds.

Pattern selection by material aging: Modeling chemical gardens in two and three dimensions

Chemical gardens are complex, often macroscopic, structures formed by precipitation reactions. Their thin walls compartmentalize the system and adjust in size and shape if the volume of the interior reactant solution is increased by osmosis or active injection. Spatial confinement to a thin layer is known to result in various patterns including self-extending filaments and flower-like patterns organized around a continuous, expanding front. Here, we describe a cellular automaton model for this type of self-organization, in which each lattice site is occupied by one of the two reactants or the precipitate. Reactant injection causes the random replacement of precipitate and generates an expanding near-circular precipitate front. If this process includes an age bias favoring the replacement of fresh precipitate, thin-walled filaments arise and grow-like in the experiments-at the leading tip. In addition, the inclusion of a buoyancy effect allows the model to capture various branched and unbranched chemical garden shapes in two and three dimensions. Our results provide a model of chemical garden structures and highlight the importance of temporal changes in the self-healing membrane material.

Solar metallurgical process for high-purity Zn and syngas production using carbon or biomass feedstock in a flexible thermochemical reactor

Co-production of high-purity Zn and syngas via carbothermal reduction of ZnO was performed in a directly-irradiated concentrated solar reactor, thereby converting and storing intermittent sunlight into high-value chemical fuels and commodities. On-sun experiments were carried out by varying operating parameters including solid carbonaceous feedstocks (either solid carbon or beech wood biomass) in batch and continuous modes at 950–1350 °C, demonstrating solar reactor flexibility and robustness. Decreasing pressure (150–400 hPa) promoted both ZnO reduction rate and net ZnO conversion above 78%, thus enhancing Zn production yield. Nevertheless, CO selectivity decreased because of rising CO2 due to the residence time decrease. A remarkable increase in gas production rates/yields, CO selectivity, and reaction extent was highlighted when increasing temperature during continuous pellets reactant injection. Furthermore, utilizing wood biomass as a sustainable green reducer was proved to be an attractive choice to produce both metallic Zn and high-quality syngas in a single process consisting of biomass gasification with solid ZnO. Zn content exceeding 90 wt% was demonstrated for both batch and continuous tests, unveiling high reactor performance for the metallurgical process. The energy content of the feedstock was upgraded by the solar power input (maximum energy upgrade factor up to 1.2), and the maximum solar-to-fuel energy conversion efficiency up to ∼ 6% was achieved with continuous reactant injection. The high-purity Zn can be further used to produce fuel via CO2-splitting in a complete and fast reaction.

Dynamic simulation of a solar-autothermal hybridized gasifier: Model principle, experimental validation and parametric study

Solar thermochemical fuel production technologies, such as biomass gasification, are confronted to the intermittency of solar irradiance. The development of dynamic simulation tools is thus required to design around-the-clock control strategies. An innovative model was developed here, based on unsteady mass and energy conservation equations, considering gas-phase thermodynamic equilibrium and heterogeneous char oxidation kinetics. The char accumulation and gas species production rates were therefore tracked throughout operation, giving insight into the reactor dynamics with optimized computational cost. The model was validated via a comparison with experimental results, regarding both thermal and chemical reactor performances. Simulations reliably predicted the evolution of reactor temperatures and syngas production rates, under both solar-only and hybridized (solar-autothermal) operation. Parametric studies regarding the impact of reactants injection rates on steady-state performances were finally proposed. Steam addition (0.22 to 0.60 g/min) increased the syngas H2:CO molar ratio significantly (1.13 to 1.47). Biomass addition (1 to 3 g/min) boosted the solar-to-fuel efficiency (0.22 to 0.47), but altered the reactor temperature. Finally, oxygen addition kept the reactor running despite fluctuations of solar power, while decreasing the total H2 + CO production and cold-gas efficiency linearly. A constant H2 + CO production (2.17 NL/min) could however be achieved by feeding additional biomass and oxygen during hybridization, thus limiting the cold-gas efficiency decrease and improving the reactor energy efficiency (0.29 to 0.40). Such a dynamic reactor model can be further applied to hybridized gasification process optimization and dynamic control under real fluctuating solar irradiation conditions.

Experimental assessment of an indirect method to measure the post-combustion flue gas flow rate in waste-to-energy plant based on multi-point measurements

In waste-to-energy plants, the determination of the flue gas flow rate in the post-combustion section is of the utmost importance, e.g., for the verification of the compliance to the minimum residence time requirements (tres>2s) or for the control of flue gas treatment reactant injection, but the harsh conditions (high temperature and content of pollutants) do not allow for a direct measurement. The present work reports an experimental assessment of an indirect approach to estimate the flue gas flow rate in the post-combustion section of a rotary kiln plant with reduced uncertainty. This method consists on the direct measurement of the flow rate at a “colder” section of the plant (the boiler outlet) combined to the simultaneous measurements of flue gas composition measurements upstream and downstream of the boiler. From these measurements it is then possible to determine the mass of false air and to retrieve the actual flue gas flow-rate in the post-combustion chamber. A massive experimental campaign has been conducted at a full-scale medical waste incinerator, in which flue gas flow rate was estimated at different waste loads and ambient conditions. The results show that the percentage of false air can be significant and simply neglecting it can lead to substantial under-performance of the plant. Issues related to the practical implementation of the methods are illustrated in detail and the possibility to extend the methodology towards an online determination of post-combustion flue gas flow rate is discussed.

Effect of injection dynamics on detonation wave propagation in a linear detonation combustor

The effect of reactant injection and mixing on detonation wave propagation is studied in a self-excited, optically-accessible linear detonation combustor operated with natural gas and oxygen. Fuel injection and mixing processes are captured with 100 kHz planar laser induced fluorescence (PLIF) measurements of acetone tracer injected into the fuel stream. Measurements are acquired at multiple orthogonal planes downstream of the reactant injection site to investigate the three-dimensional mixing field in the chamber. The fuel distribution field is correlated with simultaneously acquired OH* chemiluminescence measurements that provide a qualitative indication of heat release in the combustor. These measurements are used to provide quantitative information of the fuel injector recovery process and its impact on detonation wave structure across a range of equivalence ratios. While significant differences in the detonation wavefront are observed with change in equivalence ratio, the characterization of the fuel refill process into the chamber after the passage of the detonation wave highlights some key generalizable features. The time available for fuel recovery is consistently between 12 – 19% of the detonation wave period across an equivalence ratio range of 0.83 – 1.48. A linear correlation between injector recovery times and the ratio of the average detonation wave pressure amplitude relative to the pressure drop across the fuel injector is observed. Instantaneous and phase-averaged measurements of acetone-PLIF with the time-coincident OH* chemiluminescence images provide qualitative information of wave structure and injection dynamics along with quantification of fuel injector recovery, a key metric that drives combustor operation and performance. These measurements significantly enhance the ability to obtain detailed information on the intra- and inter-cycle spatiotemporal evolution of the reactant refill process and its coupled effects on the detonation wave structure and propagation.

Atomic layer deposition of lithium metaphosphate from H3PO4 and P4O10 facilitated via direct liquid injection: Experiment and theory

We report the use of H3PO4 as a reactant in atomic layer deposition (ALD) of lithium metaphosphate. The ALD growth cycle starts by injection of the lithium tetramethyl heptadionate (LiTMHD) precursor followed by injection of the H3PO4 reactant. Both the reactant and the precursor are injected into the ALD chamber via direct liquid injection, which allows us to achieve ALD without plasma or high temperatures. The liquid H3PO4 solution, injected 10 s after the precursor, evaporates and decomposes into the gaseous mixture of H3PO4, P4O10, and H2O. The H3PO4 and P4O10 molecules finally react with the LiTMHD molecules adsorbed at the sample substrate, which results in the film growth. The obtained films are amorphous, and the x-ray photoelectron spectroscopy measurements reveal the LiPO3 composition. The growth process exhibits the features of the ALD, namely, the saturation of the growth rate with cycle duration and the maximum growth rate when the number of the injected precursor/reactant molecules reaches a critical value. We show theoretically that the growth rate is governed by the gas-phase equilibrium between H3PO4 and P4O10, both of which are reactive but to different degrees. Depending on the temperature and other conditions, we obtain a reactive gas adjustable at will between pure H3PO4 and pure P4O10. Our theory explains essential features of the observed ALD growth. It determines which of the two reactants (H3PO4 or P4O10) causes the growth and which of them provides a faster growth.

Small-size rotating detonation engine: scaling and minimum mass flow rate

Rotating detonation engines (RDEs) have been observed to exhibit several operating modes and instabilities under different operation conditions (reactant mixture, injection pressure, engine geometry, injection mass flow rate, etc.). We develop the simplest model possible describing the operation of an RDE. This model takes into account the dependence of detonation properties on engine conditions, the injection process, and the geometric constraints. Using this model, we predict the lowest allowable reactant injection rates that allow an RDE to operate with a single detonation wave propagating in the annular combustion chamber. This model is compared with experimental results of engines running on H $${}_2$$ /O $${}_2$$ and C $${}_2$$ H $${}_4$$ /O $${}_2$$ .

Lattice Boltzmann study of porosity-permeability variation in different regimes of non-isothermal dissolution in porous media

Characterizing the process of dissolution in porous media by thermally energized reactants is of great importance to different aspects of the geothermal science and petroleum industry. Notably for the petroleum industry, understanding the porosity-permeability relationship in different dissolution regimes significantly helps the optimal design of wellbore acidizing processes. Thus, in this paper, reactive flow of a non-isothermal solvent in a complex porous medium is studied at pore scale and the evolution of permeability values with dissolution advancement are thoroughly investigated. Dimensional analysis of the governing transport equations is also performed and it is shown that generally 10 dimensionless numbers characterize such processes. The effects of Arrhenius number (Ar), temperature ratio (ψ), Peclet (Pe) and Damkohler (Da) on morphology is investigated in a wide range and the corresponding porosity-permeability diagrams are presented for each regime. It is also found that at high Pe and Da where initially wormhole pattern would be dominant, decrease of ψ below 1 (injection of cooler reactant), delays face dissolution and shifts the dissolution shape toward a more uniform pattern. In contrast, by letting ψ>1 (injection of warmer reactant), the pattern shifts toward a more facial dissolution whose intensity is characterized by Ar. At low Pe and high Da, it is found that face dissolution pattern would be dominant and letting ψ>1 does not considerably affect the pattern. However, if ψ is lowered below 1, the local reaction rates are decreased and dissolution pattern slightly shifts toward a more uniform dissolution. Finally, when both Pe and Da are low, a competition between face dissolution and uniform dissolution is established. In this case, letting ψ<1 reduces the local Da and leads to a more uniform dissolution and if ψ>1, the pattern shifts to a more facial one. The role of Ar is also discussed and shown to act as an amplifier for ψ effects.

Effects of slot injection on detonation wavelet characteristics in a rotating detonation engine

Two-dimensional numerical simulations are performed to investigate the effects of spatially discrete slot injection of reactants on the features of detonation wavelets in a rotating detonation engine (RDE). The detonation dynamics is described by a model based on the reactive Euler equations coupled with two-step, induction-reaction kinetics. By varying injection conditions and the chemical sensitivity of the reactive mixture, a parametric study is carried out to examine the influence of the injection-slot area ratio α on the detonation wavelet patterns and different flow features inside an RDE combustion chamber. The simulation results demonstrate that the injection conditions, i.e., stagnation temperature and pressure, have a similar influence on slot-ozzle rotating detonation wavelets (RDWs) as compared with the mini-nozzle RDWs reported in a previous study. The corresponding mass flow rate and inhomogeneity generated due to the presence of slot injection, however, play a key factor in the self-sustained rotating detonation and its frontal structure.

The use of polyurethane foam waste resulting from the technological process of insulation of refrigeration enclosures in obtaining constructions panels with sound-absorbing and thermally insulating properties

Refrigerated enclosures - refrigerators, refrigerated units, vans for transporting perishable goods are thermally insulated with polyurethane foam. The insulation process involves the pressure injection of the component reactants into the spaces to be insulated. Following the polyaddition reaction, the foaming-expansion process takes place with an increase in volume. Finally, a spongy polymeric mass is obtained, which filled the spaces where insulation had to be carried out and which also generated an excess of material which is subsequently removed by mechanical means. Excess material results from the initial dosage of the insulation material and must exist to ensure that the spaces to be insulated are completely filled. Polyurethane foam waste is a real problem for several reasons. With a large volume, it takes up a lot of storage space with unpleasant consequences, polyurethane foam is a slightly non-degradable reactive material that persists in the environment. The combustion of polyurethane foam waste is not an option to be adopted because the combustion, in addition to CO2, also results a series of particularly toxic substances: isocyanates, phosgene, cyan.

Injection Metal-Assisted Catalytic Etching (MACE) of Si Powder: Discovery of Low-Load MACE and Pore Distribution Tunability Using Ag, Au, Pd, Pt and Cu Catalysts

Injection of H2O2 to control both the rate and extent of etching allowed us to discover a new regime of MACE with extremely small quantities of deposited metal as a catalyst: low-load MACE (LL-MACE).1 The structure of particles subjected to LL-MACE is completely different compared to conventional MACE. Si nanowires and mesoporous micro- or nano-particles are produced with high yield, low cost and controlled properties suitable for applications in e.g. lithium-ion batteries, drug delivery, as well as biomedical imaging and contrast enhancement. Different metal catalysts behave in distinct manners than can be traced to differences in nucleation and reaction kinetics.2 Not only Ag, Au, Pd and Pt but also inexpensive Cu can be used to perform LL-MACE.Previously, controlled reactant injection and acetic acid were used to transform stain etching into the improved process known as regenerative electroless etching (ReEtching).3 Here injection and acetic acid are exploited to enhance MACE and extend it to the low-load regime. Ag, Au, Pd, Pt and Cu can be galvanically deposited onto Si powder out of solutions of HF(aq). Nucleation of deposited metal nanoparticles is made more uniform by dispersing the Si powder in acetic acid and injecting the dissolved metal ions at a controlled rate. The use of a syringe pump to deliver not only metal ions during deposition but also the oxidant (H2O2) during MACE is essential for increased product uniformity and yield. Temperatures of ~0–50 °C and grades of Si (i.e. electronics grade Si with various doping levels or metallurgical grade Si) produced significantly different pore size distributions. Doping levels and the associated changes in band bending and space charge layer width4 are linked to changes in the pore size distribution.As shown in Fig. 1(A), high loading of Ag resulted in deposition of dendrites and Ag particles. These broke into ~50–100 nm Ag nanoparticles that etched in a correlated fashion to generate parallel etch track pores. The uniform size distribution of the Ag nanoparticles was generated dynamically during etching. This conventional high-load MACE (HL-MACE) did not produce Si nanowires (Si NWs) directly. However, etch track pore walls were cleaved readily by ultrasonic agitation to form Si NWs. Etching far removed from the metal nanoparticles (remote etching) also occurred for highly doped Si.As shown in Fig. 1(B), reducing the loading of Ag by a factor of 100 to 1000 compared to HL-MACE created 10–30 nm nanoparticles that etched in an uncorrelated fashion and generated randomly directed etch track pores. Significant etching far removed from the Ag catalyst also occurred. The combination of localized and remote etching resulted in a bimodal distribution of mesoporosity peaking at ~4 nm from remote etching and 10–30 nm from localized etching. The bimodal distribution was confirmed by the BJH method of nitrogen adsorption porosimetry. The pore size distribution could be controlled by changing the process temperature, the grade of Si and the metal composition. Whereas Ag, Au, Pd and Pt performed well in both the HL and LL limits, Cu generated porosification only in the LL limit.Funded by grants #314552 and #314412 from Academy of Finland and the National Science Foundation award #1825331. The microscopy studies were performed using the facilities in the UConn/Thermo Fisher Scientific Center for Advanced Microscopy and Materials Analysis (CAMMA). 1 K. Tamarov, J. D. Swanson, B. A. Unger, K. W. Kolasinski, A. T. Ernst, M. Aindow, V.-P. Lehto, and J. Riikonen, ACS Appl. Mater. Interfaces 12, 4787 (2020). 2 K. W. Kolasinski, W. B. Barclay, Y. Sun, and M. Aindow, Electrochim. Acta 158, 219 (2015). 3 K. W. Kolasinski, N. J. Gimbar, H. Yu, M. Aindow, E. Mäkilä, and J. Salonen, Angew. Chem., Int. Ed. Engl. 56, 624 (2017). 4 E. Torralba, S. Le Gall, R. Lachaume, V. Magnin, J. Harari, M. Halbwax, J.-P. Vilcot, C. Cachet-Vivier, and S. Bastide, ACS Appl. Mater. Interfaces 8, 31375 (2016). Figure 1

Combustion mode and wave multiplicity in rotating detonative combustion with separate reactant injection

Abstract Numerical simulations with detailed chemistry are conducted for two-dimensional rotating detonative combustion with separate injection of fuel and oxidant. The influences of the fuel and oxidant compositions on combustion mode and detonation wave multiplicity are studied. It is found that in the parts of the flow beyond the fuel refill zone, there are two distinct, highly inhomogeneous zones with fuel-rich and fuel-lean compositions, respectively. Both detonative and deflagrative regimes are observed and proceed mostly under a premixed combustion mode with the deflagration confined mostly to the fuel-lean zone. The results from our simulations show that limited H2 is detonated or deflagrated close to stoichiometric conditions and more than 70% of H2 is detonated or deflagrated under fuel-lean conditions. Over 70% of the detonated H2 is consumed in a premixed combustion mode. Our analysis also suggests that the detonation fraction increases with increased inlet pressure, decreased inlet temperature or increased injection orifice number. Additionally, the range of mixture fraction over which the composition is detonable is narrower than the range for deflagration. The number of detonation waves increases with increased oxygen mass fraction in the oxidant stream, with the additional waves being formed by mutual enhancement of an explosive hot spot and a travelling shock wave. Stabilization of the multiple waves follows a chaotic period involving both co-rotating and counter-rotating waves. Furthermore, the deficit of the detonation speed relative to the ideal Chapman − Jouguet value increases with the number of waves but also decreases monotonically with the level of reactant mixing. The reactant mixing effects along the detonation wave height are further discussed through quantifying the statistics of height-wise mixture fraction, heat release rate and OH mass fraction.

Influence of water addition on MILD ammonia combustion performances and emissions

The global energy shift towards the exploitation of Renewable Energy Sources requires the development of proper energy storage and back-up technologies to deal with their intermittency and seasonality. Renewable Energy chemical storage offers the possibility of efficiently storing large amounts of energy for long time. On the other hand, ammonia is increasingly considered a feasible alternative to the use of hydrogen, due to the existence of already well assessed production technologies and transport infrastructures. However, the exploitation of ammonia as an energy carrier poses some relevant challenges. The most relevant ones concern combustion stability and NOx emissions, when ammonia is burned in traditional conditions. A promising approach to ensure combustion stability while containing NOx emissions relies on the shift from traditional to new combustion modes. MILD Combustion has been proven as a reliable alternative to reach these targets. At the same time, water addition to reactants is a well-known strategy that promote DeNOx routes in fossil fuel combustion.In this work, combustion of ammonia-air mixtures assisted by water is studied in a cyclonic burner exercised under MILD operative conditions, to evaluate the effect of water addition on NOx emissions and process stability. The analyses were carried out in premixed and non-premixed feeding conditions.Results highlighted that water addition to the reactant mixture may represent a very simple and efficient solution in determining the reduction of NOx emissions in ammonia combustion, especially in fuel-lean conditions.Moreover, the comparison between premixed and non-premixed configuration shows that it is possible to enhance the process performance through a simultaneous optimization of the burner internal flow-field and reactants injection strategies.

Effect of Reactant Injection Rate on Solidifying Aeolian Sand via Microbially Induced Calcite Precipitation

Aeolian sand is a type of special soil with a loose structure, fine and uniform particles, and poor self-stabilization ability. These characteristics easily lead to sand dune movement and wind erosion in dry desert conditions. Therefore, reinforcement technology for aeolian sand is an important research topic. Microbially induced calcite precipitation (MICP) is a novel microbial soil-strengthening technique considered in this study with a focus on the effect of the reactant injection rate on the microbial solidification of aeolian sand. The aeolian sand was solidified using MICP with different injection rates of the cementing solution. The physical and mechanical properties as well as the microstructure of the solidified aeolian sand samples were analyzed. The experimental results show that using Sporosarcina pasteurii and the cementing solution (a mixture of urea and calcium chloride) can effectively solidify aeolian sand using the MICP technology. The engineering performance of the sand was effectively improved with an unconfined compressive strength that approached 14.01 MPa. The permeability coefficient of the solidified aeolian sand was significantly reduced, and the injection rate of the cementing solution significantly affected its uniformity. When the injection rate of the cementing solution was too low, most of the calcium carbonate was generated and accumulated at the top of the sand sample. Therefore, the upper part of the sample was relatively dense and strong, while the lower part had the opposite properties. When the injection rate of the cementing solution was too high, the roles of the upper and lower parts of the sample were reversed. When the injection rate of the cementing solution was 0.278 mol L−1 h−1, the solidified aeolian sand sample was relatively uniform and had a moderate unconfined compressive strength of 4.58–5.03 MPa. The uniform and high strength of the solidified aeolian sand was obtained by controlling the reactant injection rate. The optical microscope and SEM analyses indicated that the calcium carbonate crystals were rhombic hexahedral with sizes of approximately 5–10 μm. The calcium carbonate crystals were generated from the MICP in the solidified aeolian sand, which cemented the sand particles together, filled the pores between particles, increased the density and strength of the sand, and reduced its permeability coefficient.