Статті в журналах: "Transcritical combustion"

1

Singla, G., P. Scouflaire, C. Rolon, and S. Candel. "Transcritical oxygen/transcritical or supercritical methane combustion." Proceedings of the Combustion Institute 30, no. 2 (January 2005): 2921–28. http://dx.doi.org/10.1016/j.proci.2004.08.063.

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2

Pons, L., N. Darabiha, S. Candel, G. Ribert, and V. Yang. "Mass transfer and combustion in transcritical non-premixed counterflows." Combustion Theory and Modelling 13, no. 1 (January 22, 2009): 57–81. http://dx.doi.org/10.1080/13647830802368821.

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3

ANTUNES, Eduardo, Andre SILVA, and Jorge BARATA. "Modelling of transcritical and supercritical nitrogen jets." Combustion Engines 169, no. 2 (May 1, 2017): 125–32. http://dx.doi.org/10.19206/ce-2017-222.

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The present paper addresses the modelling of fuel injection at conditions of high pressure and temperature which occur in a variety of internal combustion engines such as liquid fuel rocket engines, gas turbines, and modern diesel engines. For this investigation a cryogenic nitrogen jet ranging from transcritical to supercritical conditions injected into a chamber at supercritical conditions was modelled. Previously a variable density approach, originally conceived for gaseous turbulent isothermal jets, imploying the Favre averaged Navier-Stokes equations together with a “k-ε” turbulence model, and using Amagats law for the determination of density was applied. This approach allows a good agreement with experiments mainly at supercritical injection conditions. However, some departure from experimental data was found at transcritical injection conditions. The present approach adds real fluid thermodynamics to the previous approach, and the effects of heat transfer. The results still show some disagreement at supercritical conditions mainly in the determination of the potential core length but significantly improve the prediction of the jet spreading angle at transcritical injection conditions.

4

Giacomazzi, Eugenio, Donato Cecere, and Nunzio Arcidiacono. "Flame Anchoring of an H2/O2 Non-Premixed Flamewith O2 Transcritical Injection." Aerospace 9, no. 11 (November 11, 2022): 707. http://dx.doi.org/10.3390/aerospace9110707.

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The article is devoted to the analysis of the flame anchoring mechanism in the test case MASCOTTE C-60 RCM2 on supercritical hydrogen/oxygen combustion at 60 bar, with transcritical (liquid) injection of oxygen. The case is simulated by means of the in-house parallel code HeaRT in the three-dimensional LES framework. The cubic Peng–Robinson equation of state in its improved translated volume formulation is assumed. Diffusive mechanisms and transport properties are accurately modeled. A finite-rate detailed scheme involving the main radicals, already validated for high-pressure H2/O2 combustion, is adopted. The flow is analysed in terms of temperature, hydrogen and oxygen instantaneous spatial distributions, evidencing the effects of the vortex shedding from the edges of the hydrogen injector and of the separation of the oxygen stream in the divergent section of its tapered injector on the flame anchoring and topology. Combustion conditions are characterised by looking at the equivalence ratio and compressibility factor distributions.

5

Delplanque, J. P., and W. A. Sirignano. "Transcritical liquid oxygen droplet vaporization - Effect on rocket combustion instability." Journal of Propulsion and Power 12, no. 2 (March 1996): 349–57. http://dx.doi.org/10.2514/3.24035.

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6

Ricci, Daniele, Francesco Battista, and Manrico Fragiacomo. "Transcritical Behavior of Methane in the Cooling Jacket of a Liquid-Oxygen/Liquid-Methane Rocket-Engine Demonstrator." Energies 15, no. 12 (June 7, 2022): 4190. http://dx.doi.org/10.3390/en15124190.

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The successful design of a liquid rocket engine is strictly linked to the development of efficient cooling systems, able to dissipate huge thermal loads coming from the combustion in the thrust chamber. Generally, cooling architectures are based on regenerative strategies, adopting fuels as coolants; and on cooling jackets, including several narrow axial channels allocated around the thrust chambers. Moreover, since cryogenic fuels are used, as in the case of oxygen/methane-based liquid rocket engines, the refrigerant is injected in liquid phase at supercritical pressure conditions and heated by the thermal load coming from the combustion chamber, which tends to experience transcritical conditions until behaving as a supercritical vapor before exiting the cooling jacket. The comprehension of fluid behavior inside the cooling jackets of liquid-oxygen/methane rocket engines as a function of different operative conditions represents not only a current topic but a critical issue for the development of future propulsion systems. Hence, the current manuscript discusses the results concerning the cooling jacket equipping the liquid-oxygen/liquid-methane demonstrator, designed and manufactured within the scope of HYPROB-NEW Italian Project. In particular, numerical results considering the nominal operating conditions and the influence of variables, such as the inlet temperature and pressure values of refrigerant as well as mass-flow rate, are shown to discuss the fluid transcritical behavior inside the cooling channels and give indications on the numerical methodologies, supporting the design of liquid-oxygen/liquid-methane rocket-engine cooling systems. Validation has been accomplished by means of experimental results obtained through a specific test article, provided with a cooling channel, characterized by dimensions representative of HYPROB DEMO-0A regenerative combustion chamber.

7

DELPLANQUE, J. P., and W. A. SIRIGNANO. "Transcritical Vaporization and Combustion of LOX Droplet Arrays in a Convective Environment." Combustion Science and Technology 105, no. 4-6 (April 1995): 327–44. http://dx.doi.org/10.1080/00102209508907757.

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8

Wang, Siyuan, Haiou Wang, Kun Luo, and Jianren Fan. "The Effects of Differential Diffusion on Turbulent Non-Premixed Flames LO2/CH4 under Transcritical Conditions Using Large-Eddy Simulation." Energies 16, no. 3 (January 18, 2023): 1065. http://dx.doi.org/10.3390/en16031065.

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In this paper, a large-eddy simulation (LES) of turbulent non-premixed LO2/CH4 combustion under transcritical conditions is performed based on the Mascotte test rig from the Office National d’Etudes et de Recherches Ae´rospatiales (ONERA), and the aim is to understand the effects of differential diffusion on the flame behaviors. In the LES, oxygen was injected into the environment above the critical pressure while the temperature was below the critical temperature. The flamelet/progress variable (FPV) approach was used as the combustion model. Two LES cases with different species diffusion coefficient schemes—i.e., non-unity and unity Lewis numbers—for generating the flamelet tables were carried out to explore the effects of differential diffusion on the flame and flow structures. The results of the LES case with non-unity Lewis numbers were in good agreement with the experimental data. It was shown that differential diffusion had evident impacts on the flame structure and flow dynamics. In particular, when unity Lewis numbers were used to evaluate the species diffusion coefficient, the flame length was underestimated and the flame expansion was more significant. Compared to laminar counterflow flames, turbulence in jet flames allows chemical reactions to take place in a wider range of mixture fractions. The density distributions of the two LES cases in the mixture fraction space were very similar, indicating that differential diffusion had no significant effects on the phase transition under transcritical conditions.

9

Liu, Liuchen, Qiguo Yang, and Guomin Cui. "Supercritical Carbon Dioxide(s-CO2) Power Cycle for Waste Heat Recovery: A Review from Thermodynamic Perspective." Processes 8, no. 11 (November 15, 2020): 1461. http://dx.doi.org/10.3390/pr8111461.

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Supercritical CO2 power cycles have been deeply investigated in recent years. However, their potential in waste heat recovery is still largely unexplored. This paper presents a critical review of engineering background, technical challenges, and current advances of the s-CO2 cycle for waste heat recovery. Firstly, common barriers for the further promotion of waste heat recovery technology are discussed. Afterwards, the technical advantages of the s-CO2 cycle in solving the abovementioned problems are outlined by comparing several state-of-the-art thermodynamic cycles. On this basis, current research results in this field are reviewed for three main applications, namely the fuel cell, internal combustion engine, and gas turbine. For low temperature applications, the transcritical CO2 cycles can compete with other existing technologies, while supercritical CO2 cycles are more attractive for medium- and high temperature sources to replace steam Rankine cycles. Moreover, simple and regenerative configurations are more suitable for transcritical cycles, whereas various complex configurations have advantages for medium- and high temperature heat sources to form cogeneration system. Finally, from the viewpoints of in-depth research and engineering applications, several future development directions are put forward. This review hopes to promote the development of s-CO2 cycles for waste heat recovery.

10

Farzaneh-Gord, Mahmood, Aliakbar Mirmohammadi, Mohammadreza Behi, and Amin Yahyaie. "Heat recovery from a natural gas powered internal combustion engine by CO2 transcritical power cycle." Thermal Science 14, no. 4 (2010): 897–911. http://dx.doi.org/10.2298/tsci1004897f.

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11

Liu, Jinghang, Aofang Yu, Xinxing Lin, Wen Su, and Shaoduan Ou. "Performances of Transcritical Power Cycles with CO2-Based Mixtures for the Waste Heat Recovery of ICE." Entropy 23, no. 11 (November 21, 2021): 1551. http://dx.doi.org/10.3390/e23111551.

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In the waste heat recovery of the internal combustion engine (ICE), the transcritical CO2 power cycle still faces the high operation pressure and difficulty in condensation. To overcome these challenges, CO2 is mixed with organic fluids to form zeotropic mixtures. Thus, in this work, five organic fluids, namely R290, R600a, R600, R601a, and R601, are mixed with CO2. Mixture performance in the waste heat recovery of ICE is evaluated, based on two transcritical power cycles, namely the recuperative cycle and split cycle. The results show that the split cycle always has better performance than the recuperative cycle. Under design conditions, CO2/R290(0.3/0.7) has the best performance in the split cycle. The corresponding net work and cycle efficiency are respectively 21.05 kW and 20.44%. Furthermore, effects of key parameters such as turbine inlet temperature, turbine inlet pressure, and split ratio on the cycle performance are studied. With the increase of turbine inlet temperature, the net works of the recuperative cycle and split cycle firstly increase and then decrease. There exist peak values of net work in both cycles. Meanwhile, the net work of the split cycle firstly increases and then decreases with the increase of the split ratio. Thereafter, with the target of maximizing net work, these key parameters are optimized at different mass fractions of CO2. The optimization results show that CO2/R600 obtains the highest net work of 27.43 kW at the CO2 mass fraction 0.9 in the split cycle.

12

Wang, Shunsen, Kunlun Bai, Yonghui Xie, Juan Di, and Shangfang Cheng. "Analysis of Combined Power and Refrigeration Generation Using the Carbon Dioxide Thermodynamic Cycle to Recover the Waste Heat of an Internal Combustion Engine." Mathematical Problems in Engineering 2014 (2014): 1–12. http://dx.doi.org/10.1155/2014/689398.

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A novel thermodynamic system is proposed to recover the waste heat of an internal combustion engine (ICE) by integrating the transcritical carbon dioxide (CO2) refrigeration cycle with the supercritical CO2power cycle, and eight kinds of integration schemes are developed. The key parameters of the system are optimized through a genetic algorithm to achieve optimum matching with different variables and schemes, as well as the maximum net power output (Wnet). The results indicate that replacing a single-turbine scheme with a double-turbine scheme can significantly enhance the net power output (Wnet) and lower the inlet pressure of the power turbine (P4). With the same exhaust parameters of ICE, the maximumWnetof the double-turbines scheme is 40%–50% higher than that of the single-turbine scheme. Replacing a single-stage compression scheme with a double-stage compression scheme can also lower the value ofP4, while it could not always significantly enhance the value ofWnet. Except for the power consumption of air conditioning, the net power output of this thermodynamic system can reach up to 13%–35% of the engine power when it is used to recover the exhaust heat of internal combustion engines.

13

Ihme, Matthias, Peter C. Ma, and Luis Bravo. "Large eddy simulations of diesel-fuel injection and auto-ignition at transcritical conditions." International Journal of Engine Research 20, no. 1 (December 19, 2018): 58–68. http://dx.doi.org/10.1177/1468087418819546.

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Large eddy simulations of transcritical injection and auto-ignition of n-dodecane in a combustion chamber are performed. To this end, a diffuse-interface method is employed that solves the compressible multi-species conservation equations, and a cubic state equation together with real-fluid transport properties is employed to describe the transcritical fluid state. The reaction chemistry is represented by a finite-rate chemistry model involving a 33-species reduced mechanism for n-dodecane. Compared to commonly employed two-phase approaches, the method presented in this work does not introduce tunable parameters for spray-breakup. Large eddy simulation calculations are performed by considering the Spray A single-hole injector at non-reacting and reacting conditions at a pressure of 60 bar and temperatures between 800 and 1200 K. Quantitative comparisons with measurements for liquid and vapor penetration lengths are performed for non-reacting conditions, and sensitivity to threshold values on mixture fraction are examined. The analysis of reacting flow simulations focuses on comparisons of the instantaneous temperature and species fields for OH and CH2O at 800 and 900 K, respectively. Quantitative comparisons with measurements for ignition delay and lift-off heights as a function of ambient temperature are performed. To examine the transient ignition phase, comparisons of radially integrated OH profiles obtained from the simulations with reported measurements for OH* are performed, showing good agreement. These results show that the large eddy simulation modeling framework adequately reproduces the corresponding ignition processes, which are relevant to realistic diesel-fuel injection systems.

14

Falbo, Luigi, Diego Perrone, Pietropaolo Morrone, and Angelo Algieri. "Integration of biodiesel internal combustion engines and transcritical organic Rankine cycles for waste‐heat recovery in small‐scale applications." International Journal of Energy Research 46, no. 4 (November 28, 2021): 5235–49. http://dx.doi.org/10.1002/er.7515.

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15

Yao, Shouguang, Jing Sun, Minjie Xia, Chao Ying, and Junwei Yang. "Design and optimization of a cold energy and waste heat utilization system for LNG-powered ships with post-combustion carbon capture." Thermal Science, no. 00 (2024): 117. http://dx.doi.org/10.2298/tsci240109117y.

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The introduction of dual-carbon targets has accelerated LNG fuel adoption on vessels and driven the advancement of carbon capture technologies. This study?s aim is a 37000-deadweight tonnage liquified natural gas dual-fuel powered ship, for which chemical absorption carbon capture is applied, utilizing flue gas and liquified natural gas to supply the process?s heat and cold energy. Then a system with efficient utilization of energy and carbon capture for the LNG dual-fuel ship is designed, coupling the waste heat onboard with transcritical CO2 and organic Rankine cycle on the principle of energy cascade utilization. The system is simulated using Aspen HYSYS and the exergy analysis is carried out for this system. Then the working fluid is optimized for the system. After that, through the genetic algorithm, the system?s operating parameters are further optimized. Additionally, the system?s economic analysis is also performed. It is shown that the scheme?s exergy efficiency reaches 39.98%, and the expected cost-recovery cycle is 4.75 years.

16

Pan, Lisheng, Yuejing Ma, Teng Li, Huixin Li, Bing Li, and Xiaolin Wei. "Investigation on the cycle performance and the combustion characteristic of two CO2-based binary mixtures for the transcritical power cycle." Energy 179 (July 2019): 454–63. http://dx.doi.org/10.1016/j.energy.2019.05.010.

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17

Marchioro Ystad, P. A., A. A. Lakew, and O. Bolland. "Integration of low-temperature transcritical CO2 Rankine cycle in natural gas-fired combined cycle (NGCC) with post-combustion CO2 capture." International Journal of Greenhouse Gas Control 12 (January 2013): 213–19. http://dx.doi.org/10.1016/j.ijggc.2012.11.005.

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18

Ricci, Daniele, Francesco Battista, and Manrico Fragiacomo. "Numerical Investigation on the Thermal Behaviour of a LOx/LCH4 Demonstrator Cooling System." Aerospace 8, no. 6 (May 27, 2021): 151. http://dx.doi.org/10.3390/aerospace8060151.

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Reliability of liquid rocket engines is strictly connected with the successful operation of cooling jackets, able to sustain the impressive operative conditions in terms of huge thermal and mechanical loads, generated in thrust chambers. Cryogenic fuels, like methane or hydrogen, are often used as coolants and they may behave as transcritical fluids flowing in the jackets: after injection in a liquid state, a phase pseudo-change occurs along the chamber because of the heat released by combustion gases and coolants exiting as a vapour. Thus, in the development of such subsystems, important issues are focused on numerical methodologies adopted to simulate the fluid thermal behaviour inside the jackets, design procedures as well as manufacturing and technological process topics. The present paper includes the numerical thermal analyses regarding the cooling jacket belonging to the liquid oxygen/liquid methane demonstrator, realized in the framework of the HYPROB (HYdrocarbon PROpulsion test Bench) program. Numerical results considering the nominal operating conditions of cooling jackets in the methane-fuelled mode and the water-fed one are included in the case of the application of electrodeposition process for manufacturing. A comparison with a similar cooling jacket, realized through the conventional brazing process, is addressed to underline the benefits of the application of electrodeposition technology.

19

Unnikrishnan, Umesh, Joseph C. Oefelein, and Vigor Yang. "Subgrid modeling of the filtered equation of state with application to real-fluid turbulent mixing at supercritical pressures." Physics of Fluids 34, no. 6 (June 2022): 065112. http://dx.doi.org/10.1063/5.0088074.

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Simulation of turbulent mixing and combustion at supercritical pressures requires the use of a real-fluid equation of state (EOS) to represent the nonideal, nonlinear thermodynamic behavior of fluids under these conditions. The simplified representation of the filtered EOS in the large eddy simulation methodology introduces inconsistencies in the computed filtered thermodynamic state. This study investigates these inconsistencies and novel subgrid modeling approaches to address these issues, using high-resolution direct numerical simulation of a transcritical mixing layer. Errors incurred by not accounting for subgrid effects in the EOS are quantified, and fundamental insights are drawn regarding the nature of these effects. Then, different modeling approaches are proposed and investigated to obtain a more accurate representation of the filtered EOS. The evaluation of the filtered EOS in terms of the Reynolds-filtered state variables is considered instead of the conventional Favre-filtered variables. A dynamic gradient model is formulated by building upon the ideas of dynamic modeling to render a functional form for the subgrid EOS expressed in terms of the resolved flow gradients. A scale-similarity model formulation for the subgrid EOS is also constructed and examined. Finally, a model for the filtered EOS is derived using a presumed filtered density function that accounts for the effect of subgrid-scale fluctuations. The performance of each model is evaluated using various metrics, and the relative accuracy of each modeling approach is compared and contrasted at different filter sizes.

20

Chen, Hao, Yiming Wang, Linbo Yan, Ziliang Wang, Boshu He, and Baizeng Fang. "Energy and Exergy Analysis on a Blast Furnace Gas-Driven Cascade Power Cycle." Energies 15, no. 21 (October 31, 2022): 8078. http://dx.doi.org/10.3390/en15218078.

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Blast furnace gas is the major combustible by-product produced in the steel industry, where iron ore is reduced by coke into iron. Direct combustion of blast furnace gas after simple treatment for power generation is a common utilization method nowadays. However, this method suffers from low efficiency and high carbon intensity. The use of gas-steam combined cycle is an excellent method to improve the efficiency of blast furnace gas for power generation. However, there is a problem of insufficient utilization of low product heat, and the addition of CCS system can further reduce the power efficiency. To solve these issues, a new blast furnace gas power generation system with a Brayton cycle with supercritical CO2 and a Rankine cycle with transcritical CO2 is proposed in this work. The new system is then thermodynamically simulated by Aspen Plus, after the sub-modules are validated. The effects of molar ratio of steam to carbon, selexol/CO2 mass ratio, compression ratio, turbine import temperature and turbine inlet pressure on the system are investigated. A comparison is also performed between the new combined cycle system and the traditional combined cycle power generation system. The results show that in the new power generation system, net power efficiency of 53.29%, carbon capture efficiency of 95.78% and sulfur capture rate of 94.46% can be achieved, which is significantly better than the performance of the conventional combined cycle.

21

Mosaffa, A. H., and L. Garousi Farshi. "Novel post combustion CO2 capture in the coal-fired power plant employing a transcritical CO2 power generation and low temperature steam upgraded by an absorption heat transformer." Energy Conversion and Management 207 (March 2020): 112542. http://dx.doi.org/10.1016/j.enconman.2020.112542.

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22

Choi, Byung Chul. "Thermodynamic analysis of a transcritical CO2 heat recovery system with 2-stage reheat applied to cooling water of internal combustion engine for propulsion of the 6800 TEU container ship." Energy 107 (July 2016): 532–41. http://dx.doi.org/10.1016/j.energy.2016.03.116.

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23

Boulal, Stéphane, Nicolas Fdida, Lionel Matuszewski, Lucien Vingert, and Miguel Martin-Benito. "Flame dynamics of a subscale rocket combustor operating with gaseous methane and gaseous, subcritical or transcritical oxygen." Combustion and Flame 242 (August 2022): 112179. http://dx.doi.org/10.1016/j.combustflame.2022.112179.

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24

Fathi, Mohamad, Stefan Hickel, and Dirk Roekaerts. "Large eddy simulations of reacting and non-reacting transcritical fuel sprays using multiphase thermodynamics." Physics of Fluids, July 25, 2022. http://dx.doi.org/10.1063/5.0099154.

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We present a novel framework for high-fidelity simulations of inert and reacting sprays at transcritical conditions with highly accurate and computationally efficient models for complex real-gas effects in high-pressure environments, especially for the hybrid subcritical/supercritical mode of evaporation during the mixing of fuel and oxidizer. The high-pressure jet disintegration is modeled using a diffuse interface method with multiphase thermodynamics, which combines multi-component real-fluid volumetric and caloric state equations with vapor-liquid equilibrium calculations for the computation of thermodynamic properties of mixtures at transcritical pressures. Combustion source terms are evaluated using a finite-rate chemistry model, including real-gas effects based on the fugacity of the species in the mixture. The adaptive local deconvolution method (ALDM) is used as a physically consistent turbulence model for large-eddy simulation (LES). The proposed method represents multiphase turbulent fluid flows at transcritical pressures without relying on any semi-empirical break-up and evaporation models. All multiphase thermodynamic model equations are presented for general cubic state equations coupled with a rapid phase-equilibrium calculation method that is formulated in a reduced space based on the molar specific volume function. LES results show a very good agreement with available experimental data for the reacting and non-reacting Engine Combustion Network (ECN) benchmark Spray A at transcritical operating conditions.

25

Sharma, Abhishek, Ashoke De, and S. Sunil Kumar. "Numerical investigation of supercritical combustion dynamics in a multi-element LOx–methane combustor using flamelet-generated manifold approach." Physics of Fluids 35, no. 11 (November 1, 2023). http://dx.doi.org/10.1063/5.0172100.

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The article investigates liquid oxygen (LOx)–methane supercritical combustion dynamics in a multi-element rocket-scale combustor using large eddy simulation (LES). A complex framework of real gas thermodynamics and flamelet-generated manifold (FGM) combustion model is invoked to simulate transcritical oxygen injection and supercritical methane combustion. A benchmark Mascotte chamber, rocket combustion Modeling (RCM) test case, i.e., RCM-3 (V04)/G2 test case, is used to validate the real gas FGM model in the LES framework. The validation study accurately reproduces experimental flame structure and OH concentration, demonstrating the FGM model's importance in incorporating finite rate kinetics in LOx–methane combustion. Subsequently, the numerical framework investigates a specially designed multi-element combustion chamber featuring seven bidirectional swirl coaxial injectors. The analyses capture the complex hydrodynamics and combustion dynamics associated with multiple swirl injectors operating at supercritical pressure, effectively demonstrating the initiation of transverse acoustic waves and examining the effect of local sound speed on the evolution of acoustic modes in the combustor. The dominant frequency modes shed light on understanding the role of injectors in enhanced combustor dynamics. Spectral analysis reveals the interplay of the upstream injector and chamber acoustics due to possible frequency coupling. The results also highlight the effect of fuel injection temperature on the stability of the combustor, revealing a violent dynamic activity for lower fuel injection temperature associated with the longitudinal acoustic mode of the combustor. The investigation appropriately reproduces self-sustained limit-cycle oscillations at lower fuel injection temperatures and corroborates the conventional understanding of combustor instability.

26

Jeyaseelan, Thangaraja, Min Son, Tobias Sander, and Lars Zigan. "Experimental and modeling analysis of the transient spray characteristics of cyclopentane at sub- and transcritical conditions using a machine learning approach." Physics of Fluids 35, no. 8 (August 1, 2023). http://dx.doi.org/10.1063/5.0159979.

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Although fuel spray parameters, such as spray cone angle and penetration length, are crucial for developing high-efficiency and high-performance combustion engines, general models for predicting transient characteristics of these parameters have not been suggested. In this study, the spray characteristics of cyclopentane at sub- and transcritical conditions relevant for IC engine and rocket injections were experimentally evaluated. A single simplified model for predicting the spray cone angles and spray penetration lengths over time was developed by adopting artificial neural networks (ANN). Spray measurements were conducted by shadowgraphy and Mie scattering techniques to recognize the phase change behavior of the spray, changing the injection and chamber conditions. The ANN model was developed using a multi-layer network with six normalized inputs and four outputs. It was trained with five transient spray datasets at two subcritical and three transcritical injection conditions. It was validated with one transcritical spray dataset. The ANN prediction was assessed, and the proposed approach represents the spray characteristics of cyclopentane at sub- and transcritical conditions. According to the model results, the predicted spray parameters are in good agreement with the experimental results over a useful pressure and temperature range of 40–55 bar and 465–564 K, mean absolute percentage errors of 2.25% (shadowgraphy) and 4.92% (Mie) for the spray angles, and 1.11% (shadowgraphy) and 3.44% (Mie) for the spray penetration lengths. Moreover, the developed ANN model can predict the penetration ratio, providing information on phase changes in sprays. The developed ANN model in this study is expected to become a universal model for transient spray characteristics near the critical point. By adding the database with various fuel types and spray conditions, the universal model can be used to develop high-efficiency and high-performance combustion engines or other combustors.

27

Zeinivand, Hamed, and Mohammad Farshchi. "Numerical study of the pseudo-boiling phenomenon in the transcritical liquid oxygen/gaseous hydrogen flame." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering, October 20, 2020, 095441002096469. http://dx.doi.org/10.1177/0954410020964692.

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The interactions and effects of turbulent mixing, pseudo-boiling phenomena, and chemical reaction heat release on the combustion of cryogenic liquid oxygen and gaseous hydrogen under supercritical pressure conditions are investigated using RANS simulations. Comparisons of the present numerical simulation results with available experimental data reveal a reasonably good prediction of a supercritical axial shear hydrogen-oxygen flame using the standard k-ε turbulence model and the eddy dissipation concept combustion model with a 23 reaction steps kinetics for H2-O2 reaction. The present simulation qualitatively reproduced oxygen injection and its reaction with the co-flowing hydrogen, which is characterized by rapid flame expansion, downstream flame propagation, and expansion induced flow recirculation. Several turbulence models were used for numerical simulations. It is shown that the selection of an appropriate turbulence model for transcritical reacting flows is crucial and far more important than for subcritical reacting flows. It is indicated that the pseudo-boiling phenomena is the main reason for the considerable differences between the turbulence models in a transcritical flame. Also, it is demonstrated that the liquid oxygen core disappears faster in a non-reacting flow than in a reacting flow. The shear layer in the non-reacting flow is much stronger than reacting case; providing a large transfer of energy from the outer layer to the inner layer. At the supercritical injection conditions, the difference between the turbulence models is much less than the transcritical injection conditions.

28

Guo, Jack, Davy Brouzet, Wai Tong Chung, and Matthias Ihme. "Analysis of ducted fuel injection at high-pressure transcritical conditions using large-eddy simulations." International Journal of Engine Research, April 26, 2023, 146808742311706. http://dx.doi.org/10.1177/14680874231170659.

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Ducted fuel injection (DFI) is a proposed fuel injection concept for achieving substantial reductions in emissions. In this concept, the fuel is injected through a coannular duct, resulting in increased fuel-air mixing and minimized formation of soot and other unwanted combustion products. Apart from comprehensive experimental investigations on DFI, so far computational studies have been limited to single-point Reynolds-averaged Navier Stokes simulations. Therefore, the objective of this work is to complement these studies by performing large-eddy simulations using a diffuse-interface method to examine the physical mechanisms and combustion processes of DFI, specifically focusing on the mixing process and the effect of fuel-ducting on combustion and pollutant emissions. To this end, finite-rate chemistry simulations are performed of the DFI configuration corresponding to the Engine Combustion Network Spray A injector at transcritical conditions (n-dodecane fuel, 60 bar pressure and 1000 K temperature chamber conditions). A two-equation soot model is employed for the qualitative analysis of soot emissions. Direct comparisons of averaged and instantaneous flow field results with the Spray A configuration are performed to assess the effect of DFI on the first- and second-stage ignition and soot formation. Compared to the free-spray condition, the results show that the DFI case exhibits a combination of (i) increased mass flow rate and entrained air, (ii) larger pressure drop magnitude and flow velocity, and (iii) a closer-to-stoichiometric mixture composition (both globally and locally), each of which is conjectured to contribute toward reduced soot production.

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Chung, Wai Tong, Aashwin Ananda Mishra, and Matthias Ihme. "Interpretable data-driven methods for subgrid-scale closure in LES for transcritical LOX/GCH4 combustion." Combustion and Flame, October 2021, 111758. http://dx.doi.org/10.1016/j.combustflame.2021.111758.

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Wanstall, C. Taber, Joshua A. Bittle, and Ajay K. Agrawal. "Phase diagram to demarcate supercritical, transcritical, and continuous phase regimes for binary fluid equilibrium mixing relevant to combustion applications." Journal of Supercritical Fluids, April 2023, 105935. http://dx.doi.org/10.1016/j.supflu.2023.105935.

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Alsagri, Ali S., and Andrew D. Chiasson. "Thermodynamic Analysis and Multi-Objective Optimizations of a Combined Recompression SCO2 Brayton Cycle-TCO2 Rankine Cycles for Waste Heat Recovery." International Journal of Current Engineering and Technology, of (May 12, 2018). http://dx.doi.org/10.14741/ijcet/v.8.3.9.

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A thermodynamic analysis and optimization of a newly-conceived combined power cycle were conducted in this paper for the purpose of improving overall thermal efficiency of power cycles by attempting to minimize thermodynamic irreversibilities and waste heat as a consequence of the Second Law. The power cycle concept comprises a topping advanced recompression supercritical carbon dioxide (sCO2) Brayton cycle and a bottoming transcritical carbon dioxide (tCO2) Rankine cycle. The bottoming cycle configurations included a simple tCO2 Rankine cycle and a split tCO2 Rankine cycle. The topping sCO2 recompression Brayton cycle used a combustion chamber as a heat source, and waste heat from a topping cycle was recovered by the tCO2 Rankine cycle due to an added high efficiency recuperator for generating electricity. The combined cycle configurations were thermodynamically modeled and optimized using an Engineering Equation Solver (EES) software. Simple bottoming tCO2 Rankine cycle cannot fully recover the waste heat due to the high exhaust temperature from the top cycle, and therefore an advance split tCO2 Rankine cycle was employed in order to recover most of the waste heat. Results show that the highest thermal efficiency was obtained with recompression sCO2 Brayton cycle – split flow tCO2 Rankine cycle. Also, the results show that the combined CO2 cycles is a promising technology compared to conventional cycles.

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Perrone, Diego, Luigi Falbo, Pietropaolo Morrone, and Angelo Algieri. "Techno-Economic Investigation of Integrated Biodiesel Internal Combustion Engines and Transcritical Organic Rankine Cycles for Small-Scale Combined Heat and Power Generation." Energy Conversion and Management: X, July 2023, 100426. http://dx.doi.org/10.1016/j.ecmx.2023.100426.

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Al-Mughanam, Tawfiq, and Abdul Khaliq. "Investigation on novel natural gas fueled homogeneous charge compression ignition engine based combined power and cooling system." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, July 10, 2023. http://dx.doi.org/10.1177/09576509231188812.

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A significant part of energy of fuel supplied is lost in internal combustion engines in the form of atmospheric discharge of engine exhaust gases which are considered as a big source of engine inefficiency and formation of pollutant emissions. To address this issue, a bottoming cycle combining the transcritical CO2 (T-CO2) refrigeration cycle and the supercritical CO2 (sCO2) power cycle is employed, aiming to produce cooling for food preservation by utilizing the exhaust heat of homogeneous charge compression ignition (HCCI) engine powering the refrigerated truck. The operative variables and their effect on thermal and exergetic efficiency of HCCI engine and the combined system are investigated. At the base case operative conditions, the thermal and exergy efficiencies of natural gas fueled HCCI engine are improved significantly from 48.69% to 61.28% and from 41.14% to 42.79%, respectively, after employing the sCO2 powered T-CO2 refrigeration cycle. Promotion of equivalence ratio from 0.3 to 0.9 enhances the thermal and exergy efficiencies of HCCI engine from 47.44% to 49.54% and from 40.14% to 42.12%, respectively. Increasing of engine speed from 1400 r.p.m to 2200 r.p.m provides marginal improvement in HCCI engine efficiencies but the efficiencies of combined cycle are significantly improved from 57.67% to 65.18% and from 40.64% to 45.06%, respectively. Finally, exergy analysis applied to determine the sources of non-idealities within the system revealed that out 361 kW (100%) fuel exergy supplied to the system, HCCI engine destroys 93.31 kW (25.85%), catalytic convertor destroys15.49 kW (4.29%), and the in-cylinder heat transfer losses and system exhaust losses are found as 35.72 kW (9.91%) and 16.61 kW (4.61%), respectively.

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