Publications

2025

1. J. Chem. Eng.

   Efficient Modeling of Aerochemical Interactions in Novel Turbomachines for Conducting Low-Carbon Chemical Reactions

   Dylan Rubini ,  Budimir Rosic ,  and  Liping Xu

   Journal of Chemical Engineering (In Preparation), Jan 2025
2. Appl. Therm. Eng.

   Energy Conversion Mechanisms in Turbomachines for High-Temperature Endothermic Reactions: Redefining Energy Quality

   Dylan Rubini ,  Budimir Rosic ,  and  Liping Xu

   Applied Thermal Engineering, Jan 2025

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   A new class of turbomachines, called turbo-reactors, have emerged to decarbonize high-temperature chemical processes. These applications unlock a new aerothermochemical design space for turbomachines. This paper explains how the turbo-reactor has the potential to be a “chemically tuned” device. In contradiction with conventional design wisdom, this can be achieved by balancing entropy generation within the flow against heat absorption by the reaction. This enables the “design” of a reaction-efficient temperature profile. To do this, it is necessary to understand and quantify the distribution of the entropic and isentropic mechanisms responsible for energy conversion. This paper uses high- and low-fidelity computations to decompose the energy conversion process into mechanisms based on a spatial decomposition. A range of Mach and Reynolds number regimes are studied, as well as a multistage configuration without vaneless space. The energy conversion breakdown analysis indicates that the entropic energy conversion dominates over the isentropic component with a contribution of 65%. The dominant source of entropy production is viscous dissipation generated by the thick diffuser trailing edge, accounting for 25% of the total. The shock system provides 20% of the energy conversion, almost entirely due to reversible pressure rise rather than entropy production. The energy conversion coefficient is independent of Reynolds number over engine-relevant conditions, whereas Mach effects are more significant. Across the Mach numbers range 1.1 to 1.5, the energy conversion coefficient increases by 20%. This is lower than expected as a result of the opposing effects of reversible and irreversible energy conversion contributions.

   @article{RubiniApplTherm,
     title = {Energy Conversion Mechanisms in Turbomachines for High-Temperature Endothermic Reactions: Redefining Energy Quality},
     journal = {Applied Thermal Engineering},
     doi = {https://doi.org/10.1016/j.applthermaleng.2024.124566},
     url = {https://doi.org/10.1016/j.applthermaleng.2024.124566},
     author = {Rubini, Dylan and Rosic, Budimir and Xu, Liping},
     keywords = {Turbomachinery, endothermic chemical processes, steam cracking, turbo-reactor, loss breakdown},
     dimensions = {true},
     year = {2025},
     month = jan,
     volume = {258},
     pages = {124566},
   }

2024

1. GPPS

   Decarbonisation of High-Temperature Endothermic Chemical Reaction Processes using a Novel Turbomachine: Robustness of the Concept to Feed Variability (**Best Paper Award**)

   Dylan Rubini ,  Nikolas Karefyllidis ,  Budimir Rosic , and 2 more authors

   Journal of the Global Power and Propulsion Society, May 2024

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   This paper presents a revolutionary turbomachinery concept, referred to as the turbo-reactor, which has the potential to replace gas-fired radiant furnaces and decarbonise a wide range of hard-to-abate, high-temperature endothermic chemical reaction processes. Although previous studies by the authors have confirmed the feasibility of using a turbo-reactor for steam cracking reactions, the numerical investigation presented in this work broadens the scope of potential applications for the machine to a variety of energy-intensive chemical processes, including those used for hydrogen production. This step change in technology could be the catalyst needed to enable rapid scale-up of low-carbon hydrogen technology. The innovative design of the turbo-reactor is fundamentally based on converting all of the imparted mechanical energy into internal energy, rather than pressure. This enables temperatures of up to 1,700°C to be achieved within an axial length on the order of one metre, resulting in an increase in the power density of 50 to 1,000 times compared to a surface heat exchanger. This paper presents the first comprehensive analysis of the turbo-reactor’s robustness and controllability across a broad spectrum of feeds, chemical reaction stages, Mach number regimes, and operating points, conclusively demonstrating the feasibility of a universal stage design strategy for repeatedly imparting and dissipating energy for various endothermic reaction processes.

   @article{Rubini2024,
     journal = {Journal of the Global Power and Propulsion Society},
     volume = {8},
     year = {2024},
     month = may,
     title = {{Decarbonisation of High-Temperature Endothermic Chemical Reaction Processes using a Novel Turbomachine: Robustness of the Concept to Feed Variability <a href="https://gpps.global/tc23-awards//">(**Best Paper Award**)</a>}},
     author = {Rubini, Dylan and Karefyllidis, Nikolas and Rosic, Budimir and Xu, Liping and Nauha, Elina},
     pages = {111--126},
     doi = {10.33737/jgpps/185623},
     url = {https://doi.org/10.33737/jgpps/185623},
     dimensions = {true},
   }

2023

1. ASME JT

   A Novel Axial Energy-Imparting Turbomachine for High-Enthalpy Gas Heating: Robustness of the Aerodynamic Design (**Best Paper Award**)

   Nikolas Karefyllidis ,  Dylan Rubini ,  Budimir Rosic , and 2 more authors

   ASME Journal of Turbomachinery, Nov 2023

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   Hard-to-abate industrial processes, such as petrochemicals and cement production, have long been considered technically challenging to decarbonize. In response to the urgent demand to eliminate industrial CO2 emissions, a new class of energy-imparting turbomachines has been developed. These devices aim to convert mechanical into internal energy instead of pressurizing the gas, which enables high-temperature gas heating (up to 1700 ∘C) for a variety of applications. This article is organized into three parts. First, this article aims to demonstrate the capabilities of the novel, high-capacity, customizable, repeating-stage axial turbo-heater architecture for a hydrocarbon cracking example application. The study presents the new design requirements and working principles of this energy-imparting concept. The radically different objectives compared to a compressor enable ultra-high loading stage designs by avoiding the stability and efficiency constraints imposed on compressors. Within this new design space, the turbo-heater is able to achieve a loading coefficient ψ ≥ 4.0. Second, detailed numerical simulations of a multistage axial turbo-reactor with various vaneless space lengths are conducted. This work conclusively demonstrates the robustness and flexibility of the aerodynamic design despite employing a uniform blade design. It is emphasized that the concept is tolerant to unsteady interstage turbulent disturbances, enabling nominal work input conditions to be achieved even for the most compact arrangements. Finally, having confirmed that the aerothermal restrictions on the vaneless space length can be removed, the designer is free to tailor the design to optimize the chemical reaction by (1) tailoring the residence time distribution to improve the yield and coking rate, (2) homogenizing reaction progress by mixing-out concentration gradients, and (3) adjusting the rotational speed to account for variations in the reaction dynamics for different feedstocks.

   @article{NKDR,
     dimensions = {true},
     author = {Karefyllidis, Nikolas and Rubini, Dylan and Rosic, Budimir and Xu, Liping and Purola, Veli-Matti},
     title = {{A Novel Axial Energy-Imparting Turbomachine for High-Enthalpy Gas Heating: Robustness of the Aerodynamic Design <a href="https://www.asme.org/about-asme/honors-awards/unit-awards/asme-igti-committee-best-paper-and-tutorial-award">(**Best Paper Award**)</a>}},
     journal = {ASME Journal of Turbomachinery},
     volume = {146},
     number = {3},
     pages = {031005},
     year = {2023},
     month = nov,
     issn = {0889-504X},
     doi = {10.1115/1.4063928},
     url = {https://doi.org/10.1115/1.4063928},
     eprint = {https://asmedigitalcollection.asme.org/turbomachinery/article-pdf/146/3/031005/7059051/turbo\_146\_3\_031005.pdf},
   }

2022

1. GPPS

   A New Robust Regenerative Turbo-Reactor Concept for Clean Hydrocarbon Cracking

   Dylan Rubini ,  Nikolas Karefyllidis ,  Liping Xu , and 2 more authors

   Journal of the Global Power and Propulsion Society, Nov 2022

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   Energy consumption in the chemical and petrochemical industries is dominated by the highly energy-intensive, high-temperature hydrocarbon cracking process. This paper offers an attractive solution to potentially decarbonise the cracking industry by direct renewable electrification whilst also improving the efficiency of energy transfer and enhancing the quality of the overall cracking process. Controlled endothermic cracking reactions are generated by direct mechanical energy transfer using a new electric-motor-driven turbo-reactor to replace the fossil-fuelled radiant unit in the conventional cracking plant. This study provides an introduction to the novel concept, focusing on how the unique three-blade-row repeating stage design is exploited in order to drive the efficient energy transfer and transformation processes used to overcome the fundamental limitations of the conventional process. More specifically, this includes increasing the primary product yield, mitigating coke deposition and improving operability. A combination of URANS and high-fidelity LES are presented in order to probe the aerothermal flow physics and interactions in the rotor and diffuser. This study clearly demonstrates how the working principals of the elemental stage can be realised uniformly across the full regenerative turbo-reactor by exploiting the robust and naturally self-adjusting concept. This work highlights the high-level of controllability of the turbomachine, which allows the cracking environment and species selectivities to be tailored during operation, for example, by conducting minor alterations to the rotational speed.

   @article{Rubini2022,
     journal = {Journal of the Global Power and Propulsion Society},
     volume = {6},
     year = {2022},
     dimensions = {true},
     title = {A New Robust Regenerative Turbo-Reactor Concept for Clean Hydrocarbon Cracking},
     author = {Rubini, Dylan and Karefyllidis, Nikolas and Xu, Liping and Rosic, Budimir and Johannesdahl, Harri},
     pages = {135--150},
     doi = {10.33737/jgpps/150550},
     url = {https://doi.org/10.33737/jgpps/150550},
   }

2. ASME

   Accelerating the Development of a New Turbomachinery Concept in an Environment With Limited Resources and Experimental Data: Challenges

   Dylan Rubini ,  Nikolas Karefyllidis ,  Liping Xu , and 2 more authors

   Turbo Expo: Power for Land, Sea, and Air, Jun 2022

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   This paper presents the requirements for a tailored design ecosystem to accelerate the development of a new turbo-reactor for hydrocarbon cracking. The objective of this novel turbo-reactor concept is to eliminate carbon emissions from the radiant section of the plant. However, the time constraint for this energy- and carbon-intensive cracking industry to fully decarbonize is severely restricted. Therefore, the development of this new concept must be accelerated to a market-ready product within a limited time frame. However, the novelty of the design requirements and the unique level of complexity of the flow physics result in inadequate experimental data, with insufficient time and resources to develop a new measurement database. This shifts the design system towards computer-aided engineering platforms; however for the turbo-reactor, the uncertainty level of these low-order numerical tools (e.g., RANS and throughflow solvers) is elevated for three reasons. First, blockage, deviation and loss correlations integrated within throughflow solvers are unsuitable to capture the flow physics in the turbo-reactor. Second, RANS turbulence closure models need to be re-calibrated for this machine. Finally, due to the chemical reactions, the working fluid properties vary significantly along the gas path and strongly influence the aerodynamics. A new tailored design ecosystem is proposed to address these challenges. The relatively low Reynolds number regime throughout the turbo-reactor enables upfront and routine eddy-resolving simulations to be performed. This allows the new design system to feature a feedback mechanism in which high-fidelity CFD data is used to calibrate lower-fidelity — but less CPU intensive — design tools and empirical correlations. Crucially, the new toolchain is customized in order to capture the influence of the reactions on the thermodynamic properties, as well as to provide the aerodynamic designer with immediate insight into how stage-design modifications influence the reaction product yield distribution. This paper demonstrates the capabilities of an efficient aerodynamic-chemistry coupling methodology that has been implemented within an in-house CFD solver.

   @article{RubiniAccel,
     dimensions = {true},
     author = {Rubini, Dylan and Karefyllidis, Nikolas and Xu, Liping and Rosic, Budimir and Johannesdahl, Harri},
     title = {{Accelerating the Development of a New Turbomachinery Concept in an Environment With Limited Resources and Experimental Data: Challenges}},
     volume = {Volume 10D: Turbomachinery — Multidisciplinary Design Approaches, Optimization, and Uncertainty Quantification; Turbomachinery General Interest; Unsteady Flows in Turbomachinery},
     journal = {Turbo Expo: Power for Land, Sea, and Air},
     pages = {V10DT36A001},
     year = {2022},
     month = jun,
     doi = {10.1115/GT2022-80698},
     url = {https://doi.org/10.1115/GT2022-80698},
     eprint = {https://asmedigitalcollection.asme.org/GT/proceedings-pdf/GT2022/86120/V10DT36A001/6937204/v10dt36a001-gt2022-80698.pdf}
   }

2021

1. ASME JGTP

   A New Turbomachine for Clean and Sustainable Hydrocarbon Cracking

   Dylan Rubini ,  Liping Xu ,  Budimir Rosic , and 1 more author

   ASME Journal of Engineering for Gas Turbines and Power, Dec 2021

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   Decarbonizing highly energy-intensive industrial processes is imperative if nations are to comply with anthropogenic greenhouse gas emissions targets by 2050. This is a significant challenge for high-temperature industrial processes, such as hydrocarbon cracking, and there have been limited developments thus far. The novel concept presented in this study aims to replace the radiant section of a hydrocarbon cracking plant with a novel turboreactor. This is one of the first major and potentially successful attempts at decarbonizing the petrochemical industry. Rather than using heat from the combustion of natural gas, the novel turboreactor can be driven by an electric motor powered by renewable electricity. Switching the fundamental energy transfer mechanism from surface heat exchange to mechanical energy transfer significantly increases the exergy efficiency of the process. Theoretical analysis and numerical simulations show that the ultrahigh aerodynamic loading rotor is able to impart substantial mechanical energy into the feedstock without excess temperature difference and metal temperature magnitude. A complex shockwave system then transforms the kinetic energy into internal energy over an extremely short distance. The version of the turboreactor developed and presented in this study uses a single rotor row, in which a multistage environment is achieved regeneratively by guiding the flow through a toroidal-shaped vaneless space. This configuration leads to a reduction in reactor volume by more than two orders of magnitude compared with a conventional furnace. A significantly lower wall surface temperature, supersonic gas velocities, and a shorter primary gas path enable a controlled reduction in the residence time for chemical reactions, which optimizes the yield. For the same reasons, the conditions for coke deposition on the turboreactor surfaces are unfavorable, leading to an increase in plant availability. This study demonstrates that the mechanical work input into the feedstock can be dissipated through an intense turbulent mixing process, which maintains an ideal and controlled pressure level for cracking.

   @article{Rubini2021,
     publisher = {American Society of Mechanical Engineers,},
     dimensions = {true},
     author = {Rubini, Dylan and Xu, Liping and Rosic, Budimir and Johannesdahl, Harri},
     title = {{A New Turbomachine for Clean and Sustainable Hydrocarbon Cracking}},
     journal = {ASME Journal of Engineering for Gas Turbines and Power},
     volume = {144},
     number = {2},
     pages = {021024},
     year = {2021},
     month = dec,
     issn = {0742-4795},
     doi = {10.1115/1.4052784},
     url = {https://doi.org/10.1115/1.4052784},
   }