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Mihaescu, Mihai, ProfessorORCID iD iconorcid.org/0000-0001-7330-6965
Biography [eng]

Mihai Mihaescu is Professor at KTH Royal Institute of Technology, Docent in Fluid Mechanics (KTH, 2013), and AIAA Associate Fellow. In addition to establishing and leading a research group, he is affiliated at KTH with the Linné FLOW Centre and the Competence Center for Gas Exchange (CCGEx), being the CCGEx Director since 2019.

Dr. Mihaescu holds a PhD degree in Fluid Mechanics from Lund University (LTH, 2005). He carried out his postdoctoral studies (2005-2007) at the Department of Aerospace Engineering and Engineering Mechanics, Gas Dynamics and Propulsion Laboratory, at the University of Cincinnati (UC), USA.  After his postdoctoral studies, Mihai continued at UC, serving as Research Associate and then as Research Assistant Professor faculty position (until 2011).

Dr. Mihaescu started his career at KTH Royal Institute of Technology initially as Researcher (2011-2014). He continued as Associate Professor (2014-2020), before being promoted to Professor of Fluid Mechanics (2020).

Publications (10 of 171) Show all publications
Golliard, T. & Mihaescu, M. (2024). Computational Aeroacoustics for a Cold, Non-Ideally Expanded Aerospike Nozzle. Journal of turbomachinery, 146(2), Article ID 021003.
Open this publication in new window or tab >>Computational Aeroacoustics for a Cold, Non-Ideally Expanded Aerospike Nozzle
2024 (English)In: Journal of turbomachinery, ISSN 0889-504X, E-ISSN 1528-8900, Vol. 146, no 2, article id 021003Article in journal (Refereed) Published
Abstract [en]

In supersonic aerospace applications, aerospike nozzles have been subject of growing interest. This study sheds light on the noise components of a cold jet exhausting an aerospike nozzle. Implicit large eddy simulations (ILES) are deployed to simulate the jet at a nozzle pressure ratio (NPR)=3. For far-field acoustic computation, the Ffowcs Williams-Hawk-ings (FWH) equation is applied. A mesh sensitivity study is performed and the jet instantaneous and time-averaged flow characteristics are analyzed. The annular shock structure displays short non-attached shock-cells and longer attached shock-cells. Downstream of the aerospike, a circular shock-cell structure is formed with long shock-cells. Two-point cross-correlations of data acquired at monitoring points located along the shear layers allow to identify upstream propagating waves associated to screech. Power spectral density at monitoring points in the annular shock-cell structure allows to identify its radial oscillation modes. Furthermore, a vortex sheet model is adapted to predict the annular shock-cells length and the BBSAN central frequency. High sound pressure levels (SPL) are detected at the determined BBSAN central frequencies. Finally, high SPL are obtained at the radial oscillation frequencies for the annular shock-cell structure.

Place, publisher, year, edition, pages
ASME International, 2024
Keywords
aeroacoustics, computational fluid dynamics (CFD), nozzle, turbine aerodynamic design
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-341742 (URN)10.1115/1.4063877 (DOI)001134180600006 ()2-s2.0-85180070049 (Scopus ID)
Note

QC 20240103

Available from: 2024-01-03 Created: 2024-01-03 Last updated: 2024-02-06Bibliographically approved
Laudato, M., Zea, E., Sundström, E., Boij, S. & Mihaescu, M. (2024). Sound generation mechanisms in a collapsible tube. Journal of the Acoustical Society of America, 155(5), 3345-3356
Open this publication in new window or tab >>Sound generation mechanisms in a collapsible tube
Show others...
2024 (English)In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 155, no 5, p. 3345-3356Article in journal (Refereed) Published
Abstract [en]

Collapsible tubes can be employed to study the sound generation mechanism in the human respiratory system. The goals of this work are (a) to determine the airflow characteristics connected to three different collapse states of a physiological tube and (b) to find a relation between the sound power radiated by the tube and its collapse state. The methodology is based on the implementation of computational fluid dynamics simulation on experimentally validated geometries. The flow is characterized by a radical change of behavior before and after the contact of the lumen. The maximum of the sound power radiated corresponds to the post-buckling configuration. The idea of an acoustic tube law is proposed. The presented results are relevant to the study of self-excited oscillations and wheezing sounds in the lungs.

Place, publisher, year, edition, pages
Acoustical Society of America (ASA), 2024
Keywords
Fluid-Structure Interaction, Sound generation mechanisms, collapsible tube, acoustic tube law
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-346926 (URN)10.1121/10.0026093 (DOI)001225524400003 ()38758053 (PubMedID)2-s2.0-85193507712 (Scopus ID)
Projects
Swedish Research Council Grant No. 2022–03032.
Funder
Swedish Research Council, 2022-03032Swedish Research Council, 2020-04668
Note

QC 20240603

Available from: 2024-05-24 Created: 2024-05-24 Last updated: 2024-06-03Bibliographically approved
Golliard, T. & Mihaescu, M. (2024). Temperature Impact on an Aerospike Nozzle Jet, a Computational Aeroacoustics Approach. In: AIAA SciTech Forum and Exposition, 2024: . Paper presented at AIAA SciTech Forum and Exposition, 2024, Orlando, United States of America, Jan 8 2024 - Jan 12 2024. American Institute of Aeronautics and Astronautics (AIAA)
Open this publication in new window or tab >>Temperature Impact on an Aerospike Nozzle Jet, a Computational Aeroacoustics Approach
2024 (English)In: AIAA SciTech Forum and Exposition, 2024, American Institute of Aeronautics and Astronautics (AIAA) , 2024Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, the flow and acoustic characteristics of an aerospike nozzle jet at a Nozzle Pressure Ratio (NPR) = 3 and three different Temperature Ratios (TR) = 1, 3, 7 are presented. Implicit Large Eddy Simulations (ILES) are deployed to simulate the flow of the aerospike nozzle. The LES calculations are completed by aeroacoustic computations based on the Ffowcs Williams-Hawkings (FWH) equation. In the supersonic jet exhausting an aerospike nozzle, two shock-cell structures are observed: an annular and a circular one. In the direct vicinity of the annular nozzle, the annular jet is non-attached and reattaches further downstream at increasing distance with increasing jet Temperature Ratio (TR). The observed shock cells in the non-attached annular jet structure are longer for TR3 and TR7 compared to TR1. The shock strength in the annular jet is increasing with increasing jet TR. In the meantime, the total number of shock cells in the circular part of the jet decreases with increasing jet TR. Pressure spectra in the near-field show the presence of a strong tonal noise at upstream angles corresponding to screech tones. Two-point cross-correlations of pressure data acquired in monitoring points located along axial lines in the circular shear layer are computed to quantify the upstream propagating waves associated to this tonal component. Power spectral density of the radial velocity at several monitoring points located at the shock cells as well as at the separation bubble, highlights the main oscillation modes of the annular shock-cell structure. Supersonic convection velocities of turbulent structures are detected with increasing jet temperature by means of two-point cross-correlation. This confirms the presence of Mach waves observed in the instantaneous snapshots. The Mach waves radiation angles are in agreement with existing models. In the far-field spectra, the highest Sound Pressure Levels (SPL) are associated to those Mach waves at angles around 140° (TR3) and 120° (TR7). High skewness and kurtosis in the pressure signals indicate crackle noise at higher jet temperatures. Additionally, the shock-cell length is used to predict the central frequency of Broadband Shock-Associated Noise (BBSAN) as a function of observation angles. The far-field spectra display mixing noise as well as BBSAN, related to the interaction between the convected vortices in the shear layers and the shock-cell structure. With increasing jet temperature, higher SPL are detected in agreement with the BBSAN central frequencies which were computed using the annular and circular shock-cell length.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics (AIAA), 2024
National Category
Fluid Mechanics and Acoustics Aerospace Engineering Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-349899 (URN)10.2514/6.2024-2100 (DOI)2-s2.0-85196819366 (Scopus ID)
Conference
AIAA SciTech Forum and Exposition, 2024, Orlando, United States of America, Jan 8 2024 - Jan 12 2024
Note

QC 20240704

ISBN 978-1-62410-711-5

Available from: 2024-07-03 Created: 2024-07-03 Last updated: 2024-07-04Bibliographically approved
Jacob, S., Trigell, E., Mihaescu, M. & Åbom, M. (2023). Acoustic scattering in a small centrifugal compressor based on the use of linearized equations in a rotating frame. Journal of Sound and Vibration, 544, 117315-117315, Article ID 117315.
Open this publication in new window or tab >>Acoustic scattering in a small centrifugal compressor based on the use of linearized equations in a rotating frame
2023 (English)In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 544, p. 117315-117315, article id 117315Article in journal (Refereed) Published
Abstract [en]

Numerical solutions of acoustic wave scattering are often used to describe sound propagation through complex geometries. For cases with flow, various forms of the convected equation have been used. A better alternative that includes vortex-sound interaction is instead to use the linearized and harmonic forms of the unsteady fluid flow governing equations. In this paper, a formulation of the linearized equations that include rotational effects, in an acoustic computation using a rotating frame of reference in a stationary geometry, is presented. We demonstrate that rotational effects can be important, e.g., when computing the transmission loss through high-speed compressors. The implementation of the proposed addition to the existing schemes is both simple and numerically inexpensive. The results are expected to have an impact on the research and development related to noise control of high-performance turbo-machinery, e.g., used in automotive or aviation applications at operating conditions that can be represented by steady background flows.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Acoustic scattering, compressor noise, linearized equations, experiments
National Category
Fluid Mechanics and Acoustics Vehicle Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-322073 (URN)10.1016/j.jsv.2022.117315 (DOI)000892346700005 ()2-s2.0-85141915892 (Scopus ID)
Projects
CCGEx
Funder
Swedish Energy Agency, 33834-3
Note

QC 20230126

Available from: 2022-11-30 Created: 2022-11-30 Last updated: 2023-11-15Bibliographically approved
Laudato, M. & Mihaescu, M. (2023). Analysis of the contact critical pressure of collapsible tubes for biomedical applications. Continuum Mechanics and Thermodynamics, 36(1), 217-228
Open this publication in new window or tab >>Analysis of the contact critical pressure of collapsible tubes for biomedical applications
2023 (English)In: Continuum Mechanics and Thermodynamics, ISSN 0935-1175, E-ISSN 1432-0959, Vol. 36, no 1, p. 217-228Article in journal (Refereed) Published
Abstract [en]

The onset of self-excited oscillations in airways and blood vessels is a common phenomenon in the human body, connected to both normal and pathological conditions. A recent experimental investigation has shown that the onset of self-excited oscillations happens for values of the intramural pressure close to the contact critical pressure. The goal of this work is to analyse the dependence of the contact critical pressure on the vessel’s geometric parameters. The methodology is based on the implementation of an experimentally validated computational model of a collapsible tube. The results confirm the correlation between the contact critical pressure and the onset of self-excited oscillations in collapsible tubes. Moreover, a set of general equations to compute the contact critical pressure and the corresponding areas of collapsible tubes with arbitrary geometries has been derived.

Place, publisher, year, edition, pages
Springer Nature, 2023
Keywords
collapsible tubes, contact critical pressure, biomedical application
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-346363 (URN)10.1007/s00161-023-01271-3 (DOI)001099732400001 ()2-s2.0-85176583515 (Scopus ID)
Projects
Swedish Research Council Grant VR 2020-04857
Funder
Swedish Research Council, VR 2020-04857KTH Royal Institute of Technology
Note

QC 20240514

Available from: 2024-05-14 Created: 2024-05-14 Last updated: 2024-05-14Bibliographically approved
Laudato, M., Mosca, R. & Mihaescu, M. (2023). Buckling critical pressures in collapsible tubes relevant for biomedical flows. Scientific Reports, 13(1)
Open this publication in new window or tab >>Buckling critical pressures in collapsible tubes relevant for biomedical flows
2023 (English)In: Scientific Reports, E-ISSN 2045-2322, ISSN 2045-2322, Vol. 13, no 1Article in journal (Refereed) Published
Abstract [en]

The behaviour of collapsed or stenotic vessels in the human body can be studied by means of simplified geometries like a collapsible tube. The objective of this work is to determine the value of the buckling critical pressure of a collapsible tube by employing Landau’s theory of phase transition. The methodology is based on the implementation of an experimentally validated 3D numerical model of a collapsible tube. The buckling critical pressure is estimated for different values of geometric parameters of the system by treating the relation between the intramural pressure and the area of the central cross-section as the order parameter function of the system. The results show the dependence of the buckling critical pressures on the geometric parameters of a collapsible tube. General non-dimensional equations for the buckling critical pressures are derived. The advantage of this method is that it does not require any geometric assumption, but it is solely based on the observation that the buckling of a collapsible tube can be treated as a second-order phase transition. The investigated geometric and elastic parameters are sensible for biomedical application, with particular interest to the study of the bronchial tree under pathophysiological conditions like asthma.

Place, publisher, year, edition, pages
Springer Nature, 2023
Keywords
Tube law, Buckling critical pressures, collapsible tubes, biomedical flows
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-328406 (URN)10.1038/s41598-023-36513-6 (DOI)001005311300026 ()37291334 (PubMedID)2-s2.0-85161432330 (Scopus ID)
Funder
Swedish Research Council, VR 2020-04857
Note

QC 20230612

Available from: 2023-06-09 Created: 2023-06-09 Last updated: 2023-07-21Bibliographically approved
Golliard, T. & Mihaescu, M. (2023). Computational Aeroacoustics for a Cold, Non-Ideally Expanded Aerospike Nozzle. In: Proceedings of ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition, GT 2023. Paper presented at ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition, GT 2023, Boston, United States of America, Jun 26 2023 - Jun 30 2023. American Society of Mechanical Engineers (ASME), Article ID v13ct33a004.
Open this publication in new window or tab >>Computational Aeroacoustics for a Cold, Non-Ideally Expanded Aerospike Nozzle
2023 (English)In: Proceedings of ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition, GT 2023, American Society of Mechanical Engineers (ASME) , 2023, article id v13ct33a004Conference paper, Published paper (Refereed)
Abstract [en]

In supersonic aerospace applications, aerospike nozzles have been subject of growing interest. These devices lead to enhanced thrust performance compared to conventional nozzles due to continuous altitude adaption and improved thrust vector control. However, supersonic non-ideally expanded jets are known to generate high levels of noise. The aeroacoustic behaviour of circular and rectangular nozzles has been largely discussed whereas data on the aeroacoustic behaviour of aerospike nozzles is scarce. For further industrial development, the identification of the noise generation mechanisms in such configurations is necessary. This study sheds light on the main noise components of a cold jet exhausting an aerospike nozzle. Implicit Large Eddy Simulations (ILES) are deployed to simulate the flow of the cold aerospike at a Nozzle Pressure Ratio (NPR) = 3. For far-field acoustic computation, the Ffowcs-Williams Hawkings (FWH) equation is applied. A mesh sensitivity study is first performed. Then, the configuration is analyzed in terms of near-field instantaneous and time-averaged flow characteristics. It is of crucial interest to characterize the features of the shock-cell structures. The annular shock structure near the aerospike bluff body displays two non-attached shock-cells of length L/Dj ∼ 0.43. The annular jet is then reattaching and this reattachment leads to longer shock-cells of length L/Dj ∼ 0.77. Downstream of the bluff body, a second expansion process takes place and leads to the emergence of a circular shock-cell structure with a first shock-cell length of L/Dj ∼ 1.20. The interaction between the vortical flow structures in the shear layers and the shocks generates Broadband Shock-Associated Noise (BBSAN). In order to enhance understanding of the noise generation mechanism for this configuration, several analyses are performed. Two-point cross-correlations of data acquired in monitoring points located along axial lines in the circular shear layers are used for quantifying the upstream propagating waves associated to a strong tonal component at a Strouhal number St = 0.51. This strong tonal component is known as screech. It is generated by a feedback mechanism between the coherent fluid flow structures propagating downstream in the jet shear layer and the upstream propagating acoustic waves generated at the same frequency by vortex-shock interactions, waves that are interacting with the nozzle lip and excite shear layer instabilities at the frequency of screech. Power spectral density of the radial velocity at monitoring points in the annular jet structure displays three main peaks at St = 0.68, St = 1.21 and St = 2.59. These frequencies correspond to the oscillation modes of the annular shock-cell structure in radial direction. Furthermore, a vortex sheet model is adapted to predict the length of the annular shock-cells. A good agreement is reached between the analytically derived shock-cell length and the simulation results. The shock-cell length is used to predict the central frequency of BBSAN as a function of observation angles. The far-field spectra show mixing noise as well as Broadband Shock-Associated Noise, related to the interaction between the convected vortices in the shear layers and the shock-cell structure. High sound pressure levels (SPL) are detected in agreement with the BBSAN central frequencies which were computed using the annular and circular shock-cell length. Finally, high SPL are obtained at the radial oscillation frequencies for the annular shock-cell structure.

Place, publisher, year, edition, pages
American Society of Mechanical Engineers (ASME), 2023
Keywords
acoustic analogy, aeroacoustics, aerospike nozzle, Ffowcs Williams-Hawkings, Large eddy simulation, supersonic jet noise
National Category
Fluid Mechanics and Acoustics Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-340382 (URN)10.1115/GT2023-101947 (DOI)001214818300057 ()2-s2.0-85177171478 (Scopus ID)
Conference
ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition, GT 2023, Boston, United States of America, Jun 26 2023 - Jun 30 2023
Note

Part of ISBN 9780791887103

QC 20231204

Available from: 2023-12-04 Created: 2023-12-04 Last updated: 2024-06-14Bibliographically approved
Laudato, M., Mihaescu, M., Zea, E. & Boij, S. (2023). Computational aeroacoustics in flexible conduits with application to biomedical fluid dynamics. In: 184th Meeting of the Acoustical Society of America: . Paper presented at Journal of the Acoustical Society of America (pp. A194). Chicago, USA: Acoustical Society of America (ASA), 153
Open this publication in new window or tab >>Computational aeroacoustics in flexible conduits with application to biomedical fluid dynamics
2023 (English)In: 184th Meeting of the Acoustical Society of America, Chicago, USA: Acoustical Society of America (ASA) , 2023, Vol. 153, p. A194-Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

Flexible tubes are simple yet powerful tools for the modeling of respiratory and circulatory systems [1, 2]. In the last decade, access to high-performance computational resources has allowed the implementation of realistic numerical models of human vessels based on Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI) simulations. Interestingly, the recently proven correlation [3] between CFD observables (like the pharyngeal airway's resistance) and clinical data (such as the Apnoea Hypopnea Index in Obstructive Sleep Apnoea patients) suggests a possible development of diagnostic methods based on numerical simulations. This work aims to investigate the extension of these correlations to the aeroacoustics characteristics of flexible conduits by means of a fully coupled FSI numerical model based on the Large Eddy Simulation method. These results have relevant applications to studying diseases of the human upper vocal tract, voice production, obstructive sleep apnoea, and adventitious lung sounds, such as wheezing and crackling.

[1] Grotberg, J. B., & Jensen, O. E. (2004). Annu. Rev. Fluid Mech., 36, 121–147.

[2] Schwartz, A. R., & Smith, P. L. (2013). The Journal of Physiology, 591(Pt 9), 2229.

[3] Schickhofer L., Malinen J., Mihaescu M., J. Acoust. Soc. Am. - JASA, 145 (4): 2049–2061, 2019. https://doi.org/10.1121/1.5095250

Place, publisher, year, edition, pages
Chicago, USA: Acoustical Society of America (ASA), 2023
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics; Biological Physics
Identifiers
urn:nbn:se:kth:diva-326362 (URN)10.1121/10.0018632 (DOI)001000287901183 ()
Conference
Journal of the Acoustical Society of America
Note

QC 20230516

Available from: 2023-04-30 Created: 2023-04-30 Last updated: 2023-09-01Bibliographically approved
Hong, B., Venkataraman, V., Mihaescu, M. & Cronhjort, A. (2023). Crank angle-resolved mass flow characterization of engine exhaust pulsations using a Pitot tube and thin-wire thermocouples. Applied Thermal Engineering, 121725-121725, Article ID 121725.
Open this publication in new window or tab >>Crank angle-resolved mass flow characterization of engine exhaust pulsations using a Pitot tube and thin-wire thermocouples
2023 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, p. 121725-121725, article id 121725Article in journal (Refereed) Published
Abstract [en]

Characterizing pulsating flow in high-temperature, high-pressure engine exhaust gas is crucial for the development and optimization of exhaust energy recovery systems. However, the experimental investigation of engine exhaust pulses is challenging due to the difficulties in conducting crank angle-resolved measurements under these unsteady flow conditions. This study contributes to characterizing mass flow pulses from an isolated cylinder exhaust of a heavy-duty diesel engine using a single-pipe measurement system, developed for pulsating flow measurement. A Pitot tube-based approach is adopted to measure exhaust mass flow pulsations, complemented by fast temperature measurements obtained using customized unsheathed thin-wire thermocouples. The on-engine experiment is performed by isolating the in-cylinder trapped mass and the valve opening speed to produce different exhaust pulse waveforms. The adopted approach’s sensitivity in resolving instantaneous mass flows is evaluated analytically and experimentally, considering attenuated temperature measurement effects. Based on exhaust flow measurements, mass flow pulses are analyzed with regard to blow-down and scavenge phases. Under the load sweep, the main waveform change occurs during the blow-down phase, with pulse magnitude increasing with the load. In contrast, as the engine speeds up with a comparable trapped mass, the exhaust mass distribution in the blow-down phase decreases from 75.5% at 700 rpm to 41.9% at 1900 rpm. Additionally, it is observed that cycle-to-cycle variations in mass flow pulses align with combustion stability during the blow-down phase and are predominantly influenced by gas-exchange processes during the scavenge phase.

Place, publisher, year, edition, pages
Elsevier BV, 2023
National Category
Applied Mechanics
Research subject
Machine Design; Industrial Engineering and Management
Identifiers
urn:nbn:se:kth:diva-337750 (URN)10.1016/j.applthermaleng.2023.121725 (DOI)001091673900001 ()2-s2.0-85173216542 (Scopus ID)
Funder
Swedish Energy Agency, 33834-3
Note

QC 20231009

Available from: 2023-10-07 Created: 2023-10-07 Last updated: 2023-11-20Bibliographically approved
Hong, B., Lius, A., Mahendar, S., Mihaescu, M. & Cronhjort, A. (2023). Energy and exergy characteristics of an ethanol-fueled heavy-duty SI engine at high-load operation using lean-burn combustion. Applied Thermal Engineering, 120063-120063, Article ID 120063.
Open this publication in new window or tab >>Energy and exergy characteristics of an ethanol-fueled heavy-duty SI engine at high-load operation using lean-burn combustion
Show others...
2023 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, ISSN 1359-4311, p. 120063-120063, article id 120063Article in journal (Refereed) Published
Abstract [en]

Ethanol, as the most produced renewable biofuel, is considered a promising low-carbon alternative to petroleum-based fuels in the transport sector due to its high energy density and auto-ignition resistance. The lean-burn combustion in spark-ignition (SI) engines has the potential to further improve thermal efficiency in regard to knock mitigation and the reduction of combustion temperature. However, the characteristics of lean-burn combustion in an ethanol-fueled engine in relation to the combustion losses and the gas-exchange process remain unclear, especially for high-load operation. This study contributes with a deeper understanding of the high-load performance of an ethanol-fueled heavy-duty SI engine using lean-burn combustion. Based on the experimental results from a single-cylinder engine test, a 6-cylinder engine model is built by integrating a validated predictive combustion model to characterize the lean-burn combustion process. The engine’s thermal efficiency and combustion phasing are evaluated for knock limited operation and then compared to the theoretical optimum which is regardless of knock. The energy and exergy balances are applied to evaluate the effect of dilution with excess air ratios up to 1.8. Losses through heat transfer, exhaust flow, and incomplete combustion are quantified. In addition, entropy generated through combustion is discussed to identify the relationship between exergy destruction and different operating conditions. In the context of lean-burn combustion, the thermal efficiency at high-load operation incrementally increases from 40.4% at stoichiometric condition to 47.3% at an excess air ratio of 1.8. At the same time, the exergy destruction through combustion increases by 3.3 percentage points across the selected dilution range. Furthermore, the challenging requirements to realize lean-burn combustion with lower exhaust gas temperatures and higher intake boost pressures is assessed through an exergy analysis of the turbocharging system.

Place, publisher, year, edition, pages
Elsevier BV, 2023
Keywords
Ethanol; Lean-burn combustion; Knock; Thermal efficiency; Exergy loss; Heavy-duty SI engines
National Category
Energy Engineering
Research subject
Energy Technology; Machine Design
Identifiers
urn:nbn:se:kth:diva-323203 (URN)10.1016/j.applthermaleng.2023.120063 (DOI)000924802400001 ()2-s2.0-85146960134 (Scopus ID)
Funder
Swedish Energy Agency, 33834-3
Note

QC 20230123

Available from: 2023-01-21 Created: 2023-01-21 Last updated: 2023-10-12Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7330-6965

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