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Mihaescu, Mihai
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CFD-Driven Preliminary Investigation of Ethanol-Diesel Diffusive Combustion in Heavy-Duty Engines

KTH Royal Institute of Technology-Nicola Giramondi, Mihai Mihaescu, Anders Christiansen Erlandsson
Scania CV AB-Anders Jäger
  • Technical Paper
  • 2019-01-2192
Published 2019-12-19 by SAE International in United States
The introduction of renewable alcohols as fuels for heavy-duty engines may play a relevant role for the reduction of the carbon footprint of the transport sector. The direct injection of ethanol as main fuel and diesel as pilot fuel in the engine combustion chamber through two separate injectors may allow good combustion controllability over the entire engine operating range by targeting diffusive combustion. Closed-cycle combustion simulations have been carried out using AVL FIRE coupled to AVL TABKIN for the implementation of the Flamelet Generated Manifold (FGM) chemistry reduction technique in order to investigate the influence of the injection system geometry and the injection strategy of pure ethanol and diesel fuel on ignition characteristics and combustion at different operating conditions.
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A Steady-State Based Investigation of Automotive Turbocharger Compressor Noise

KTH Royal Institute of Technology-Mihai Mihaescu, Mats Abom
Volvo Car Group-Magnus Knutsson
Published 2018-06-13 by SAE International in United States
The challenging problem of noise generation and propagation in automotive turbocharging systems is of real interest from both scientific and practical points of view. Robust and fast steady-state fluid flow calculations, complemented by acoustic analogies can represent valuable tools to be used for a quick assessment of the problem during e.g. design phase, and a starting point for more in-depth future unsteady calculations.Thus, as a part of the initial phase of a long-term project, a steady-state Reynolds Averaged Navier-Stokes (RANS) flow analysis is carried out for a specific automotive turbocharger compressor geometry. Acoustic data are extracted by means of aeroacoustics models available within the framework of the STAR-CCM+ solver (i.e. Curle and Proudman acoustic analogies, respectively). This part of the work focuses on the discussion and comparison of the aeroacoustic models, and their suitability towards predicting flow and acoustics trends corresponding to the operating conditions investigated. However, given the unsteady nature of acoustics, the project will have to develop towards an investigation of the problem using more expensive, but more accurate, Large Eddy Simulation (LES)…
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Particle Number Reduction in Automotive Exhausts by Controlled Grouping

Ben Gurion University of the Negev-David Katoshevski
KTH Royal Institute of Technology, CCGEx-Ghulam Mustafa Majal, Mikael Karlsson, Mihai Mihaescu
Published 2018-04-03 by SAE International in United States
Particulate emissions from internal combustion engines is a well-known issue with direct implications on air quality and human health. Recently there is an increased concern about the high number of ultrafine particles emitted from modern engines. Here we explore a concept for grouping these particles, reducing their total number and shifting the relative size distribution towards fewer larger particles. Particles having a non-zero relaxation time may be manipulated to yield regions of high particle concentration, accommodating agglomeration, when introduced into an oscillating flow field. The oscillating flow field is given by simple periodic geometrical changes of the exhaust pipe itself. It is discussed how the shape of these geometrical changes and also the engine pulses effect the grouping behavior for different size particles, including when Brownian motion becomes relevant. Simulations are performed using a bespoke 1D-model sufficient for the basic parameter studies of the concept given here.
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A Comparison of On-Engine Surge Detection Algorithms using Knock Accelerometers

KTH Royal Institute of Technology-Andreas Cronhjort, Mihai Mihaescu
Scania CV AB-Ola Stenlaas
Published 2017-10-08 by SAE International in United States
On-engine surge detection could help in reducing the safety margin towards surge, thus allowing higher boost pressures and ultimately low-end torque. In this paper, experimental data from a truck turbocharger compressor mounted on the engine is investigated. A short period of compressor surge is provoked through a sudden, large drop in engine load. The compressor housing is equipped with knock accelerometers. Different signal treatments are evaluated for their suitability with respect to on-engine surge detection: the signal root mean square, the power spectral density in the surge frequency band, the recently proposed Hurst exponent, and a closely related concept optimized to detect changes in the underlying scaling behavior of the signal. For validation purposes, a judgement by the test cell operator by visual observation of the air filter vibrations and audible noises, as well as inlet temperature increase, are also used to diagnose surge. The four signal treatments are compared with respect to their reliability as surge indicator and the time delay between surge onset and indication. Results show that the signal power in the…
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Optimal Pressure Based Detection of Compressor Instabilities Using the Hurst Exponent

SAE International Journal of Engines

KTH Royal Institute of Technology-Bertrand Kerres, Mihai Mihaescu
University of Cincinnati-Matthieu Gancedo, Ephraim Gutmark
  • Journal Article
  • 2017-01-1040
Published 2017-03-28 by SAE International in United States
The compressor surge line of automotive turbochargers can limit the low-end torque of an engine. In order to determine how close the compressor operates to its surge limit, the Hurst exponent of the pressure signal has recently been proposed as a criterion. The Hurst exponent quantifies the fractal properties of a time series and its long-term memory. This paper evaluates the outcome of applying Hurst exponent based criterion on time-resolved pressure signals, measured simultaneously at different locations in the compression system. Experiments were performed using a truck-sized turbocharger on a cold gas stand at the University of Cincinnati. The pressure sensors were flush-mounted at different circumferential positions at the inlet of the compressor, in the diffuser and volute, as well as downstream of the compressor. Results show that the previously identified threshold value distinguishing between surge and stable operation when the analysis was carried out for a different and smaller compressor can be used also for this much larger compressor. The investigation concerning the sensor locations reveals that pressure sensors at the outlet or shortly…
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Analysis of the Turbocharger Compressor Surge Margin Using a Hurst-Exponent-based Criterion

SAE International Journal of Engines

KTH Royal Institute of Technology-Bertrand Kerres, Vineeth Nair, Andreas Cronhjort, Mihai Mihaescu
  • Journal Article
  • 2016-01-1027
Published 2016-04-05 by SAE International in United States
Turbocharger compressors are limited in their operating range at low mass flows by compressor surge, thus restricting internal combustion engine operation at low engine speeds and high mean effective pressures. Since the exact location of the surge line in the compressor map depends on the whole gas exchange system, a safety margin towards surge must be provided. Accurate early surge detection could reduce this margin. During surge, the compressor outlet pressure fluctuates periodically. The Hurst exponent of the compressor outlet pressure is applied in this paper as an indicator to evaluate how close to the surge limit the compressor operates. It is a measure of the time-series memory that approaches zero for anti-persistence of the time series. That is, a Hurst exponent close to zero means a high statistical preference that a high value is followed by a low value, as during surge. Maps of a passenger-car sized turbocharger compressor with inlet geometries that result in different surge lines are measured on a cold gas stand. It is demonstrated that the Hurst exponent in fact…
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Assessment of the 3D Flow in a Centrifugal compressor using Steady-State and Unsteady Flow Solvers

KTH Royal Institute of Tech.-Elias Sundström, Bernhard Semlitsch, Mihai Mihaescu
Published 2014-10-13 by SAE International in United States
Numerical analysis methods are used to investigate the flow in a ported-shroud centrifugal compressor under different operating conditions, i.e. several mass flow rates at two different speed lines. A production turbocharger compressor is considered, which is widely used in the heavy automotive sector. Flow solutions obtained under steady-state and transient flow assumptions are compared with available experimental data.The steady-state Reynolds Averaged Navier-Stokes method is used to assess the overall time averaged flow and the global performance parameters. Additionally, the Large Eddy Simulation (LES) approach is employed to capture the transient flow features and the developed flow instabilities at low mass flow rates near the surge line.The aim of this study is to provide new insights on the flow instability phenomena in the compressor flow near surge. Comparison of flow solutions obtained for near-optimal efficiency and near-surge conditions are carried out. The unsteady features of the flow field are quantified by means of Fourier transformation analysis, Proper Orthogonal Decomposition and Dynamic Mode Decomposition. For a near optimal efficiency set-up the frequency spectra are broad-banded with no…
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Numerical Flow Analysis of a Centrifugal Compressor with Ported and without Ported Shroud

KTH Royal Institute of Technology-Bernhard Semlitsch, JyothishKumar V, Mihai Mihaescu, Laszlo Fuchs
University of Cincinnati-Ephraim Gutmark, Matthieu Gancedo
Published 2014-04-01 by SAE International in United States
Turbochargers are commonly used in automotive engines to increase the internal combustion engine performance during off design operation conditions. When used, a most wide operation range for the turbocharger is desired, which is limited on the compressor side by the choke condition and the surge phenomenon. The ported shroud technology is used to extend the operable working range of the compressor, which permits flow disturbances that block the blade passage to escape and stream back through the shroud cavity to the compressor inlet. The impact of this technology on a speed-line at near optimal operation condition and near surge operation condition is investigated.A numerical study investigating the flow-field in a centrifugal compressor of an automotive turbocharger has been performed using Large Eddy Simulation. The wheel rotation is handled by the numerically expensive sliding mesh technique. In this analysis, the full compressor geometry (360 deg) is considered. Numerical solutions with and without ported shroud for a near optimal operation condition and near-surge operation condition. The flow-field of the different cases is analyzed to elucidate the functionality…
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