| 1. |
- Hong, Beichuan, Ph.D. student, 1989-, et al.
(author)
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Crank angle-resolved mass flow characterization of engine exhaust pulsations using a Pitot tube and thin-wire thermocouples
- 2023
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In: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311 .- 1873-5606. ; , s. 121725-121725
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Journal article (peer-reviewed)abstract
- 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.
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| 2. |
- Hong, Beichuan, Ph.D. student, 1989-, et al.
(author)
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Numerical Analysis of Engine Exhaust Flow Parameters for Resolving Pre-Turbine Pulsating Flow Enthalpy and Exergy
- 2021
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In: Energies. - : MDPI AG. - 1996-1073. ; 14:19
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Journal article (peer-reviewed)abstract
- Energy carried by engine exhaust pulses is critical to the performance of a turbine or any other exhaust energy recovery system. Enthalpy and exergy are commonly used concepts to describe the energy transport by the flow based on the first and second laws of thermodynamics. However, in order to investigate the crank-angle-resolved exhaust flow enthalpy and exergy, the significance of the flow parameters (pressure, velocity, and temperature) and their demand for high resolution need to be ascertained. In this study, local and global sensitivity analyses were performed on a one-dimensional (1D) heavy-duty diesel engine model to quantify the significance of each flow parameter in the determination of exhaust enthalpy and exergy. The effects of parameter sweeps were analyzed by local sensitivity, and Sobol indices from the global sensitivity showed the correlations between each flow parameter and the computed enthalpy and exergy. The analysis indicated that when considering the specific enthalpy and exergy, flow temperature is the dominant parameter and requires high resolution of the temperature pulse. It was found that a 5% sweep over the temperature pulse leads to maximum deviations of 31% and 27% when resolving the crank angle-based specific enthalpy and specific exergy, respectively. However, when considering the total enthalpy and exergy rates, flow velocity is the most significant parameter, requiring high resolution with a maximum deviation of 23% for the enthalpy rate and 12% for the exergy rate over a 5% sweep of the flow velocity pulse. This study will help to quantify and prioritize fast measurements of pulsating flow parameters in the context of turbocharger turbine inlet flow enthalpy and exergy analysis.
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| 3. |
- Kovács, András, et al.
(author)
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Role of heterophase interfaces on local coercivity mechanisms in the magnetic Al0.3CoFeNi complex concentrated alloy
- 2023
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In: Acta Materialia. - : Elsevier BV. - 1359-6454. ; 246
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Journal article (peer-reviewed)abstract
- Microstructural features across different length scales have a profound influence on the coercivity of magnetic alloys. Whereas the role of homophase boundaries on the pinning of magnetic domain walls is well established, the influence of heterophase interfaces on domain wall motion is complex and poorly understood. Here, we use state-of-the-art electron microscopy techniques to show that the magnetization reversal process in an Al0.3CoFeNi magnetic complex concentrated alloy (CCA), which is responsible for its coercivity, changes dramatically from a nucleation-type mechanism in the FCC+L12 state of the CCA, with a domain wall width of 171 nm, to a pinning type mechanism in the microstructure with colonies of FCC/L12 nanorods embedded in a BCC/B2 matrix, with a domain wall width of 35 nm. Our work reveals that heterophase FCC/BCC interfaces have a much stronger effect on coercivity than isostructural chemically ordered/disordered interfaces and provides a powerful guide to the rational design of microstructure to tune magnetic properties in both complex concentrated alloys and conventional magnetic alloys.
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| 4. |
- Mahendar, Senthil Krishnan, et al.
(author)
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Numerical Investigation of Increasing Turbulence through Piston Geometries on Knock Reduction in Heavy Duty Spark Ignition Engines
- 2019
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In: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Journal article (peer-reviewed)abstract
- Knock in heavy duty (HD) spark ignition (SI) engines is exacerbated by a large bore diameter and a higher flame travel distance. An increase in turbulence close to TDC can improve combustion speed and reduce knock through low residence time for end gas auto-ignition. Since HD SI engines are usually derived from diesel engines, it is common to have a swirl motion that does not dissipate into turbulence. To increase flame speed and limit knock, squish can be used to produce turbulence close to TDC. In this study, two different piston bowl geometries are examined: The re-entrant and quartette. The influence of squish area on turbulence production by these piston geometries were investigated using motored simulations in AVL FIRE. The effect of increased turbulence on knock reduction was analyzed using a calibrated 1D GT-Power model of a HD SI engine and the performance improvement was estimated. The effect of clearance height and input swirl level on turbulence was studied for both piston geometries to determine their sensitivity. A lower squish area quartette piston provided the same knock advantage corresponding to a higher squish area re-entrant piston due to additional turbulence production by swirl breakdown. With zero swirl, there was no difference in the turbulence produced by re-entrant and quartette pistons, however, a considerable increase in TKE was observed compared to the baseline swirl level re-entrant case as piston driven flow imparted more turbulence early in the compression stroke.
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| 5. |
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| 6. |
- Mahendar, Senthil, et al.
(author)
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The Impact of Miller Valve Timing on Combustion and Charging Performance of an Ethanol- and Methanol-Fueled Heavy-Duty Spark Ignition Engine
- 2021
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In: SAE International Journal of Engines. - : SAE International. - 1946-3936 .- 1946-3944. ; 14:5, s. 733-748
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Journal article (peer-reviewed)abstract
- Combustion engines and liquid fuels are likely to continue playing a central role in freight transportation with renewable fuels reducing carbon emissions. Ethanol and methanol are future renewable fuels with a knock resistance that make them suitable for heavy-duty (HD) spark ignition (SI) engines. This simulation work focuses on the potential for improving the efficiency of an ethanol- and methanol-fueled HD SI engine using early intake valve closing Miller valve timing. With Miller valve timing, the expansion ratio and thermodynamic efficiency can be increased while maintaining the same effective compression ratio. However, Miller timing requires increased boost pressure to retain the same trapped air mass and also suffers from reduced in-cylinder turbulence. Unlike previous simulation studies, a validated semi-predictive combustion model was used to resolve the implication of turbulence reduction on burn rate and its impediment in extracting higher thermodynamic efficiency with Miller timing discussed. The observed increase in burn duration adversely affected knock and the overall efficiency benefit from Miller timing. At stoichiometric conditions, a 2-3% increase in brake efficiency was observed with Miller timing by increasing the geometric compression ratio even with a relatively low turbocharger efficiency of 49%. At lean conditions, the increase in burn duration and pumping loss was significant for both fuels demanding a minimum turbocharger efficiency of 55% to gain an improvement in brake efficiency from Miller timing. If the degree of Miller timing is constrained by a single-stage turbocharger, Miller timing showed only a 0.7% point efficiency increase at lean conditions due to the reduced burn rate. If the burn rate can be increased, similar to 2.5% increase in brake efficiency can be achieved using Miller timing leading to over 48% brake efficieny for both fuels thus making the HD SI engine competitive to HD diesel engines.
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| 7. |
- Venkataraman, Varun, et al.
(author)
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Analyzing Engine Exhaust Gas Temperature Pulsations and Gas-Dynamics Using Thin-Wire Thermocouples
- 2024
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In: Journal of engineering for gas turbines and power. - : ASME International. - 0742-4795 .- 1528-8919. ; 146:7, s. 1-13
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Journal article (peer-reviewed)abstract
- The exhaust of internal combustion engines (ICEs) is characterized by rapid large amplitude exhaust gas temperature (EGT) pulsations that demand high-bandwidth measurements for accurate instantaneous and mean EGTs. While measurement technique challenges constrain on-engine EGT pulse measurements, reduced-order system simulations numerically estimate the EGT pulse and its mean to overcome the measurement limitation. Notwithstanding high-bandwidth pressure measurements, model calibration and validation for the EGT are confined to mean indications using sheathed thermal sensors like thermocouples and resistance thermometers. These EGT measurements are susceptible to errors caused by heat transfer, flow unsteadiness, and the thermal inertia of the sensor. Exposed thin-wire thermocouples provide an intermediate solution to the robustness-to-response tradeoff of thermal sensors. While the thermocouples' thermal inertia significantly affects the measured EGT pulse, the signal derivative (un-scaled dynamic error) provides greater insight by indicating the EGT waveform. This study utilizes a 50.8 μm Type-K thermocouple to contrast the exhaust pressure and EGT pulses through the measured signal and its derivative. Experiments in a single-pipe exhaust of a heavy-duty diesel engine with isolated engine speed and load sweeps present significant differences between the pressure and indicative EGT waveforms. It also highlights a rapid pre-pulse fluctuation unique to the EGT pulse waveform caused by exhaust gas-dynamics and impacted by heat transfer. The study motivates the need for increased bandwidth EGT measurements to improve model validation of EGT pulse estimates while showcasing the utility of thin-wire thermocouples.
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| 8. |
- Venkataraman, Varun, et al.
(author)
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Modelling Considerations for Resistance Wire Thermometers Applied to Internal Combustion Engines
- 2021
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In: SMSI 2021 - Sensors and Instrumentation. - : AMA Service GmbH. ; , s. 201-202
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Conference paper (peer-reviewed)abstract
- This study delves into the modelling of resistance wire thermometers (RWTs) within the applicationcontext of measuring the exhaust gas temperature pulse in internal combustion engines. The modelwas developed in a commercial simulation software utilizing the heat balance equation. Disparitieswere found between different model representations of the prongs due to differences in the heat transfer within the sensor, which impacts its expected dynamic response. The appropriate modelling choicewill be made upon validation with shock tube experiments for different RWT designs
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| 9. |
- Venkataraman, Varun, et al.
(author)
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Resistance Wire Thermometers for Temperature Pulse Measurements on Internal Combustion Engines
- 2020
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Conference paper (peer-reviewed)abstract
- This study revisits the design of resistance wire thermometers (RWTs) for measuring time-resolved temperature pulsations of the exhaust gas on internal combustion engines. RWTs with gold coated tungsten wires were fabricated and tested on a heavy-duty diesel engine. Experimental results indi-cate their utility in such harsh environments with the addition of a protective ceramic coating over the welded joints. The influence of the coating on sensor geometry and response will be elucidated through shock tube and gas stand experiments.
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| 10. |
- Venkataraman, Varun, et al.
(author)
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Thin-Wire Thermocouple Design for Exhaust Gas Temperature Pulse Measurements in Internal Combustion Engines
- 2023
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In: SAE International Journal of Engines. - : SAE International. - 1946-3936 .- 1946-3944. ; 16:7
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Journal article (peer-reviewed)abstract
- Accurate exhaust gas temperature (EGT) measurements are vital in the design and developmentprocess of internal combustion engines (ICEs). The unsteady ICE exhaust flow and thermal inertia of commonly used sheathed thermocouples and resistance thermometers require high bandwidth EGT pulse measurements for accurate cycle-resolved and mean EGTs. The EGT pulse measurement challenge is typically addressed using exposed thin-wire resistance thermometers or thermocouples.The sensor robustness to response tradeoff limits ICE tests to short durations over a few exhaust conditions. Larger diameter multiwire thermocouples using response compensation potentially overcomes the tradeoff. However, the literature commonly adopts weaker slack wire designs despiteindications of coated weld taut wires being robust. This study experimentally evaluates the thin-wirethermocouple design placed in the exhaust of a heavy-duty diesel engine over wide-ranging exhaust conditions for improving both sensor robustness and accuracy of the measured EGT. The assessed design parameters included the wire diameter (51 μm to 254 μm), the exposed wire length, and thewires placed slack or taut with coated weld faces. All taut wires with ceramic-coated weld faces endured over 3 h of engine operation, while similar diameter slack wires (51 μm and 76 μm) were sensitive to the exhaust condition and exposed wire length. Reducing the wire diameter from 76 μmto 51 μm significantly impacted response improvements as evidenced at certain test conditions bya peak-peak EGT increase of 92 °C, a mean EGT drop of 26 °C, and a doubling of the sensitivity ofmean EGT cycle-to-cycle variations to ±12 °C. Increasing the exposed wire length showed less significant response improvements. The Type-K thin-wire thermocouples showed negligible drift, thereby indicating the possibility of using smaller and longer wires built taut with coated weld facesfor improved accuracy of EGT measurements in ICEs.
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