Thermoelectric Generators for Waste Heat Recovery in Heavy-Duty Vehicles

Modern heavy-duty vehicles have to fulfill the highest demands in terms of economy and ecology, i. e. reduction of total cost of ownership, fuel consumption and pollutant emissions. A holistic technically and economically optimized waste heat recovery system in the form of a thermoelectric generator, which takes into account mechanical, electrical, thermoelectric and thermodynamic as well as economic aspects, can contribute to the achievement of these objectives. Two application scenarios are considered, heavy-duty vehicles with conventional diesel engines and with stoichiometric natural gas engines. Thermoelectric generator concepts were developed that combine high electrical power (peak power of about 3000 W for the natural gas heavy-duty vehicle) with low negative impact on the overall vehicle. As a result of this research study significantly higher fuel savings are achieved compared to the state of the art. For the diesel vehicle fuel reductions in dynamic driving scenarios are between 0.5 - 1.5 %, CO2-emission reductions are between 4 – 15 gCO2/km and the minimum amortization period is 1.4 years. The economic use of the system is demonstrated considering the total cost of ownership. Better results are obtained for natural gas vehicles due to the higher exhaust enthalpy. These are 1.8 - 2.8%, 13 - 35 gCO2/km, and 0.7 years. A functional model has successfully validated the simulation environment with an average deviation of less than 6 %. An electrical output power of up to 2700 W was measured under the boundary conditions of the natural gas engine. The results obtained increase the technological maturity level, which has been low to date, and contribute significantly to getting thermoelectrics closer to series maturity in technological and economic aspects

Delayed improvement local search

Local search is a fundamental tool in the development of heuristic algorithms. A neighborhood operator takes a current solution and returns a set of similar solutions, denoted as neighbors. In best improvement local search, the best of the neighboring solutions replaces the current solution in each iteration. On the other hand, in first improvement local search, the neighborhood is only explored until any improving solution is found, which then replaces the current solution. In this work we propose a new strategy for local search that attempts to avoid low-quality local optima by selecting in each iteration the improving neighbor that has the fewest possible attributes in common with local optima. To this end, it uses inequalities previously used as optimality cuts in the context of integer linear programming. The novel method, referred to as delayed improvement local search, is implemented and evaluated using the travelling salesman problem with the 2-opt neighborhood and the max-cut problem with the 1-flip neighborhood as test cases. Computational results show that the new strategy, while slower, obtains better local optima compared to the traditional local search strategies. The comparison is favourable to the new strategy in experiments with fixed computation time or with a fixed target.publishedVersio

3 kW Thermoelectric Generator for Natural Gas-Powered Heavy-Duty Vehicles – Holistic Development, Optimization and Validation

Emissions from heavy-duty vehicles need to be reduced to decrease their impact on the climate and to meet future regulatory requirements. The use of a cost-optimized thermoelectric genera-tor based on total cost of ownership is proposed for this vehicle class with natural gas engines. A holistic model environment is presented that includes all vehicle interactions. Simultaneous op-timization of the heat exchanger and thermoelectric modules is required to enable high system efficiency. A generator design combining high electrical power (peak power of about 3,000 W) with low negative effects was selected as a result. Numerical CFD and segmented high-temperature thermoelectric modules are used. For the first time, the possibility of an eco-nomical use of the system in the amortization period of less than << 2 years is available, with a fuel reduction in a conventional vehicle topology of already up to 2.8%. A significant improve-ment in technology maturity was achieved and the power density of the system was significant-ly improved to 298 W/kg and 568 W/dm3 compared to the state of the art. A functional model successfully validated the simulation results with an average deviation of less than 6%. An elec-trical output power of up to 2,700 W was measured

HD-TEG: Effizienzsteigerungspotential bei Nutzfahrzeugen durch den Einsatz eines neuartigen Abwärmenutzungssystems (Thermoelektrik)

In diesem Projekt wurde die Effizienzsteigerung von modernen schweren Nutzfahrzeugen durch den Einsatz eines neuartigen Abwärmenutzungssystems demonstriert. Dabei wurde erstmalig ein nutzfahrzeugspezifisches System basierend auf der Thermoelektrik mit Hilfe eines gesamtheitlichen Entwicklungsansatzes entwickelt und das Potential dieser Technologie für heutige und zukünftige Nutzfahrzeuge dargestellt. Als Referenzfahrzeug diente ein innovatives Serien-Nutzfahrzeug mit Erdgasmotor, welches als eine Schlüsseltechnologie für den zukünftigen emissionsärmeren Straßengüterverkehr im Nah- sowie im Fernbereich gilt. Projektschwerpunkte waren gleichermaßen die Effizienzsteigerung des thermoelektrischen Systems und des Fahrzeuges sowie die Kostensenkung des Systems durch Verwendung von seriennahen Aufbautechnologien und Fertigungsverfahren. Die Systemkosten von Abwärmenutzungssystemen im Nutzfahrzeug müssen sich anwendungsspezifisch in möglichst kurzer Nutzungszeit im Realbetrieb amortisieren. Dazu wurde eine Bauweise des TEG gewählt, die eine hohe Energieausbeute bei gleichzeitig geringem Gewicht verspricht und somit Vorteile sowohl unter Realfahrbedingungen als auch in relevanten Fahrzyklen bietet. Eine neuartige ganzheitliche Auslegungsmethode bietet das Potential, thermoelektrische Systeme in Zukunft deutlich effizienter auslegen zu können. Hierbei wurden neben der Systemauslegung erstmals auch alle Wechselwirkungen mit dem Nutzfahrzeug betrachtet und quantifiziert. Die Umsetzung dieser Ansätze wurden in mehreren Funktionsmustern dargestellt. Durch die enge Zusammenarbeit der Projektpartner, konnte das Wissen und die umfangreiche Erfahrung beider in das Projekt einfließen, um der Technologie im Nutzfahrzeug zum Durchbruch zu verhelfen. Als Ergebnis konnte erstmalig ein Abwärmenutzungssystem in Form eines Thermoelektrischen Generators für ein innovatives Erdgasnutzfahrzeug wirtschaftlich ausgelegt werden. Die berechnete Amortisation wurde zumeist in einer Zeit von kleiner als zwei Jahren, unter Annahme der Serienentwicklung des Systems, erzielt. Die Kraftstoffreduktion liegt bei bis zu 2,5 %, das entspricht rund 1 kg/100 km Kraftstoff. Zukünftiges Potential liegt bei weiteren 1,2 Prozentpunkten. Bei einer Hardwarerealisierung wurde am Funktionsmuster über 2,5 kW elektrische Leistung gemessen

Thermoelectric Generators with High Potential for Waste Heat Recovery in Heavy-Duty Vehicle Applications: Validation by a Functional Prototype with up to 2.7 kW

This research study demonstrates the engineering and measurement of a TEG prototype for heavyduty vehicles applications. The thermoelectric module area corresponds to approximately 1370 cm2 and consists of 144 segmented thermoelectric high-power modules based on bismuth telluride and skutterudite. The experimental setup enables the validation of the technology thermoelectric up to technology readiness level 5, which is rare in scientific publications on a 1:1 scale. The measured performance data of a functional prototype will be presented, as well as the electrical output power and compared with the simulated values. As a result, the simulative holistic design method of thermoelectric generators developed at the DLR Institute of Vehicle Concepts is successfully verified. In the measurement points performed, the accuracy of the simulated temperatures reaches in average more than 98%. The accuracy of the simulated output power is in average more than 94% and the minimum deviation is only -0.5%. The maximum electrical output power of 2,700 W could be measured at hot gas inlet temperature of 745 °C, mass flow of 0.25 kg/s, coolant inlet temperature of 20 °C and volume flow of 0.5 dm3/s. A significant improvement in the system level of thermoelectric generators for heavy-duty vehicles could be reached and the power density of the system could be increased to 174 W/kg and 326 W/dm3 compared to the state of the art based on the experimental measured values

Galactic Cosmic Ray induced absorbed dose rate in deep space – Accounting for detector size, shape, material, as well as for the solar modulation

Depending on the radiation field, the absorbed dose rate can depend significantly upon the size of the detectors or the phantom used in the models. In deep space (interplanetary medium) the radiation field is on avarage dominated by Galactic Cosmic Ray (GCR) nuclei. Here, the deep space dose rate that a typical small silicon slab detector measures is compared to a larger phantom corresponding to an ICRU sphere with a 15 cm radius composed of water. To separate and understand respective effects from the composition, size and shape differences in the detectors, this comparison is implemented in several steps. For each phantom, the absorbed dose rate due to GCR nuclei up to Z = 28, as a function of solar modulation conditions, is calculated. The main components of the GCR flux are protons, followed by helium nuclei and electrons, with Z > 2 nuclei accounting for approximately 1% of the total number of particles. Among the light nuclei with Z > 2, most abundant ones are C, N and O. In this study, we use the GEANT4 model to calculate the absorbed dose (energy deposited as ionization, divided by mass) due to the GCR flux provided by the Badhwar-O’Neill 2010 (BON-10) model. Furthermore, we investigate how the determined absorbed dose rate changes throughout the solar cycle by varying the GCR models from solar minimum to solar maximum conditions. The developed model is validated against the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) microdosimeter measurements. In our current approach, we do not consider the effects of shielding, which will always be present under realistic scenarios. A second goal of this study is to quantify the contribution of each Z = 1, …, 28 GCR nuclei to absorbed dose rate, in relation to the phantom characteristics. For each Z we determine the most relevant energy range in the GCR spectra for absorbed dose rate estimations. Furthermore, we calculate a solar modulation dependent conversion factor to convert absorbed dose rate measured in silicon to absorbed dose rate in water. This information will improve our understanding of the radiation environment due to GCR in the near-Earth deep space and also benefit further modeling efforts by limiting the number and energy range of primary particle species that have to be considered

Sicherstellung der Reproduzierbarkeit von Forschungsergebnissen durch Bewahrung des Zugriffs auf Forschungssoftware

Forschungsdaten sind nur im jeweiligen Kontext sinnvoll interpretier- und nachnutzbar – Bestandteil dieses Kontexts ist auch jegliche Software, die zur Erstellung und Verarbeitung der entsprechenden Forschungsdaten genutzt wurde. Im Folgenden werden mit Blick auf gute wissenschaftliche Praxis und die FAIR-Prinzipien primär organisatorische Aspekte im Umgang mit Forschungssoftware untersucht, sowie mit strategische Überlegungen angestellt, wie Forschungssoftware langfristig eingesetzt werden kann. Dazu werden aktuelle Entwicklungen im Bereich rechtlicher und organisatorischer Überlegungen präsentiert und konkrete Empfehlungen ausgesprochen. Dieses Papier wird vom Arbeitskreis der Leiterinnen und Leiter der wissenschaftlichen Rechenzentren in Baden-Württemberg (ALWR) unterstützt

First year of energetic particle measurements in the inner heliosphere with Solar Orbiter's Energetic Particle Detector

Context. Solar Orbiter strives to unveil how the Sun controls and shapes the heliosphere and fills it with energetic particle radiation. To this end, its Energetic Particle Detector (EPD) has now been in operation, providing excellent data, for just over a year. Aims. EPD measures suprathermal and energetic particles in the energy range from a few keV up to (near-) relativistic energies (few MeV for electrons and about 500 MeV nuc−1 for ions). We present an overview of the initial results from the first year of operations and we provide a first assessment of issues and limitations. In addition, we present areas where EPD excels and provides opportunities for significant scientific progress in understanding how our Sun shapes the heliosphere. Methods. We used the solar particle events observed by Solar Orbiter on 21 July and between 10 and 11 December 2020 to discuss the capabilities, along with updates and open issues related to EPD on Solar Orbiter. We also give some words of caution and caveats related to the use of EPD-derived data. Results. During this first year of operations of the Solar Orbiter mission, EPD has recorded several particle events at distances between 0.5 and 1 au from the Sun. We present dynamic and time-averaged energy spectra for ions that were measured with a combination of all four EPD sensors, namely: the SupraThermal Electron and Proton sensor (STEP), the Electron Proton Telescope (EPT), the Suprathermal Ion Spectrograph (SIS), and the High-Energy Telescope (HET) as well as the associated energy spectra for electrons measured with STEP and EPT. We illustrate the capabilities of the EPD suite using the 10 and 11 December 2020 solar particle event. This event showed an enrichment of heavy ions as well as 3He, for which we also present dynamic spectra measured with SIS. The high anisotropy of electrons at the onset of the event and its temporal evolution is also shown using data from these sensors. We discuss the ongoing in-flight calibration and a few open instrumental issues using data from the 21 July and the 10 and 11 December 2020 events and give guidelines and examples for the usage of the EPD data. We explain how spacecraft operations may affect EPD data and we present a list of such time periods in the appendix. A list of the most significant particle enhancements as observed by EPT during this first year is also provided.Ministerio de Economía y CompetitividadAgencia Estatal de Investigació

PTF1 J082340.04+081936.5: A Hot Subdwarf B Star with a Low-mass White Dwarf Companion in an 87-minute Orbit

We present the discovery of the hot subdwarf B star (sdB) binary PTF1 J082340.04+081936.5. The system has an orbital period of P_(orb) = 87.49668(1) minutes (0.060761584(10) days), making it the second-most compact sdB binary known. The light curve shows ellipsoidal variations. Under the assumption that the sdB primary is synchronized with the orbit, we find a mass of M_(sdB) = 0.45_(-0.07)^(+0.09) M_⊙, a companion white dwarf mass of M_(WD) = 0.46_(-0.09)^(+0.12) M_⊙, and a mass ratio of q = M_(WD)/M_(sdB) = 1.03_(-0.08)^(+0.10). The future evolution was calculated using the MESA stellar evolution code. Adopting a canonical sdB mass of M_(sdB) = 0.47 M_⊙, we find that the sdB still burns helium at the time it will fill its Roche lobe if the orbital period was less than 106 minutes at the exit from the last common envelope (CE) phase. For longer CE exit periods, the sdB will have stopped burning helium and turned into a C/O white dwarf at the time of contact. Comparing the spectroscopically derived log g and T_(eff) with our MESA models, we find that an sdB model with a hydrogen envelope mass of 5 x 10^(-4) M_⊙ matches the measurements at a post-CE age of 94 Myr, corresponding to a post-CE orbital period of 109 minutes, which is close to the limit to start accretion while the sdB is still burning helium