MAESTRO: An Adaptive Low Mach Number Hydrodynamics Algorithm for Stellar Flows

Many astrophysical phenomena are highly subsonic, requiring specialized numerical methods suitable for long-time integration. In a series of earlier papers we described the development of MAESTRO, a low Mach number stellar hydrodynamics code that can be used to simulate long-time, low-speed flows that would be prohibitively expensive to model using traditional compressible codes. MAESTRO is based on an equation set derived using low Mach number asymptotics; this equation set does not explicitly track acoustic waves and thus allows a significant increase in the time step. MAESTRO is suitable for two- and three-dimensional local atmospheric flows as well as three-dimensional full-star flows. Here, we continue the development of MAESTRO by incorporating adaptive mesh refinement (AMR). The primary difference between MAESTRO and other structured grid AMR approaches for incompressible and low Mach number flows is the presence of the time-dependent base state, whose evolution is coupled to the evolution of the full solution. We also describe how to incorporate the expansion of the base state for full-star flows, which involves a novel mapping technique between the one-dimensional base state and the Cartesian grid, as well as a number of overall improvements to the algorithm. We examine the efficiency and accuracy of our adaptive code, and demonstrate that it is suitable for further study of our initial scientific application, the convective phase of Type Ia supernovae.Comment: Accepted to Astrophysical Journal Suppliment (http://iop.org). 56 pages, 15 figures

Simulation of lean premixed turbulent combustion

There is considerable technological interest in developingnew fuel-flexible combustion systems that can burn fuels such ashydrogenor syngas. Lean premixed systems have the potential to burn thesetypes of fuels with high efficiency and low NOx emissions due to reducedburnt gas temperatures. Although traditional scientific approaches basedon theory and laboratory experiment have played essential roles indeveloping our current understanding of premixed combustion, they areunable to meet the challenges of designing fuel-flexible lean premixedcombustion devices. Computation, with itsability to deal with complexityand its unlimited access to data, hasthe potential for addressing thesechallenges. Realizing this potential requires the ability to perform highfidelity simulations of turbulent lean premixed flames under realisticconditions. In this paper, we examine the specialized mathematicalstructure of these combustion problems and discuss simulation approachesthat exploit this structure. Using these ideas we can dramatically reducecomputational cost, making it possible to perform high-fidelitysimulations of realistic flames. We illustrate this methodology byconsidering ultra-lean hydrogen flames and discuss how this type ofsimulation is changing the way researchers study combustion

Numerical Simulation of a Laboratory-Scale Turbulent SlotFlame

We present three-dimensional, time-dependent simulations ofthe flowfield of a laboratory-scale slot burner. The simulations areperformed using an adaptive time-dependent low Mach number combustionalgorithm based on a second-order projection formulation that conservesboth species mass and total enthalpy. The methodology incorporatesdetailed chemical kinetics and a mixture model for differential speciesdiffusion. Methane chemistry and transport are modeled using the DRM-19mechanism along with its associated thermodynamics and transportdatabases. Adaptive mesh refinementdynamically resolves the flame andturbulent structures. Detailedcomparisons with experimental measurementsshow that the computational results provide a good prediction of theflame height, the shape of the time-averaged parabolic flame surfacearea, and the global consumption speed (the volume per second ofreactants consumed divided by the area of the time-averaged flame). Thethickness of the computed flamebrush increases in the streamwisedirection, and the flamesurface density profiles display the same generalshapes as the experiment. The structure of the simulated flame alsomatches the experiment; reaction layers are thin (typically thinner than1 mm) and the wavelengths of large wrinkles are 5--10 mm. Wrinklesamplify to become long fingers of reactants which burn through at a neckregion, forming isolated pockets of reactants. Thus both the simulatedflame and the experiment are in the "corrugated flameletregime.

The Analysis of Non-road Vehicle Engine Operating Conditions in Terms of Emission Regulations

W pracy przedstawiono analizę obecnie obowiązujących przepisów prawnych dotyczących emisji związków szkodliwych spalin dla pojazdów o zastosowaniach pozadrogowych (non-road). Przegląd ten obejmuje Europę i Stany Zjednoczone. Ponadto zaprezentowano charakterystyki gęstości czasowej pracy silników wybranych pojazdów o zastosowaniach pozadrogowych, ładowarek i wodzideł polowych i przeprowadzono ich analizę odniesieniu do obowiązującego testu homologacyjnego.The paper presents an analysis of legal regulations in force related to toxic emissions from non-road vehicles. This analysis covers Europe and The U.S. furthermore, time density characteristics of engines of selected non-road vehicles have been presented in the paper (loaders, tractors) and analyzed in reference to the homologation test

The measurement of exhaust emissions from the engines fitted in agricultural tractors under real operating conditions

The exhaust emissions tests from non-road vehicles including machines used in agriculture are currently performed on engine dynamometers in NRSC and NRTC tests. Such tests do not entirely reflect the real machine operating conditions. Real operating conditions are characterized by variable loads and variable engine speeds and to a large extent they depend on other factors that occur under operation (variable weather conditions). In light of the growing emission requirements in relation to transport it seems justified to determine the real emissions under real operating conditions. This testing method is one of the main trends in the development of the emission testing methodology worldwide. The tests performed under real operating conditions should be used for the optimization of future powertrains used in both road and non-road vehicles. The results of such tests should also be included in the works on the improvement of the emissions legislation. The paper presents the results of the emission tests from the engines fitted in agricultural tractors (plowing). For the measurement of the emissions a portable exhaust emissions analyzer SEMTECH DS. by SENSORS was used. Based on the obtained results an analysis was developed of selected engine parameters. The performed analysis is a comparison of two tractors performing similar field work. In the final part of the paper the authors present the possibilities and trends in further works related to the emissions measurements under real operating conditions from vehicles used in agriculture

The measurement of exhaust emissions from the engines fitted in agricultural tractors under real operating conditions

The exhaust emissions tests from non-road vehicles including machines used in agriculture are currently performed on engine dynamometers in NRSC and NRTC tests. Such tests do not entirely reflect the real machine operating conditions. Real operating conditions are characterized by variable loads and variable engine speeds and to a large extent they depend on other factors that occur under operation (variable weather conditions). In light of the growing emission requirements in relation to transport it seems justified to determine the real emissions under real operating conditions. This testing method is one of the main trends in the development of the emission testing methodology worldwide. The tests performed under real operating conditions should be used for the optimization of future powertrains used in both road and non-road vehicles. The results of such tests should also be included in the works on the improvement of the emissions legislation. The paper presents the results of the emission tests from the engines fitted in agricultural tractors (plowing). For the measurement of the emissions a portable exhaust emissions analyzer SEMTECH DS. by SENSORS was used. Based on the obtained results an analysis was developed of selected engine parameters. The performed analysis is a comparison of two tractors performing similar field work. In the final part of the paper the authors present the possibilities and trends in further works related to the emissions measurements under real operating conditions from vehicles used in agriculture

Time density of engine operation in combine-harvester vehicles in the aspect of the emission legislation

Artykuł dotyczy problemu emisji związków szkodliwych spalin z silników kombajnów zbożowych. W pracy przedstawiono wyniki badań i analiz dotyczących warunków pracy tych silników. Wykonano analizę, na podstawie której określono zakresy najczęściej wykorzystywanych obciążeń i prędkości obrotowych silników. Uzyskane charakterystyki gęstości czasowej (rozkład prędkości i obciążenia w czasie) silników odniesiono do punktów pomiarowych testu homologacyjnego badań emisji związków toksycznych spalin. Na tej podstawie wysunięto wnioski odnośnie korelacji między punktami testu badawczego a najczęściej wykorzystywanymi zakresami pracy silników kombajnów. Zaproponowano również dalsze kierunki badań i analiz dotyczących poruszanego problemu.The paper concerns the problem of toxic emission from non-road vehicles. The paper presents the results of the investigations and analysis related to the engine operating conditions of a combine-harvester. An analysis has been performed based on which a range of the most frequently used loads and engine speeds were determined. The obtained time density characteristics (distribution of speeds and loads in time) of the engines were compared to the measurement points of the toxic emission homologation cycle. On this basis conclusions have been drawn regarding the correlation between the measurement points of the cycle and the most frequently used areas of loads and speeds of combine-harvester. Further suggestions for the investigations and analysis have also been made referring to the issue at hand. Besides, based on the obtained results certain proposals have been formed for further development of the non-road vehicles emission legislation

Badania emisji związków toksycznych spalin z pojazdów o zastosowaniach pozadrogowych z wykorzystaniem analizatorów PEMS

The paper discusses the issue of exhaust emissions from non-road vehicle engines. In the first part of the paper American regulations on the procedures of engine testing in operation were briefly characterized. The said regulations are a novel solution and were introduced as one of the first of this type worldwide. In the next part of the paper the authors presented the results of the exhaust emission tests from a farm tractor performed under actual operating conditions during fieldwork. For this purpose PEMS (Portable Emissions Measurement System) was used. The tests were carried out for different test procedures such as the NTE (NotTo-Exceed) procedure. The analysis of the test results was performed chiefly in the aspect of the NTE test applicable in the U.S. The analysis pertains chiefly to the engine operating conditions and exhaust emissions. European legislation currently does not require such tests and that is why the presented tests are related to the American procedures. The performed tests and their analysis led to a formulation of conclusions related to the engine operating conditions and its exhaust emissions.Artykuł dotyczy problemu badań emisji związków toksycznych spalin z silników pojazdów o zastosowaniach pozadrogowych (nonroad). W pierwszej części artykułu krótko scharakteryzowano przepisy amerykańskie nt. procedur badań silników w eksploatacji. Przepisy te są nowatorskim rozwiązaniem i zostały wprowadzone jako jedne z pierwszych tego typu rozwiązań na świecie. W dalszej części artykułu przedstawiono wyniki badań emisji związków toksycznych spalin silnika ciągnika rolniczego, wykonane w rzeczywistych warunkach eksploatacji, podczas wykonywania prac polowych. Do tego celu wykorzystano aparaturę PEMS (Portable Emissions Measurement System). Badania te wykonano dla różnych procedur badawczych, m.in. w teście NTE (NotTo-Exceed). Analizę wyników badań przeprowadzono głównie w aspekcie testu NTE, obowiązującego w Stanach Zjednoczonych. Analiza ta dotyczy przede wszystkim warunków pracy silników oraz emisji związków szkodliwych. Europejskie regulacje prawne w chwili obecnej nie nakładają obowiązku wykonywania takich badań, dlatego w zaprezentowane badania odnoszą się do procedur amerykańskich. Wykonane badania i ich analiza pozwoliły na sformułowanie wniosków dotyczących warunków pracy i emisji z silnika