Author
Ulrich Maas
Other affiliations: Zuse Institute Berlin, BorgWarner Inc., University of Stuttgart ...read more
Bio: Ulrich Maas is an academic researcher from Karlsruhe Institute of Technology. The author has contributed to research in topics: Ignition system & Combustion. The author has an hindex of 36, co-authored 270 publications receiving 7272 citations. Previous affiliations of Ulrich Maas include Zuse Institute Berlin & BorgWarner Inc..
Papers published on a yearly basis
Papers
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TL;DR: In this article, a general procedure for simplifying chemical kinetics is developed, based on the dynamical systems approach, in contrast to conventional reduced mechanisms no information is required concerning which reactions are to be assumed to be in partial equilibrium nor which species are assumed to remain in steady state.
1,492 citations
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01 Dec 1996
TL;DR: The Navier-Stokes Equations for Three-dimensional Reacting Flows (NSFE) as discussed by the authors describe the Navier Stokes equation for three-dimensional reacting flows.
Abstract: Introduction * Fundamental Definitions and Phenomena * Experimental Investigation of Flames * Mathematical Description of Premixed Laminar Flat Flames * Thermodynamics of Combustion Processes * Transport Phenomena * Chemical Kinetics * Reaction Mechanisms * Laminar Prefixed Flames * Laminar Nonpremixed Flames * Ignition Processes * The Navier-Stokes Equations for Three-Dimensional Reacting Flows * Turbulent Reacting Flows * Turbulent Nonpremixed Flames * Turbulent Premixed Flames * Combustion of Liquid and Solid Fuels * Low-Temperature Oxidation, Engine Knock * Formation of Nitric Oxides * Formation of Hydrocarbons and Soot.
1,176 citations
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TL;DR: In this article, a detailed reaction mechanism and a multispecies transport model were used to simulate the explosion limits of the hydrogen-oxygen system and the minimum ignition energies for various mixture compositions, pressures, radii of the external energy source and ignition times.
440 citations
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01 Jan 1992TL;DR: In this paper, a general procedure for simplifying chemical kinetics and its use in reacting flow models is developed, which is based on the dynamical systems approach, and results are presented for the CO/H2/air system both for a simple homogeneous closed system and a flow reactor.
Abstract: A general procedure for simplifying chemical kinetics and its use in reacting flow models is developed, which is based on the dynamical systems approach. In contrast to conventional reduced mechanisms no information is required concerning which reactions are to be assumed to be in partial equilibrium nor which species are assumed to be in steady state. Based on a local eigenvector analysis, the method identifies the fast time scales of the chemical reaction systems, which differ typically by orders of magnitude. Assuming that the fastest relaxation processes in chemical reactions proceed infinitely fast (i.e., are in local equilibrium), it is then possible to reduce the state space globally, such that it can be described by means of only a small number of reaction progress variables. The only “inputs” to the procedure are the detailed kinetics mechanism and the number of degrees of freedom required in the simplified scheme. Then the state properties given by the simplified scheme are automatically determined as functions of the coordinates associated with the degrees of freedom. A tabulation procedure allows an efficient use of the results in CFD codes. Furthermore a general procedure for coupling the reduced mechanism with other than chemical processes like flow and molecular transport is discussed. Results are presented for the CO/H2/air system both for a simple homogeneous closed system and a flow reactor.
271 citations
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TL;DR: In this paper, the method of simplifying chemical kinetics based on Intrinsic Low-Dimensional Manifolds (ILDMs) is modified to deal with the coupling of reaction and diffusion processes.
Abstract: In the present work, the method of simplifying chemical kinetics based on Intrinsic Low-Dimensional Manifolds (ILDMs) is modified to deal with the coupling of reaction and diffusion processes. Several problems of the ILDM method are overcome by a relaxation to an invariant system manifold (Reaction–Diffusion Manifold – REDIM). This relaxation process is governed by a multidimensional parabolic partial differential equation system, where, as an initial solution, an extended ILDM is used. Furthermore, a method for the solution and tabulation of the manifold is proposed in terms of generalized coordinates, with a subsequent procedure for the integration of the reduced system on the found manifold. This modification of the ILDM significantly improves the performance of the concept and allows us to extend its area of applicability. Illustrative comparative calculations of detailed and reduced models of flat laminar flames verify the approach.
195 citations
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TL;DR: In this paper, a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) is presented.
Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These
9,929 citations
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2,687 citations
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TL;DR: Atomistic modeling with ReaxFF provides a useful method for determining the initial events of oxidation of hydrocarbons under extreme conditions and can enhance existing combustion models.
Abstract: To investigate the initial chemical events associated with high-temperature gas-phase oxidation of hydrocarbons, we have expanded the ReaxFF reactive force field training set to include additional transition states and chemical reactivity of systems relevant to these reactions and optimized the force field parameters against a quantum mechanics (QM)-based training set. To validate the ReaxFF potential obtained after parameter optimization, we performed a range of NVT−MD simulations on various hydrocarbon/O2 systems. From simulations on methane/O2, o-xylene/O2, propene/O2, and benzene/O2 mixtures, we found that ReaxFF obtains the correct reactivity trend (propene > o-xylene > methane > benzene), following the trend in the C−H bond strength in these hydrocarbons. We also tracked in detail the reactions during a complete oxidation of isolated methane, propene, and o-xylene to a CO/CO2/H2O mixture and found that the pathways predicted by ReaxFF are in agreement with chemical intuition and our QM results. We o...
1,815 citations
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TL;DR: In this article, a general procedure for simplifying chemical kinetics is developed, based on the dynamical systems approach, in contrast to conventional reduced mechanisms no information is required concerning which reactions are to be assumed to be in partial equilibrium nor which species are assumed to remain in steady state.
1,492 citations