Joseph F. Grcar

Ammonia conversion and NOx formation in laminar coflowing nonpremixed methane-air flames

This paper reports on a combined experimental and modeling investigation of NOx formation in nitrogen-diluted laminar methane diffusion flames seeded with ammonia. The methane-ammonia mixture is a surrogate for biomass fuels which contain significant fuel-bound nitrogen. The experiments use flue-gas sampling to measure the concentration of stable species in the exhaust gas, including NO, O2, CO, and CO2. The computations evolve a two-dimensional low Mach number model using a solution-adaptive projection algorithm to capture fine-scale features of the flame. The model includes detailed thermodynamics and chemical kinetics, differential diffusion, buoyancy, and radiative losses. The model shows good agreement with the measurements over the full range of experimental NH3 seeding amounts. As more NH3 is added, a greater percentage is converted to N2 rather than to NO. The simulation results are further analyzed to trace the changes in NO formation mechanisms with increasing amounts of ammonia in the fuel.

A taxonomy of integral reaction path analysis

Achieving understanding through combustion modelling is limited by the ability to recognize the implications of what has been computed and to draw conclusions about the elementary steps underlying the reaction mechanism. This difficulty can be overcome in part by making better use of reaction path analysis in the context of multidimensional flame simulations. Following a survey of current practice, an integral reaction flux is formulated in terms of conserved scalars that can be calculated in a fully automated way. Conditional analyses are then introduced, and a taxonomy for bidirectional path analysis is explored. Many examples illustrate the resulting path analyses and uncover some new results about laminar non-premixed methane-air jets.

Min-max identities on boundaries of convex sets around the origin

Min-max and max-min identities are found for inner products on the boundaries of compact, convex sets whose interiors contain the origin. The identities resemble the minimax theorem but they are different from it. Specifically, the value of each min-max (or max-min) equals the value of a dual problem of the same type. Their solution sets can be characterized geometrically in terms of the enclosed convex sets and their polar sets. However, the solution sets need not be convex nor even connected.

Tools for simulation of laboratory-scale premixed turbulent flames

We have entered a new era in turbulent combustion calculations, where we can now simulate a detailed laboratory-scale turbulent reacting flow with sufficient fidelity that the computed data may be expected to agree with experimental measurements. Moreover, flame simulations can be used to help interpret measured diagnostics, validate evolving flame theories, and generally allow exploration of the system in ways not previously available to experimentalists. In this paper, we will discuss our adaptive projection algorithm for low speed reacting flow that has helped make these types of simulations feasible, and two sets of new issues that are associated with application of this approach to simulating real flames. Using a recently computed flame simulation as an example, we will discuss issues concerning characterization of the experimental conditions and validation of the computed results. We also discuss recent developments in the analysis and interpretation of extremely large and complex reacting flow datasets, and a new approach to simulating premixed turbulent flames relevant to laboratoryscale combustion experiments-a feedback-controlled flame stabilization method.