A review of wildland fire spread modelling, 1990-present, 1: Physical and quasi-physical models

In recent years, advances in computational power and spatial data analysis (GIS, remote sensing, etc) have led to an increase in attempts to model the spread and behaviour of wildland fires across the landscape. This series of review papers endeavours to critically and comprehensively review all types of surface fire spread models developed since 1990. This paper reviews models of a physical or quasi-physical nature. These models are based on the fundamental chemistry and/or physics of combustion and fire spread. Other papers in the series review models of an empirical or quasi-empirical nature, and mathematical analogues and simulation models. Many models are extensions or refinements of models developed before 1990. Where this is the case, these models are also discussed but much less comprehensively.Comment: 31 pages + 8 pages references + 2 figures + 5 tables. Submitted to International Journal of Wildland Fir

Emission Reduction and Assisted Combustion Strategies for Compression Ignition Engines with Subsequent Testing on a Single-Cylinder Engine

Due to increasingly stringent regulations set forth by the Environmental Protection Agency, engine researchers and manufacturers are testing and developing various emission reduction strategies for compression ignition engines. This thesis contains three sections where the author details two separate strategies for emission reduction and assisted combustion. Combustion resulting from compression ignition diesel engines contains high levels of nitrogen oxides (NOx) due to their lean operating characteristics. A common NOx reduction strategy used by most automotive manufactures involves the use of cooled EGR (exhaust gas recirculation) to reduce combustion temperatures. However, a downfall to this method is the formation of particulate matter (PM) from the reduced combustion temperatures. This reduction in NOx emissions with resulting increasing PM emissions describes the well-known NOx-PM tradeoff. Typically, a reduction in one of the emissions will result in an increase in the other. Chapter two documents the construction and testing of a cooled EGR system for a single cylinder diesel engine along with subsequent performance and emission analysis. The result of the cooled EGR system demonstrates a reduction in brake specific NOx due to reduced combustion temperatures, while decreasing brake specific PM due to increased turbulence. Resulting performance calculations displayed a slight increase in fuel consumption. Chapter three analyzes the effects of ozone-assisted combustion on a single cylinder diesel engine. This work starts with a summarization of the literature in the field, which supports the simplified combustion model for determination of trends. Experimentation results demonstrate the addition of ozone causes a decrease in ignition delay, which produces slightly higher in-cylinder temperatures. Due to the elevated temperatures and ozone decomposition, NOx production increases, while PM decreases through radial atomic oxygen chemistry. Additionally, carbon monoxide emissions increase while hydrocarbon levels decrease. The changes in fuel consumption resulting from ozone injection are negligible. Of additional importance, this work verifies findings in the literature that demonstrate the effects of adding more ozone is negligible above a certain level of ozone injection (20 ppm in this effort). This is due to high concentrations of ozone facilitating its own destruction during the compression process of the engine

Combustion and pollutant characteristics of IC engines fueled with hydrogen and diesel/hydrogen mixtures using 3D computations with detailed chemical kinetics

In order to develop design guidelines for optimum operations of internal combustion engines fueled with alternative fuels, a comprehensive understanding combustion behavior and the pollutant formation inside the cylinder are needed. The first part of this thesis aimed to numerically study the engine performance and in-cylinder pollutant formation in a spark ignition engine fueled with hydrogen. Advanced simulations were performed using multi- dimensional software AVL FIRE coupled with CHEMKIN. The detailed chemical reactions with 29 steps of hydrogen oxidation with additional nitrogen oxidation reactions were also employed. Formation rates of nitrogen oxides (NOx) within the engine were accurately predicted using the extended Zeldovich mechanism with parameters adjusted for a carbon-free fuel. The computational results were first validated against experimental results with different equivalence ratios and then employed to examine a spark-ignition engine fueled with hydrogen under different operating conditions. Strategies that could have significant effects on the engine performance and emissions, such as exhaust gas recirculation (EGR) and ignition timing were also investigated. Furthermore, the maximization of engine power and minimization of NOx emissions were considered as conflicting objectives for preliminary optimization. Finally, a skeletal reaction mechanism was developed to include the reaction kinetics of diesel and hydrogen fuel mixtures to investigate in-cylinder combustion processes of such a dual fuel compression-ignition engine. The model was then employed to examine the effects of exhaust gas recirculation (EGR) and N2 dilution on NOx emissions --Abstract, page iii

CMC Modelling of Enclosure Fires

This thesis describes the implementation of the conditional moment closure (CMC) combustion model in a numerical scheme and its application to the modelling of enclosure fires. Prediction of carbon monoxide (CO) in the upper smoke layer of enclosure fires is of primary interest because it is a common cause of death. The CO concentration cannot be easily predicted by empirical means, so a method is needed which models the chemistry of a quenched, turbulent fire plume and subsequent mixing within an enclosed space. CMC is a turbulent combustion model which has been researched for over a decade. It has provided predictions of major and minor species in jet diffusion flames. The extension to enclosure fires is a new application for which the flow is complex and temperatures are well below adiabatic conditions. Advances are made in the numerical implementation of CMC. The governing combustion equations are cast in a conserved, finite volume formulation for which boundary conditions are uniquely defined. Computational efficiency is improved through two criteria which allow the reduction in the size of the computational domain without any loss of accuracy. Modelling results are compared to experimental data for natural gas fires burning under a hood. Comparison is made in the recirculating, post-flame region of the flow where temperatures are low and reactions are quenched. Due to the spatial flux terms contained in the governing equations, CMC is able to model the situation where chemical species are produced in the high temperature fire-plume and then transported to non-reacting regions. Predictions of CO and other species are in reasonable agreement with the experimental data over a range of lean and rich hood-fire conditions. Sensitivity of results to chemistry, temperature and modelling closures is inves- tigated. Species predictions are shown to be quite different for the two detailed chemical mechanisms used. Temperature conditions within the hood effect the for- mation of species in the plume prior to quenching and subsequently species predic- tions in the post-flame region are also effected. Clipped Gaussian and ß-function probability density functions (PDFs) are used for the stochastic mixture fraction. Species predictions in the plume are sensitive to the form of the PDF but in the post-flame region, where the ß-function approaches a Gaussian form, predictions are relatively insensitive. Two models are used for the conditional scalar dissipation: a uniform model, where the conditional quantity is set equal to the unconditional scalar dissipation across all mixture fraction space; and a model which is consistent with the PDF transport equation. In the plume, predictions of minor species are sensitive to the modelling used, but in the recirculating, post-flame region species are not significantly effected

Buoyancy Effects on Concurrent Flame Spread Over Thick PMMA

The flammability of combustible materials in a spacecraft is important for fire safety applications because the conditions in spacecraft environments differ from those on earth. Experimental testing in space is difficult and expensive. However, reducing buoyancy by decreasing ambient pressure is a possible approach to simulate on-earth the burning behavior inside spacecraft environments. The objective of this work is to determine that possibility by studying the effect of pressure on concurrent flame spread, and by comparison with microgravity data, observe up to what point low-pressure can be used to replicate flame spread characteristics observed in microgravity. Specifically, this work studies the effect of pressure and microgravity on upward/concurrent flame spread over 10 mm thick polymethyl methacrylate (PMMA) slabs. Experiments in normal gravity were conducted over pressures ranging between 100 and 40 kPa and a forced flow velocity of 200 mm/s. Microgravity experiments were conducted during NASAs Spacecraft Fire Experiment (Saffire II), on board the Cygnus spacecraft at 100 kPa with an air flow velocity of 200 mm/s. Results show that reductions of pressure slow down the flame spread over the PMMA surface approaching that in microgravity. The data is correlated in terms of a non-dimensional mixed convection analysis that describes the convective heat transferred from the flame to the solid, and the primary mechanism controlling the spread of the flame. The extrapolation of the correlation to low pressures predicts well the flame spread rate obtained in microgravity in the Saffire II experiments. Similar results were obtained by the authors with similar experiments with a thin composite cotton/fiberglass fabric (published elsewhere). Both results suggest that reduced pressure can be used to approximately replicate flame behavior of untested gravity conditions for the burning of thick and thin solids. This work could provide guidance for potential ground-based testing for fire safety design in spacecraft and space habitats

Advances in Modeling of Fluid Dynamics

This book contains twelve chapters detailing significant advances and applications in fluid dynamics modeling with focus on biomedical, bioengineering, chemical, civil and environmental engineering, aeronautics, astronautics, and automotive. We hope this book can be a useful resource to scientists and engineers who are interested in fundamentals and applications of fluid dynamics

The NASA SBIR product catalog

The purpose of this catalog is to assist small business firms in making the community aware of products emerging from their efforts in the Small Business Innovation Research (SBIR) program. It contains descriptions of some products that have advanced into Phase 3 and others that are identified as prospective products. Both lists of products in this catalog are based on information supplied by NASA SBIR contractors in responding to an invitation to be represented in this document. Generally, all products suggested by the small firms were included in order to meet the goals of information exchange for SBIR results. Of the 444 SBIR contractors NASA queried, 137 provided information on 219 products. The catalog presents the product information in the technology areas listed in the table of contents. Within each area, the products are listed in alphabetical order by product name and are given identifying numbers. Also included is an alphabetical listing of the companies that have products described. This listing cross-references the product list and provides information on the business activity of each firm. In addition, there are three indexes: one a list of firms by states, one that lists the products according to NASA Centers that managed the SBIR projects, and one that lists the products by the relevant Technical Topics utilized in NASA's annual program solicitation under which each SBIR project was selected

Effective Ignition Control in Advanced Combustion Engines

The primary objective of the research was to study the limitations of the conventional spark ignition architecture with respect to ultra-lean and dilute combustion and develop ignition technologies and strategies that can facilitate such combustion strategies. A range of strategies using conventional and modified ignition coil systems were used in combustion chamber and engine tests to understand the effectiveness of the energy delivery mechanisms and different energy profiles. At operating conditions where the conventional ignition strategies had difficulties in achieving adequate ignition stability, the use of enhanced energy levels with different energy profiles for the achievement of effective ignition under high dilution ratio engine operating conditions was found to be necessary. A novel multiple-site ignition system was developed. It has been demonstrated to effectively deliver of ignition energy and achieved higher tolerance for lean combustion and high-dilution modes of combustion. A radio-frequency non-thermal plasma ignition system was developed to investigate its ability to address some of the deficiencies of the spark ignition architecture. Compared to the conventional spark ignition architecture, the ignition volume induced by the corona discharge was greater in size and its growth was less impeded with the absence of a close ground electrode. The rapid energization and discharge characteristics additionally offered a more flexible control path. The formation of multiple ignition sites was possible, although implementation of the system in the engine environment has proven to be a continuing challenge