"From the standpoint of industrial safety, explosions present a major hazard, particularly for chemical plants and refineries, where accidental releases of large quantities of flammable material can often occur. When an explosion does take place at one of these facilities, the greatest hazards are often large-scale deflagrations, which can result in significant damage to individual buildings or even widespread damage over a large area, as in the case of unconfined vapor cloud explosions. At these scales, the formation of flame instabilities significantly increase the overall burning rate of the flame and the severity of the event.Without an adequate understanding of the mechanisms which govern the growth of these flame instabilities, and how they interact, existing modeling techniques are unable to accurately predict the consequences of these events. This creates considerable uncertainty in the protection requirements for these facilities. To improve our understanding of the mechanisms behind the development of large-scale flame instabilities, a comprehensive experimental study was performed examining the onset and growth of spherical-flame instabilities for propane-air, methane-air, and hydrogen-air flames at large scale. Across these fuels, a range of concentrations were studied, allowing for the growth of these instabilities to be evaluated for both thermal-diffusively stable and unstable flames. In addition, the interaction between weak initial turbulence and the growth of these instabilities was also examined. From the experimental work, it was shown that the critical radius for onset of instability varies linearly with mixture Markstein length, consistent with smaller-scale studies seen in the literature. For mixtures with positive Markstein length, an oscillatory rate of flame acceleration was observed that had not been previously identified. These oscillations were consistent with the fractal theory of spherical-flame acceleration and the formation of discrete length scales of instability. In the case of thermal-diffusively unstable mixtures, with negative Markstein length, no oscillations were observed; however, the rate of flame acceleration was consistent with a 4/3 power law exponent described in the literature. When weak initial turbulence was introduced, it was found that thermal-diffusively stable flames, with positive Markstein length, behave similar to mixtures with negative Markstein length under quiescent conditions. Specifically, initial turbulence significantly reduced the critical radius for onset of instability and increased the overall rate of spherical-flame acceleration in these mixtures. Using a number of assumptions inferred from the experimental work, an analytical model was developed to describe the growth of flame instabilities on a spherical flame, considering a fractal approach where multiple length scales grow on the flame surface simultaneously. This model shows how the growth of these instabilities can have a significant impact on the flame speed and overall rate of fuel consumption, and why they must be accounted for in the development of models describing large-scale flames. In particular, this work shows how turbulence plays a key role in determining the onset of instability and the rate of spherical- flame acceleration that occurs. This analytical model can be used to provide insight into the development of new engineering correlations or provide a basis for the development of sub-grid CFD models that quantify the effect of flame instabilities at large scale." --

This book explores the potential of hydrogen combustion in thermal engines and serves as a foundation for future research. Hydrogen, a well-established energy carrier, has been used in internal combustion engines for centuries, but despite progress and industry interest, hydrogen engines have yet to reach mass production. In light of recent efforts to combat climate change with clean energy and environmentally-friendly technologies, the use of hydrogen in thermal engines is gaining momentum. This book examines the unique challenges of hydrogen combustion due to its wide flammability limits, high auto-ignition temperature, and high diffusivity. It reviews current knowledge on the fundamental and practical aspects of hydrogen combustion and considers current developments and potential future advancement.