Special Issue on Contemporary Combustion Experimentation and Modeling for Clean and Efficient Power Generation: Issues and Challenges

Reactive flow, i.e., the study of processes where the timescales relevant to chemical conversion couple with the ones of convective and diffusive transport, presents an intriguing pair of properties. On one hand, it lies at the heart of clean and efficient design of energy conversion systems, such as power plants and internal combustion engines. It is universally accepted that the potential of both novel and classic fuels (anything from recycled plastics to coal) and classic and innovative processes (from wood combustion to reactivity-controlled compression ignition and low-temperature combustion) will only be fully realized through the thorough understanding and control of the underlying thermodynamic, kinetic, and fluid-mechanical fundamentals.

On the other hand, it is perhaps a testimony to the limitations of human capabilities that, despite their apparent simplicity and obvious practical relevance that has attracted huge research interest, these processes still challenge the limits of human knowledge. In an age where anything from genomics to wireless communication seems to be a solved problem, the fact of the matter is that the simplest problems of hydrodynamics (let’s say, a pipe flow) remain basically unsolved in their general form. Add to this the immense complexity of the oxidative chemistry that is typically involved in energy conversion processes and you end up with one of the most challenging and, at the same time, most exciting fields of science and technology.

The inherent difficulty of the field lends itself to the establishment of a very healthy relation between experiments, modeling, and computations. Exactly because precise solutions are not available (in theory, not even the existence of general solutions to Navier-Stokes has been proven!), the necessary but on occasion unexciting validation processes that are typical of other fields cannot really be pursued here. Instead, computation and experimentation are to be seen as two independent methodologies to approach the same set of problems. The two independent “tools” offer different but complementary capabilities and perspectives that contribute to the solution of the common problem rather than going through the perhaps redundant exercise of validating each other. On one hand, modern experimentation can provide solid data that guide theoretical understanding and therefore build the modeling foundation of computations. On the other hand, high-fidelity computation can guide technological innovation into regimes where experimental validation is either too difficult or simply impossible.

In this special issue, we are trying to provide the readers of JEE with a vista in this collaborative relation of experiments and computation in modern energy engineering. In particular, the issue includes 16 papers that employ a wide spectrum of computational and experimental methodologies for the study of a wide variety of energy-conversion technologies. The contributions to the special issue include anything from papers that demonstrate new theoretical and computational methodologies (such as second-law analysis and computational singular perturbation) to experimentation with scanning electron microscopy of coal particles and power generation from recycled plastics. Corresponding to pressing current societal needs, there is a particular focus on renewable fuels and emissions with a specific emphasis on automotive technologies. Diesel and biodiesel injection are studied in several articles with a particular emphasis on ${\mathrm{NO}}_{\mathrm{x}}$ emissions. The potential of a series of novel, possibly renewable fuels such as biobutanol, animal fat, wood gas, and kerosene for automotive application is examined both experimentally and computationally. However, the practical situations covered in the issue also expand to stationary power plants, covering coal combustion, swirl burners, and power generation from recycled material.

It is, of course, realized that the sample that we provide cannot be expected to exhaust every single aspect of the computational and experimental study of energy conversion processes, but we believe that readers will get a representative view of the state of the art. Our hope is that the special issue will act as reference material for practitioners of related research, as an instrumental introduction to the scientific and technological challenges for the uninitiated, and above all, as a catalyst for the furtherance of fruitful discourse between experimentalists, modelers, and computational researchers of energy-related technologies.

We would like to thank all of the authors for their valuable contributions and the referees for conducting thorough and detailed reviews that have raised even further the level of the contributed papers. We express our gratitude to the Editor in Chief of the Journal, Dr. Chung-Li Tseng, for the opportunity and his excellent cooperation during the production of this special issue.