Ammonia, a molecule that is gaining more interest as a fueling vector, has been considered as a candidate to power transport, produce energy, and support heating applications for decades. However, the particular characteristics of the molecule always made it a chemical with low, if any, benefit once compared to conventional fossil fuels. Still, the current need to decarbonize our economy makes the search of new methods crucial to use chemicals, such as ammonia, that can be produced and employed without incurring in the emission of carbon oxides. Therefore, current efforts in this field are leading scientists, industries, and governments to seriously invest efforts in the development of holistic solutions capable of making ammonia a viable fuel for the transition toward a clean future. On that basis, this review has approached the subject gathering inputs from scientists actively working on the topic. The review starts from the importance of ammonia as an energy vector, moving through all of the steps in the production, distribution, utilization, safety, legal considerations, and economic aspects of the use of such a molecule to support the future energy mix. Fundamentals of combustion and practical cases for the recovery of energy of ammonia are also addressed, thus providing a complete view of what potentially could become a vector of crucial importance to the mitigation of carbon emissions. Different from other works, this review seeks to provide a holistic perspective of ammonia as a chemical that presents benefits and constraints for storing energy from sustainable sources. State-of-the-art knowledge provided by academics actively engaged with the topic at various fronts also enables a clear vision of the progress in each of the branches of ammonia as an energy carrier. Further, the fundamental boundaries of the use of the molecule are expanded to real technical issues for all potential technologies capable of using it for energy purposes, legal barriers that will be faced to achieve its deployment, safety and environmental considerations that impose a critical aspect for acceptance and wellbeing, and economic implications for the use of ammonia across all aspects approached for the production and implementation of this chemical as a fueling source. Herein, this work sets the principles, research, practicalities, and future views of a transition toward a future where ammonia will be a major energy player.

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Review on ammonia as a potential fuel: from synthesis to economics

Combustion of fuels to generate energy is integral to various human activities, both domestic and industrial. However, the predominance of hydrocarbon fuel usage produces emissions containing pollutants that cause multiple environmental complications and risks to human health. Therefore, replacement of conventional fuels to achieve zero carbon emission is of utmost importance. In terms of carbon-free fuel, ammonia offers several advantages over hydrogen. However, its low burning velocity and high fuel NOx emissions inhibit large-scale usage. Hence, hydrogen and methane have been studied in this review as possible secondary fuels to aid ammonia combustion and address the aforementioned issues. This review starts from the suitability of ammonia fuel as energy vector in terms of physicochemical and combustion characteristics, moving through the kinetics and mechanisms of ammonia-based and ammonia-fuel combustion. The impacts and limitations of each system are also addressed, thus providing a comparison on each system. Particularly, this review assesses and discusses the advantages and mechanisms involved with secondary fuel addition to the ammonia combustion, presenting the role of key reaction differences and the change in key reaction mechanism under different conditions at the level of reaction mechanisms. Finally, this review covers future perspectives and challenges on the usage and development of ammonia-based fuels, emphasizing the maturity of ammonia-based and ammonia-fuel combustion kinetics. Herein, this work summarizes the principles of the combustion reactions of ammonia-based and ammonia-fuel systematically and serves as a theoretical reference of ammonia-fuel combustion kinetics for transitioning into future practical applications where ammonia is an important energy vector.

A review on ammonia, ammonia-hydrogen and ammonia-methane fuels

The plasma membrane of a eukaryotic cell is impermeable to most hydrophilic substances, yet the insertion of these materials into cells is an extremely important and universal requirement for the cell biologist. To address this need, many transfection techniques have been developed including viral, lipoplex, polyplex, capillary microinjection, gene gun and electroporation. The current discussion explores a procedure called optical injection, where a laser field transiently increases the membrane permeability to allow species to be internalized. If the internalized substance is a nucleic acid, such as DNA, RNA or small interfering RNA (siRNA), then the process is called optical transfection. This contactless, aseptic, single cell transfection method provides a key nanosurgical tool to the microscopist—the intracellular delivery of reagents and single nanoscopic objects. The experimental possibilities enabled by this technology are only beginning to be realized. A review of optical transfection is presented, along with a forecast of future applications of this rapidly developing and exciting technology.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2009.0463

Single cell optical transfection.

Physical methods for genetic plant transformation.

Advancements of combustion technologies in the ammonia-fuelled engines

Combustion of ammonia (NH3) presents a number of challenges due to its low reactivity, poor flame stability, very low flame speed and high NOx emissions in a range of burning conditions. Therefore, its application in combustion systems requires device modifications, either by adapting existing systems or developing new ones. In this work, a novel combustor fired by a swirl and bluff-body stabilized burner was designed and tested. Initially, flame stability diagrams were established for NH3/H2 fuel mixtures. Then, emissions of NOx and unburnt NH3 were measured for a range of equivalence ratios and NH3 mole fractions in the fuel mixture. In addition, in-flame data for O2 and NOx concentrations and gas temperature were measured for five combustor operating conditions. A parallel mathematical modelling exercise was performed to obtain a qualitative knowledge of the burner aerodynamics and assist the interpretation of the experimental results. The predicted aerodynamic pattern suggests the establishment of an extended central recirculation zone that allows long residence times in the near burner region (NBR) that are critical to ensure stable combustion of the NH3/H2/air mixtures. The measurements revealed that the burner presents a wide range of stable flames for x N H 3 between 0.6 and 0.8, showing the positive effects of adding relatively small amounts of H2 to the fuel mixture. The in-flame data show that the flame initiates close to the burner inlet and presents two main reaction zones. NOx is formed in the NBR and is consumed afterwards, through selective non-catalytic reduction reactions. Overall, the present laboratory combustor performs well in terms of flame stability and both NOx and NH3 emissions, and it is foreseen that industrial combustors based on the present design would be able to ensure flame stability and NOx and NH3 emissions control with simple complementary systems.

Characteristics of NH3/H2/air flames in a combustor fired by a swirl and bluff-body stabilized burner

Thermal and hydraulic characteristics of turbulent water flow in a transverse corrugated tube with various corrugation direction (inward/outward) and corrugation shape (triangle, curve, rectangle, ...

Numerical investigation of heat transfer and friction characteristics for turbulent flow in various corrugated tubes

A modified, non-damaging, protocol for the production of fertile transgenic wheat (Triticum aestivum L. cultivar Giza 164) plants by laser micropuncture was developed. The new homemade setup secures the transformation of as many as 60 immature embryo-derived calli (10000 cells each) in less than one hour using a UV excimer laser with two dimensional translation stages, a suitable computer program and a proper optical system. Five-day-old calli were irradiated by a focused laser microbeam to puncture momentarily made self-healing holes (∼0.5 µm) in the cell wall and membrane to allow uptake of the exogenous DNA. The plant expression vector pAB6 containing bar gene as a selectable marker for the herbicide bialaphos resistance and GUS (uidA) gene as a reporter gene was used for transformation. No selection pressure was conducted during the four-week callus induction period. Induced calli were transferred to a modified MS medium with 1 mg l−1 bialaphos for regeneration, followed by selection on 2 mg l−1 bialaphos for rooting. Three regenerated putative transgenic events were evaluated for the integration and stable expression of both genes and results indicated that this modified procedure of laser-mediated transformation can be successfully used in transforming wheat.

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Production of fertile transgenic wheat plants by laser micropuncture.

A new burner is developed and its performance is experimentally studied. The principle of this new burner, circumferential alternative air and fuel burner (CAFB) is to admit fuel and air circumferentially alternative patterns. This burner also allow for swirling both fuel and air jets injecting from different circumferential holes. The outlet angle of air and fuel jet is changed between 0, 15, 30, 45 and 60 injection angles. A new definition and number for swirl is defined, this is called the Injection Swirl Number (ISN) and found to be accurate to describe the flame characteristics. Complete test rig was developed to facilitate characterization of the new burner. A new micro controller traverse mechanism was programmed and fabricated to control the sensitively moving of the thermocouple and gas analyzer sampling probe in all directions. Measurements of gas temperature at different positions, and the oxygen concentrations at the flame centerline were made. The thermal and chemical flame heights were obtained from the maximum temperature and oxygen concentration at the flame centerline. The visible flame height was obtained from direct photography and Infrared (IR) radiometry. The vortex breakdown creation period as a results of a high intensity swirling flow were been captured by the infrared radiation camera. Comparisons of the new CAFB with other flames have also been performed. Experiments showed that the flame height decreases with the increase of the injection jet angles which improves the mixing between air and fuel generating an intense combustion zone and, hence, shortens the flame length. A new injection swirl ratio has been introduced for the new CAFB burner namely the injection swirl number (ISN), ISN = tan θ, where θ is the injection angle. The injection swirl number (ISN) used is 0, 0.26, 0.58, 1 and 1.75 which corresponding to the injection angles 0, 15, 30, 45 and 60 degree respectively. An empirical correlation has been derived for the new CAFB burner flame length as a function of the new derived (ISN).

M. A. Yehia

Papers

Review on ammonia as a potential fuel: from synthesis to economics

Characteristics of NH3/H2/air flames in a combustor fired by a swirl and bluff-body stabilized burner

Numerical investigation of heat transfer and friction characteristics for turbulent flow in various corrugated tubes

Production of fertile transgenic wheat plants by laser micropuncture.

Effect of Fuel and Air Injection Pattern on Combustion Dynamics in Confined and Free Diffusion Flame