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Summary: In recent years, ammonia has shown great potential for future green fuel. However, ammonia combustion is a challenging task due to its narrow flammability limit, low flame speed, and slow kinetics compared with conventional hydrocarbon fuels. The blending of ammonia with higher reactive fuel such as hydrogen seems a novel alternative to overcome these difficulties. So, a comprehensive study of NH3/H2/air combustion characteristics is necessary. In the literature, numerous ammonia reaction models can be found, but most of them failed to demonstrate good combustion characteristics with NH3/H2/air mixtures. A new NH3/H2/air reaction model is suggested or proposed in the present work by referring to the previously available literature. The newly proposed reaction model consists of 32 species and 259 reactions. Model validation for laminar flame speed and ignition delay time at different operating conditions are performed in this study using the newly proposed reaction mechanism. Also, an extensive chemical kinetic modeling for heat release rate, flame speed and OH sensitivity analysis, reaction pathway analysis, and NOx emission characteristics of NH3/H2/air mixture is studied. The results show that the proposed reaction model closely follows the experimental trends, and lesser inconsistency is observed than the other reaction models compared in this study. All referenced reaction models used in the present work for comparison shows large discrepancies with experimental results of NH3/H2/air combustion, especially more discrepancies are observed at higher hydrogen enrichment conditions. Hydrogen enrichment positively affects the heat release rate intensity and flame speed of NH3/air mixture. Through the addition of hydrogen, the burning velocity of ammonia can be increased up to the level of hydrocarbon fuels, and the combination of ammonia and hydrogen blend can be used as an effective industrial fuel. [ABSTRACT FROM AUTHOR]

• Fuel gets consumed much earlier in a porous combustor compared to the dumb combustor. • Emissions are lower for the stacks of 10+20 PPI compared to the stacks of 10 PPI. • Combustion efficiency is higher for 10+20 PPI stacks compared to 10 PPI stacks. • Combustor exit temperature is lower in 10+20 PPI stacks compared to 10 PPI stacks. Ammonia is now being explored as a potential gas turbine fuel because of its renewable and carbon-free nature. Ammonia combustion possesses various limitations, such as high NO emissions, low burning velocity, and high auto-ignition temperature. Moreover, dual-fuel combustion approaches can be used to mitigate these drawbacks. However, the limitations of available information about the resulting emissions are insufficient to encourage widespread adoption. In this work, an NH 3 /CH 4 -air fueled self-recuperative high aspect ratio annular tubular porous burner is developed for gas turbine power applications. In this burner, an annular zone surrounds the combustion chamber to preheat the incoming air, while two perforated discs are mounted between the combustor and annular zone for uniform distribution of air. Eight Zirconia foams (4 of 10 PPI and 4 of 20 PPI) are stacked at the upstream side of the combustor. Experimentally, air preheat temperature, combustor exit temperature, NO, and CO emissions are analyzed and measured for various ammonia addition (0–41 % by weight) percentages, equivalence ratio of 1.0, and heat inputs of 17 & 21 kW for 10 PPI and a combination of 10 and 20 PPI porous foams. A preheated air stream coming from the annular zone speeds up fuel dissociation and helps in stabilizing the flame on the upstream side of the combustor. Combustor exit temperatures are lower in sandwich cases of 10 + 20 PPI than the porous foams of 10 PPI. However, with porous foams of 10 PPI, the air preheat temperature is higher. The insertion of porous foams shows better recirculation of heat and stable combustion is observed for higher percentages of ammonia and higher thermal inputs. The OH radicals are distributed for larger areas inside the dumb combustor, while for porous combustion, it is distributed near the porous foams. The porous sandwich cases of 10 + 20 PPI shows higher combustion efficiency compared to 10 PPI and without porous cases. The chemical kinetic analysis shows that the HNO and HCO radicals act as the main intermediate channel for NO and CO production. [ABSTRACT FROM AUTHOR]

• Effect of steam dilution in a non-premixed combustion model is studied numerically. • High pressure condition with liquid fuel (kerosene) spray is considered. • Sensitivity analysis shows steam affects the chemical kinetics of combustion. • Steam dilution accelerates the oxidation of hydrocarbons and CO. • Distributed reaction zone is a function of both pressure and dilution. In the present study, numerical analysis on the effect of steam dilution and high pressure on liquid fuel swirl combustion is carried out using a turbulent non-premixed combustion model. Tangential air injection scheme is adopted in a conical combustor. High recirculation is achieved inside the combustor due to the swirl pattern produced by the tangential air inlets. n-Dodecane, which is a major component of kerosene and Jet-A fuel, is selected as fuel in the present study. The thermal intensity of 5.37 MW/m3 with 21.1 kW thermal input is considered for the computational study. The chamber pressure is varied from 1 to 20 atm, keeping the momentum of inlet airflow constant. Steam added in the oxidizer as a diluent is varied from 0 to 20% by mass. Computational Fluid Dynamics (CFD) analysis using RANS (Reynolds Averaged Navier-Stokes) equations is performed to understand the flow characteristics and study the effect of steam dilution and pressure on NO formation. Realizable k- ε turbulence model is used in the present study to capture the flow behavior due to the swirling motion. Spray characteristics are modelled using the Discrete Phase Model. The chemical representation is realized using scalar conservation concept with β -PDF model. Detailed chemical kinetic analysis with ignition delay characteristics, rate of species production, reaction behavior and sensitivity analysis is carried out. It is observed that the ignition delay decreases rapidly with pressure and very slowly with steam dilution. Effect of pressure and dilution on the OH concentration and olefins are discussed. Peak flame temperature and NO formation decreased with the steam addition. Emission characteristics are presented in the paper. [ABSTRACT FROM AUTHOR]