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Reforming ammonia to hydrogen using engine exhaust waste heat is a promising technology to improve the combustion performance and reduce the exhaust emissions of ammonia-fueled engines. However, there are still a research gap between the laboratory-level catalytic reforming tests and the practical application in engine systems. In particular, there are urgent needs to further understanding the ammonia reforming characteristics and developing the simulaiton models for the engine system optimization. In this paper, we conducted the experiments of catalytic reforming NH 3 to H 2 to study the effects of the reaction temperature, gas hour space velocity (GHSV) and pressure on the thermo-catalytic decomposition characteristicsxin. The results indicate that both the ammonia catalytic conversion and reforming efficiency exhibit an increasing trend with the rise in reaction temperature, while these two parameters demonstrate a decreasing trend with the increase in GHSV and pressure. The rate of hydrogen production is directly proportional to temperature, GHSV, and reaction pressure. Conversely, the energy required per unit of hydrogen production decreases with temperature but increases with GHSV and reaction pressure. The energy flow analysis shows that increasing the reforming temperature increases the reforming losses, but the total calorific value of the reformate increases, which is expected to improve the overall efficiency of ammonia fueled engines and reduce the unburned ammonia emissions. Simulation results show that, the improved Temkin-Pyzhev global rate model can significantly improve the accuracy of the ammonia catalytic decomposition process prediction. [Display omitted] • A novel energy flow analysis method for thermo-catalytic reforming is presented. • A precise predictive model for thermo-catalytic characteristics is established. • The thermo-catalytic system has a system efficiency of up to 94%. • The thermo-catalytic system has a reforming efficiency of up to 112%. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3), hydrogen (H 2) and methane (CH 4) as zero- or low-carbon fuels are considered as highly promising alternative fuels. Turbulent non-premixed jet combustion is a prospective way in practical combustion devices for ammonia, hydrogen and methane, but the relevant experimental researches are rare, while such information is critical for the development and validation of numerical models. In this paper, the laser diagnostic studies are carried out in a constant volume combustion chamber to investigate the characteristics of the 50%NH 3 +50%H 2 blend jet with or without ignition in comparison to H 2 , CH 4 and NH 3 jets. Firstly, the morphological developments and concentration distributions of the four gas jets without ignition are compared. Then, the OH or NO distributions in the non-premixed gas jet flames are clarified by the planar laser-induced fluorescence techniques. The generation and consumption processes of OH and NO are elucidated by the one-dimensional simulation. The results show that the four jets exhibit a similar morphological development with the nearly same jet angles, except for a little slower tip penetration of 50%NH 3 +50%H 2 blend. The equivalence ratio of the 50%NH 3 +50%H 2 blend and NH 3 jets along the jet axis are lower than those in the CH 4 and H 2 jets due to the difference in the flow rate and stoichiometric number. The H 2 jet exhibits the highest combustion intensity, featuring faster flame propagation, the shortest lift-off length and an apparently higher OH radical intensity, while the NH 3 jet fails to develop a stable flame. The mixture in the 50%NH 3 +50%H 2 blend jet is too lean, resulting in a weaker combustion intensity than the H 2 and CH 4 jets. However, the NO intensity in the 50%NH 3 +50%H 2 jet flame is remarkably stronger than those of the H 2 and CH 4 jet, due to the much higher amount of fuel-type NO converted from NH 3 than that of thermal NO. A self-reducing (SR) zone can be observed where OH is produced and then consumed in the 50%NH 3 +50%H 2 blend, H 2 and CH 4 jet flames. However, the NO SR zone is only observable in the 50%NH 3 +50%H 2 blend jet flames, probably owing to the consumption by the NH 2 and NH radicals. • The laser diagnostic was used to obtained the OH and NO distributions. • The 50%NH 3 +50%H 2 , H 2 , CH 4 and NH 3 jets exhibit a similar morphologic development. • The equivalence ratios of the 50%NH 3 +50%H 2 blend and NH 3 jets are the lowest. • The fuel-type NO makes the strongest NO intensity in 50%NH 3 +50%H 2 blend flames. • For the first time a self-reducing zone was observed for the OH and NO. [ABSTRACT FROM AUTHOR]