NH₃ has emerged as a promising candidate for low-carbon gas turbines, with NO_x emission issues being mitigated by air-staged combustion. However, the role of fuel/air mixing quality (represented by unmixedness) in NO_x formation in NH₃ systems remains poorly explored. In this study, the characteristics of NO_x formation under the effects of unmixedness have been numerically investigated using an NH₃/CH₄ fired air-staged model combustor consisting of perfectly stirred reactors (PSRs) and plug flow reactors (PFRs), employing the 84-species, 703-reaction Tian mechanism under H/J heavy duty gas turbine conditions. It was found that a primary-stage equivalence ratio of 1.2–1.5 corresponds to a low NO_x formation region under perfectly mixed fuel and air conditions. In this region, a relatively low NO_x formation is achieved when the unmixedness is less than 0.12 and NO_x formation exhibits low sensitivity to fuel/air unmixedness. Based on these findings and the fact that the air-staged combustion loses its advantage in reducing NO_x emissions when the unmixedness exceeds 0.12 across all equivalence ratios, recommended mixing quality thresholds for different equivalence ratios are proposed to guide combustor design and operation optimization. A parametric study of chemical reaction pathways at different unmixedness levels in the two stages demonstrates that NO_x is mainly formed in the main combustion zone of the secondary stage via the HNO pathway, which results in NO_x formation rising to thousand ppm when unmixedness exceeds 0.3, although NO_x reduction through NHi and N₂O pathways partially offsets contributions from the HNO and thermal NO_x pathways. To leverage the NO_x reduction potential of the NH_i and N₂O pathways, the residence time in both stages should be carefully adjusted to help suppress NO_x to as low as 48 ppm. The results of this study are important for engineering applications, providing guidance for the design of NH₃ fired combustors aimed at significantly reducing NO_x formation.

"We undertook this difficult study to understand fatigue," said senior author Daniel Forger, a University of Michigan professor of mathematics. "We're seeing profound changes in the brain over the course of the day as we stay awake and they seem to be corrected as we go to sleep."

We experimentally demonstrate encrypted image transmission over 40 km of optical fiber with high decryption fidelity and achieve a 10 Gbit/s optical encryption rate using a lithium niobate photonic chip. This represents the first implementation of public-key encryption at the physical optical layer. 

Quanta Books is delighted to announce two new upcoming books by mathematician Terence Tao and theoretical physicist David Tong. Six Math Essentials will be Tao’s first math book written for a popular audience. Tong’s book, Everything Is Fields, will illuminate quantum field theory — the physics that explains the fundamental makeup of the universe — drawing from Tong’s distinguished track record as a quantum field theorist and public communicator.