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AbstractThe adoption of zero-carbon fuel like ammonia will play a key role in the achievement of carbon neutrality targets. This work reports a comparative study on the effect of premixed equivalence ratio (Φpremix aried from 0.8 to 1.25) on combustion and emission characteristics of ammonia-fueled engine operating initially under (a) compression ignition (CI) mode (ignited by dodecane pilot injection), and then converted to (b) spark ignition (SI) mode (by replacing fuel injector with spark plug). The experiments were performed in a single-cylinder engine (compression ratio = 16.4:1). The ammonia energy fraction was maintained at 95% during the CI mode and 100% ammonia in the SI mode. The power output and indicated thermal efficiency are lower in SI mode than in CI mode, certainly due to the occurrence of multiple auto-ignition sites. Indeed, the unburned ammonia emissions were observed to be higher in SI mode as compared to CI mode, especially in rich conditions. As expected, the carbon-based emissions reduced significantly in SI operating mode are very low, only due to lubricant oil leakages. N2O emissions were higher at near stoichiometric-rich conditions (Φpremix = 1.05–1.25) emissions but remain negligible in SI mode, except at the highest equivalence ratio (1.25). As N2O has very high global warming potential (265 times CO2 after 100 years) CO2—equivalent impact was evaluated by considering both N2O and CO2 emissions.

01 Sep 2025·Fuel

Investigating the role of NH2* as an indicator of preferential diffusion effects in premixed NH3/air flames

Author: Halter, Fabien ; Chauveau, Christian ; Dayma, Guillaume ; Khan-Ghauri, Maryam ; Petersen, Eric L. ; Mathieu, Olivier ; Karan, Alka

The objective of this work is to use an economical diagnostic tool - chemiluminescence of NH₂* - to give direct information on the H₂ preferential diffusion effects in premixed ammonia-air flames.Abundant quantities of NH₂* are produced in ammonia-air flames which makes it an interesting tracer of heat release, as stated in a previous study.Evidence of preferential diffusion was observed using a Bunsen-type burner and attributed to ammonia decomposition into hydrogen leading to preferential diffusion.In this study, new analyses based on addnl. experiments and simulations are proposed to support and quantify this hypothesis.Mixtures of equivalence ratios 0.9-1.4 have been investigated.With a Bunsen burner, we were unable to stabilize flames leaner than 0.9.The flow velocities required to stabilize these flames are very low (<0.2 m/s) due to the low flame speed of ammonia/air mixturesSpectroscopic and local chemiluminescence measurements of the flames were calibrated against a quartz-tungsten halogen lamp.The unique spectrum of each equivalence ratio depicting the reactivity of the flame was studied, and the ratio of two excited species: NH₂*/OH* was used to provide a rough estimate of the equivalence ratio.This NH₂*/OH* ratio was later applied to estimate the local equivalence ratio along the flame contour.Anal. of the NH₂* profiles along the flame contour for various cases revealed changes in intensity and profile thickness, indicating the effects of H₂ preferential diffusion.Relative lower intensities and thicker profiles of NH₂* indicated a low reactivity and vice-versa.Since NH₂* can be used as a good indicator, a sub-mechanism to predict these profiles has been proposed.The rate constants of pure collision reactions were determined using the collision theory, and the rate constant of the chemiluminescence reaction was determined exptl.Other involved reactions and species were identified using a sensitivity anal. on NH₂ and NH₂*.The proposed sub-mechanism was compared with the exptl. profiles, and the impact of the base mechanism has been stated.

01 Aug 2025·Journal of Engineering for Gas Turbines and Power

Experimental Characterization of Superheated Ammonia Spray From a Single-Hole Spray M Injector

Author: Mounaïm-Rousselle, Christine ; Bjørgen, Karl O. P. ; Desclaux, Anthony ; Hespel, Camille

AbstractThe growing recognition of ammonia as a carbon-free alternative fuel for both transportation and power generation is underscored by numerous studies. While the use of gaseous ammonia injection has been extensively considered, research on the direct injection of liquid ammonia remains relatively scarce, especially in the case of internal combustion engines (ICE). The application of liquid ammonia in gas turbines offers economic and size-related advantages over gaseous ammonia injection. But the liquid ammonia's instantaneous spray flash-boiling and its high latent heat of vaporization induce the necessity of employing preheated swirling air to enhance flame stability, mitigating the strong cooling effect induced. The preference for direct injection of liquid ammonia is driven by its efficacy in controlling in-cylinder air–fuel ratios and optimizing thermal efficiency. This study presents macroscopic and near-field Schlieren measurements of a one-hole Engine Combustion Network (ECN) Spray M, representative of direct liquid injector for engine, with ammonia for different degrees of superheating. Spray angles and penetration length are provided as a function of the superheat degree with also a focus near the injector nozzle. Additionally, in-spray temperature measurements are presented, providing the first valuable information for modeling purposes.

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Pipeline Snapshot as of 08 Jun 2025

The statistics for drugs in the Pipeline is the current organization and its subsidiaries are counted as organizations,Early Phase 1 is incorporated into Phase 1, Phase 1/2 is incorporated into phase 2, and phase 2/3 is incorporated into phase 3

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