Ammonia is a promising zero-carbon fuel for maritime applications, but its poor ignition and combustion characteristics limit its efficient use in engines. While hydrogen-enriched combustion can enhance ammonia combustion and improve engine performance, onboard hydrogen storage remains challenging for long-voyage ships due to safety and cost constraints. In-cylinder reforming offers a catalyst-free pathway to generate hydrogen directly from ammonia. The resulting hydrogen-rich exhaust can then be recirculated to other cylinders to enhance combustion, enabling ammonia-hydrogen co-combustion with a single ammonia fuel supply. However, its practical applicability is fundamentally constrained by the inherently narrow rich-burn operability of ammonia. To address this limitation, this study proposes a pre-chamber-assisted in-cylinder reforming concept that integrates active pre-chamber turbulent jet ignition into a dedicated reforming cylinder. By establishing a locally near-stoichiometric mixture within the pre-chamber, reliable ignition can be achieved, enabling stable combustion in the main-chamber even under highly fuel-rich conditions, thereby effectively extending the rich-burn limit beyond that of spark ignition. After validating the numerical model against experimental data under ammonia-rich condition, hydrogen production and engine performance were systematically evaluated under both spark ignition (SI) and pre-chamber (PC) modes across a range of spark timings and equivalence ratios. For both the SI and PC modes, the excess ammonia conversion ratio shows a gradual decline with increasing equivalence ratio, whereas hydrogen production rises under moderately rich conditions owing to the increased availability of excess ammonia. Under moderately rich conditions, the two modes exhibit comparable hydrogen production and indicated work. Although the PC mode enhances ignition and accelerates combustion, it also increases heat transfer losses, leading to a slight reduction in indicated work under these conditions. However, at higher equivalence ratios (φ > 1.4), the proposed concept achieves substantially higher indicated work, improved ammonia-to-hydrogen conversion efficiency, and increased hydrogen production compared to SI operation. These results demonstrate that pre-chamber-assisted combustion provides an effective pathway to extend the ammonia-rich limit and therefore increase the total hydrogen production, offering a promising solution for high-efficiency ammonia-hydrogen engines with single ammonia fuel supply.

The growing pursuit of carbon-neutral fuels has spotlighted liquid ammonia as a zero-carbon energy carrier for engines and gas turbines. However, its low boiling point causes intense flash boiling upon injection, drastically altering spray behavior compared to conventional non-flashing fuels like methanol. This study experimentally examines how a crossflow air stream affects a superheated liquid ammonia jet, in comparison to a nonsuperheated methanol jet. High-speed diffused back-illumination in a wind tunnel was used to capture spray morphology while varying injection pressure and crossflow velocity over a broad range of momentum flux ratios (q) and aerodynamic Weber number (We). The results reveal that under intense superheat (high Rp), ammonia sprays exhibit a radically different trajectory: the jet undergoes near-instantaneous explosive breakup into a vapor-liquid plume, yielding much shorter penetration and greater lateral deflection than the methanol sprays. Flash boiling enhances atomization (producing finer, more uniformly distributed droplets) but also weakens the jet's resistance to the crossflow, making the ammonia spray penetration relatively insensitive to increased injection momentum. In contrast, methanol jets follow classical shear-driven behavior, with higher q yielding deeper penetration and less deflection. Mechanistically, the ammonia jet's fragmentation is governed by internal vapor generation (superheat-driven) rather than external aerodynamic forces, decoupling its atomization from crossflow effects. These insights provide guidance for ammonia-fueled combustors: controlling the fuel's thermal conditions (e.g. injection temperature or ambient pressure) to moderate superheat is key to optimizing spray penetration and dispersion in crossflow environments, which is crucial for efficient and stable combustion in engines and turbines.

Ammonia-diesel dual-fuel compression ignition engines have been recognized as a promising solution for achieving low or zero carbon emission targets in the maritime industry. However, the exhaust gas emissions of ammonia fueled engines including unburned NH3, N2O and NOx are unusually higher than traditional diesel engines, which should be controlled. Unfortunately, the formation mechanisms of these emissions in ammonia fueled engines remain unclear. This study employs the combined approach of using numerical simulations and experiments, as well as the dynamic phi-T map analysis to investigate the in-cylinder distributions and formation mechanisms of unburned NH3, N2O, and NOx with respect to mixture reactivity, equivalence ratio, ambient temperature and pressure. The result shows that the nitrogenous emissions are primarily associated with the turbulent flame propagation in the premixed mixture of 100 % ammonia energetic ratio (AER) regions. While N2O primarily forms at the NH3 flame front, and resides at the unburned NH3 boundary zones, particularly in regions like the center of combustion chamber and near the cylinder walls. Unburned NH3 is found to accumulate in areas inaccessible to the flame, such as piston ring crevices and vicinity of combustion chamber walls, while NOx emissions predominantly occur in the burned zone behind the flame front of ammonia combustion and 72.5 % of the NOx emissions comes from the fuel ammonia. The formation and consumption of NOx, N2O, and unburned NH3 emissions are determined by local variations of equivalence ratio, temperature, and AER in the cylinder. By combining the dynamic phi-T maps with CFD simulations, this study captures the emission formation processes and identifies the specific equivalence ratio-temperature generation regions of NOx, N2O, and unburned NH3.

Background:Fat mass and obesity-associated (FTO) protein, an m6A RNA demethylase, plays diverse roles in cancer, but its function in lung adenocarcinoma (LUAD) remains unclear.Methods:TCGA data analysis, clinical samples, and in vitro assays were used to assess FTO expression and function. Mechanistic studies, including RIP, meRIP, luciferase reporter, FISH, and ChIP assays, were performed to explore FTO-mediated regulation of KDM5A and downstream PTEN/PI3K/Akt signaling.Results:FTO was significantly downregulated in LUAD and associated with poor prognosis. Overexpression of FTO inhibited LUAD cell proliferation, invasion, and EMT. Mechanistically, FTO suppressed KDM5A protein translation by demethylating m6A sites, impairing YTHDF1-mediated recognition. Reduced KDM5A expression increased PTEN transcription via elevated H3K4me3, leading to PI3K/Akt inactivation. Rescue experiments confirmed KDM5A overexpression reversed the effects of FTO.Conclusions:FTO inhibits LUAD progression through an m6A-dependent FTO/YTHDF1/KDM5A/PTEN axis. These findings establish FTO as a tumor suppressor and potential therapeutic target in LUAD.

Background:Tumor mutational burden (TMB) summarizes the number of nonsilent mutations in a tumor but does not show whether these alterations cluster within a small set of pathways or extend across several oncogenic programs. To address this distinction, we developed a 10-pathway burden (10-PB) framework and defined the 10-PB score as the number of altered canonical oncogenic pathways per tumor. We then evaluated whether this mutation-based measure of pathway breadth provides information complementary to TMB in non-small cell lung cancer (NSCLC). Methods:Nonsilent mutations were mapped to 10 canonical oncogenic pathways to construct the 10-PB score. We first described pathway-level alteration patterns and then examined associations of 10-PB with survival and treatment response. Its incremental value relative to TMB was assessed using multivariable models, likelihood-ratio tests, and Akaike information criterion. Bootstrap resampling, continuous-risk analyses, and leave-one-pathway-out models were used to evaluate the stability and endpoint-specific structure of the findings. External MSK-based cohorts were used for validation. Results:Most tumors showed alterations in 2-4 pathways, indicating that multi-pathway involvement is common in NSCLC. LUAD and LUSC showed distinct pathway-level profiles. Higher 10-PB was associated with shorter overall survival and progression-free survival after adjustment for clinicopathologic factors and TMB. Model comparisons suggested that 10-PB adds prognostic information to TMB-based models. In the treatment-response analysis, higher 10-PB showed an exploratory association with unfavorable response. Leave-one-pathway-out analyses suggested endpoint-specific patterns, with NOTCH more closely associated with progression-free survival and adverse response, and TGF-β and PI3K more closely associated with overall survival. External cohorts showed broadly consistent results. Conclusion:The 10-PB framework extends mutation-based assessment of NSCLC by describing how broadly nonsilent mutations involve canonical oncogenic pathways. This pathway-breadth measure complements TMB and may help refine prognosis-oriented stratification, while its treatment-response associations should be viewed as exploratory. Prospective validation and integration with functional pathway-activity data are needed before clinical application.

Methanol holds significant promise as a sustainable fuel for turbojet engines in unmanned aerial vehicles (UAVs). To better adapt to methanol's properties and overcome the inherently poor atomization of the pre-evaporation tube, a novel pre-evaporation tube is developed with side-wall air inlets to enhance atomization performance and thereby improve the evaporation ratio. Utilizing backlit imaging, four distinct flow patterns-annular flow with continuous liquid film (AC), annular flow with semi-continuous liquid film (AS), annular flow with discrete liquid film (AD), and dispersed flow (DF) are identified. Further results show that increase of the ratio of the air and fuel (RAF) and temperatures suppress liquid films, with the modified design promoting DF dominance. A high-resolution composite defocus shadowgraph (CDS) technique which reaches the 3.57 mu m/pix is proposed and being used to quantify the evaporation ratio (ER) and droplet distributions. The results demonstrate that ER is quadratic dependence on RAF due to competing atomization enhancement and residence time reduction. The results also show that the modified pre-evaporation tube achieves higher ER than the traditional. CDS and background-oriented schlieren (BOS) integrated analysis delineates three spray regions (droplet core, transition zone, pure vapor) and shows linear radial decay of vapor concentration in the pure vapor area.

Ammonia has been regarded as a promising alternative fuel for the maritime sector, but current ammonia engines still face challenges such as high unburned ammonia and limited thermal efficiency owing to the poor combustion characteristics of ammonia fuel, especially for the medium- and high-speed engines. The addition of hydrogen has recently attracted significant attention as an effective strategy to enhance ammonia combustion performance. However, the direct use of hydrogen in maritime applications remains challenged by storage and transportation constraints. Since ammonia serves as an excellent hydrogen carrier, it provides the feasibility to generate hydrogen via ammonia decomposition or reforming, thereby enabling ammonia-hydrogen cocombustion through single ammonia fuel supply. Compared with the route that couples an external ammonia reformer, the in-cylinder reforming gas recirculation route achieved through ammonia-rich combustion in one or more dedicated reforming cylinder(s) can avoid the use of catalysts and additional energy consumption. Unfortunately, existing studies have mainly focused on evaluating the feasibility of the in-cylinder reforming route, leaving significant potential for further exploration. Therefore, this study numerically investigates the effects of intake temperature, wall temperature, piston profile, and compression ratio on the excess ammonia conversion, hydrogen production, and thermal efficiency of the reforming cylinder. Results indicate that wall temperature management can enhance the performance of the reforming cylinder owing to the improved excess ammonia conversion in the near-wall region, with the potential to increase the conversion from around 84% to 93%. Although increasing the intake temperature promotes excess ammonia conversion, it also increases in-cylinder heat transfer losses and reduces the thermal efficiency of the reforming cylinder. Compared with wall and intake temperature management, which usually require thermal barrier coatings or additional energy input, optimizing the combustion chamber parameters, such as the compression ratio, is more feasible. Increasing the compression ratio enhances thermal efficiency but comes at the cost of reduced ammonia conversion and hydrogen production and a compression ratio of 19 exhibits relatively superior overall performance. At a compression ratio of 19, the excess ammonia conversion reaches approximately 84%, enabling the reforming cylinder to supply hydrogen accounting for 21.7% of the total energy input to the remaining cylinders. Under most conditions, the hydrogen produced by one reforming cylinder, when recirculated into the other three cylinders, corresponds to around a 20% hydrogen enrichment level.

Hydrogen-assisted pre-chamber jet ignition effectively overcomes the low reactivity challenge that hinders the practical application of carbon-free ammonia in engines. However, fundamental optical studies on the effects of pre-chamber mixture reactivity and nozzle orifice orientation on hydrogen-assisted ammonia combustion remain limited. In this study, the effects of the pre-chamber mixture reactivity, i.e., the excess air ratio and oxygen concentration, and the configuration of radial and tangential orifice nozzles on the ignition and combustion behaviors of ammonia initiated by jet ignition are optically investigated using Schlieren imaging. The findings reveal that the excess air ratio of the pre-chamber mixture markedly influences the evolution of hot jets and ignition behavior of secondary hot jets. Increasing the excess air ratio from 1.50 to 2.00 results in a delayed hot jet ejection and a reduced penetration velocity. The balance between jet velocity and reactivity enables localized re-ignition in the main chamber at an excess air ratio of 1.75. Moreover, enriching the pre-chamber with oxygen significantly affects both jet penetration and ignition behavior. Oxygen enrichment markedly advances the ignition timing initiated by secondary hot jets. The combustion duration exhibits a decrease-to-increase pattern due to the hot jet characteristics. Although oxygen-enriched combustion leads to increased NOx formation, it can effectively reduce unburned NH3 and N2O emissions. Regarding nozzle orifice orientation, the tangential-orifice design promotes earlier ignition than the radial configuration. However, hot jets from the tangential orifices result in longer combustion duration and higher unburned NH3 emissions owing to their reduced penetration velocity.

Pre-chamber turbulent jet ignition holds significant potential for improving ammonia combustion. Hydrogenand oxygen-enriched combustion in the pre-chamber can further enhance ammonia combustion. However, fundamental research on this enhanced combustion mechanism remains limited. This study systematically examines the individual impacts of oxygen-enriched combustion in a hydrogen-enriched multi-orifice pre-chamber and nozzle geometry specifications on jet behavior in a nonreactive environment, as well as the impact of the jet behavior on ammonia ignition behavior, combustion processes, and emissions in a reactive environment. The results show that oxygen enrichment significantly enhances ignition characteristics, with three ignition modes observed as the oxygen concentration increases from 30 % to 70 % by volume: localized re-ignition, jet-induced secondary ignition, and jet flame ignition. With increasing oxygen concentration, combustion duration decreases initially and then increases. Unburned NH3 and N2O emissions decrease, while NOx emissions slightly increase with oxygen enrichment. In the pre-chamber nozzle design, two nozzles with identical cumulative orifice areas, i. e., six 1.50 mm orifices and three 2.12 mm orifices, demonstrate that larger orifices improve ammonia ignition. On the other hand, when both nozzles have an identical orifice diameter, the nozzle featuring a smaller cumulative orifice area enhances ignition behavior as it generates higher-velocity hot jets. For two nozzles featuring the same number of orifices and similar hot jet velocities, the nozzle featuring the larger orifice demonstrates superior ignition behavior. These findings could offer valuable insights into enhancing ammonia combustion and optimizing nozzle design.

Under the 2050 net-zero emissions target, the maritime sector considers ammonia, a carbon-free fuel, to be a highly promising alternative. Scaled-model experiments following similarity theory play a crucial role in minimizing cost, energy, and time in the development of new engines. Unfortunately, although it has been conducted on different-sized diesel engines, no information is available on the accelerated development of ammonia engines. In this work, the single-valued condition and similarity law for scaled-model experiments of ammonia engines are summarized, primarily focusing on the high-pressure direct-injection mode. After confirming the accuracy of numerical simulations using experimental data from liquid ammonia sprays and ammonia engines, the potential of scaled-model experiment is studied using two ammonia engines with bore diameters of 175 mm (i.e. the large engine) and 95 mm (i.e. the small engine) under various engine speeds and 90 % ammonia energetic ratio. The results show that spray development, heat release rate, in-cylinder pressure and temperature, indicated thermal efficiency, NOx and N2O emissions are highly similar between different-sized engines, indicating the effectiveness of similarity theory in facilitating new ammonia engine development. In particular, based on the similarity law summarized in this study, the differences in peak in-cylinder pressure and temperature between the large and small engines are smaller than 2 %, while the difference in indicated thermal efficiency is smaller than 5 %. However, due to the inherent difference in surface area-to-volume ratio between the large and small engines, the small engine experiences increased heat transfer losses and reduced temperatures near the wall, leading to a higher proportion of unburned ammonia residue in the near-wall region. The above results are deemed invaluable for the intensive development of ammonia engines of different sizes.

High-pressure direct-injection (HPDI) of ammonia into engine cylinder could provide superior potentials than low-pressure premixed mode in terms of unburned ammonia and nitrous oxide (N2O) emissions, but direct injection of another high reactivity fuel is usually needed to trigger the ammonia spray combustion, complicating cylinder head injector arrangement. To this end, we propose a novel concept of HPDI of ammonia into a premixed lean hydrogen mixture, in which the spark-ignited hydrogen flame enables and enhances the ammonia spray combustion via hydrogen entrainment. This study investigates the combustion and emission characteristics of the HPDI ammonia in the lean premixed hydrogen mixture using a constant volume combustion vessel by varying ambient pressure, hydrogen concentration and injection timing. For the hydrogen-air mixture with the excess air ratio (2) of 3.0 and ambient pressure of 2.5 MPa, near-complete combustion of the HPDI ammonia occurs with low N2O emissions below 10 ppm. When 2 of the hydrogen mixture is increased to 5.0, the ammonia combustion efficiency decreases to around 40 %. Decreasing the ambient pressure enhances the combustion efficiency. When the ambient pressure decreases to 1.0 MPa, the combustion efficiency could increase to 90 % with the early injection case, but with higher NOx and N2O emissions.

Micro-mixing combustion is a potential gas turbine combustion technology suitable for hydrogen and hydrogencontaining syngas. The impacts of hydrogen blending ratio and equivalence ratio on flame structure of syngas (a mixture of H2, CO) were investigated in a lab-scale gas turbine model burner. Flame luminescence and planar laser-induced fluorescence measurements of the OH radicals were employed for quantitative assessment of the flame structure. The flame boundary is extracted by the adaptive threshold method, and the flame wrinkle is analyzed by the probability density function and flame edge node network topology method. The results show that, as the H2 blending ratio of the hydrogen-rich syngas is in the range of 50%-100%, the flame wrinkle curvature is concentrated near zero, and the convex structures at the flame wrinkles occur more frequently than concave structures. For the hydrogen flames, the node degree distribution of flame edge nodes changes significantly at different times, but the probability density function of node degree at flame front is basically the same. With increasing the equivalence ratio, the distribution of the hydrogen flame edge radius size is more complex, but the node degree reduces. While the equivalence ratio increases above 0.645, the increased turbulence intensity results in a higher probability of the key wrinkles.

In dual-fuel engines, pilot diesel injection critically influences combustion dynamics by initiating alternative fuel ignition, yet excessive replacement ratios may introduce disturbances within the nozzle, impacting external jet atomization and subsequent combustion processes. This study employs high-speed UV-LAS and OH* chemiluminescence imaging techniques to resolve transient mixture formation and flame development, comparing pilot injection (simulated with minimal needle valve activation) against main injection under varied injection pressures and ambient temperatures. Results demonstrate that pilot injection dominates liquid length control-surpassing ambient temperature effects and showing negligible pressure influence-where internal nozzle flow variations emerge as the primary driver of enhanced atomization when ambient enthalpy suffices for evaporation. Auto-ignition timing exhibits strong sensitivity to ambient temperature but minimal pilot-main differences due to comparable stoichiometric mixtures at ignition sites. Flame propagation dynamically self-regulates by targeting vapor-phase penetration, transitioning from entrainment-controlled to combustion-driven expansion. Quantitative analysis confirms pilot injection strategically modulates spatial mixture distribution: enriching near-stoichiometric/fuel-rich zones (phi > 0.8) to enhance low-reactivity fuel (e.g., ammonia) ignition, while rapid post-injection homogenization establishes >90 % lean mixtures (phi <= 0.8) within 0.5 ms after EOF. These findings establish pilot injection as a precision tool for in-cylinder equivalence ratio control, providing actionable strategies to optimize nozzle dynamics and combustion phasing in advanced dual-fuel systems.

The utilization of ammonia as an alternative fuel in combustion engines is gaining attention due to its carbon-free nature. However, the conventional method of introducing gaseous ammonia into the intake manifold reduces engine volumetric efficiency and power output. Using liquid ammonia (LNH3) injection can mitigate these issues, but the atomization and evaporation characteristics of LNH3 sprays are not fully understood due to flash boiling and aerodynamic interaction. In this study, high-speed diffused back-illumination (DBI) and Schlieren techniques were employed to capture the liquid and vapor phase evolutions, while high-resolution microscopic drop size imaging (MDSI) and laser-induced breakdown spectroscopy (LIBS) were used to measure droplet size distribution and fuel concentration. The results show that the ambient pressure significantly affects spray morphology, with lower pressures leading to broader dispersion due to higher superheat levels. A bimodal drop size distribution is found under flare-flashing conditions, transitioning to a more uniform distribution as ambient pressure increases. Additionally, ambient pressure plays a crucial role in fuel-air mixing compared to injection pressure, whose influence is nearly negligible under flare-flashing conditions. These findings provide valuable insights into the behavior of LNH3 sprays, which are essential for optimizing ammonia injection strategies and improving engine performance.

Hydrogen and ammonia are the fuels with the high potential for the future carbon-free engine systems. Considering the low chemical reactivity of ammonia, using the direct-injection hydrogen jet ignition is a promising method to realize the high-efficiency combustion of ammonia. Based on this, a systematic and comprehensive investigation of the direct-injection hydrogen jet ignition under engine-like conditions is carried out for the first time, including the jet characteristic, fuel mixing characteristic, and combustion characteristics. In particular, combined with the fuel mixing characteristic, combustion research at different ignition positions of hydrogen jet is carried out. The corresponding features are investigated in the constant volume combustion vessel with the injection pressures of 3.0 MPa, 5.0 MPa, 7.0 MPa, and 9.0 MPa and the ambient pressure of 1.0 and 2.0 MPa, using high-speed imaging technology. The fuel concentration distributions of the hydrogen jet are quantitatively investigated by the laser-induced breakdown spectroscopy technology. From the results, for the evolution of the tip penetration distance of the high-pressure hydrogen jet with the time t after injection onset, a four-stage behavior of the e-t, t, t0.5 and t0.25 dependence is proposed to explain the relationship between the tip penetration distance and t. The jet angles in the steady injection duration are between 30 and 50 degree. The equivalence ratio reduces with the distance away from the nozzle or the nozzle axis, and increases with the increased injection pressure. In the jet area of 10 mm away from the nozzle, the equivalence ratio changes from 0.2 to 4.0. The higher injection pressure could accelerate the flame development and reduce the lift-off height. The maximum burning velocities could exceed 200 m/s in the initial ignition stage as the turbulence produced by the high-pressure injection, and then quickly decrease to less than 50 m/s. The position closer to the nozzle is more conductive to the initial flame kernel. More importantly, the results reveal that a good ignition characteristic is also shown at the position far from the nozzle and slightly away from the nozzle axis, resulting from the fast-burning velocity after the initial ignition stage.

The integration of ammonia engines with exhaust heat reformers not only facilitates efficient hydrogen storage and stable supply but also mitigates the challenges of low thermal efficiency and high unburned ammonia content in ammonia engines. However, the optimal temperature for ammonia thermal catalytic reforming typically exceeds the exhaust temperature of the engine, thereby significantly limiting the on-board applicability of this system in ammonia engines. Non-thermal plasma has the potential to enhance the conversion rate of thermo-catalytic reforming, but the closely-coupled effects of two methods are rarely reported. In this study, we developed multiple reforming configurations by integrating dielectric barrier discharge (DBD) reactors with fixed bed reactors (FBR). Systematic experimental investigations were carried out to analyze the reforming characteristics of each configuration under conditions of low energy consumption and low temperature. Firstly, in the single-plasma reforming mode, we optimized the discharge structure to evaluate reforming performance under various conditions. Next, under low specific input energy (SEI) conditions, we compared the reforming characteristics with and without Ru catalysts. The results showed that, under low-energy consumption and without an external heat source, the catalyst’s promoting effect was limited. Based on these findings, we integrated thermal catalysis with plasma and respectively constructed the series and closely-coupled reforming systems, obtaining the data of ammonia decomposition under various operating conditions. Finally, we compared the reforming characteristics of the aforementioned modes under engine exhaust temperature conditions to identify the optimal reforming approach. Overall, the integration of thermal catalysis effectively mitigates the high energy consumption issue in plasma systems. However, in the series reforming system, the non-overlapping plasma and thermal catalytic regions led to inhibition of subsequent ammonia decomposition into hydrogen, reducing overall system efficiency. In contrast, the closely-coupled mode not only achieves optimal reforming performance under the same operating conditions but also sustains high ammonia decomposition efficiency at relatively low temperatures. Mechanistically, in the closely-coupled mode, as the temperature increases, the dominant reaction within the system gradually shifts from plasma-driven reforming to thermally catalyzed reforming. The findings of this study provide critical support for achieving comprehensive coverage of on-board hydrogen production systems and further advancing ammonia engine technology.

In order to rapidly achieve the goal of global net-zero carbon emissions, ammonia (NH3) has been deemed as a potential alternative fuel, and reforming partial ammonia to hydrogen using engine exhaust waste heat is a promising technology which can improve the combustion performance and reduce the emission of ammonia-fueled engines. However, so far, comprehensive research on the correlation between the reforming characteristic for accessible engineering applications of ammonia catalytic decomposition is not abundant. Moreover, relevant experimental studies are far from sufficient. In this paper, we conducted the experiments of catalytic decomposition of ammonia into hydrogen based on a fixed-bed reactor with Ru-Al2O3 catalysts to study the effects of reaction temperature, gas hour space velocity (GHSV) and reaction pressure on the decomposition characteristics. At the same time, energy flow analysis was carried out to explore the effects of various reaction conditions on system efficiency. The results show that both the ammonia catalytic conversion and decomposition efficiency increase with the reaction temperature increasing. However, these two parameters decrease with the increases of GHSV and reaction pressure, the former due to the reduction of ammonia retention time in the reactor as GHSV accelerates, and the latter due to the high-pressure environment inhibiting the overall reaction towards ammonia decomposition. In addition, the maximum conversion rate of 86% and a peak decomposition efficiency of 112% were achieved at 853 K, 2000 h-1, and 0.1 MPa. The energy flow analysis shows that increasing the reaction temperature increases the decomposition losses, but the total calorific value of the reformate increases, which is expected to improve the combustion efficiency of ammonia fueled engines and reduce the unburned ammonia emissions. Furthermore, GHSV has a negligible impact on decomposition losses. This paper contributes to the database of hydrogen production from the ammonia thermo-catalytic decomposition, analyze the energy flow distribution of the catalytic decomposition process, and provides important information for development of zero-carbon ammonia-hydrogen fueled engines.

Ammonia combustion initiated by hydrogen-fueled pre-chamber jets is a prospective combustion concept for enhancing ammonia combustion. However, the related fundamental studies on the ignition, combustion, and emissions characteristics of various ammonia + hydrogen blends by hydrogen-fueled pre-chamber jets are still inadequate. In this work, the effects of various ammonia + hydrogen blends in the main chamber with the hydrogen volumetric blending ratio ranging from 0 % to 50 % and the orientations of the orifice, i.e., inclined and straight orifice, are optically studied by the double-pass Schlieren imaging. The results indicate that increasing the hydrogen blending ratio markedly enhances the ignition characteristics of the mixture, resulting in the identification of three distinct ignition modes: re-ignition, secondary jet ignition, and jet flame ignition. The combustion regimes shift from the broken reaction zone to thin reaction zone. Increasing the hydrogen blending ratio improves the ammonia combustion efficiency from 96.9 % to 98.6 %, significantly reducing the unburned ammonia emissions. A high proportion of blended hydrogen increases the NOx emissions, while both low and high blends cause the reduction of N2O emissions. Additionally, the presence of straight orifice enhances the combustion of the mixture, while its emission levels remain comparable to those of the nozzle featuring all inclined orifices.

Active pre-chamber turbulent jet ignition has the potential to enhance the combustion of low-reactivity fuels. However, the related fundamental studies on the jet ignition mechanism are inadequate, especially for the independent effects of the zero-carbon fuel blends on the jet development characteristics, isolating the impact of the main chamber combustion. In this work, the effects of the fuel compositions ranged from the 30%H2+70% NH3 blend to pure H2 and also comprised the pure CH4 for comparison and the initial pressures in the prechamber are studied by the two-pass high-speed Schlieren method. The results show that the hot turbulent jet developments present great differences for the pre-chamber charged with various H2+NH3 blends across the hydrogen blend ratios varying from 30 % to 100 % in volumetric fraction. Moreover, the evolutions of the hot turbulent jet from the pre-chamber charged with the 50%H2+50%NH3 blend and pure CH4 are similar. As the initial pressure increases, there is a gradual deceleration in the development of the pre-chamber jet, and the turbulent jet development characteristics depend on the pressure ratio rather than the pressure difference across the pre-chamber and main chamber. This study could provide important insights for the development of zerocarbon fuel engines.