Pure Ammonia Research Articles

Effect of NH3 addition on soot morphology and nanostructure evolution in laminar ethylene diffusion flame

Ammonia, as a carbon neutral alternative fuel, has attracted wide attention. However, due to the defects in the combustion performance of pure ammonia, it is still necessary to further solve this problem in practical utilization. The purpose of this paper is to study the influence of ammonia on the morphology of soot and the evolution of nanoparticle structure in laminar flame of ethylene. In this work, the soot collected by thermophoresis probe was observed by the high resolution transmission electron microscope (HRTEM), and the image information in HRTEM images was statistically processed, and the graphitization degree of soot was measured by X-ray diffraction (XRD) spectrum of soot samples. The experimental results show that the addition of ammonia can inhibit the growth of soot nuclei and delay the formation of incipient soot, and has different effects on the evolution of soot morphology and structure in ethylene flame. It is noteworthy that the soot samples collected in the upstream part of the ammonia-doped flame show more mature core–shell structure in HRTEM images and more graphitized XRD diffraction data than those collected in pure ethylene flame. The main reason may be the chemical effect of ammonia and the thermal effect caused by the reduction of flame radiation loss, which have different effects on the nanostructure and morphology of soot at different stages of soot formation. Fringe structure model is used to describe and explain the influence of soot in flame with height before and after ammonia doped.

Ammonia detection in water with balloon-like plastic optical fiber sensor

This work presents the demonstration of a plastic optical fiber (POF)-based ammonia sensor. The sensor head is formed by bending an unclad fiber optic sensor into a balloon-like structure. The bending radius of the balloon-like bent fiber optic sensor is varied from 1.0 to 2.5 cm. The performance of each sensor is tested using ammonia solution with concentration ranging from 0 to 15 mg l−1. Results show that the optimized performances of the proposed sensor occur when the bending radius is fixed at 1.5 cm. At this bending radius, the sensor illustrates the sensitivity of − 0.0024 (mg/l)−1 with linearity of 0.97 and resolution of − 4.17 mg l−1. For comparison, the bent sensor is compared to the straight sensor and performances of the former is found to be more superior. In addition, the balloon-like bent sensor is further tested with real water samples. The sensor sensitivity is found to be − 0.0022 (mg/l)−1 with linearity of 0.95 and resolution of − 4.54 mg l−1. The result shows that the sensor has comparable performance in the ammonia detection for both pure ammonia and real water samples. In essence, this balloon-like bent sensor functions without additional coating on the sensor head, making it favorable in terms of the simplicity of the design.

A novel multiple spark ignition strategy to achieve pure ammonia combustion in an optical spark-ignition engine

Ammonia is an attractive carbon-free fuel that has the potential to reduce the need for conventional hydrocarbons (HC) and reduce emissions of undesirable pollutants such as CO, CO2, particulates, and unburned hydrocarbons. However, ammonia has different combustion characteristics than conventional HC fuel. Ammonia is difficult to ignite and has a low combustion rate, resulting in large cyclic variations. In addition, nitrogen oxides (NOx) emissions in the exhaust tract are a major challenge when using ammonia as a fuel directly in engines. In this study, the effect of multiple spark ignition sites on the combustion of pure ammonia in an optical spark ignition engine (SI) was investigated. The experiment was conducted with four spark plugs mounted equidistantly on a special metal liner and one spark plug fitted at the top of the cylinder head. The multiple flames emitted from the different spark ignition sites were captured by natural flame luminosity (NFL) imaging. In the results, the conventional single spark ignition is compared with multiple ignitions. It was found that single spark ignition resulted in lower in-cylinder pressure, longer combustion duration, and higher combustion instability due to the poor ammonia fuel combustion rate. However, firing multiple spark plugs significantly improved combustion stability, increased engine power, and shortened the combustion period under the same operating conditions. In addition, the flame kernels produced by multiple ignition sites resulted in higher NOx emissions in the exhaust tract due to the higher temperatures in the cylinder. In addition, this study also investigated the effect of three different air–fuel equivalence ratios (λ) of 1.0, 1.2, and 1.4 on the combustion characteristics of ammonia fuel. The maximum NOx level was obtained for λ: 1.2 because the excess air in the mixture oxidizes the ammonia and provides abundant oxygen to generate more NOx. Further reducing the ammonia fuel and increasing the excess air to λ: 1.4 dramatically reduced NOx emissions due to the lower pressures and temperatures in the cylinder resulting from the longer combustion period.

Performances and pollutant emissions of spark ignition engine using direct injection for blends of ethanol/ammonia and pure ammonia

Combustion and emissions characteristics of a spark-ignition engine using direct injection of ethanol blended with ammonia and also pure ammonia were investigated in this study. The experiments were conducted using five different fuel compositions of ethanol/ammonia (C2H5OH/NH3): 100/0, 75/25, 50/50, 25/75, and 0/100. Two strategies of injection were conducted to reach homogenous or stratified conditions with three different intake pressures, 0.5, 1.0, and 1.5 bar corresponding to 2.8, 7.9, and 12 bar of IMEP. The performances and the pollutants emissions are compared as a function of fuel compositions at identical IMEP. High stability is observed for all blends and even for pure ammonia. However, operating conditions are more restrictive for pure ammonia: the injection must be executed during the intake phase to be in a fully premixed mode to guarantee engine stability. Delaying the injection time for pure ammonia is not possible and requires the split of injections with 50% of the ammonia amount injected during the intake. The thermal efficiency is improved by adding 25% of NH3 in ethanol but NOx emissions increase. The stratified strategy for blends improves the combustion durations and the addition of ammonia decreases the NOx emission compared to the homogeneous strategy. On the contrary, CO emissions roughly increase for blends. The presence of NH3 in the fuel composition clearly influences the change of formation of NOx and CO between both strategies.

Performance evaluation of a micro partial admission impulse axial turbine in a combined ammonia-water cooling and electricity absorption cycle

The integration of an expander in an absorption machine allows it to produce cooling and electricity simultaneously. This technology holds great promise for its ability to harness low-temperature heat sources more efficiently than production with separate cycles. The integration of a turbine is currently being studied in an experimental ammonia-water absorption chiller at CEA INES. Given the very small mass flow rate and enthalpy drop, a partial admission impulse axial turbine has been selected for the application. Due to lack of experimental data, a 3D model of the impulse turbine was generated and its functioning studied with CFD simulations using pure ammonia. A compressible real gas 1D model of the turbine was later developed in EES® for the ammonia-water mixture and compared to CFD simulation, adjusting loss term parameters to match CFD results, thus achieving an average discrepancy below 7% in the considered range of operating conditions (inlet pressure 14-10 bar, outlet pressure 5 bar, inlet temperature 120 °C and rotational speed of 10–100 thousand RPM). The tuned 1D expander model was then integrated in a previously developed 0D model of the absorption cycle to demonstrate its robustness and potential to be used in the study of complex combined cycles. An overall energy efficiency is introduced and used to map the performance of the cycle for changing operating conditions. Results show the potential of the combined cycle to produce both power and cooling even at small scale, highlighting at the same time, the constraints imposed by this type of expander on the combined cycle.

Novel ammonia-driven chemically recuperated gas turbine cycle based on dual fuel mode

The potential safety hazards of hydrogen are relatively large due to its high flame propagation speed, strong permeability, small quenching distance and wide flammability limits. Decarbonization movement around the world has already driven ammonia (NH3) to become a potential solution for carbon-free economy and power generation with well-established infrastructure. Based on the principle of complementary fuel advantages and integrated cascade energy utilization, this study innovatively develops a novel power cycle based on a partial ammonia decomposition chemical reaction. The new design significantly ameliorates the problems of incomplete combustion of ammonia, as well as the safety hazards of hydrogen. By integrating with a chemically-recuperated unit, the exhaust heat can be fully utilized since the low-temperature waste heat is further used for evaporation of liquid NH3 and NH3 cracking processes. The thermal efficiency in the new design reaches 35.48–36.09% which is at least 21.67% higher than that (29.16–31.79%) in the reference system. The optimal condition is found as the ammonia split ratio reaches the maximum at 1 with a H2 molar ratio of 62.80–64.38%. The power generation efficiency can be improved to 43.55–43.90%, showing obvious advantages over pure ammonia condition. For a future carbon-free economy, this study should provide a new and efficient way for ammonia utilization.

Complexities in the structural evolution with pressure of water-ammonia mixtures.

The structural evolution with pressure of icy mixtures of simple molecules is a poorly explored field despite the fundamental role they play in setting the properties of the crustal icy layer of the outer planets and of their satellites. Water and ammonia are the two major components of these mixtures, and the crystal properties of the two pure systems and of their compounds have been studied at high pressures in a certain detail. On the contrary, the study of their heterogeneous crystalline mixtures whose properties, due to the strong N-H⋯O and O-H⋯N hydrogen bonds, can be substantially altered with respect to the individual species has so far been overlooked. In this work, we performed a comparative Raman study with a high spatial resolution of the lattice phonon spectrum of both pure ammonia and water-ammonia mixtures in a pressure range of great interest for modeling the properties of icy planets' interiors. Lattice phonon spectra represent the spectroscopic signature of the molecular crystals' structure. The activation of a phonon mode in plastic NH3-III attests to a progressive reduction in the orientational disorder, which corresponds to a site symmetry reduction. This spectroscopic hallmark allowed us to solve the pressure evolution of H2O-NH3-AHH (ammonia hemihydrate) solid mixtures, which present a remarkably different behavior from the pure crystals likely to be ascribed to the role of the strong H-bonds between water and ammonia molecules characterizing the crystallites' surface.

A study of flame dynamics and structure in premixed turbulent planar NH3/H2/air flames

Ammonia (NH3) has received considerable attention as a near future carbon-free synthetic fuel due to its economic storage/transportation/distribution, and its potential to be thermally decomposed to hydrogen (H2). To promote the low burning velocity and heat of combustion of ammonia, one viable option is to enrich pure ammonia with hydrogen. In this study, two quasi direct numerical simulations (quasi-DNS) with detailed chemistry and the mixture-averaged transport model are examined to study stoichiometric planar ammonia/hydrogen/air flames under decaying turbulence. The reactants temperature and pressure are set to 298 K and 1 atm, respectively. The initial turbulent Karlovitz number is changed from 4.3 to 16.9, implying that all the test conditions are located within the thin reaction zones combustion regime. The results indicate that the density-weighted flame displacement speed ([Formula: see text]), on average, is higher than the unstrained premixed laminar burning velocity ([Formula: see text]) value for both test cases. This suggests that the flame elements propagate faster than their laminar flame counterpart. With increasing the Karlovitz number, the turbulent burning velocity and the wrinkled flame surface area increase by about 35%. Furthermore, the mean flame stretch factor defined as the ratio of the turbulent to the laminar burning velocity divided by the ratio of the wrinkled to the unwrinkled flame surface area is equal to 1.08. This indicates that the local flamelet velocity value, on average, is higher than the unstrained premixed laminar burning velocity. In addition, the results show that the mean value of the local equivalence ratio for the turbulent conditions is higher than its laminar counterpart due to the preferential diffusion of hydrogen and turbulent mixing. Furthermore, the net production rate of hydrogen is shown to be negatively correlated with the flame front curvature suggesting that the local burning rate is intensified in positively curved regions.

Simultaneous anaerobic carbon and nitrogen removal from primary municipal wastewater with hydrogel encapsulated anaerobic digestion sludge and AOA-anammox coated hollow fiber membrane

In this study, a one-stage continuous-flow membrane-hydrogel reactor integrating both partial nitritation-anammox (PN-anammox) and anaerobic digestion (AD) was designed and operated for simultaneous autotrophic nitrogen (N) and anaerobic carbon (C) removal from mainstream municipal wastewater. In the reactor, a synthetic biofilm consisting of anammox biomass and pure culture ammonia oxidizing archaea (AOA) were coated onto and maintained on a counter-diffusion hollow fiber membrane to autotrophically remove nitrogen. Anaerobic digestion sludge was encapsulated in hydrogel beads and placed in the reactor to anaerobically remove COD. During the pilot operation at three operating temperature (25, 16 and 10 °C), the membrane-hydrogel reactor demonstrated stable anaerobic COD removal (76.2 ± 15.5 %) and membrane fouling was successfully suppressed allowing a relatively stable PN-anammox process. The reactor demonstrated good nitrogen removal efficiency, with an overall removal efficiency of 95.8 ± 5.0 % for NH4+-N and 78.9 ± 13.2 % for total inorganic nitrogen (TIN) during the entire pilot operation. Reducing the temperature to 10 °C caused a temporary reduction in nitrogen removal performance and abundances of AOA and anammox. However, the reactor and microbes demonstrated the ability to adapt to the low temperature spontaneously with recovered nitrogen removal performance and microbial abundances. Methanogens in hydrogel beads and AOA and anammox on the membrane were observed in the reactor by qPCR and 16S sequencing across all operational temperatures.

Recalibration of carbon-free NH3/H2 fuel blend process: Qatar's roadmap for blue ammonia

Due to growing concerns about carbon emissions, using zero-carbon fuels has become an interesting alternative to overcome this problem. The NH3(70%)-H2(30%) fuel blend is an innovative fuel example that has the potential to replace conventional hydrocarbon fuels. Studies on the NH3(70%)-H2(30%) fuel blend have shown its superior combustion performance and its effect on enhancing cycle efficiency compared to other compositions of the NH3–H2 blends. However, without calibrating ammonia plants and simply mixing portions of the produced pure ammonia to hydrogen at the desired molar fraction essentially requires coupling ammonia plants with other hydrogen-producing plants, leading to potential difficulties in commercializing the unused (as fuel in the NH3–H2/air gas turbines) hydrogen portions from the hydrogen-producing plan. Therefore, in this paper, as an attempt to utilize the existing ammonia production infrastructure and facility without acquiring major changes that could lead to resisting the adoption of the NH3(70%)-H2(30%) fuel blend, the independent parameters of a conventional ammonia plant have been calibrated, and the reactors have been sized to provide a continuous supply of the NH3(70%)-H2(30%) fuel blend with the exact molar fraction to run a power plant. Calibrating of the ammonia plant has been performed using an ASPEN PLUS model.

Process design and optimization of onsite hydrogen production from ammonia: Reactor design, energy saving and NOX control

Ammonia is an important commodity for both direct and indirect applications. It can be used directly as a carbon-free fuel source as well as for the purpose of renewable hydrogen storage and transport. In this study, hydrogen production from ammonia decomposition in a multi catalytic packed bed reactor with an intermediate heating system is reported using Aspen Plus V.12. The process simulation model results have been validated through experimental data for commercially available Ru/Al2O3 catalyst and Temkin-Phyzev reaction kinetics. The results exhibit that ammonia decomposition is a highly endothermic reaction, therefore requires significant heat energy. The decomposition parameters such as temperature and pressure are optimized for large-scale ammonia decomposition. For the ammonia combustion, thermal efficiency, fuel-saving, and product yield are analyzed and optimum values are found to be 59%, 22% and 77% for each parameter, respectively. During the pure ammonia combustion, NOX emissions are a major issue. To monitor the NOX emissions, parameters such as equivalence ratio, temperature and pressure are analyzed to witness the optimum operating conditions. To improve the flame quality such as laminar velocity, minimum ignition temperature, and adiabatic flame temperature of the ammonia combustion, waste hydrogen stream from the pressure swing adsorption (PSA) unit is blended with the fuel ammonia. The blending of hydrogen with fuel ammonia resulted in higher NOX emissions, which can be reduced by recirculation of 30% of the flue gas with air–fuel stream.

Investigation and Study of Ammonium Hydroxide and Biodiesel Blend as an IC Engine Fuel

The use of conventional fossil fuel has resulted in global warming. Biodiesel is a substitute fuel obtained from vegetable oil by transesterification process which can replace conventional diesel. Good alternative to traditional hydrocarbon-based fuel is ammonia combined with a biofuel. Ammonia is free of Carbon and can be extracted from sustainable renewable energy sources. It can be used with slight modifications on current IC engines. However running the engine on pure ammonia poses a lot of challenges which needs to be tackled. Running the engine on Biodiesel results in slightly more NOx emission, compared with traditional fuel. In the present study an experimentation has been carried out to examine the effect of biodiesel and ammonium hydroxide blend on ICE performance, emission and combustion aspects, in terms of specific fuel consumption, brake thermal efficiency, Nitrogen oxides (NOx) and Hydrocarbon (HC), Carbon monoxide (CO) and Carbon dioxide emissions. Biodiesel blends are examined using a single cylinder four stroke Kirloskar ICE. Experiments have been performed with varying percentages of ammonium hydroxide (3%, 6%, 9%) and B50 (50% diesel and 50% Karanja biodiesel) blended with Diesel and then compared with base line conventional diesel. This paper will help in understanding how percentage variation in ammonium hydroxide and biodiesel blend will effect emission and performance.

A comparative study of oxidation of pure ammonia and ammonia/dimethyl ether mixtures in a jet-stirred reactor using SVUV-PIMS

Oxidation of pure ammonia or ammonia/dimethyl ether (NH3/DME) mixtures in O2/Ar in a jet-stirred reactor (JSR) at atmospheric pressure was experimentally studied using a synchrotron vacuum ultraviolet photoionization mass spectrometer (SVUV-PIMS) and a gas chromatograph (GC) to analyse the reaction intermediates and product species. Particular attention was given to the effect of DME addition on NH3 → NH2, a critical step that initiates NH3 oxidation and subsequent formation of nitrogen oxides. The initial mole fraction of NH3 was set to 0.01, and for the NH3/DME mixture, the NH3/DME molar ratio was set to 1. The experiments were performed at two equivalence ratios of ϕ = 1.0 and 0.2 in the temperature range of 500 – 1100 K. A kinetic model for NH3/DME oxidation was developed and kinetic analysis was performed. It was found that the addition of DME significantly promotes the NH3 to NH2 pathway and the mechanisms of this promotion effect are different at low and high temperatures. At a low temperature (∼ 600 K), NH3 → NH2 is mainly promoted by OH radicals produced from the DME low-temperature chain-branching reactions, while at a high temperature (∼ 1000 K), mainly by OH radicals produced from the reactions consuming HO2 and H radicals, which were formed from DME high temperature oxidation. At T > 800 K with ϕ = 0.2, the addition of DME promotes the formation of nitrogen oxides, however, at a low temperature of 600 K, the addition of DME only promotes the formation of N2O and NO2 but not NO. A reaction pathway analysis indicates that the oxidation of NO into NO2 at low temperature is promoted by HO2 and CH3OCH2O2, the intermediate products from the low temperature oxidation of DME.

Transfer Functions of Ammonia and Partly Cracked Ammonia Swirl Flames

The replacement of hydrocarbon fuels by ammonia in industrial systems is challenging due to its low burning velocity, its narrow flammability range, and a large production of nitric oxide and nitrogen dioxide when burned close to stoichiometric conditions. Cracking a fraction of ammonia into hydrogen and nitrogen prior to injection in the combustion chamber is considered a promising strategy to overcome these issues. This paper focuses on evaluating how different levels of ammonia cracking affect the overall burning velocity, the lean blow-off limit, the concentration of nitric oxide and nitrogen dioxide, and the flame response to acoustic perturbations. Swirl stabilized premixed flames of pure ammonia–air and ammonia–hydrogen–nitrogen–air mixtures mimicking 10%, 20%, and 28% of cracking are experimentally investigated. The results show that even though ammonia cracking is beneficial for enhancing the lean blow-off limit and the overall burning velocity, its impact on pollutant emissions and flame stability is detrimental for a percentage of cracking as low as 20%. Based on an analysis of the flame dynamics, reasons for these results are proposed.

Nitrogen Oxides and Ammonia Removal Analysis Based on Three-Dimensional Ammonia-Diesel Dual Fuel Engine Coupled with One-Dimensional SCR Model

Ammonia, as an alternative fuel for internal combustion engines, can achieve nearly zero carbon emissions. Although the development of the pure ammonia engine is limited by its poor combustion characteristics, ammonia–hydrocarbon mixed combustion can effectively improve the combustion of ammonia fuel. With the increase in the ammonia fuel proportion in the fuel mixture, a large number of nitrogen oxides (NOX) and unburned ammonia may be discharged, which have a poor impact on the environment. In this study, the performance of selective catalytic reduction (SCR) aftertreatment technology in reducing NOX and ammonia emissions from ammonia–diesel dual-fuel engines was investigated using simulation. A good cross-dimensional model was established under the coupling effect, though the effect of a single-dimensional model could not be presented. The results show that when the exhaust gas in the engine cylinder is directly introduced into the SCR without additional reducing agents such as urea, unburned ammonia flowing into SCR model is in excess, and there will be only ammonia at the outlet; however, if the unburned ammonia fed into the SCR model is insufficient to reduce NO, the ammonia concentration at the outlet will be 0. NOX can be 100% effectively reduced to N2 under most engine conditions; thus, unburned ammonia in exhaust plays a role in reducing NOX emissions from ammonia–diesel dual-fuel engines. However, when the concentration of unburned ammonia in the exhaust gas of an ammonia–diesel dual-fuel engine is large, its ammonia emissions are still high even after the SCR. In addition, the concentrations of N2O after SCR do not decrease, but increase by 50.64 in some conditions, the main reason for which is that by the action of the SCR catalyst, NO2 is partially converted into N2O, resulting in an increase in its concentration at the SCR outlet. Adding excessive air or oxygen into the SCR aftertreatment model can not only significantly reduce the ammonia concentration at the outlet of the model without affecting the NOX conversion efficiency of SCR, but inhibit N2O production to some extent at the outlet, thus reducing the unburned ammonia and NOX emissions in the tail gas of ammonia–diesel dual-fuel engines at the same time without the urea injection. Therefore, this study can provide theoretical guidance for the design of ammonia and its mixed-fuel engine aftertreatment device, and provide technical support for reducing NOX emissions of ammonia and its mixed fuel engines.

Characterisation of direct ammonia proton conducting tubular ceramic fuel cells for maritime applications

A tubular cell with a BCZYZ electrolyte was fabricated by the extrusion and dip coating. The cell was tested for an extended operation time of 170 h in pure ammonia fuel, showing exceptional stability and potential for direct ammonia fuel cell.

Visualization study on the effects of pre-chamber jet ignition and methane addition on the combustion characteristics of ammonia/air mixtures

As a carbon-free green fuel, ammonia has recently attracted more and more attention. However, the application of ammonia as an alternative fuel in internal combustion engines is a challenge due to its low chemical reactivity. Thus, more fundamental researches on the combustion characteristics of ammonia are necessary to enhance the ignition and combustion of ammonia in internal combustion engines. In this study, the effects of pre-chamber jet ignition and different methane additions on the combustion characteristics of ammonia/air mixtures were investigated experimentally. The experimental results showed that pre-chamber jet ignition could improve the combustion performance of the premixed ammonia/air and ensure combustion stability at a low equivalence ratio, compared with spark direct ignition. For the jet ignition mode, the optimal equivalence ratio of the ammonia/air mixtures was between 1.0 and 1.1. The combustion duration was determined by the flame transverse propagation velocity, which was minimally influenced by the jet flame. For both jet ignition and direct ignition modes, a higher initial pressure would hinder the flame propagation resulting in a longer combustion duration, while an increase in the maximum pressure led to an increase in the average pressure rise rate. And for both ignition modes, the promotion of increasing methane addition from 0 to 10% on the pure ammonia combustion was higher than that of increasing methane addition from 10% to 20% on the combustion, and small amounts (10% and 20%) of methane addition had a less promotion on pure ammonia combustion at a higher initial pressure.

Minimum ignition energy of hydrogen–ammonia blends in air

We present a numerical analysis to calculate the minimum ignition energy of hydrogen–ammonia blends in air at both under and over atmospheric pressure. Unlike previous calculations, we used the full compressible and reactive Navier–Stokes equations coupled with detailed chemical kinetics (San Diego mechanism for hydrogen, complemented with the San Diego chemistry for nitrogen). The effect of the size of the energy deposition region and the deposition time are considered to determine the most efficient method to ignite the mixture. Our calculations also evaluate the impact of the gas compressibility on the minimum ignition energy after a sudden energy deposition. The results are validated first by comparing the minimum ignition energy of pure hydrogen–air mixtures as a function of the equivalence ratio ϕ with available experimental data and previous numerical results. Then, fuel blends made of mixtures of hydrogen and ammonia (NH3) are considered to calculate the minimum ignition energy as a function of fuel composition, equivalence ratio and pressure. The full range of ammonia volumetric content in the blend is varied between the extreme cases of pure hydrogen and pure ammonia. For each fuel blend, we computed a wide range of equivalence ratios ϕ that, in the case of pure hydrogen at atmospheric conditions, ranged from ϕ=7 to ϕ≃0.07, near the lean flammability limit, to theoretically explain the experimental evidence of ultra-lean flames reported in the literature.

Numerical Investigation of Rich-Lean Staging in a SGT-750 Scaled Dry Low Emission Burner With Partially Decomposed Ammonia

Abstract Ammonia is emerging as a very convenient hydrogen- and energy-carrier in the context of present efforts to curb carbon emissions from the power-generation and transport sectors. As opposed to hydrogen, the properties of ammonia make it significantly simpler to transport and store. Early exploratory work on the combustion of pure ammonia in laboratory-scale gas turbine combustors revealed that the adoption of a longitudinal rich-lean staging strategy in the operation of the device is a convenient approach to minimize NOx and N2O emissions from fuel-bound nitrogen oxidation. Moreover, recent experimental evidence acquired at SINTEF confirms that the low-emission performance achieved with rich-lean staging also applies to the combustion of partially decomposed ammonia. In this paper, we report a comprehensive numerical modeling study that exploits large eddy simulation (LES) in conjunction with detailed chemical kinetics and a chemical reactors network (CRN) model to assess a rich-lean staging strategy applied to the combustion of partially decomposed ammonia in the Siemens Energy fourth-generation dry low emission (DLE) burner. Data analysis performed from both numerical modeling approaches, LES and CRN, confirm that the rich-lean staging strategy tested in the present study indeed results in significantly lower emissions compared to the conventional operational profile of the burner. Furthermore, reaction pathways analysis performed on the CRN data reveals important details that characterize the different evolution of nitrogen species between the nonstaged and staged operation of the burner, ultimately leading to the observed difference in NOx and N2O emissions

Experimental investigation on the performance of pure ammonia engine based on reactivity controlled turbulent jet ignition

Ammonia-based internal combustion engines (ICEs) produce carbon-free emissions. However, the application of ammonia in ICEs results in difficult ignition, combustion instability, and reduced engine performance. In this study, the pre-chamber turbulent jet ignition (TJI) technology was applied to overcome these issues. Two TJI modes based on a self-designed scavenging pre-chamber were proposed in the engine experiments. These modes were air-assisted injection mode (TJI mode 1) and air-assisted injection mode with an air-scavenging process (TJI mode 2). The results demonstrated that the TJI system optimized the combustion stability and improved the burning rate of the ammonia engine. TJI combustion mode had a superior indicated mean effective pressure (IMEP), coefficient of IMEP variation (CoVIMEP), and indicated specific fuel consumption (ISFC) compared with the SI mode, particularly the TJI mode 2 with scavenging process. The NOx and NH3 emissions were high for the ammonia engine regardless of the ignition mode. However, the emissions decreased after adopting the TJI combustion mode. This study provides valuable insights into the application of the TJI ammonia engine to achieve zero-carbon emissions.