Publications

Using renewably produced ammonia as a zero-carbon fuel is gaining momentum due to its ease of transportation and storage as a hydrogen vector. This is particularly true for partially cracking ammonia immediately prior to use, injecting a blend of NH3, H2 and N2. Challenges with this fuel combination relate to the emissions of NOx and unburned NH3, as well as understanding flame stability for practical applications. In this study, a 20 %(vol.) cracked ammonia blend was investigated using a fully premixed swirl burner, operating at a thermal power of 10 kW with steam injection of 30 %(vol.) of the fuel and preheating inlet temperatures of up to 390 K, for a range of equivalence ratios from lean to rich. Emissions of NO, NO2, N2O, NH3, H2, O2 and H2O were recorded, along with OH*, NH* and NH2* chemiluminescence. Additionally, a numerical investigation was conducted using CHEMKIN-PRO to elucidate the main reactions responsible for reducing emissions by providing a rate of production analysis. The 20 %(vol.) cracked ammonia blend was found to reduce NO, NO2 and N2O significantly, with an increase in NH3 emissions at rich conditions and instabilities at both lean and rich extremes, compared to the widely investigated 70/30(vol %) ammonia/hydrogen blend. Humidification reduced NO and NO2 emissions due to a reduction in HNO production via OH and NH but caused an increase in N2O by reducing the flame temperature and unburned NH3 emissions at rich, low power conditions due to combustion instabilities. Unburned H2 emissions however were reduced, likely relating to a reduction in exhaust temperature thermally cracking less unburned NH3 into H2 and N2.

The transition to clean energy is crucial for mitigating the impacts of climate change and achieving sustainable development. Reliance on fossil fuels, which are integral to manufacturing and transportation, remains a major contributor to greenhouse gas (GHG) emissions. Biomass gasification presents a renewable energy alternative that can significantly reduce emissions. However, proper disposal of municipal solid waste (MSW) and agricultural residues, such as date palm waste (DPW), is an increasing global challenge, including in Qatar. This study evaluates the economic feasibility of implementing an MSW and DPW gasification plant for clean electricity generation in Qatar. The country’s growing population and economic development have led to substantial waste production, making it an ideal location for waste-to-energy (WTE) initiatives. Using discounted cash flow (DCF) analysis, the study estimates the capital cost of a 373 MWth facility at approximately $12.07 million, with annual operating costs of about $4.09 million and revenue of $26.88 million in 2023. The results indicate a net present value (NPV) of $245.77 million, a return on investment (ROI) of 84.80%, a payback period of approximately 5 years over a 20-year project lifetime and a net reduction of 206,786 tonnes CO2 annually. These findings demonstrate the economic viability of biomass gasification in Qatar while contributing to reduced GHG emissions and advancing the country’s sustainability goals under Qatar National Vision 2030.

No abstract is provided for this article.

Due to its ease of storage and existing global distribution network, interest in the use of renewably produced ammonia for decarbonising energy systems is growing. Partially cracking ammonia can overcome the flame stability challenges of this fuel, but demonstrations of high-power ammonia-based swirl flames with acceptable emissions have yet to be realised. Therefore, the present study examines the effects of varying swirl number and nozzle design on the static stability and emissions from 20% (vol.) cracked ammonia swirl flames for a wide range of equivalence ratios (0.3 < Φ < 2.2) and thermal powers of 5, 10 and 15kW. Additionally, a reference case of 100kW thermal power at stoichiometric conditions was tested. Stable flames were shown across a broad range of equivalence ratios, swirl numbers and nozzle geometries although flame morphologies varied greatly. Of note was a geometric swirl number of 1.75 paired with a long nozzle, which enabled the transition to a flat, Coanda jet flow flame at equivalence ratios of 0.6 and 0.7. For a geometric swirl number of 1.45, shortening the nozzle resulted in significantly shorter, wider V-shape flames with greatly improved rich blowoff limits. This was found to be a desirable characteristic for reaching high thermal power with a constant nozzle throat diameter – i.e. dump plane velocity – as a widened flame brush prevents jet-like flames, which are susceptible to pinching off. This can also be achieved by increasing the swirl number, although to a lesser extent. However, with a widened flame brush, careful consideration must be given to confinement diameter to avoid flame impingement which has potential to increase local heat loss and hence reduce combustion efficiency, resulting in an increase in unburned NH3 emissions. With the same geometric swirl number of 1.45, the shorter nozzle configuration resulted in higher NO emissions, potentially due to the shorter nozzle forming shorter, wider flames, meaning there was less residence time for NH2 to consume NO in the flame zone. This difference was less noticeable at rich conditions, with all configurations reaching negligible NO emissions by Φ = 1.15

The characteristics of pool fire burning of methyl esters/biodiesels of palm, soybean, coconut and their blends with diesel were compared against baseline

Ammonia/hydrogen fuel blends have gathered interest as a promising solution for the development of a hydrogen economy, with advantages in storage cost or combustion properties compared to pure hydrogen or pure ammonia, respectively. In that pursuit, the present work reports the trends of nitrogen oxide emissions for ammonia/hydrogen blends at atmospheric conditions. NO, NO2 and N2O productions/consumptions are approached in detail in combination with unburnt ammonia. All cases are measured in a turbulent, swirl-stabilised flame configuration across hydrogen fuel fractions from 0% to 25% and equivalence ratios from 0.55 to 1.30. A detailed chemistry analysis was conducted using a chemical reactor network (CRN) employing detailed reaction chemistry. The results show that NO and NO2 emissions peaks around Φ = 0.8, whereas considerable amount of N2O is generated at very lean conditions, Φ ≤ 0.65. Availability of OH radicals and O/H pools in the flames contribute towards fuel NO formation, which in turn produces NO2 and N2O. However, very lean conditions lead to lower temperatures that ensure the survival of N2O. The results identified Φ = 1.05–1.2 as the optimum equivalence ratios for reduced NOX emissions in ammonia/hydrogen blends, with further understanding of the flame chemistry responsible behind these emissions.

In order to achieve carbon neutrality, the use of ammonia as a fuel for power generation is highly anticipated. The utilization of a binary fuel consisting of ammonia and hydrogen can address the weak flame characteristics of ammonia. In this study, the product gas characteristics of ammonia/hydrogen/air premixed laminar flames stabilized in a stagnation flow were experimentally and numerically investigated for various equivalence ratios for the first time. A trade-off relationship between NO and unburnt ammonia was observed at slightly rich conditions. At lean conditions, NO reached a maximum value of 8,700 ppm, which was larger than that of pure ammonia/air flames. The mole fraction of nitrous oxide (N2O) which has large global warming potential rapidly increased around the equivalence ratio of 0.6, which was attributed to the effect of a decrease in flame temperature downstream of the reaction zone owing to heat loss to the stagnation wall. To understand this effect further, numerical simulations of ammonia/hydrogen/air flames were conducted using the stagnation flame model for various equivalence ratios and stagnation wall temperatures. The results show that the important reactions for N2O production and reductions are NH +NO = N2O + H, N2O + H = N2 + OH, and N2O (+M) = N2 + O (+M). A decrease in flame temperature in the post flame region inhibited N2O reduction through N2O (+M) = N2 + O (+M) because this reaction has a large temperature dependence, and thus N2O was detected as a product gas. N2O is reduced through N2O (+M) = N2 + O (+M) in the post flame region if the stagnation wall temperature is sufficiently high. On the other hand, it was clarified that an increase in equivalence ratio enhances H radical production and promotes N2O reduction by H radical through the reaction of N2O + H = N2 + OH.

Increased public concerns and stricter regulatory frameworks promote the role of bioliquids (liquid fuel for energy purposes other than for transport, including electricity and heating and cooling, produced from biomass). This is a driving force for development and employment of micro-gas turbines (MGTs) due to their ability to combust bioliquids with less favorable properties in a decentralized manner. Gas turbines are characterized by relatively high combustion efficiency at relatively low concentrations of harmful emissions, relatively high effective efficiency and durability when utilizing a common portfolio of gas turbine approved fuels. It is thus desired to preserve these advantages of gas turbines also while burning bioliquids and further relying on their scalability that is crucial to efficient support of decentralized energy production at small scales. To support these objectives, MGT technology needs to allow for utilization of bioliquids with much wider spectrum of physical and chemical properties compared to common commercially available MGTs in a single MGT-based plant. In this view, the present study is providing the first thorough overview of challenges and solutions encountered by researchers across the wide area of bioliquids in MGTs.

Alternative fuels are under scrutiny for mitigating carbon dioxide emissions. One of these alternatives is ammonia, which can be produced from waste sources, renewable energy and even nuclear power with potentially zero carbon emissions over most of its life cycle. The difficulties of pure ammonia combustion, partially due to its low flame speed and flammability, can be addressed by doping ammonia mixtures with hydrogen, which increases the reactivity of these blends and allows combustion features similar to those of some fossil fuels. However, NOx emissions are still a problem when burning ammonia, with some circumstances where emissions are even worse than with fossil-based systems. This is a consequence of the considerable formation of N2O, a greenhouse gas that is known to possess up to 300 times the Global Warming Potential (GWP) of carbon dioxide, making these regimes unsuitable for the purpose of fuel replacement to combat climate change. Therefore, this work shows bespoke results for unburned NH3 and NOx emissions, specifically NO, NO2 and N2O, at various conditions of operation whilst employing ammonia-hydrogen blends in a tangential swirl burner representative of industrial gas turbines. The results show a good compromise of NOx emissions at the near 1.05 - 1.2 equivalence ratio, with further understanding behind the chemistry that precludes the formation/consumption of these unwanted emissions for full deployment of ammonia-based energy systems.

This work reports on the chemiluminescence signature of premixed ammonia-methane-air swirling flames. Wide ranges of equivalence ratios (0.6 ≤ Φ ≤ 1.3), ammonia fractions in the fuel blend (0 ≤ XNH3 ≤ 0.70), and Reynolds numbers (10,000 ≤ Re ≤ 40,000) were investigated to understand effects of these parameters on the light emitted by these flames. Excited radicals contributing to chemiluminescence in the UV and visible ranges were confirmed, namely NO*, OH*, NH*, CN*, CO2*, CH*, and NH2*. With non-intrusive flame monitoring in mind, various ratios of chemiluminescence intensities were carefully studied because these allow removing effects of time-varying flame surface area that is inherent in turbulent flames. Consistent with previous findings in laminar flames, ratios CN*/OH*, CN*/NO*, and NH*/CH* were found to be promising candidates. Ratios CN*/OH* and CN*/NO* were identified as potential surrogates for equivalence ratio if XNH3 ≥ 0.20 and 0.05 ≤ XNH3 ≤ 0.50, respectively. Ratio NH*/CH* was identified as a potential surrogate for the ammonia fraction in the fuel blend provided that equivalence ratio is roughly known. Ratio Blue/NH2*, obtained exclusively from measurements in the visible range, is another interesting surrogate for the ammonia fraction but its sensitivity to Reynolds number may limits its range of applications. Trends of measured exhaust NO concentration with equivalence ratio and ammonia fraction were found to qualitatively match that of NO*, NH*, and CN*, implying that emissions from these excited radicals could be used to monitor the NO performance of practical ammonia-methane-air flames.