Nitric oxide formation analysis using chemical reactor modelling and laser induced fluorescence measurements on industrial swirl flames

This thesis investigates nitric oxide formation in the combustion of fuel compositions representative of those produced by the power generator gas turbines. As power generation gas turbine manufacturers and operators strive for improvements in thermal efficiency while abiding by the emissions regulation put into place, more detailed understanding of formation of different emissions is required to accurately simulate combustion of increasingly volatile gaseous fuel supplies. Detailed modelling of an industrial scale high-pressure generic swirl burner has been carried out to predict the formation of oxides of nitrogen at exhaust. Three new models are proposed based on the models available in the literature and simulation results are compared against each other as well as with the experimental data. The predictions from the selected model at different conditions has been appraised against the experimental results using several chemical kinetics mechanisms from the literature to validate the proposed chemical reactor model. Nitric oxide formation analysis is also carried out by taking in-flame nonintrusive laser induced fluorescence measurements for the first time on industrial swirl flames with a range of gaseous fuel. These experimental nitric oxide formation distributions are supported through the use of experimentally derived heat release intensities and numerical calculations. Changes in NO formations at different physical conditions with methane and methane-hydrogen fuel blends are discussed. Two calibration techniques are discussed and performed at the latter part of the thesis for quantification of the qualitative nitric oxide distribution data from this study in future. Data generated from this investigation provide opportunities for future validation work of chemical kinetics modelling and computational fluid dynamics analysis. In addition to that, results from this thesis will also inform gas turbine manufacturers on potential burner design modifications for better management of oxides of nitrogen emissions. Based on this work, future investigations may focus on quantitative nitric oxide formation analysis in alternative fuels like ammonia-methane-hydrogen blends

Advancements of combustion technologies in the ammonia-fuelled engines

The worldwide decarbonisation movement has turned ammonia into one of the attractive alternative fuel for power generation. This paper reviews the progress of ammonia combustion technologies in spark ignition engine, compression ignition engine, and gas turbine. Relevant publications from prominent academic journals were acquired from credible scholarly databases and analysed. Ammonia dissociation and separate hydrogen supply were typically employed to deliver hydrogen to enhance ammonia reaction in the spark ignition engine. To achieve satisfactory engine performances with thermal efficiency of around 30%, a hydrogen mass fraction of roughly 10% is required for the ammonia/hydrogen engine. Engine parameters optimisation may be needed to increase hydrogen mass fraction further. Aqueous ammonia elevates heat release rate of full load compression ignition engine by almost 10%. However, prolonged ignition delay could potentially lead to higher engine noise levels. Multiple fuel injection optimisation is seemingly a more promising solution for improving ammonia compression ignition engine performances. In recent years, partial premixed combustion has gained considerable interest in hydrogen/ammonia gas turbine combustion research. This is mainly due to its ability to operate at equivalence ratio as low as 0.4, and in the slight fuel-rich regime. For operation at equivalence ratio 1.05, the nitric oxide concentration was decreased by a factor of approximately 5.9 when compared with that of stoichiometric condition. In all, ammonia offers a practical opportunity for sustainable power generation via internal combustion engines and gas turbine. Ground-breaking combustion technologies are crucial to boost the adoption of ammonia in these engines

Numerical Investigation on the Head-on Quenching (HoQ) of Laminar Premixed Lean to Stoichiometric Ammonia–Hydrogen-Air Flames

The Head-on Quenching (HoQ) of laminar premixed ammonia–hydrogen-air flames under lean to stoichiometric condition is numerical investigated. Detailed chemistry including 34 reactive species and detailed multi-component transport model including thermal diffusion (Soret effect) are applied. The quenching distance is considered as a representative quantity for the HoQ process, and the influence of different system parameters on it has been investigated. These parameters involve fuel/air equivalence ratios, hydrogen content in gas mixture and pressure. It was found that an increase of quenching distance can be caused by a lower hydrogen addition and a leaner mixture condition. Furthermore, it was found that, regardless of the gas mixture, the quenching distance decreases monotonically with increasing pressure, obeying a power function with the exponent − 0.7. Moreover, numerical results show a relation between the quenching Peclet number and the dimensionless wall heat flux normalized by the flame power. Additionally, sensitivities of quenching distances with respect to the transport model, considering the heat loss in the wall and the chemical kinetics are studied

Empirical and numerical investigation of turbulent flows in a novel design burner for ammonia/hydrogen combustion

Ammonia-hydrogen fuel blends are an attractive option for the decarbonization of the energy sector with improved combustion characteristics over pure ammonia fuels. However, further research into methods of reducing NOx and NH3 emissions is necessary for combustors operating with these fuel blends. This paper details a novel burner design for partially premixed ammonia-hydrogen fuel injection incorporating considerations for waste heat, unburnt ammonia and improved combustion residence times. Laser Doppler anemometry (LDA) and computational fluid dynamics using a 3D RANS realizable k-epsilon model were employed to characterise the three-dimensional isothermal flow field of the design. The results show a promising flow profile with an anchored flame, a central recirculation zone and increased residence times

Experimental study of ammonia addition in premixed methane flames

Ammonia is a hydrogen carrier fuel that does not produce CO2 emissions in direct combustion. While ammonia combustion systems have been successfully trialled in a wide range of applications including aircraft engines and gas turbines, ammonia’s low laminar burning velocity and high ignition energy is one of the barriers to its more widespread use. The design and use of ammonia-methane combustors helps overcome these barriers, while also acting as a pathway to a lower-carbon economy. Hence the purpose of this study was to investigate the flame behaviour in terms of stability and emissions production in premixed methane swirl stabilised flames with both diffusion and premixed ammonia injection configurations. Temperature measurements, OH*, and NH2* chemiluminescence measurements were taken. Product gas values were measured for up to 50% (vol.) of ammonia and for 0.8 to 1.4 equivalence ratios at two power ratings (i.e. 6.4 and 10.7 kW). Chemiluminescence results for these conditions show radical concentration’s centre of gravity moving lower with an increase in ammonia concentration. NH2* radicals peaking at 30% ammonia volume fraction. This study also found correlations between radical formation and temperature profiles for numerical validation purposes

Methodology and comparison of quantitative NO-LIF imaging in a bunsen burner with numerical simulation results

A planar laser induced fluorescence (P LIF) technique is applied to quantify nitric oxide (NO) concentration in a premixed bunsen burner with a CH4 -air flame doped with NO (up to 1300 ppm). This experimental data will be used as the calibration method for quantitative in-flame NO measurements in a high-pressure generic swirl burner at Cardiff University’s Gas Turbine Research Centre. Methodology of modelling premixed bunsen burner combustion experiment in CHEMKIN for predicting NO emissions in a wide variation of premixed methane flames is also described here. Chemical kinetics simulation results from a wide range of fuel flow rates have been compared and analysed with the experimental data in this paper. Our open bunsen burner flame experienced about 15 – 25% reduction in seeded NO level at 25mm above the burner exit. Calibration curves were obtained for both online and offline by measuring NO -PLIF intensity at varying level of NO seeding. These results from both the LIF and simulations will complement each other in subsequent works

The development and testing of a CH4/NH3/H2 combustion system for a 50kW micro gas turbine

In an effort to target lower global warming emissions, carbon-free fuels are a cheap, long-term energy storage solution. Ammonia-hydrogen fuel blends are a good compromise for combustion characteristics and storage/transportation costs, and may be blended with methane to aid the transition to a carbon-free economy. This study outlines the emissions challenges in the utilisation of an industrial scale swirl burner for CH4/NH3/H2 blends. To address these challenges, a novel combustor design has been proposed for the conversion of a 50kW APU. Swirl burner emissions for NH3/H2/CH4 blends were studied and LDA validated CFD defined hydrodynamic behaviour of the NIK15 burner design, with plans for future combustion studies. Prototype APU combustor designs are under development to accommodate this new design