Combustion and emission performance of CO2/CH4/biodiesel and CO2/CH4/diesel blends in a Swirl Burner Generator

Renewable biomass derived fuels are of increasing attention for industrial and aerospace applications due to worldwide depletion of fossil fuels and stricter environmental legislations. These facts have prompted continuous development for clean, sustainable and alternative fuels that produce low emissions. Even more, fuel flexibility is a required feature to meet all the former characteristics while reducing operating cost in gas turbines. Thus, some alternative fuels such as syngas or biodiesel can be used for gas turbines as these can comply with these requirements while being obtained from various processes, making them potential candidates for sustainable power generation. On the other hand in many combustion applications, the fuel is originally present as either liquid or solid. To assist mixing and the overall burning rate, the fuel is frequently first atomised and then sprayed into the combustion chamber. Most of the existing approaches dealing with combustion flows are limited to single-phase injection. To remove this limit, a new model for multiphase combustion has been developed. Therefore, this experimental work investigated the performance of a swirl burner using various mixtures of CO2/CH4 blends with either diesel or biodiesel derived from cooking oil. A 20 kW swirl burner was employed to analyse gas turbine combustion features under atmospheric conditions to quantify flame stability and emissions by using these fuels. A TESTO 350XL gas analyser was used to determine NOx and CO emission trends. Comparison between the blends was carried out at different equivalence ratios. CH* chemiluminescence diagnostics was also used and linked with the levels of emissions created through the trials. The results revealed that the use of biodiesel and CO2/CH4 blends mixtures resulted in lower CO production, i.e. 87% lower for the case at 10% CO2. Results showed that a notable reduction of ~50% in NOx was obtained at all conditions for the biodiesel /CO2/CH4 blends. Diesel based flames showed high CH* intensity at the axial profile compared to the biodiesel blends due to their high sooting tendency

Flame structure, spectroscopy and emissions quantification of rapeseed biodiesel under model gas turbine conditions

The spray combustion characteristics of rapeseed biodiesel/methyl esters (RME) and 50% RME/diesel blend were investigated and compared with conventional diesel fuel, using a model swirl flame burner. The detailed database with well-characterised boundary conditions can be used as validation targets for flame modelling. An airblast, swirl-atomized liquid fuel spray was surrounded by air preheated to 350°C at atmospheric pressure. The reacting droplet distribution within the flame was determined using phase Doppler particle anemometry. For both diesel and RME, peak droplet concentrations are found on the outside of the flame region, with large droplets migrating to the outside via swirl, and smaller droplets located around the centreline region. However, droplet concentrations and sizes are larger for RME, indicating a longer droplet evaporation timescale. This delayed droplet vaporisation leads to a different reaction zone relative to diesel, with an extended core reaction. In spite of the longer reaction zone, RME flames displayed no sign of visible soot radiation, unlike the case of diesel spray flame. Blending 50% RME with diesel results in significant reduction in soot radiation. Finally, RME emits 22% on average lower NOx emissions compared to diesel under lean burning conditions.The financial support from the Ministry of Higher Education and Universiti Teknologi Malaysia (Research university matching grant vot no.: 00M45) and Ministry of Science, Technology and Innovation (MOSTI) Malaysia (vot no.: 03-01-06-KHAS01) is gratefully acknowledged

Effectiveness of Hindman's theorem for bounded sums

We consider the strength and effective content of restricted versions of Hindman's Theorem in which the number of colors is specified and the length of the sums has a specified finite bound. Let $\mathsf{HT}^{\leq n}_k$ denote the assertion that for each $k$-coloring $c$ of $\mathbb{N}$ there is an infinite set $X \subseteq \mathbb{N}$ such that all sums $\sum_{x \in F} x$ for $F \subseteq X$ and $0 < |F| \leq n$ have the same color. We prove that there is a computable $2$-coloring $c$ of $\mathbb{N}$ such that there is no infinite computable set $X$ such that all nonempty sums of at most $2$ elements of $X$ have the same color. It follows that $\mathsf{HT}^{\leq 2}_2$ is not provable in $\mathsf{RCA}_0$ and in fact we show that it implies $\mathsf{SRT}^2_2$ in $\mathsf{RCA}_0$. We also show that there is a computable instance of $\mathsf{HT}^{\leq 3}_3$ with all solutions computing $0'$. The proof of this result shows that $\mathsf{HT}^{\leq 3}_3$ implies $\mathsf{ACA}_0$ in $\mathsf{RCA}_0$

Biodiesel sustainability: The global impact of potential biodiesel production on the energy–water–food (EWF) nexus

A data-driven model is used to analyse the global effects of biodiesel on the energy–water–food (EWF) nexus, and to understand the complex environmental correlation. Several criteria to measure the sustainability of biodiesel and four main limiting factors for biodiesel production are discussed in this paper. The limiting factors includes water stress, food stress, feedstock quantity and crude oil price. The 155-country model covers crude oil prices ranging from USD10/bbl to USD160/bbl, biodiesel refinery costs ranging from -USD0.30/L to USD0.30/L and 45 multi-generation biodiesel feedstocks. The model is capable of ascertaining changes arising from biodiesel adoption in terms of light-duty diesel engine emissions (NO, CO, UHC and smoke opacity), water stress index (WSI), dietary energy supply (DES), Herfindahl–Hirschman index (HHI) and short-term energy security. With the addition of potential biodiesel production, the renewable energy sector of global primary energy profile can increase by 0.43%, with maximum increment up to 10.97% for Malaysia. At current crude oil price of USD75/bbl and refinery cost of USD0.1/L, only Benin, Ireland and Togo can produce biodiesel profitably. The model also shows that water requirement varies non-linearly with multi-feedstock biodiesel production as blending ratio increases. Out of the 155 countries, biodiesel production is limited by feedstock quantity for 82 countries, 47 are limited by crude oil price, 20 by water stress and 6 by food stress. The results provide insights for governments to set up environmental policy guidelines, in implementing biodiesel technology as a cleaner alternative to diesel

Soot volume fraction measurements over laminar pool flames of biofuels, diesel and blends

© 2018 The Combustion Institute. Biodiesel and blends with petroleum diesel have shown their potential as renewable alternative fuels for engines, with additional benefits of low particulate matter and low sulfate emissions. In this paper we measure the soot volume fraction produced by three different methyl esters processed biodiesels (extracted from palm (PME), soy (SME) and coconut (CME)), and their blends with petroleum diesel, in a series of co-flow stabilized laminar pool flames, using laser induced-incandescence (LII) and laser extinction optical methods. The soot volume fraction measurement results show that all neat biodiesels produce only up to 33% of the total soot volume compared to pure diesel, and that the total soot volume correlates directly with the degree of unsaturation of the biodiesels. Blending leads to approximately linear behaviour of total soot volume, with a shift in slope with smaller sensitivity towards neat diesel

Recovery of diesel-like fuel from waste palm oil by pyrolysis using a microwave heated bed of activated carbon

Microwave pyrolysis using a well-mixed bed of activated carbon as both the microwave absorber and reaction bed was investigated for its potential to recover useful products from waste palm cooking oil – a cooking oil widely used in Asia. The carbon bed provided rapid heating (∼18 °C/min) and a localized reaction hot zone that thermally promoted extensive pyrolysis cracking of the waste oil at 450 °C, leading to increased production of a biofuel product in a process taking less than 25 min. It also created a reducing reaction environment that prevented the formation of undesirable oxidized compounds in the biofuel. The pyrolysis produced a biofuel product that is low in oxygen, free of sulphur, carboxylic acid and triglycerides, and which also contains light C$_{10}$-C$_{15}$ hydrocarbons and a high calorific value nearly comparable to diesel fuel, thus showing great potential to be used as fuel. This pyrolysis approach offers an attractive alternative to transesterification that avoids the use of solvents and catalysts, and the need to remove free fatty acids and glycerol from the hydrocarbon product. The pyrolysis apparatus operated with an electrical power input of 1.12 kW was capable of producing a biofuel with an energy content equivalent to about 3 kW, showing a positive energy ratio of 2.7 and ≥73% recovery of the energy input to the system. The results show that the pyrolysis approach has huge potential as a technically and energetically viable means for the recovery of biofuels from the waste oil.The authors acknowledge the financial support by the Ministry of Science, Technology and Innovation and the Ministry of Higher Education Malaysia for the conduct of the research under the E-Science fund (UMT/RMC/SF/13/52072(5), Vot 52072) and the FRGS grant (FRGS/1/2016/TK07/UMT/02/3, Vot 59434).This is the author accepted manuscript. The final version is available from Elsevier via https://doi.org/10.1016/j.energy.2016.09.07

Quantification of carbon particulates produced under open liquid pool and prevaporised flame conditions: Waste cooking oil biodiesel and diesel blends

The soot volume fraction (SVF) of waste cooking oil (WCO) biodiesel and blends was quantified and compared under the same total carbon flow rate via two experimental setups, namely prevaporised diffusion jet flames and pool flames using extinction calibrated laser induced-incandescence (LII). The spatial SVF distribution shows that for diesel-rich fuels, soot formation peaks near the flame and is convected downstream, whereas biodiesel flames show a more evenly distributed SVF at the flame center region. An increase in biodiesel fraction in diesel results in a reduced propensity for soot, as evident in both pool and vapour flames. Comparison of the radial profiles of SVF along the centerline shows broader SVF profiles for pool flames, reflecting the longer residence times for soot diffusion and growth compared to vapour flames, which reflected the lower mass flux for the pool burner. The total soot produced from pool flames was found to be higher than vapour flame by a factor of two for the same fuel mass consumption rate. WCO biodiesel exhibited the lowest total SVF value regardless of flame type owing to the combined effects of lack of aromatic compounds and fuel chemistry. The soot primary particle sizes produced by WCO biodiesel show lower mean diameter values by a factor of approximately 1.5 compared to diesel-produced soot. The pool flames produced carbon particulates of larger mean diameter by around 22% and 8% for diesel and WCO biodiesel, respectively, relative to the counterpart vapour flames, as a result of extended soot surface growth period.Royal Society-Newton Advanced Fellow (NA160115) Academy of Sciences Malaysia (ASM) Malaysian Industry-Government Group for High Technology (MIGHT

Synthesis of single-walled carbon nanotubes in rich hydrogen/air flames

© 2020 Elsevier B.V. We explore the production of single-walled carbon nanotubes (CNTs) in a stream surrounded by rich premixed laminar H2/air flames using a feedstock containing ethanol and ferrocene. The as-produced nanomaterials were characterised by Raman spectroscopy, transmission electron microscopy, scanning electron microscopy and X-ray diffraction. A formation window of equivalence ratios of 1.00–1.20 was identified, and single-walled CNT bundles with individual CNTs of an average diameter of 1 nm were observed. The formation of CNTs was accompanied by the production of highly crystalline Fe3O4 nanoparticles of a size of 20–100 nm. The investigation of the limiting factors for the CNT synthesis was carried out systematically, assisted by numerical modelling. We conclude that the key factors affecting CNT synthesis are the surrounding flame temperatures, and the concentration of carbon available for CNT nucleation.EPSRC (ANAM