Browsing by Author "Williams, Mike"
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Item Open Access Catalytic effects on the nonisothermal oxidation of solid fuels by oxygen: an experimental study(American Chemical Society, 2019-09-24) Nyombi, Antony; Williams, Mike; Wessling, RolandThe role played by catalysts in solid fuel reactivity toward oxygen as a viable method for reducing toxic combustion emissions was studied. Catalyst (1 wt % Pd–Sn/alumina) treated and untreated solid fuels were analyzed using thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) coupled with a gas detection system at heating rates of 20–40 °C/min and airflow rates of 30–100 mL/min. The relative CO emission factors, NOx, CH4, energy output, and combustion efficiency were determined as well as values of the activation energy (Ea) and pre-exponential factor (A) for the oxidation of the solid fuels. Results showed that the catalyst treatment enhanced the energy output by more than 22% and reduced CO emission factors by up to 87%. The temperature for release of nitrogen compounds was considerably reduced; however, the amounts produced were not impacted. The combustion efficiency was also improved by up to 60%. In terms of reactivity, catalyst treatment lowered the Ea for oxidation especially at 0.2 ≤ α ≤ 0.8. Catalyst treated samples had more free active sites on their surfaces, which decreased at temperatures of >500 °C possibly due to thermal deactivation of the catalyst. This is a viable method for minimizing toxic emissions from solid fuel combustion and enhancing energy output for domestic and industrial applications.Item Open Access Determination of kinetic parameters and thermodynamic properties for Ash (Fraxinus) wood sawdust slow pyrolysis by thermogravimetric analysis(Taylor and Francis, 2018-08-15) Nyombi, Antony; Williams, Mike; Wessling, RolandAsh (Fraxinus) wood sawdust pyrolysis under nitrogen was conducted using 2, 5, 10, 15, and 20°C/min heating rates. Friedman and Starink methods were used for kinetic analysis while y(α) master plots were used for pyrolysis mechanisms prediction. The mean activation energy were 198 and 202 kJ/mol for Friedman and Starink, respectively. The master plots predicted that the pyrolysis process could be a combination of diffusion, geometrical contraction, nucleation, and reaction order models. The pre-exponential factors were in the range 1012 to 1019 s−1. Gibbs free energy was 180 −185 kJ/mol. The entropy values were negative up to α = 0.75 indicating high orderliness of products relative to reactants but changed to positive at higher conversions implying likely disorderliness of the products compared to reactants. The calorific value of Ash (Fraxinus) wood sawdust was 18.3 MJ/kg.Item Open Access Effects of Particulate Contamination and Jet Fuel Chemistry on the Nucleation of Water and Ice in Aircraft Fuel Systems(Cranfield University, 2022-04) Ugbeh-Johnson, Judith; Carpenter, Mark; Mai, Nathalie; Williams, MikeThe aviation industry is currently facing increasing environmental and energy challenges regarding its fuel use. Research is therefore currently under way to develop new sustainable aviation fuels. Understanding the properties of these fuels (along with the changing properties of existing fuel types) is required to understand their impact on aircraft fuel systems. Water solubility, water settling and ice formation in fuel are such properties of interest. The presence of water in jet fuel/fuel systems has been a long-standing issue in the aviation industry. Therefore, it is important to precisely identify the conditions and features that may exacerbate this phenomenon, understanding how fuel composition, temperature, water droplet sizes, flowrate and pipe surface affect ice formation and water solubility. Currently, there is relatively limited data regarding water solubility/settling rate and ice formation in sustainable fuels, specifically those specified in ASTM D7566. This work gives a comprehensive account of the recent advances and technologies in the literature indicating conditions that might lead to the nucleation of water and ice in aircraft fuel systems. These conditions have then been applied to characterizing dispersed water droplets in alternative fuels and conventional Jet A-1. Subsequently, the requirements have been applied to the design, set up, and effectiveness of an ice test rig to understand the types and amounts of ice that can be produced from different sustainable aviation fuel blends. In doing so, this work has helped shed light on the role of fuel composition in ice accretion and whether ice accumulation on a pump inlet strainer may impact pump performance. Furthermore, the results from this work will serve as a basis for design guidelines to minimise ice formation within an aircraft fuel system and help identify some potential/sustainable jet fuel candidates for ASTM D7566 certified jet fuels.Item Open Access Examination of misconceptions surrounding fatal fire victims(Elsevier, 2023-07-27) Harding, Mary-Jane; Márquez-Grant, Nicholas; Williams, MikeFire deaths are not unusual in forensic investigative practice but due to the destructive nature of fire they are often very difficult to investigate. With the need to identify the deceased and the events surrounding the manner and cause of death, knowledge of thermally induced alteration to the human body is important. Within the fire investigation community, a number of misconceptions have been present for years regarding the protrusion of the tongue as an indicator of life during the fire, and fractured skulls as the result of brains boiling and skulls exploding. This work presents qualitative analysis on the experimental burning of 42 unembalmed human donated cadavers by the San Luis Obispo Strike Team (SLOFIST) on their annual Forensic Fire Death Investigation Course (FFDIC) between 2017 and 2019. Prior to burning, the position of the tongue within the dental arch was confirmed and sharp, blunt, surgical and gunshot trauma to the cranium documented. Temperature was recorded from ignition through to suppression with thermocouples present both within the scene and the body. Post burn analysis on the position of the tongue, observation of cranial fractures and presence of brain tissue were recorded and analysed in conjunction with thermocouple data, fire scene dynamics and body demographics. The results provide a more comprehensive understanding of the thermal environmental factors involved in producing the phenomena that facilitate these misconceptions, identifying that a more thorough understanding of individual fire scenes and their development is essential when interpreting alteration and injury to the body of the fatal fire victim.Item Open Access Examining thermally induced movement of the fatal fire victim(Elsevier, 2024-01-23) Harding, Mary-Jane; Marquez-Grant, Nicholas; Williams, MikeInvestigating a fatal fire scene comprises analysis not only of the fire’s development to identify the point of fire origin and ignition source, but analysis of a victim’s position and their relationship within the scene. This work presents both qualitative and quantitative results from experimentation investigating the effect of a real fire environment on the human body, and how the position of a victim at the post burn investigation stage may be significantly different to the position at fire ignition. Qualitative observations were undertaken on the burning of 39 compartment and vehicle scenes from ignition through to suppression, each containing a human cadaver. The results of analysis question the validity of previous work based on cremation observations. Quantitative results were produced by recording 13 points on the body on the X, Y and Z axis, both pre and post burn on a smaller dataset of ten compartment burns. Results have enabled a more robust assessment of thermally induced movement of the body within the scene along each axis, evidencing that pugilism is not the universal reaction of the fatal victim to thermal exposure, with extension of the upper limbs far more common than has been previously reported.Item Open Access Mechanical impregnation of Pd-Sn/alumina and Cu-Mn/graphite on charcoal to minimise carbon monoxide emissions(Elsevier, 2018-11-23) Nyombi, Antony; Williams, Mike; Wessling, RolandThis study investigated how to minimize carbon monoxide (CO) emissions from charcoal by impregnating with Pd-Sn/alumina and Cu-Mn/graphite. Samples were heated isothermally with continuous monitoring of residual CO using electrochemical and infra-red sensors. With 0.2wt% Pd-Sn/alumina, 26.9% and 44.4% were recorded as lowest and highest residual CO. On the other hand, when 2wt% Cu-Mn/graphite was used, 15.6%, and 25.3% were observed as lowest and highest residual CO. The activity of the catalysts decreased with temperature and increased with catalyst loading. This method could be used on briquettes, wood boiler chips and other solid carbonaceous materials to minimise CO emissions.Item Open Access Reactivity and free radical chemistry of lilac (Syringa vulgaris) charcoal(American Chemical Society, 2019-01-28) Nyombi, Antony; Williams, Mike; Wessling, RolandThe reactivity, and surface chemistry of charcoal determine its combustion behaviour, and these properties depend on the source of the original wood, production conditions and treatment. Here we studied the properties of charcoal derived from lilac (Syringa vulgaris). Its reactivity was tested by isothermal and non-isothermal thermogravimetric analysis and differential scanning calorimetry in air and nitrogen. The free radical concentration was determined by measuring the electron spin resonance of fresh charcoal, after washing with HCl, and after degassing in air with or without nitrogen. We found that lilac is highly reactive, igniting at 250–300 oC with peak combustion at 320–520 oC. The quantity of oxygen consumed and heat released during oxidation increased with temperature. The free radical concentration in the untreated charcoal was 5.29 x 1018 spins/g, compared to 3.49 x 1019 spins/g after acid washing, 7.06 x 1019 spins/g after exposure to air, and 3.75 x 1017 spins/g after degassing with nitrogen before exposure to air. The line width of all the charcoal samples was 11.6–11.9 G. However, degassing the charcoal in nitrogen followed by exposure to air at low temperatures resulted in a four-fold increase in the line width to 41.8 G. The exposure of lilac charcoal to air alone at low temperatures resulted in the formation of persistent peroxyl radicals superimposed on the main peak. The g-values of charcoal samples that were untreated, acid washed, degassed in N2 + air, and degassed in air alone (main peak) were 2.00481, 2.00477, 2.00260 and 2.00483, respectively. The g-values of the peroxyl radicals superimposed on the main peak were 2.0155, 2.0138, 2.0020 and 2.0007, respectively. The reactivity, and free radical content suggest that lilac charcoal is particularly suitable for applications involving energetic materials, catalysis and co-firing.Item Open Access Toxic emissions from smouldering combustion of woody biomass and derived char with a case study of CO build-up in an ISO container(Taylor & Francis, 2019-05-30) Nyombi, Antony; Williams, Mike; Wessling, RolandCarbon monoxide (CO) from the use of biomass products causes some deaths in the United Kingdom every year. This study was undertaken to evaluate the amount of CO from five species of wood sawdust, and charcoal with a case study of CO in a confined ISO container. Laboratory experiments were conducted at temperatures between 350°C and 600°C under flowing air. Results showed a strong dependence of CO emissions on temperature and airflow. The CO emissions in the ISO container were above the recommended exposure limits due to poor ventilation.Item Open Access When is carbon monoxide most dangerous: Safety concerns at Festivals(2017-01-11) Nyombi, Antony; Williams, Mike; Wessling, RolandThis study investigated the effect of temperature & air flow on CO evolved from barbecue charcoal. The amounts of CO were analysed using FTIR and Electrochemical sensors and the colours of charcoal at different temperatures were analysed with reference to a black body radiator. Results show that carbon conversion increased linearly with temperature. CO evolution started at a point when the charcoal was still black. Maximum amounts of CO were recorded at 400-450 oC but these then reduced as temperatures rose to 600 oC. Air flow had little effect on carbon conversion and the amounts of CO evolved. Temperature played a dominant but not linear role in CO evolution. Charcoal attained a reddish colour visible to the naked eye at 550 oC. This intensified to glowing red at higher temperatures. These results would help to inform about CO evolution even during the cooling process of charcoal.Item Open Access When is CO most dangerous: Safety issues at festivals(Cranfield University, 2018-08-08 10:50) Nyombi, Antony; Wessling, Roland; Williams, MikeThis video describes the preliminary work done to show the production of CO at various temperatures as charcoal burns.