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The presented investigation develops a modelling technique, which allows measurement in a dynamically similar gas jet, to be related to the diesel engine injection process in the presence of air swirl. Modelling experiments have been performed for direct injection processes from both the centre and the circumference of the combustion chamber. A tracer gas technique has been employed, by which, concentration of jet nozzle gas in the simulated air swirl was measured, thus yielding information on model predicted trajectory, spread and local fuel concentration. Gas concentration was measured using a specially developed hot wire anemometry technique which allowed measurement in a transient pulsed jet simulation. The modelling theory was developed on the basis that spray droplet velocity relative to the air entrained into the spray is small after an initial jet disintegration, and droplet formation process. Consequently the fuel spray is assumed to behave as an air jet bearing a mist of liquid droplets. Favourable comparison of model gas jet and engine fuel spray behaviour is initially made with published film data. Further comparison of engine performance and associated high speed photographic results, with the model predicted fuel dispersion and local concentration levels, is made from data obtained on a modified Petter PM test engine. The results indicate that model predicted rich fuel regions, both at the combustion chamber wall and within the Jet core correspond to smoke generation areas recorded on the high speed films. Similarly, experimental engine performance parameters such as exhaust emission levels' rate of pressure rise, and peak pressure are shown to directly relate to the model predicted dispersion of fuel. The conclusions drawn are that the modelling technique has potential in optimising the fuel injection equipment specification at the design stage and effectively represents the behaviour of the modelled engine fuel spray.

Biochars have traditionally been associated with soil amendment but are also useful in a number of sectors as they show potential to be cost-effective, multi-functional products particularly if they are produced from waste biomass. Current research is geared towards enhancing char agronomic value via physical, chemical and/or biological means although further studies are still required to gain a better understanding of the parameters which can be optimized to produce chars with specific functionality. This research set out to evaluate the potential for hydrochars and biochars derived from herbaceous and treated municipal waste to be used for nitrogen and phosphorus recovery from simulated wastewater, in addition to ammonia gas emission reduction during co-composting. This study also focused on providing more insight on some of the factors influencing hydrochar and biochar performance in nutrient-rich environments and investigating the potential for modifying char characteristics for enhanced nutrient recovery. Consequently, analysis of the physicochemical properties of hydrochars and biochars produced from paprika waste from a greenhouse, the treated organic fraction of municipal waste, greenwaste and pig manure has been performed. Comparisons are also made with relatively low-contaminant hydrochars and biochars derived from bark-free holm oak wood. Processing parameters include hydrothermal carbonization at 250°C for 60 min, slow pyrolysis at 400–700°C and gasification at 600–750°C over 30–60 min residence times. As oak and paprika waste chars possess carbon contents >50%, these have been categorised as Class 1 biochars in accordance with the international biochar initiative product specifications, while hydrochars and slow pyrolysis biochars derived from municipal waste, presscake, and greenwaste are ranked as Class 2–3 chars. in spite of differences in biomass inorganic content, the various feedstocks decompose into chars in a similar manner. Char morphological properties are observed to be more dependent on processing temperature and reactor system than to feedstock property, based on the substantial differences in surface area of holm oak biochars produced using three different reactor types. However, from batch sorption tests with synthetic wastewater, char surface area and porosity are of less importance than char oxygen and inorganic mineral contents in terms of ammonium and phosphate sorption, respectively. Overall however, all chars demonstrate similarly low capacities for ammonium and phosphate sorption (up to 14.6% and 7%, respectively). Conversely, in terms of ammonia removal, two of the hydrochars selected for further study are shown to possess higher ammonia emission reduction capacities relative to their biochar counterparts in 17-day laboratory co-composting trials. These differences are likely attributable to the acidic functional groups present in the hydrochars. While both oak and greenhouse waste hydrochars demonstrated higher levels of inorganic nitrogen (ammonium and nitrate) mineralization relative to their biochar counterparts, mineralization and carbon dioxide evolution was more prominent in the latter hydrochar. These findings are in agreement with previous studies in the literature, which have shown that hydrochars possess more mineralizable carbon and nitrogen species than biochars. Following from an understanding of the respective effects of char acid oxygen groups and inorganic content on char ammonium and phosphate sorption capacities, attempts have been made to enhance these properties via mild chemical activation of biomass or char samples. Results show that modest increases in both ammonium and ammonia sorption capacity of the chars can be achieved following acid treatment, while phosphate sorption can be enhanced from low levels (2.1–3.6%) to relatively high levels (66.4–70.3%) by impregnation with magnesium. Various treatments will understandably produce different effects on the different hydrochars. This is evident in the case of greenhouse waste, which experiences a considerable increase in ammonia sorption capacity following potassium hydroxide treatment of greenhouse waste 250°C hydrochar and 400°C biochar, from 3.3% to 44.1% in the latter char while the effect is less pronounced following sulphuric acid treatment. Overall, findings from this study suggest that it is possible to enhance waste-derived char capacity for ammonia / ammonium and phosphate recovery by treatment of chars or char precursors (raw feedstock) via mild chemical activation processes.

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Bioprocessing involves using complete cells or any of their components for the manufacture of products such as pharmaceuticals, fuel, health products and precursor compounds for plastics. Bioprocessing can provide sustainable routes for the manufacture of products which are traditionally manufactured from fossil-derived chemicals. The stirred tank reactor (STR) is the prevalent fermenter/reaction vessel in industry due to its simplicity and cost. However; the basic design has not changed for centuries. This thesis describes the use of oscillatory baffled reactors (OBRs) for bioprocessing. Generally, the “niche application” of OBRs is in performing ‘long’ processes in plug flow conditions, so they should be suitable for many bioprocesses. In this thesis, four research projects using OBRs are presented: modelling of plug flow and OBR design; enzymatic saccharification; microalgae culture; and anaerobic digestion (AD). A robust method to maximise plug flow in various OBR designs is described. Second order, polynomial models (R2=92.1% and 97.3%) were used to maximise plug flow at Ψ=1.9. The net flow rate (Q) was shown to affect the quality of plug flow which has implications for OBR design. Enzymatic saccharification was conducted in reactors based on OBR and STR technology. The OBR required 94-99% less power to achieve the necessary mixing intensities to maximise glucose production. Chlamydomonas reinhardtii was cultured in a modified OBR for use as a photobioreactor (PBR). Maximum growth rates were increased by 95% in the OBR compared to cultures conducted in T-flasks. A flotation effect was observed that suggests that a dual culture and harvest device for microalgae is possible. Anaerobic digestion of dairy slurry and co-digestion with glycerol was conducted in digesters based on OBR and STR technology. The OBR achieved a maximum specific methane yield 28% higher than the STR. However, blockages occurred in the OBR and 89% less power was required for temperature control in the STR, predominantly due to differences in surface areas to volume ratios. Overall, OBR technology was successfully used in three bioprocesses, with improvements demonstrated over traditional technologies such as STR and/or T- flasks. Commercial systems based on OBR technology could be designed, provided that sufficient data is generated to overcome the risks associated with adoption of a novel technology such as OBRs.