The thesis presents an experimental investigation of combustion performance and emissions of waste cooking oil (WCO) based biodiesel. To evaluate the comparative performance of biodiesel and diesel, combustions tests were conducted using Continuous Combustion rig (CCR) and Land Rover VM diesel engine. Firstly, physical properties of WCO biodiesel and diesel samples were measured in the laboratory. Elemental analysis of WCO biodiesel showed that there are differences between the functional groups in diesel and biodiesel which lead to major differences in the combustion characteristics of the two fuel types. It was found that biodiesel had 10% lower carbon content, almost no sulphur content for biodiesel and up to 12% more oxygen content compared with diesel. This explains the lower caloric value for WCO biodiesel (up to l8 %) compared with diesel. However, higher oxygen content and double bounds in WCO biodiesel increase its susceptibility to oxidation. The CCR test results showed an increase in combustion gas temperature with the increases in biodiesel blend ratio in diesel. This was due to a faster reaction rate for biodiesel than that of diesel leading to a faster brakeage of the hydrocarbon chain to release more heat. The engine tests were performed to measure the torque and emissions for different engine speeds and loads. In general a decrease in engine torque with up to 9% for biodiesel was observed, which was due to the lower calorific value of biodiesel compared with that of diesel. The brake specific fuel consumption (BSFC) increased as the biodiesel blend ratio in diesel increases due a greater mass of fuel being injected at a given injection pressure, compared with diesel. Using WCO blends ratio up to 75% in diesel showed a reduction in exhaust emission compared with diesel, however, at the cost of increased fuel consumption. A common conclusion can be drawn in favour of the WCO biodiesel as being a greener alternative to petro-diesel when used in blend with diesel. However, due to large variations in the biomass used for biodiesel production could lead to variations in physical and chemical properties between biodiesel produced from different biomass. Therefore more stringent standards need to be imposed for biodiesel quality in order to diminish the effect of variation in physicochemical properties on engine performance and emissions. The future work in developing standard test procedures for establishing fuel properties and limits/targets would be beneficial in using a large amount of waste cooking oil in the production of biodiesel, thus contributing to reduction in CO2 and waste minimisation.

[pt] A análise do ciclo de vida (ACV) é uma ferramenta útil para dimensionar e expor os crescentes impactos ambientais, econômicos e sociais causados por produtos e processos industriais, principalmente quando estes possuem uma cadeia de suprimentos complexa, como é o caso dos principais combustíveis do ciclo diesel (diesel A, biodiesel éster e diesel verde). Utilizando diferentes cenários possíveis para a matriz de combustíveis diesel no Brasil como contexto e a ACV simplificada a partir da estrutura metodológica descrita pela ABNT como ferramenta, esse estudo buscará responder qual o combustível do motor diesel que, ao longo do seu ciclo de vida, gera menos emissões de CO2 na atmosfera, utilizando esse indicador como forma de quantificar os impactos ambientais desses produtos. Uma das principais conclusões é que as duas alternativas renováveis reduzem significativamente as emissões de CO2, quando comparadas com o diesel de origem fóssil. Isso acontece porque enquanto o combustível fóssil gera emissões de CO2 na sua etapa de matéria-prima (petróleo), os biocombustíveis capturam CO2 na etapa equivalente (plantas). Outra conclusão é em relação ao maior impacto de algumas etapas (como consumo e matéria prima) em relação a outras (como produção e transporte). Finalmente, concluiu-se também que a possibilidade de se utilizar o diesel verde sem a necessidade de mistura com o diesel de origem fóssil nos motores à combustão é uma vantagem ambiental desse biocombustível em relação ao biodiesel éster. / [en] LCA (Life Cycle Assessment) is a useful tool for assessing and exposing the growing environmental, economic, and social impacts caused by products and industrial processes, especially when they have a complex supply chain, as is the case with the main fuels of the diesel cycle (diesel A, FAME biodiesel, and HVO). Using different possible scenarios for the diesel fuel matrix in Brazil as context and a simplified LCA methodological structure described by ABNT as a tool, this study aims to answer which diesel engine fuel, over its life cycle, generates fewer CO2 emissions into the atmosphere, using this indicator to quantify the environmental impacts of these products. One of the main conclusions is that both renewable alternatives significantly reduce CO2 emissions when compared to fossil-origin diesel. This is because while fossil fuel generates CO2 emissions in its raw material stage (petroleum), biofuels capture CO2 in the equivalent stage (plants). Another conclusion relates to the greater impact of some stages (such as consumption and raw material) compared to others (such as production and transportation). Finally, it was also concluded that the possibility of using HVO without the need for blending with fossil-origin diesel in combustion engines is an environmental advantage of this biofuel over FAME biodiesel.