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Pure biodiesel is non-toxic, biodegradable and greenhouse gas neutral alternative fuel with potential successful future but reduced quantitative information is available about the impact of biodiesel on engine durability and long period usage effects. In this study, a commercial light duty Diesel engine installed on an engine test bench has been operated fuelled with pure biodiesel (B100 referred to the EN-14214 standard) during a period test of 300 hours in order to analyze engine performance and components behavior. A engine characterization has been completed using conventional diesel fuel (EN 590). Then, following a specific defined operation cycle and fuelled with pure biodiesel, a study over different engine components such as: engine oil, fuel filters, Diesel Particulate Filter (DPF), so on, has been done in order to obtain possible negative effects and modifications required over maintenance policies applied to them.

Compressed natural gas (CNG) is a promising alternative fuel due to several main reasons, specially the strict engine emission regulations all over the world. This has made that lot's of cities have decided to use CNG as an alternative fuel in their urban transport fleets or in other urban tasks. Nevertheless, due to the recent implementation of the CNG technology in automotive sector, several problems related to lubrication have been detected, mostly affecting a reduction of the oil drain period and these problems showed no relationship with a particular fleet nor with the lubricant's brand used. These effects will have a very important weight on fleet manager's decision to select CNG as an alternative fuel, thus this reduction does not only increase the cost in engine oil, there are other maintenance actions referred to this basic period of oil drain, thus also increases other more significant costs.

This paper reports the results obtained in the ECOBUS Project. This project has been supported by the LIFE Program, one of the spearheads of European Union's environmental policy. The main aim for this project was to convert used cooking oil into biodiesel and then use this biodiesel in urban buses, contributing to reducing in one hand waste cooking oil that can create problems in the drainage city system and water contamination and on the other hand reducing engine polluting emissions. Departamento de Máquinas y Motores Térmicos (DMMT) facilities at the Universidad Politécnica de Valencia (Spain) were used to conduct detailed performance and emission measurements in a Diesel engine similar to those used by the urban transport operator in Valencia (Empresa Municipal de Transporte, EMT). The test engines were operated with conventional Diesel fuel (EN 590) and three different biodiesel blends: 30, 50 and 70%, using the pure biodiesel obtained from used cooking oil (EN 14214).