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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.

Biodiesel blends are promising alternatives to diesel fuel, but, reduced quantitative information is available on the impact of biodiesel on engine systems behaviour, durability and economical aspects in fleet cost management. A representative sample of urban buses fuelled with B50 was compared with the same type of vehicle fuelled with conventional petroleum fuel. The objective was to assess the effects of B50 upon important parameters such as: fuel consumption, power loss and drivability; the effects on the fuel system and engine oil and the implications regarding the maintenance programme. These implications could be very relevant upon a fleet manager's decision to select biodiesel as an alternative fuel. The results obtained show that there was no difference in the serviceability of the buses fuelled with B50 compared with those fuelled with petroleum diesel fuel, and additionally, no change in the maintenance programme was required for this type of B50 fuel.

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).

This paper is structured into two different parts: Firstly, it describes a methodology to evaluate wear conditions in internal combustion engines in order to go beyond the classical evaluation based on specified wear concentration limits provided by engine manufacturers or commercial oil laboratories. The proposed methodology uses spectrometric wear debris measurement data and typical maintenance data to obtain a more representative parameter of wear condition, defined as “compensated wear rate”, that takes into account particular engine operating conditions affecting wear concentration measurements. Later, an evaluation of this compensated wear rate is carried out using statistical criteria and considering individual engine characteristics such as engine age, type of service, engine metallurgy, environmental conditions of work etc.

This paper presents a study and review of the data collected in an Engine Fault Diagnosis System using oil analysis, used for diagnose different industrial vehicle engines (trucks, buses, road construction equipment, etc.). This system is being used since the beginning of the 1990s decade. The information acquired in this system has generated an important database that collects the information about the oil status at drain moment and further collateral information. Knowledge about oil properties (viscosity, TBN, detergency), and oil contamination, (insolubles content, soot from combustion, fuel dilution, and water) during engine operation, provide an important information about lubricants efficiency, optimal drain period and engine status that it has a direct influence on vehicles running cost. The study has been performed with a statistical tool which allows the characterisation of the main parameters of oil behaviour, in addition to the relationship between them.

One of the most important handicaps when using the oil analysis technique for predictive maintenance, is the processing of the results. The oil analysis technique allows obtaining relevant information about the state of the lubricant, the engine and other auxiliary elements. However, it is necessary, to process this information and to define the references with which the numerical results obtained must be compared. In the system considered the different analyses performed on the oil sample have been divided into three different types: oil properties, oil contaminants and engine wear elements. Consequently, each type of result is evaluated in a different way. Finally, the evaluation process of the different analyses allows the system to qualify each analysis with a numerical value which will be used in an expert system.