| Although the effect of biodiesel properties on the performance and emissions of compression ignition engines are being studied since several decades ago, there is still some lack of knowledge, especially regarding oxidation process or NOx and non-regulated emissions. This situation contributes to create an opposition from car and fuels manufactures, making difficult to reach the targets that most of the countries have in the use of these biodiesel fuels. The present thesis deepens on this subject by, on the one hand, a complete, novel bibliographic study of properties, performance and emissions and, on the other hand, a collection of results derived from new experimental tests in an automotive engine running under both stationary and transient conditions.; The body of work collected and analyzed in the bibliographic section is presented in an orderly manner, covering, for each of the properties or emissions studied, (a) the different effects of diesel and biodiesel fuels, (b) the effect of the biodiesel raw material, (c) the trend (linear, asymptotic) when blending diesel and biodiesel fuels and (d) even the effect of common substances found in the biodiesel fuels (ethanol, glycerides, peroxides,...). Those properties (cold flow, oxidation stability) and emissions (nitrogen oxides, particle sizes) which are widely recognized to be the most problematic and unknown have been extensively studied. In general, biodiesel fuels results in poor cold flow properties, poor oxidation stability characteristics and a reduction in particulate emissions. On the contrary, some discrepancies were found regarding NOx emissions and particle size.; Regarding the experimental tests, these were carried out in a turbocharged, 2.2 liters, direct injection diesel engine using four biodiesel fuels with different origin and unsaturation level, pure and blended in 30 and 70% with a reference diesel fuel. This fuel matrix was designed to look not only for the effect of biodiesel fuels but also for the effect of the origin of the biodiesel fuel (more or less unsaturated). Conclusions were obtained by applying statistics methods Sharp reductions in particulate matter and opacity (even greater in transient than in stationary conditions) were found when testing biodiesel fuels. Unsaturation level was found to have significant effects in NOx, particle size and combustion timing. |
