Within this thesis is an investigation and appraisal of alternative automotive fuels, internal combustion engine technology and emission reduction techniques. A review of the developments in engine technology, with specific focus on improvements in engine efficiency and emission reductions was undertaken. Tighter emission legislation imposed after the Kyoto agreement has resulted in technological advances in the field of internal combustion engines improving the economy of modern motor vehicles while reducing their emissions of C02 and particulate matter. As part of an EU funded project entitled "Magnetic Movement Valve for Miller Cycle operation of engines", the application of a novel secondary valve apparatus to an internal combustion engine was investigated through the use of computer modelling. It was shown that the secondary valve concept is capable of controlling the output of an internal combustion engine, while increasing the operating efficiency and reducing the emission of NOx through the use of Miller cycle operation and throttle free load control. A development programme of the engine and the secondary valve apparatus, carried out in conjunction with EU project partners, resulted in a marketable engine incorporating the new technology which is now in production within Europe and the Far East. An engine test-bed facility was commissioned to investigate the emissions and performance of a diesel engine fuelled by a variety of biodiesel / diesel fuel blends. It was found that incremental addition of biodiesel to a low sulphur diesel fuel resulted in a decrease in engine power and an increase in fuel consumption, CO2 and NOx emissions. The particulates levels of pure biodiesel emissions were found to be much lower (by mass and number concentration) than that of the low sulphur diesel fuel. From analysis of the exhaust gases it was found that the average size of the particulates is larger for biodiesel fuel than for the low sulphur diesel fuel.