The combustion and emissions performance of fuel blends in modern combustion systems has been investigated with the intention of reducing emissions, improving efficiency and assessing the suitability of future automotive fuels. The combustion systems used in this study include Homogeneous Charge Compression Ignition (HCCI) and Direct Injection Spark Ignition (DISI). By adding a small quantity (10%) of diesel to gasoline, the HCCI combustion of this ‗Dieseline‘ mixture shows a 4% increase in the maximum and a 16% reduction in the minimum loads (IMEP) achievable. The NOX emissions are reduced, with greater than 30% savings seen for high engine loads. The addition of bio-fuels (ethanol and 2,5 di-methylfuran) to gasoline in HCCI combustion resulted in reduced ignitability giving rise to a 0.25 bar IMEP reduction of the maximum load. A 70% increase in NOX emissions is seen at an engine load of 3.5 bar IMEP. The addition of ethanol and to a lesser extent 2,5 di-methylfuran (DMF) to gasoline in DISI combustion shows increased combustion efficiency. The NOX emissions are reduced with ethanol, but are increased with the addition of DMF. At wide open throttle the bio-fuels show up to a 3 percentage point increase in efficiency through the use of more favourable spark timings brought about by the increased octane ratings and enthalpies of vaporisation. The PM emissions from DISI combustion can be reduced by up to 58% (mass) with the addition of ethanol. The soluble organic fraction forms a significant part of the total PM, particularly for the higher ethanol blends at wide open throttle. The addition of DMF however increases the total PM by up to 70% (mass) through the incomplete combustion of the ring structure.