<div class="htmlview paragraph">In view of the impending exhaust emission and fuel quality legislation in Europe, the motor industry is faced with developing engines giving low levels of HC and NO_x emissions while operating on unleaded gasoline and retaining good fuel economy.</div> <div class="htmlview paragraph">Ricardo have designed an advanced open chamber combustion system with vertical in-line valves, designated the “Nebula” combustion chamber. The design is based on converting the intake generated air motion into turbulence near to TDC, thus producing a fast burn characteristic. Initial development was carried out on a 86 × 86mm Hydra single cylinder research engine, where spark plug position and intake port swirl ratio were optimised. This work demonstrated potential of the “Nebula” concept which showed a considerable reduction in HC and NO_x emissions at part load.</div> <div class="htmlview paragraph">The “Nebula” combustion chamber has been applied to a 1.35 litre engine in a European vehicle. The engine is designed to use single point injection with microprocessor control of fuelling and ignition. The engine also utilises a simple variable geometry intake system which allows high swirl ratios to be used to give good lean mixture operation at light load, without degrading wide open throttle volumetric efficiency. Exhaust emissions and fuel economy potential are demonstrated over the ECE 15 drive cycle.</div>