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In HCCI you do not have the same control of the combustion like in SI and Diesel engines. Controlling the start of a combustion event is a difficult task and requires feedback from previous cycles. This feedback can be retrieved from ion current measurements. By applying a voltage over the spark gap, ions will lead a current and a signal that represents the combustion in the cylinder will be retrieved. Voltages of 450 V were used. The paper describes a new method to enhance the combustion phasing from the Ion current trace in HCCI engines. The method is using the knowledge of how the signal should look. This is known due to the fact that the shape of the ion current signal is similar from cycle to cycle. This new observation is shown in the paper. Also the correlation between the ion current and CA50 was studied. Later the signals have been used for combustion feedback.

Homogenous charge compression ignition (HCCI) has been identified as a promising way to increase the efficiency of the spark-ignited engine, while maintaining low emissions. The challenge with HCCI combustion is excessive pressure rise rate, quantified here with Ringing Intensity. Turbocharging enables increased dilution of the charge and thus a reduction of the Ringing Intensity. The engine used is an SI four cylinder base with 2.2L displacement and is equipped with a turbocharger. Combustion phasing control is achieved with individual intake/ exhaust cam phasing. Fuel injection with spray guided design is used. Cycle resolved combustion state is monitored and used for controlling the engine either in closed or open loop where balancing of cylinder to cylinder variations has to be done to run the engine at high HCCI load. When load is increased the NOx levels rise, the engine is then run in stoichiometric HCCI mode to be able to use a simple three-way catalyst.

This work investigates the performance potential of an engine running with partially premixed combustion (PPC) using commercial diesel engine hardware. The engine was a 2.01 SAAB (GM) VGT turbocharged diesel engine and three different fuels were run - RON 70 gasoline, RON 95 Gasoline and MK1 diesel. With the standard hardware an operating range for PPC from idle at 1000 rpm up to a peak load of 1000 kPa IMEPnet at 3000 rpm while maintaining a peak pressure rise rate (PPRR) below 7 bar/CAD was possible with either RON 70 gasoline and MK1 diesel. Relaxing the PPRR requirements, a peak load of 1800 kPa was possible, limited by the standard boosting system. With RON 95 gasoline it was not possible to operate the engine below 400 kPa. Low pressure EGR routing was beneficial for efficiency and combined with a split injection strategy using the maximum possible injection pressure of 1450 bar a peak gross indicated efficiency of above 51% was recorded.