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The Homogeneous Charge Compression Ignition (HCCI) principle holds promise to increase efficiency and to reduce emissions from internal combustion engines. As HCCI combustion lacks direct ignition timing control and auto-ignition depends on the operating condition, control of auto-ignition is necessary. Since auto-ignition of a homogeneous mixture is very sensitive to operating conditions, a fast combustion phasing control is necessary for reliable operation. To this purpose, HCCI modeling and model-based control with experimental validation were studied. A six-cylinder heavy-duty HCCI engine was controlled on a cycle-to-cycle basis in real time by applying in-cylinder pressure feedback. A low-complexity physical model was developed, aiming at describing the major thermodynamic and chemical interactions in the course of an engine stroke. The model shows the importance of thermal interaction between the combustion and the cylinder walls.

Engine tests have been performed on a 9.6 liter spark-ignited engine fueled by natural gas and a mixture of 25/75 hydrogen/natural gas by volume. The scope of the work was to test two strategies for low emissions of harmful gases; lean burn operation and stoichiometric operation with EGR and a three-way catalyst. Most gas engines today, used in city buses, utilize the lean burn approach to achieve low NOx formation and high thermal efficiency. However, the lean burn approach may not be sufficient for future emissions legislation. One way to improve the lean burn strategy is to add hydrogen to the fuel to increase the lean limit and thus reduce the NOx formation without increasing the emissions of HC. Even so, the best commercially available technology for low emissions of NOx, HC and CO today is stoichiometric operation with a three-way catalyst as used in passenger cars.