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Today, the potential of HCCI engines, i.e., their high efficiency with low NO and particulate emissions, is very well known. Besides this potential, the problems that are related to HCCI engines, particularly the control, are also known issues. In order to be able to develop and assess the control strategies for HCCI engines, one needs models for the control development. In addition to mean value models crank-angle resolved control-oriented computer codes have also been developed lately (e.g., Boost RT). In these codes, complex 1D gas dynamics and complex combustion models are omitted, while the in-cylinder calculation is crank-angle resolved. Simple combustion models are variations of Vibe and the combustion defined by a table. Since the HCCI combustion is controlled by the state of the gas in the cylinder, parameters of Vibe functions depend on the factors that define this state.

The paper presents the experimental study of an active pre-chamber volume variations on engine performance and emissions. The experiments were performed on a test setup equipped with a single cylinder engine. The modular and custom-made pre-chamber design was used, enabling the variation of pre-chamber volume in the range of 3-5% of clearance volume. During the variation of pre-chamber’s geometrical parameters, the ratio of total nozzle area to the pre-chamber volume was fixed at a value of approximately 0.033 cm-1. At a given pre-chamber volume the variation of engine load was achieved by the change of excess air ratio in the main chamber from stochiometric mixture to lean limit, while the engine speed was fixed to 1600 rpm. For each pre-chamber variation and on each of the investigated operating points, a spark sweep was performed to obtain the highest indicated efficiency while satisfying the imposed restrictions regarding combustion stability and knock occurrence.