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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.

It is a well-known fact that HCCI combustion offers the possibility of achieving high efficiency with low emissions, but with the challenges in combustion control and ability to adjust to changing environmental conditions. To resolve the aforementioned challenges, a pre-chamber induced homogeneous charge compression ignition (PC-HCCI) combustion mode was experimentally tested with aim of providing initial operating boundaries in terms of combustion stability and obtaining initial performance results. The single cylinder engine equipped with active pre-chamber and compression ratio (CR) of 17.5 was fueled by gasoline. The initial experiments were performed at the engine speed of 1600 rpm with intake air temperatures varied from 33°C to 100°C to verify the possibility of achieving the PC-HCCI combustion mode and to compare the achieved engine performance and emission results with both PCSI and pure HCCI combustion modes used as reference cases.