Abstract: An internal combustion engine system is provided. The system includes an engine defining a combustion chamber, a clean emission module and an air supply unit. The clean emission module is fluidly connected to an exhaust conduit from the combustion chamber. The air supply unit is configured to supply air into the combustion chamber and includes a compressor and a flow control device provided between the compressor and the combustion chamber. The compressor is configured to receive air from an air inlet via a first passage and supply the compressed air into the combustion chamber via a second passage. The flow control device is configured to selectively reduce the supply of compressed air into the combustion chamber such that an air fuel ratio in the combustion chamber is maintained between 15:1 to 18:1 at 20-90% engine load during a regeneration period for the clean emissions module.