1) The document discusses improving the air-swirl ratio in a 4-stroke diesel engine through modifications to the inlet poppet valve to enhance engine performance and reduce harmful emissions. 2) The researchers designed and 3D modeled a modified inlet poppet valve with four balls attached to the seat surface to disrupt airflow and create turbulence. 3) Experiments were conducted on a single cylinder diesel engine test rig to compare the performance and emissions of the standard and modified inlet valves. The modified valve improved combustion and reduced emissions of hydrocarbons, carbon monoxide and nitrogen oxides but lowered efficiency slightly.