Nishida, K., Ogawa, T., Hashizume, T., Ishiyama, S. et al., "Small Bore Diesel Engine Combustion Concept," SAE Technical Paper 2015-01-0788, 2015, doi:10.4271/2015-01-0788.
Small bore diesel engines often adopt a two-valve cylinder head and a non-central injector layout to expand the port flow passage area. This non-central injector layout causes asymmetrical gas flow and fuel distribution, resulting in worse heat losses and a less homogenous fuel-air mixture than an equivalent four-valve cylinder head layout with a central injector. This paper describes the improvement of piston bowl geometry to achieve a more homogeneous gas flow and fuel-air mixture. This concept reduced fuel consumption by 2.5% compared to the original piston bowl geometry, while also reducing NOx emissions by 10%.