Numerical investigation of natural gas-diesel dual-fuel engine with different piston geometries and radial clearances

Abstract

Piston crevices are the major source of hydrocarbon emissions for spark ignition engine. It is similar for natural gas-diesel (NG-diesel) dual fuel engine, maybe even worse in high compression ratio and lean burn NG-diesel engine at low load. The aim of this paper is to numerically investigate combustion and methane emissions of YC-6K NG-diesel engine with different radial clearances. Four piston clearances (0.5 mm, 0.76 mm, 1.0 mm and 1.54 mm) and four different piston geometries were employed. Three diesel-spray-orientated (DSO) piston bowls were designed based on diesel injectors of YC-6K with the purpose of supplying more natural gas and air mixture to diesel spray jets, in addition, a protrusion-ring was designed at the bowl rim of DSO pistons to enhance methane flame propagation. The results showed that both in-cylinder pressure and heat release rate (HHR) of all three DSO pistons increased due to higher turbulence kinetic energy comparing to the original piston design (OPD). Methane emissions of pistons with radial clearance of 0.76 mm were lower than that of other radial clearances for DSO pistons.