Emission characterization of small entrainment ratio cooling of engine exhaust gas in climate laboratory postprint

Abstract: The objective of this paper is to study the influencing factors and laws regarding the cooling and emission of engine exhaust with a low entrainment ratio in a climate laboratory. For a typical engine with a small bypass ratio, a numerical simulation method is adopted, taking into account the composition of the engine's tail gas and the variable-specific heat properties of the fluid. The influences of the exhaust pipe diameter, the distance of the pipe inlet, and spray cooling on the emission characteristics of engine tail gas with a low entrainment ratio are analyzed. The simulation results show that the entrainment ratio is linearly related to the exhaust pipe diameter and increases as the pipe diameter increases. The distance of the pipe inlet has relatively little influence on the entrainment ratio, yet there exists an optimal value for it. Spray cooling disrupts the surge structure of the entrainment flow field, reducing the velocity loss of the tail-gas jet and increasing the entrainment ratio.