Effect of vibration and pressure on the air-bioCNG mixture inside the manifolds of dual-fuel diesel engines

Abstract

The vibration generated by diesel engines may influence air and gaseous fuel mixing in dual-fuel mode. This study is performed on the manifolds of single and twin-cylinder engines in diesel-bioCNG dual-fuel mode. It examines the effect of the engine vibration and variable manifold pressure on the flow behaviour of the air-bioCNG mixture. The objective is to observe the flow inside the manifolds and mixture quality at the outlet. The mentioned work has found little attention till date. The computational comparison of the flow characteristics inside the intake manifold of the single-cylinder engine is done for an F-shape manifold of the twin-cylinder engine during suction stroke. The experiments are conducted to record both the engines' vibration signature and cycle data. For this, the same operating parameters are maintained: compression ratio of 16.5, engine speed of 1500 rpm, engine load range (0 Nm to 34 Nm) and 80% bioCNG substitution. It employs the boundary conditions, such as the vibration amplitude along three axes, variable manifold pressure, and the mass flow rates of air and bioCNG. The parameters to analyse the mixture flow are pressure, velocity, turbulence, helicity and mass fraction of CH4. The mixture at the manifold outlet of the single-cylinder engine improved to average uniformity index of 0.9924, indicating better homogeneity. Further, the manifold of twin-cylinder engine attained the indexes of 0.1484 and 0.2401 for its two cylinders, showing non-homogeneity.