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.
The bioCNG with 90% of methane makes a potential renewable alternative of CNG for the application in dual-fuel diesel engine. The bioCNG is to be inducted in the manifold through port injection. The work is aimed to find the optimum port length and port-injector diameter. The objective is to mix bioCNG homogenously with air, before entering the engine. This would create an opportunity for major replacement of diesel to reduce the running cost of the vehicle. The two injector diameters (7 mm and 10 mm) and four port lengths (0 mm, 100 mm, 150 mm and 200 mm) are investigated. The manifold has a diameter of 28.5 mm and the port-injector is inclined at 35° to the manifold axis. The geometries are simulated in ANSYS Workbench 19.2, and post-processed in Tecplot. The results show that the port length of 200 mm with an injector diameter of 7 mm delivered homogeneous mixture in dual-fuel mode.
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