Effect of Different Parameters on Spray Tip Penetration in a Constant Volume Combustion Chamber

A comprehensive work has been carried out by performing simulations on a constant volume combustion chamber (CVCC) where a spray of liquid n-heptane is injected in a volume of compressed air maintained at a given pressure and temperature, thereby initiating combustion. The computation time is set to 2.5 ms, time step is 1 micro second and 12000 parcels are injected for each computational cycle. The geometry consists of a block filled with air with a 0.02×0.02 meter base and a length of 0.1 meter. An injector which is a single hole unit injector (hollow cone) with diameter 140 micrometer and outer cone angle of 15o, modelled for a common rail injection system with a given fuel mass flow rate is centrally placed on the top boundary where n-heptane (C7H16) fuel spray is injected. Unit injector is also used in certain simulations. Standard k-ϵ model is used for turbulence. OpenFOAM is used for simulating spray combustion behaviour. The solver used for implementation is dieselFoam. Finite volume method is used to numerically solve the Navier-Stokes equations for any 3D grid of unstructured polyhedral cells. It is observed that ReitzKHRT Break up model together with Standard evaporation model and Trajectory collision model provides the best result for spray tip penetration length (STPL). This combination is used with subsequent simulations. Also, an increase in ambient temperature from 800K to 1500K leads to a higher flame temperature, and enhancement in STPL (for an optimum value of 1000K), further increase in ambient temperature decreases STPL. Higher values for STPL are obtained for an outer cone angle of 20o. As ambient pressure is increased, the flame temperature increases, however STPL decreases.An increase in injection pressure leads to an enhanced STPL.