Porous Versus Porthole Fuel Injection in a Radical Farming Scramjet: Numerical Analysis

Numerically computed engine performance of a nominally two-dimensional radical farming scramjet with porous (permeable carbon/carbon ceramic) and porthole fuel injection is presented. Inflow conditions with Mach number, stagnation pressure, and enthalpy of 6.44, 40.2 MPa, and 4.31 MJ/kg, respectively, and fuel/air equivalence ratio of 0.44 were maintained, along with engine geometry. Hydrogen fuel was injected at an axial location of 92.33 mm downstream of the leading edge for each investigated injection method. Results from this study show that porous fuel-injection results in enhanced mixing and combustion compared to porthole fuel injection. This is particularly evident within the first half of the combustion chamber, where porous fuel injection resulted in mixing and combustion efficiencies of 76 and 63%, respectively. At the same location, porthole fuel injection resulted in efficiencies respectively of 58 and 46%. Key mechanisms contributing to the observed improved performance were the formation of an attached oblique fuel-injection shock and associated stronger shock-expansion train ingested by the engine, enhanced spreading of the fuel in all directions, and a more rapidly growing mixing layer.