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Initiation of Ignition in Ammunition
Published in Ajoy K. Bose, Military Pyrotechnics, 2021
The base bleed igniter composition ensures uninterrupted burning of base bleed propellant during flight. The base bleed propellant produces gases, thereby reducing the vacuum at the base on its ongoing trajectory and thus reduces the base drag, enabling the projectile to have higher range.
Numerical study of guide vane effects on reacting flow characteristics in a trapped vortex combustor
Published in Combustion Science and Technology, 2018
where is the static pressure, is the density, is the velocity, and is the reference area. The numerator is calculated through adding all the pressure forces in the axial direction. The dynamic pressure term is computed from the combustor inflow conditions, and the reference area is the cross section of the fore-body. The computed combustor drags of the four cases are shown in Figure 16. The benchmark case has a pressure drag coefficient of 1.1. When the square-tipped guide vane is added, the drag coefficient is increased by around 45% to 1.579. For the sharp-tipped guide vane, the pressure drag coefficient is increased by around 25% to 1.392, which is smaller than the square-tipped guide vane. For case 4 with both the sharp-tipped guide vane and a cavity fuel injection, the pressure drag coefficient is 1.151, with only about 5% increase compared with the benchmark case. From case 2 to case 3, the geometry modification of the guide vane from the square tip to the sharp tip provides 17% decrease in combustor drag. From case 3 to case 4 in which the guide vanes are the same, the cavity fuel injection provides additional 22% drag reduction. The drag reduction with cavity fuel injections in case 4 is very similar to the base bleed drag reduction method that is widely used in extending the range of projectiles. In the current cavity combustor, one large component of the drag comes from the low cavity pressure. This low pressure acting on the cavity front surface and the guide vane vertical surfaces lead to large aerodynamic drag. However, when the gaseous fuel is injected into the cavity (Lefebvre, 2010; Ezhil Kumar and Mishra, 2017), these fuel injections acting as the gas generator in the base bleeding projectile can elevate the pressure level inside the cavity so that drag can be reduced.