Liquid rocket engine injector with variable flow area
A variable flow area injector for a liquid rocket engine. The injector has a poppet with a variable outer width portion and a housing with a variable inner width portion. An annular flow path is defined between the variable width portions. Increased throttling of the engine passively increases the annular flow area of the injector by forcing the poppet in a distal direction. Decreased throttling allows a restoring spring to move the poppet in a proximal direction to decrease the annular flow area. A bellows can be included to dampen movement of the poppet. The bellows may be in a propellant-filled cavity separate from the main propellant flow path and have a series of openings through which the separate propellant flows.
1. An injector for a rocket combustion chamber, the injector comprising:
a housing defining a longitudinal axis and having a proximal end and a distal end, the housing defining a variable inner width;
a poppet configured to move within the housing along the longitudinal axis, wherein a variable annular flow path for a propellant is located between a variable outer width of the poppet and the variable inner width of the housing; and
a spring configured to bias the poppet along the longitudinal axis,
wherein movement of the poppet toward the proximal end causes a cross-sectional area of the variable annular flow path to decrease, and wherein movement of the poppet toward the distal end causes the cross-sectional area of the variable annular flow path to increase, and
wherein the housing further comprises a plurality of ports distributed annularly about the housing through which the propellant enters the housing.
2. The injector of claim 1 , wherein the plurality of ports are upstream of the variable annular flow path.
3. The injector of claim 1 further comprising a bellows configured to dampen movement of the poppet.
4. The injector of claim 3 , wherein the bellows is positioned at the proximal end of the housing.
5. The injector of claim 3 , wherein the bellows comprises one or more openings configured to allow propellant to flow into and out of an interior of the bellows along a flow path that is outside of the variable annular flow path.
6. The injector of claim 1 , wherein the spring causes a first force on the poppet biasing the poppet toward the proximal end, and wherein a flow of the propellant along the variable annular flow path causes a second force on the poppet biasing the poppet toward the distal end.
7. The injector of claim 1 further comprising a first stop and a second stop configured to limit travel of the poppet along the longitudinal axis within the housing to thereby limit a maximum area and a minimum area of the variable annular flow path.
8. An injector for a rocket combustion chamber, the injector comprising:
a flow path configured for a propellant to flow therethrough, the flow path bounded outwardly by an inner surface of a housing protruding inwardly, the inner surface having a variable housing width section along a longitudinal direction, the flow path bounded inwardly by an outer surface of a poppet protruding outwardly, the outer surface having a variable poppet width section along the longitudinal direction, the variable housing width section and the variable poppet width section defining therebetween a variable annular flow path section; and
a spring disposed at a proximal end of the housing and causing a biasing force on the poppet,
wherein movement of the poppet toward the proximal end of the housing along the longitudinal direction causes a reduction in a cross-sectional area at a first location of the variable annular flow path section, and movement of the poppet toward a distal end of the housing along the longitudinal direction causes an increase in the cross-sectional area at the first location of the variable annular flow path section.
9. The injector of claim 8 , wherein movement of the poppet toward the proximal end causes the outer surface of the poppet to move closer to the inner surface of the housing, and wherein movement of the poppet toward the distal end causes the outer surface of the poppet to move away from the inner surface of the housing.
10. The injector of claim 8 further comprising entrance ports distributed about a sidewall of the housing upstream of the variable annular flow path section and configured to receive the propellant therethrough.
11. The injector of claim 8 , wherein the cross-sectional area at the first location of the variable annular flow path section is circular.
12. The injector of claim 8 , wherein the cross-sectional area at the first location of the variable annular flow path section has a maximum cross-sectional area of no more than about 0.250 in 2 and a minimum cross-sectional area of no less than about 0.008 in 2 .
13. The injector of claim 8 further comprising a bellows configured to dampen movement of the poppet and comprising a series of openings configured to receive propellant into an interior of the bellows.
14. The injector of claim 8 , wherein the variable housing width section reduces in width in the longitudinal direction to a minimum width throat portion and increases in width from the minimum width throat portion in the longitudinal direction.
15. The injector of claim 8 , wherein the variable poppet width section increases in width to a maximum width portion and then decreases in width from the maximum width portion in the longitudinal direction.
16. A method of passively varying a flow rate of a propellant injected into a rocket combustion chamber, the method comprising:
receiving the propellant into a housing of an injector, the housing defining a longitudinal axis, a proximal end and a distal end;
applying a biasing force with a spring to a poppet disposed within the housing; and
causing a movement of the poppet within the housing along the longitudinal axis in response to a change in flow rate of the propellant,
wherein the propellant enters the housing at a location between the proximal end and an annular flow area between the poppet and the housing, wherein the movement of the poppet toward the proximal end causes an outer surface of the poppet to move closer to an inner surface of the housing at the annular flow area, and wherein movement of the poppet toward the distal end causes the outer surface of the poppet to move away from the inner surface of the housing at the annular flow area.
17. The method of claim 16 further comprising dampening movement of the poppet with a bellows.
18. The method of claim 16 further comprising varying the biasing force from the spring on the poppet as the poppet moves.
19. The method of claim 16 further comprising maintaining a ratio of A) a pressure drop across the injector to B) a pressure within the rocket combustion chamber in fluid communication with the injector within a target range of 15% to 25% across a range of the flow rate of the propellant.