Rotating detonation engine multi-stage mixer

1. A fuel mixer for mixing a fuel and an oxidizer prior to detonation in a rotating detonation engine, comprising:

a combustion channel configured to transport a final mixture of the fuel and the oxidizer to an unobstructed annulus in which a rotating detonation wave travels at least one of clockwise or counterclockwise along an entire circumference of the annulus for combustion in the annulus;

an inner annulus located radially inward from the unobstructed annulus and configured to transport at least a portion of the oxidizer towards the unobstructed annulus of the combustion channel;

a first fuel outlet configured to transport a first portion of the fuel;

a second fuel outlet positioned downstream from the first fuel outlet and configured to transport a second portion of the fuel;

a mixture channel positioned upstream from the combustion channel and the unobstructed annulus and downstream from the inner annulus, at least partially located in the inner annulus, and configured to receive the first portion of the fuel from the first fuel outlet and to transport a first mixture having the first portion of the fuel and at least some of the oxidizer;

a transport channel extending from the inner annulus to the combustion channel and configured to transport the first mixture having the first portion of the fuel and the at least some of the oxidizer; and

a secondary outlet positioned upstream from the combustion channel and the unobstructed annulus and configured to output a supplemental mixture of the fuel and the oxidizer that includes at least one of the fuel or the oxidizer into the transport channel such that the first mixture and the supplemental mixture combine in the combustion channel to form the final mixture.

2. The fuel mixer of claim 1 , wherein the first mixture has a first fuel-air equivalence ratio that is greater than or less than 1 and the final mixture has a second fuel-air equivalence ratio that is closer to 1 than the first fuel-air equivalence ratio.

3. The fuel mixer of claim 1 , wherein the combustion channel is defined by the unobstructed annulus of the rotating detonation engine.

4. The fuel mixer of claim 1 , wherein the combustion channel provides a volume for the final mixture to be combined prior to circumferential passage of the rotating detonation wave.

5. The fuel mixer of claim 1 , wherein the mixture channel is positioned upstream from the secondary outlet, the first mixture has a first fuel-air equivalence ratio, and a difference between the first fuel-air equivalence ratio and 1 is sufficiently great that the first mixture fails to detonate upstream from the secondary outlet.

6. The fuel mixer of claim 1 , further comprising at least one tertiary outlet positioned upstream from the combustion channel and configured to transport at least one tertiary mixture of the fuel and the oxidizer that includes at least one of the fuel or the oxidizer such that the first mixture, the supplemental mixture, and the tertiary mixture combine in the combustion channel to form the final mixture.

7. The fuel mixer of claim 1 , wherein the first mixture has a first fuel-air equivalence ratio that is selected based on an oxidizer type of the oxidizer, a fuel type of the fuel, a pressure experienced at the mixture channel, and a temperature experienced at the mixture channel.

8. A rotating detonation engine, comprising:

an unobstructed annulus configured to receive a final mixture of a fuel and an oxidizer such that a rotating detonation wave in the unobstructed annulus travels at least one of clockwise or counterclockwise along an entire circumference of the unobstructed annulus for combustion in the unobstructed annulus;

an inner annulus located radially inward from the unobstructed annulus and configured to transport at least a portion of the oxidizer towards the unobstructed annulus of the combustion channel;

a combustion channel configured to fill with the final mixture of the fuel and the oxidizer for combustion in the unobstructed annulus;

a first fuel outlet configured to transport a first portion of the fuel;

a second fuel outlet positioned downstream from the first fuel outlet and configured to transport a second portion of the fuel;

a mixture channel positioned upstream from the combustion channel and the unobstructed annulus and downstream from the inner annulus, at least partially located in the inner annulus, and configured to receive the first portion of the fuel from the first fuel outlet and to transport a first mixture having the first portion of the fuel and at least some of the oxidizer;

a transport channel extending from the inner annulus to the combustion channel and configured to transport the first mixture having the first portion of the fuel and the at least some of the oxidizer; and

a secondary outlet positioned upstream from the combustion channel and the unobstructed annulus and configured to output a supplemental mixture of the fuel and the oxidizer that includes at least one of the fuel or the oxidizer into the transport channel such that the first mixture and the supplemental mixture combine in the combustion channel to form the final mixture.

9. The rotating detonation engine of claim 8 , wherein the first mixture has a first fuel-air equivalence ratio that is greater than or less than 1 and the final mixture has a second fuel-air equivalence ratio that is closer to 1 than the first fuel-air equivalence ratio.

10. The rotating detonation engine of claim 8 , wherein the combustion channel is defined by the unobstructed annulus of the rotating detonation engine.

11. The rotating detonation engine of claim 8 , wherein the combustion channel provides a volume for the final mixture to be combined prior to circumferential passage of the detonation.

12. The rotating detonation engine of claim 8 , wherein the mixture channel is positioned upstream from the secondary outlet, the first mixture has a first fuel-air equivalence ratio, and a difference between the first fuel-air equivalence ratio and 1 is sufficiently great that the first mixture fails to detonate upstream from the secondary outlet.

13. The rotating detonation engine of claim 8 , further comprising at least one tertiary outlet positioned upstream from the combustion channel and configured to transport at least one tertiary mixture of the fuel and the oxidizer that includes at least one of the fuel or the oxidizer such that the first mixture, the supplemental mixture, and the tertiary mixture combine in the combustion channel to form the final mixture.

14. The rotating detonation engine of claim 8 , wherein the first mixture has a first fuel-air equivalence ratio that is determined based on an oxidizer type of the oxidizer, a fuel type of the fuel, a pressure experienced at the mixture channel, and a temperature experienced at the mixture channel.

15. A gas turbine engine, comprising:

a turbine section configured to convert exhaust into torque;

a compressor section configured receive the torque from the turbine section and to utilize the torque to compress fluid; and

a rotating detonation engine configured to generate the exhaust and having:

an unobstructed annulus configured to receive a final mixture of a fuel and an oxidizer such that a rotating detonation wave in the unobstructed annulus travels at least one of clockwise or counterclockwise along an entire circumference of the unobstructed annulus for combustion in the unobstructed annulus,

an inner annulus located radially inward from the unobstructed annulus and configured to transport at least a portion of the oxidizer towards the unobstructed annulus of the combustion channel,

a combustion channel configured to fill with the final mixture of the fuel and the oxidizer for combustion in the unobstructed annulus,

a first fuel outlet configured to transport a first portion of the fuel,

a second fuel outlet positioned downstream from the first fuel outlet and configured to transport a second portion of the fuel,

a mixture channel positioned upstream from the combustion channel and the unobstructed annulus and downstream from the inner annulus, at least partially located in the inner annulus, and configured to receive the first portion of the fuel from the first fuel outlet and to transport a first mixture having the first portion of the fuel and at least some of the oxidizer,

a transport channel extending from the inner annulus to the combustion channel and configured to transport the first mixture having the first portion of the fuel and the at least some of the oxidizer, and

a secondary outlet positioned upstream from the combustion channel and the unobstructed annulus and configured to output a supplemental mixture of the fuel and the oxidizer that includes at least one of the fuel or the oxidizer into the transport channel such that the first mixture and the supplemental mixture combine in the combustion channel to form the final mixture.

16. The gas turbine engine of claim 15 , wherein the mixture channel is positioned upstream from the secondary outlet, the first mixture has a first fuel-air equivalence ratio, and a difference between the first fuel-air equivalence ratio and 1 is sufficiently great that the first mixture fails to detonate upstream from the secondary outlet.

17. The gas turbine engine of claim 15 , wherein the rotating detonation engine further includes at least one tertiary outlet positioned upstream from the combustion channel and configured to transport at least one tertiary mixture of the fuel and the oxidizer that includes at least one of the fuel or the oxidizer such that the first mixture, the supplemental mixture, and the tertiary mixture combine in the combustion channel to form the final mixture.