JP6085472B2 - Scramjet engine and combustion control method - Google Patents

Description

  The present invention relates to a scramjet engine. In particular, the present invention relates to combustion control in a scramjet engine.

  A ramjet engine is known as a type of jet engine. A ramjet engine uses air compression by ram pressure associated with high-speed flight instead of a mechanical compressor. More specifically, air compression is performed at the inlet by ram pressure, and supersonic airflow is decelerated to subsonic speed. In the combustion chamber, fuel is injected with respect to the subsonic air flow, and combustion (subsonic combustion) occurs. Such a ramjet engine is limited to a high speed region such as a supersonic region (Mach 3 to 5 is most efficient), but since a mechanical compressor is not used, the viewpoint of weight reduction of the fuselage To preferred.

  On the other hand, when the flying speed exceeds Mach 5, when the supersonic airflow sucked is decelerated to subsonic speed, the pressure loss of the sucked airflow and the air resistance related to the aircraft increase, which is inefficient (worst The engine will be difficult to operate). Therefore, a technique for supersonic combustion is also proposed in which the supersonic air flow that has been sucked is guided to the combustion chamber in supersonic speed. This is called a scramjet (supersonic combustion ramjet) engine.

  FIG. 1 schematically shows the configuration of a typical scramjet engine. The supersonic air flow sucked into the inlet 110 is guided to the combustion chamber 120 while remaining supersonic. In the combustion chamber 120, fuel is injected with respect to the supersonic air flow, and combustion (supersonic combustion) occurs. Then, the combustion gas generated by the combustion is ejected from the nozzle 130, and a propulsive force is obtained by the reaction. In such a scramjet engine, the air flow is not decelerated below the sonic speed over the entire engine area from intake to exhaust, so that high engine performance is maintained in a wide Mach number range.

  However, in the case of a scramjet engine, the time required for the supersonic air flow to pass through the combustion chamber 120 is as short as several milliseconds. Therefore, how quickly the fuel is ignited, that is, improvement in ignitability is one of the important issues.

  Patent Document 1 (Japanese Patent Laid-Open No. 8-334213) discloses a two-stage injection method aimed at improving the ignitability in a supersonic combustor. Specifically, as shown in FIG. 2, the two fuel injection units 101 and 102 are arranged separately on the upstream side and the downstream side along the direction of the mainstream air. Of the two fuel injection units, the fuel injection unit 102 on the downstream side mainly injects fuel, and the fuel injection unit 101 on the upstream side injects fuel in an auxiliary manner. By injecting the main fuel from the downstream fuel injection section 102 into the supersonic airflow, an oblique shock wave 103 is formed as shown in FIG. Further, a rotating flow is generated before the oblique shock wave 103 to form a circulation region 104. A small amount of auxiliary fuel injected from the upstream fuel injection section 101 flows along the combustion chamber wall and is supplied to the circulation region 104. As a result, the fuel concentration in the circulation region 104 increases and the self-ignition temperature decreases. That is, the ignitability is improved.

JP-A-8-334213

  In the case of the method shown in FIG. 2, flame holding is mainly performed in the downstream region (region where the flow velocity is relatively low) of the oblique shock wave 103. That is, the flame holding position is determined depending on the position of the fuel injection unit 102 on the downstream side. However, from the viewpoint of increasing the engine specific thrust or downsizing the engine, it is desirable to perform the flame holding on the upstream side as much as possible.

  One object of the present invention is to provide a new combustion control system for a scramjet engine.

  [Means for Solving the Problems] will be described below using the numbers and symbols used in [Best Mode for Carrying Out the Invention]. These numbers and symbols are added in parentheses in order to clarify the correspondence between the description of [Claims] and [Best Mode for Carrying Out the Invention]. However, these numbers and symbols should not be used for the interpretation of the technical scope of the invention described in [Claims].

  In one aspect of the invention, a scramjet engine is provided. The scramjet engine includes a first fuel injection section (10) that injects the first fuel (11) into the combustion chamber (120), and a first fuel injection section (10) along the direction (X) of the mainstream air. A second fuel injection unit (20) that is provided downstream and injects the second fuel (21) into the combustion chamber (120), and controls the injection amounts of the first fuel (11) and the second fuel (21). And a control unit (30). The control unit (30) determines the injection amount of the second fuel (21) in the second period (P2) after the first period (P1), and the injection of the second fuel (21) in the first period (P1). The amount and the injection amount of the first fuel (11) in the second period (P2) are reduced.

  In another aspect of the present invention, a combustion control method for a scramjet engine is provided. The scramjet engine includes a first fuel injection section (10) that injects a first fuel (11) into a combustion chamber (120), and a downstream of the first fuel injection section (10) along the direction (X) of mainstream air. And a second fuel injection section (20) for injecting the second fuel (21) into the combustion chamber (120). The combustion control method uses the injection amount of the second fuel (21) in the second period (P2) after the first period (P1), the injection amount of the second fuel (21) in the first period (P1), and A step of reducing the injection amount of the first fuel (11) in the second period (P2).

  According to the present invention, a new combustion control system for a scramjet engine is provided.

FIG. 1 is a schematic diagram showing the configuration of a typical scramjet engine. FIG. 2 is a schematic diagram showing the two-stage injection method disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 8-334213). FIG. 3 is a schematic diagram for explaining combustion control in the scramjet engine according to the first embodiment of the present invention. FIG. 4 is a schematic diagram for explaining the combustion control in the scramjet engine according to the first embodiment of the present invention. FIG. 5 is a timing chart that schematically shows the combustion control method according to the first embodiment of the present invention. FIG. 6 is a timing chart that schematically shows the combustion control method according to the comparative example. FIG. 7 is a conceptual diagram showing a comparison between the comparative example and the present embodiment. FIG. 8 is a schematic diagram for explaining the combustion control in the scramjet engine according to the second embodiment of the present invention.

  A scramjet engine and a combustion control method according to an embodiment of the present invention will be described with reference to the accompanying drawings.

1. First Embodiment FIG. 3 shows a configuration of a scramjet engine according to a first embodiment of the present invention, in particular, a configuration related to fuel injection into a combustion chamber 120 (see FIG. 1). The scramjet engine includes a first fuel injection unit 10, a second fuel injection unit 20, and a control unit 30.

  The first fuel injection unit 10 injects the first fuel 11 into the combustion chamber 120. The second fuel injection unit 20 injects the second fuel 21 into the combustion chamber 120. Further, when the direction of the main flow air (supersonic air flow) flowing through the combustion chamber 120 is the X direction, the second fuel injection unit 20 is provided downstream of the first fuel injection unit 10 along the X direction. ing. In other words, in the X direction, the first fuel injection unit 10 is disposed on the upstream side of the second fuel injection unit 20, and the second fuel injection unit 20 is on the downstream side of the first fuel injection unit 10. Has been placed.

  The control unit 30 is configured to control the injection amount of the first fuel 11 from the first fuel injection unit 10 and the injection amount of the second fuel 21 from the second fuel injection unit 20.

  Next, combustion control in the scramjet engine according to the present embodiment will be described.

  First, the control at the time of ignition will be described with reference to FIG. At the time of ignition, the control unit 30 sets the injection amounts of the first fuel 11 and the second fuel 21 to “some degree”. Here, “some degree” means the degree to which an oblique shock wave is formed by the injection of fuel with respect to the supersonic air flow.

  More specifically, the first fuel injection unit 10 injects a certain amount of the first fuel 11 with respect to the supersonic air flow in the combustion chamber 120. As a result, a first oblique shock wave 12 is formed on the upstream side of the injected first fuel 11. Further, a rotational flow is generated before the first oblique shock wave 12, and a first subsonic region (first circulation region) 13 is formed.

  Further, the second fuel injection unit 20 injects a certain amount of the second fuel 21 with respect to the supersonic air flow in the combustion chamber 120. As a result, a second oblique shock wave 22 is formed on the upstream side of the injected second fuel 21. Further, a rotational flow is generated before the second oblique shock wave 22, and a second subsonic region (second circulation region) 23 is formed.

  As shown in FIG. 3, the second subsonic region 23 is formed between the first fuel injection unit 10 and the second fuel injection unit 20. In the present embodiment, the control unit 30 sets the injection amount of the second fuel 21 so that the second subsonic region 23 reaches just downstream of the first fuel injection unit 10. Since the flow velocity is low in the second subsonic region 23, the first fuel 11 injected from the first fuel injection unit 10 is easily ignited in the second subsonic region 23. That is, the ignitability is improved.

  Next, the control after ignition will be described with reference to FIG. Even after ignition, the control unit 30 maintains the injection amount of the first fuel 11 at “a certain level”. As a result, the first oblique shock wave 12 and the first subsonic region 13 are maintained. Therefore, flame holding is possible in the region downstream of the first oblique shock wave 12 (the region where the flow velocity is relatively low).

  On the other hand, since flame holding is possible in the downstream region of the first oblique shock wave 12, it is not necessary to maintain the injection of the second fuel 21 at “a certain level” during the flame holding period. That is, during the flame holding period, the control unit 30 can reduce the injection amount of the second fuel 21 compared to the time of ignition. Alternatively, the control unit 30 may stop the injection of the second fuel 21 during the flame holding period. In any case, the injection amount of the second fuel 21 is set to be smaller than the injection amount of the first fuel 11 during the flame holding period.

  As a result, the flame holding is mainly performed in a region downstream of the first oblique shock wave 12. That is, the flame holding position is determined depending on the position of the first fuel injection unit 10 on the upstream side. It is preferable that the flame holding is performed on the upstream side from the viewpoint of increasing the engine specific thrust or downsizing the engine.

  FIG. 5 schematically shows the combustion control system according to the present embodiment. In the ignition period P1 (see FIG. 3), the control unit 30 sets the respective injection amounts of the first fuel 11 and the second fuel 21 to “some degree”. In the flame holding period P2 (FIG. 4) following the ignition period P1, the control unit 30 maintains the injection amount of the first fuel 11 at “a certain level”. On the other hand, the control unit 30 reduces the injection amount of the second fuel 21 in the flame holding period P2 than the injection amount of the second fuel 21 in the ignition period P1 and the injection amount of the first fuel 11 in the flame holding period P2. For example, the control unit 30 stops the injection of the second fuel 21 in the flame holding period P2. With such a combustion control method, the flame holding position is determined depending on the position of the first fuel injection unit 10 on the upstream side.

  FIG. 6 schematically shows a combustion control method (see FIG. 2) in the case of Patent Document 1 as a comparative example. In the case of the comparative example, the downstream second fuel 21 is used as the main fuel. The first fuel 11 on the upstream side is only used supplementarily for ignition. In this case, the flame holding position is determined depending on the position of the fuel injection unit 102 on the downstream side.

  FIG. 7 shows a comparison between the comparative example and the present embodiment. It is assumed that the distance in the X direction between the first fuel injection unit 10 and the second fuel injection unit 20 is “α”. Further, it is assumed that the length necessary for flame holding is “L”. At this time, the minimum required combustor length is considered. In the case of the comparative example, a combustor length of at least “L + α” is necessary. On the other hand, in the present embodiment, a combustor length of at least “L” is sufficient. That is, according to the present embodiment, the engine can be reduced in size and weight.

  Alternatively, the area of the combustor that receives pressure is increased by the amount by which the flame holding position is shifted upstream, so that the engine specific thrust increases.

  As described above, according to the present embodiment, the ignitability of the scramjet engine is improved. Furthermore, it becomes possible to reduce the size and weight or increase the specific thrust.

2. Second Embodiment FIG. 8 shows a configuration according to a second embodiment of the present invention. A duplicate description with the first embodiment is omitted. According to the second embodiment, the cavity 40 (recessed portion) is provided in the wall of the combustion chamber 120 at a position between the first fuel injection unit 10 and the second fuel injection unit 20.

  At the time of ignition, the ignitability is improved by the interaction between the cavity 40 and the second subsonic region 23. Further, in the flame holding period, the flame holding property is improved by the interaction between the cavity 40 and the downstream region of the first oblique shock wave 12.

  The scramjet engine according to the present invention can be applied to flying objects, aircraft, rockets, and the like.

  The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiments, and can be appropriately changed by those skilled in the art without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 10 1st fuel injection part 11 1st fuel 12 1st diagonal shock wave 13 1st subsonic region 20 2nd fuel injection part 21 2nd fuel 22 2nd diagonal shock wave 23 2nd subsonic region 30 Control part 40 Cavity P1 Ignition period P2 flame holding period

Claims (5)

A first fuel injection section for injecting a first fuel into the combustion chamber;
A second fuel injection section provided downstream of the first fuel injection section along the direction of mainstream air and injecting second fuel into the combustion chamber;
A control unit that controls the injection amount of each of the first fuel and the second fuel,
The control unit determines the injection amount of the second fuel in a second period after the first period, the injection amount of the second fuel in the first period, and the injection amount of the first fuel in the second period. In addition to reducing the injection amount of the second fuel in the first period, the subsonic region formed before the oblique shock wave formed by the injection of the second fuel is immediately downstream of the first fuel injection unit. A scramjet engine set to reach . The scramjet engine according to claim 1,
The control unit sets an injection amount of the first fuel so that an oblique shock wave is formed by the injection of the first fuel. Scramjet engine. A scramjet engine according to any one of claims 1 to 2 ,
The control unit is a scramjet engine that stops the injection of the second fuel in the second period. A first fuel injection section for injecting a first fuel into the combustion chamber;
A second fuel injection section provided downstream of the first fuel injection section along the direction of mainstream air and injecting second fuel into the combustion chamber;
A control unit for controlling the respective injection amounts of the first fuel and the second fuel;
A cavity provided in a wall of the combustion chamber at a position between the first fuel injection portion and the second fuel injection portion ;
Equipped with a,
The control unit determines the injection amount of the second fuel in a second period after the first period, the injection amount of the second fuel in the first period, and the injection amount of the first fuel in the second period. More Scramjet engine. A combustion control method for a scramjet engine,
The scramjet engine is
A first fuel injection section for injecting a first fuel into the combustion chamber;
A second fuel injection unit provided downstream of the first fuel injection unit along the direction of mainstream air and injecting a second fuel into the combustion chamber;
In the combustion control method, the injection amount of the second fuel in a second period after the first period is determined based on the injection amount of the second fuel in the first period and the injection of the first fuel in the second period. Including steps to reduce than quantity ,
The injection amount of the second fuel in the first period is set so that the subsonic region formed before the oblique shock wave formed by the injection of the second fuel reaches immediately downstream of the first fuel injection unit. combustion control method.

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