CN112648638A - Scramjet engine based on combined combustion law - Google Patents

Scramjet engine based on combined combustion law Download PDF

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CN112648638A
CN112648638A CN202011483949.3A CN202011483949A CN112648638A CN 112648638 A CN112648638 A CN 112648638A CN 202011483949 A CN202011483949 A CN 202011483949A CN 112648638 A CN112648638 A CN 112648638A
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section
heating
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mach number
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席志华
陈浩颖
张海波
胡晨旭
郑前钢
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Nanjing University of Aeronautics and Astronautics
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Nanjing University of Aeronautics and Astronautics
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23R—GENERATING COMBUSTION PRODUCTS OF HIGH PRESSURE OR HIGH VELOCITY, e.g. GAS-TURBINE COMBUSTION CHAMBERS
    • F23R3/00—Continuous combustion chambers using liquid or gaseous fuel
    • F23R3/42—Continuous combustion chambers using liquid or gaseous fuel characterised by the arrangement or form of the flame tubes or combustion chambers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02K—JET-PROPULSION PLANTS
    • F02K7/00—Plants in which the working fluid is used in a jet only, i.e. the plants not having a turbine or other engine driving a compressor or a ducted fan; Control thereof
    • F02K7/10—Plants in which the working fluid is used in a jet only, i.e. the plants not having a turbine or other engine driving a compressor or a ducted fan; Control thereof characterised by having ram-action compression, i.e. aero-thermo-dynamic-ducts or ram-jet engines
    • F02K7/14—Plants in which the working fluid is used in a jet only, i.e. the plants not having a turbine or other engine driving a compressor or a ducted fan; Control thereof characterised by having ram-action compression, i.e. aero-thermo-dynamic-ducts or ram-jet engines with external combustion, e.g. scram-jet engines
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
    • G06F2119/08—Thermal analysis or thermal optimisation

Abstract

The invention discloses a scramjet engine based on a combined combustion rule, wherein a combustion chamber of the scramjet engine is a multistage combustion chamber formed by sequentially connecting four sections, namely an equal-area section, an isobaric section, an equal-Mach number section and an isothermal section, along the direction from an inlet to an outlet, and the equal-area section, the isobaric section, the equal-Mach number section and the isothermal section respectively use an equal-area heating rule, an isobaric heating rule, an equal-Mach number heating rule and an isothermal heating rule; a fuel injection point is provided at the inlet of each segment. Compared with the prior art, the invention can effectively improve the performance of the scramjet engine, and simultaneously ensures that the engine is not over-temperature and over-pressure and cannot generate thermal blockage.

Description

Scramjet engine based on combined combustion law
Technical Field
The invention relates to the field of modeling and control of hypersonic aircrafts, in particular to a scramjet engine.
Background
Hypersonic vehicles (Hypersonic vehicles) generally refer to vehicles with an incoming stream mach number greater than 5. The novel multifunctional electric heating water heater is favored by all countries in the world with the advantages of speed advantage, breaking capacity and the like. In order to achieve better performance of hypersonic aircraft, the power plant usually adopts a scramjet engine. The combustion chamber is an important component of the scramjet engine, and the working performance and the heating rule of the combustion chamber greatly influence the thrust performance and the specific impact performance of the scramjet engine.
Many researches have been conducted at home and abroad aiming at modeling and simulation of the scramjet engine and the combustion chamber thereof. Ferri, through Combustion tests, raised the problem of matching the heating law to the shape of the Combustion chamber, where aerodynamic matching to the complete Combustion process (fuel injection, mixing and Combustion) was considered in designing the Combustion chamber, and therefore, the heating process was analyzed extensively in the research on the thermodynamic cycle process of scramjet engines [ Ferri A, Fox H. Ikawa creates an scramjet engine combustion chamber model using the area expansion factor method, and can perform combustion chamber calculation and performance evaluation [ Ikawa H. Rapid method for design and performance prediction of integrated super combustion engine injection [ J ]. Journal of performance and Power,1991,7(3):437 444 ]. Kummtnitha in order to improve the mixing efficiency of supersonic air flow and Hydrogen fuel, a passive technology is adopted, and the mixing efficiency of a scramjet engine combustion chamber is improved by designing different types of surfaces at the bottom of the combustion chamber, so that the combustion efficiency is improved [ Kummitha O.Numerical analysis of passive technology for optimizing the performance of scientific jet combustor [ J ]. International Journal of Hydrogen Energy,2017,42(15):10455- ]. A certain research is made in various colleges and universities in China aiming at a scramjet engine model, and a multi-target control method research is developed by taking a hydrocarbon fuel regeneration cooling scramjet engine as a research object inherited by the university of Harbin industry. From the control perspective, the overtemperature and mode conversion problems of the scramjet combustion chamber are researched [ horse inherits ] research on a control method of a hydrocarbon fuel regenerative cooling scramjet engine [ D ]. Harbin university of industry, 2020 ]. Wu Mr. of the university of national defense science and technology deeply studies the optimization problem of the integrated runner design of the scramjet by means of numerical simulation, direct-coupled test and the like, and comprehensively discusses the influence of various design factors on the engine components and system performance [ Wu Mr. Wu M. On the basis of considering the quasi-one-dimensional Euler equation of finite rate chemical reaction, Euhefeng et al, combined with the university of fertilizer industry, developed a quasi-one-dimensional calculation method [ Euhefeng, Zhang, Lidebao ] for the performance analysis of a scramjet combustor by increasing the source terms of cross-sectional area variation, wall friction and additive quality [ J ] propulsion technology, 2020, 41 (3): 623-631].
In summary, at present, certain research achievements exist at home and abroad in the aspect of improving the performance of the combustion chamber of the scramjet engine, most researches are carried out on the basis of the equal-area heating law, and some researches are carried out on the basis of the heating law of isostatic pressure, isostatic temperature or equal mach number. The research of analyzing and establishing a multi-stage combustion chamber integrating various heating laws from the thermal cycle point of view is still blank.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects in the prior art, combine various thermodynamic cycle characteristics and provide the scramjet based on the combined combustion rule, which can effectively improve the performance of the scramjet, and simultaneously ensure that the engine is not over-temperature and over-pressure and cannot generate heat blockage.
The invention specifically adopts the following technical scheme to solve the technical problems:
a scramjet engine based on a combined combustion law is characterized in that a combustion chamber of the scramjet engine is a multistage combustion chamber formed by sequentially connecting four sections, namely an equal-area section, an equal-pressure section, an equal-Mach number section and an equal-temperature section, along the direction from an inlet to an outlet, wherein the equal-area section, the equal-pressure section, the equal-Mach number section and the equal-temperature section respectively use an equal-area heating law, an equal-pressure heating law, an equal-Mach number heating law and an equal-temperature heating law; a fuel injection point is provided at the inlet of each segment.
Preferably, the profile parameters of the multistage combustion chamber are obtained by optimizing through an optimization algorithm under the condition that the constraints of temperature, Mach number and pressure are met and the thrust of the scramjet engine at the design point is maximally optimized.
Further preferably, the profile parameters are horizontal included angles and throttle rates of the sections of the multistage combustion chamber.
Further preferably, the optimization algorithm is a hybrid penalty function method.
Preferably, the equal area heating process of the equal area segment is described using the following model:
Figure BDA0002838438210000021
Figure BDA0002838438210000022
Figure BDA0002838438210000031
Figure BDA0002838438210000032
wherein σaThe total pressure recovery coefficient in the equal-area heating process,
Figure BDA0002838438210000033
static pressure drop for equal area heating process, cvSpecific heat at constant volume, Q as heat added, gamma as specific heat ratio, M as Mach number, T as static temperature, TtP is the static pressure and gamma is the specific heat ratio; subscript "3" is the inlet cross section of the equal area section, subscript "And 4' is an outlet section of the equal-area section.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the invention comprehensively considers the characteristics of various typical heating processes and establishes the multistage combustion chamber of the scramjet engine. In the range of the maximum static temperature limit, the maximum static pressure limit and the heat blockage limit of the scramjet engine, the maximum thrust of the scramjet engine can be obtained to the maximum extent through the profile design and optimization of the multistage combustion chamber.
Drawings
FIG. 1 is a T-S diagram of a scramjet engine based on an equal area heating law;
FIG. 2 is a maximum heating ratio for an equal area heating process;
FIG. 3 is a T-S diagram of a scramjet engine based on isobaric heating laws;
FIG. 4 is a T-S diagram of a scramjet engine based on isothermal heating law;
FIG. 5 is a T-S diagram of a scramjet engine based on an equal Mach number heating law;
FIG. 6 is a graph of a combined heating process T-S that takes into account Mach number constraints;
FIG. 7 is a T-S plot of a combined heating process considering pressure limitations, Mach number limitations;
FIG. 8 is a T-S diagram of a combined heating process considering temperature limitation and Mach number limitation;
FIG. 9 is a T-S diagram of a combined heating process considering pressure limits, temperature limits, and Mach number limits;
FIG. 10 is a multi-stage combustor geometry diagram;
FIG. 11 is a graph showing the profile variation and axial parameter distribution at the design point, wherein (a), (b), (c) and (d) are the profile height distribution, Mach number distribution, static temperature distribution and static pressure ratio distribution along the axial direction, respectively.
Detailed Description
Aiming at the defects in the prior art, the solution idea of the invention is to combine the characteristics of various typical thermodynamic cycles and establish a multistage combustion chamber model of the scramjet engine so as to improve the performance of the combustion chamber.
Specifically, the invention provides a combined combustion law-based scramjet engine, wherein a combustion chamber of the scramjet engine is a multistage combustion chamber formed by sequentially connecting four sections, namely an equal-area section, an isobaric section, an equal-Mach number section and an isothermal section, along the direction from an inlet to an outlet, and the equal-area section, the isobaric section, the equal-Mach number section and the isothermal section respectively use an equal-area heating law, an isobaric heating law, an equal-Mach number heating law and an isothermal heating law; a fuel injection point is provided at the inlet of each segment.
By adopting the technical scheme, different combined heating laws can be realized by adjusting the fuel quantity of different fuel injection points under the constraints of Mach number, temperature and pressure and under the limitation of the thermal blockage condition.
For the public understanding, the technical scheme of the invention is explained in detail in the following with the accompanying drawings:
1. the multistage combustion chamber profile design:
the invention establishes a scramjet engine multistage combustion chamber based on a combined heating rule. The combined heating law refers to a heating law combining two or more of equal-area heating, isobaric heating, isothermal heating and equal-mach-number heating, which are respectively analyzed and explained below.
(1) The equal-area heating rule is as follows:
the equal-area heating law is common in a ramjet engine and a rocket engine, and generally appears in the design of the heating law of the cylindrical combustion chamber, and compared with other heating laws, the total pressure recovery coefficient of the equal-area heating law is the highest. For the equal area heating process, it is assumed that section 3 is the equal area section inlet section and section 4 is the equal area section outlet section. The isosurface heating process is described by the relative static pressure drop (Δ p/p), where Δ p is a 3-4 process static pressure drop, which allows for static pressure to be easily measured in practice and is closely related to the heating process. The T-S diagram of the scramjet engine based on the equal-area heating law is shown in figure 1.
The first law of thermodynamics is satisfied during the heating process, and its differential form can be expressed as:
dQ＝cpdT-υdp (1)
in the formula, Q is added heat; upsilon is specific volume, cpThe specific heat capacity at constant pressure, T at a static temperature, p at a static pressure, and upsilon 1/ρ.
The differential form of the state equation can be obtained:
Figure BDA0002838438210000041
wherein R is a general gas constant.
The equal-area heating process satisfies a continuous equation and a momentum equation, and thus:
Figure BDA0002838438210000051
Figure BDA0002838438210000052
wherein v is velocity;
Figure BDA0002838438210000053
is the mass flow per unit area.
Substituting the formula (3) into the formula (4) to obtain:
Figure BDA0002838438210000054
substituting the formula (2) and the formula (5) into the formula (1) to obtain:
Figure BDA0002838438210000055
in the formula, cvThe subscript "3" is the constant area segment inlet for constant specific heat capacity.
Integrating equation (6) over the course of 3-4 yields:
Figure BDA0002838438210000056
in the formula (I), the compound is shown in the specification,
Figure BDA0002838438210000057
Figure BDA0002838438210000058
subscript "4" is the equal area segment outlet.
Changing Δ p to p4-p3In formula (7), the finishing is as follows:
B/2·Δp2-(Bp3-A)Δp+Q＝0 (10)
the relative static pressure drop can be obtained by solving the equation (10)
Figure BDA0002838438210000059
Comprises the following steps:
Figure BDA00028384382100000510
in the formula, Tt3The total temperature of the inlet of the equal-area section is equal, and when the incoming flow is supersonic, the formula (11) is plus.
From the momentum theorem and equations (1) to (11):
Figure BDA00028384382100000511
Figure BDA00028384382100000512
Figure BDA0002838438210000061
in the formula, σaTotal pressure recovery coefficient, p, for equal area heating processt3，pt4Respectively equal area section inlet and outlet total pressure.
As can be seen from equation (11), in the equal-area heating process, the amount of heat may not be infinitely added when the inflow conditions are constant. When the root number in the formula (11) is zero, the maximum amount of heat that can be added under the condition and the maximum heating ratio τ can be obtainedmaxWherein the maximum heat quantity and the maximum heating ratio have the following relationship:
Figure BDA0002838438210000062
therefore, the expression of the maximum heating ratio can be obtained from the expressions (11) and (15), and at the same time, the relationship between the maximum heating ratio and the incoming flow mach number can be obtained, as shown in fig. 2. As can be seen from the graph, when the incoming flow is in the subsonic speed state, the maximum heating ratio decreases with the increase of the mach number, and the descending speed is fast; when the incoming flow is in a supersonic state, the maximum heating ratio increases with the increase of the mach number, and the increasing speed gradually becomes slower until finally approaching a stable value. Obviously, in order to keep the equal-area heating process in the maximum thrust state all the time, the heating ratio should be ensured to be constant at the maximum heating ratio.
(2) Isobaric heating law:
in addition to the equal-area heating law, the equal-pressure heating law is also considered in the multistage combustion chamber of the scramjet engine, on one hand, the influence of the back pressure of the combustion chamber on the isolation section is considered, and the engine cannot be started due to the excessively high back pressure of the combustion chamber; another aspect is the pressure requirements of the scramjet engine architecture. For the isobaric heating process, it is assumed that section 3 is the isobaric section inlet section and section 4 is the isobaric section outlet section. The pressure is constant during the heating process, and the velocity of the gas flow is constant during this process, i.e. v4＝v3. The T-S diagram of the scramjet engine based on the isobaric heating law is shown in figure 3.
From the continuous equation:
Figure BDA0002838438210000063
wherein A is the area, T is the static temperature, Q is the heat added during the isobaric process, cpIs a constant pressure specific heat capacity; subscript "3" is the isobaric section inlet and subscript "4" is the isobaric section outlet.
The relationship between the total temperature and the static temperature and the heating amount can be known as follows:
Figure BDA0002838438210000071
in the formula, τ is a heating ratio, and γ is a specific heat ratio.
From the constant speed, one can obtain:
Figure BDA0002838438210000072
wherein M is Mach number.
The total pressure recovery coefficient obtained by equations (16) to (18) is:
Figure BDA0002838438210000073
(3) isothermal heating law:
the scramjet engine combustion chamber works in a high-temperature and high-speed state, and the temperature of the combustion chamber cannot be too high due to the limitation of factors such as materials, structures and the like of the combustion chamber, so that the temperature of the combustion chamber is limited. In order to be able to achieve sufficient engine performance, an isothermal heating law is used which allows more heat to be added to the engine, which is close to the actual situation where the maximum combustion chamber temperature is limited by the dissociation reaction. For the isothermal heating process, it is assumed that section 3 is the isothermal section inlet section and section 4 is the isothermal section outlet section. The T-S diagram of the scramjet based on the isothermal heating law is shown in figure 4.
The equation of state and the equation of momentum can be used:
Figure BDA0002838438210000074
where v is the velocity, R is the universal gas constant, T is the static temperature, and p is the static pressure.
Integrating the above equation over the course of 3-4, we can obtain:
Figure BDA0002838438210000075
in the formula, the subscript "3" is an isothermal section inlet, and the subscript "4" is an isothermal section outlet.
The formula is finished to obtain:
Figure BDA0002838438210000076
in the formula, M is Mach number, tau is heating ratio, and gamma is specific heat ratio.
The relationship between the static pressures obtained by the equations (20) to (22) is:
Figure BDA0002838438210000081
from this, it can be obtained that the total pressure recovery coefficient in this process is:
Figure BDA0002838438210000082
(4) heating law with equal Mach number:
the constant Mach number heating law is a specific heating law of a power system of the hypersonic aircraft, and the heating law is suitable for a scramjet engine, so that the characteristics of the heating law are necessarily researched. For an equal mach heating process, it is assumed that section 3 is the equal mach section inlet section and section 4 is the equal mach section outlet section. The T-S diagram of the scramjet based on the equal Mach heating law is shown in figure 5.
The momentum equation, the state equation and the Mach number define that:
Figure BDA0002838438210000083
wherein γ is a specific heat ratio, M is a Mach number, T is a static temperature, and p is a static pressure.
Integration of the above equation over the course of 3-4 gives:
Figure BDA0002838438210000084
in the formula, subscript "3" is equal mach number section import, and subscript "4" is equal mach number section export.
Since the Mach number is constant in this process, p is known3/p4＝pt3/pt4，T3/T4＝Tt3/Tt4(in the formula, TtTo total temperature, PtTotal pressure) thus giving:
Figure BDA0002838438210000085
Figure BDA0002838438210000086
wherein τ is a heating ratio.
The combination of different heating process working characteristics can obtain that the total pressure recovery coefficient of the equal-area heating process is the highest, but is constrained by the maximum heating ratio. The isobaric heating process is only inferior to the equal-area heating process, the maximum heating ratio constraint does not exist in the process, but with the addition of heat, the phenomenon that supersonic airflow is converted into subsonic airflow, namely the phenomenon that the Mach number is less than 1, can occur. The Mach number can be restrained by the constant Mach number heating law, in the constant Mach number section, the static temperature of the combustion chamber exceeds the limit with the addition of heat, and the constant static temperature heating law can ensure that the highest temperature of the combustion chamber does not exceed the maximum static temperature limit. From the above, the single heating law cannot fully exert the performance of the scramjet, so the invention provides the design of the multistage combustion chamber of the scramjet based on the combined heating law.
The combined heating rule of the invention is based on the equal-area heating rule and is combined with other heating rules, and the Mach number of the whole process is required to be ensured to be not less than 1 in the heating process, and the whole process does not exceed the maximum static temperature limit and the maximum static pressure limit of an engine.
(5) The combined heating law considering the mach number limit is as follows:
if no condition is imposed, the optimal combined heating law is the combination of the equal-area heating law and the equal-mach-number heating law, as shown in fig. 6, wherein the processes 0-3 and 9-10 are respectively a compression process and an expansion process, the processes 3-4 are equal-area heating processes, and the processes 4-9 are equal-mach-number heating processes with mach number of 1. When there is no limitation on the conditions such as temperature and pressure, it is necessary to set the heating ratio in the equal-area heating process to the maximum heating ratio, and the mach number is set to 1 at the end of the process, and the equal-mach-number heating process is continued.
(6) Considering the pressure limit, the combined heating law of mach number limit:
the pressure of the scramjet heating process needs to be limited, and the limiting pressure is recorded as Pmax. For the combined heating law with pressure limitation and Mach number limitation, the combination of the equal-area heating law, the isobaric heating law and the equal-Mach number heating law needs to be considered, such as the processes of 0-3-4-9-10 in the figure 7, and after the equal-area heating process, the maximum pressure limitation P of the combustion chamber is reachedmaxAt the moment, the heating is carried out along the isobaric line, the Mach number is continuously reduced along with isobaric heating, when the Mach number is reduced to 1, the isobaric heating process is finished, and the heating is carried out along the heating line with the Mach number equal to 1.
(7) Considering the temperature limit, the combined heating law of mach number limit:
the working characteristics of the scramjet determine the material requirementsThe method is characterized in that a high-temperature resistant function is required, however, the temperature which can be borne by the current material is limited to a certain extent, in addition, the gas is dissociated or ionized due to too high temperature, the performance of the scramjet engine is affected, for the combined heating law with temperature limitation and Mach number limitation, the combination of the equal-area heating law, the isothermal heating law and the equal-Mach number heating law needs to be considered, and the termination temperature of the equal-area heating process under the condition of the maximum heating ratio is recorded as TmaxIn the process of 0-3-4-9-10 in FIG. 8, the maximum heating ratio is adopted in the equal-area heating process, the Mach number is stopped to be 1, the equal-Mach number heating process with the Mach number of 1 is continued, and when the heating temperature reaches the limit temperature TmaxEnding the Mach number heating process at a temperature TmaxIsothermal heating process of (1).
(8) Considering the combined heating law of temperature limit, pressure limit, mach number limit:
when the temperature limit, the pressure limit and the Mach number limit are simultaneously considered in the scramjet, the equal-area heating law and the equal-pressure heating law need to be considered, the equal-temperature heating law and the equal-Mach number heating law are combined, and the maximum temperature limit is recorded as TmaxWith maximum pressure limit denoted Pmax. After the equal area heating process, the combustion chamber first reaches the maximum pressure limit P, as in the process 0-3-4-9-10 of FIG. 9maxAt the moment, the heating is carried out along the isobaric line, the Mach number is continuously reduced along with isobaric heating, when the Mach number is reduced to 1, the isobaric heating process is ended, the heating process is carried out along the Mach number equal to 1, and when the heating temperature reaches the limiting temperature TmaxEnding the Mach number heating process at a temperature TmaxIsothermal heating process of (1).
By combining the above analysis, the Mach number limit, the temperature limit and the pressure limit need to be considered in the heating process of the scramjet engine, and the Mach number is not less than 1, the temperature does not exceed the maximum static temperature and the pressure meets the starting requirement of the engine in the heating process. Based on the condition limitation of the scramjet engine, the working characteristics of different heating processes and the change of the inlet area and the outlet area, the combined heating device suitable for the combined heating is designedThe combustion chamber configuration of the process, as shown in fig. 10, is an axisymmetric configuration of the multi-stage combustion chamber model, which is shown as the portion above the axis of symmetry. The model consists of an equal-area section, an isobaric section, an equal-Mach number section and an isothermal section, wherein the model comprises 4 fuel injection points. Under the constraints of Mach number, temperature and pressure, different combined heating laws are realized by adjusting the fuel quantity of different fuel injection points. The regulation law being when constraints are satisfied, i.e.
Figure BDA0002838438210000101
Calculating the parameters of the corresponding heating section according to the formulas (1) to (28) to obtain the outlet parameters of the heating section; when constraints are not satisfied, i.e.
Figure BDA0002838438210000102
The heating section is calculated assuming an adiabatic process and its exit parameters are obtained.
The geometry of the preliminarily designed multi-stage combustor model is shown in table 1:
TABLE 1 geometry of the Multi-stage combustor model
Figure BDA0002838438210000103
2. And (3) multistage combustion chamber profile optimization:
among the multiple combustion chamber profiles, the combustion chamber profile capable of enabling the thrust performance of the scramjet engine to achieve the optimal thrust performance at a design point exists, namely, the horizontal included angle alpha of a heating section of the combustion chamber is adjusted under the constraints of temperature, Mach number and pressurei(i ═ 1,2,3) and throttle ratio
Figure BDA0002838438210000104
The thrust of the scramjet engine model reaches the maximum at the design point. Therefore, the scramjet profile optimization problem can be described as:
Figure BDA0002838438210000111
in the formula, F is the thrust of the scramjet engine; mkThe Mach number of different sections of the scramjet engine is shown.
The hybrid penalty function method and the genetic algorithm are adopted to optimally design the profile of the scramjet engine by taking the maximum thrust as a target at a design point, the optimization result is shown in table 2, the hybrid penalty function method and the genetic algorithm are optimized relative to a reference value, the equal-pressure segment angle is increased, the equal-pressure segment angle and the equal-temperature segment angle are decreased, and the equality constraint error is less than 0.5%, so that the optimized angle can be regarded as satisfying equality constraint, the thrust of the scramjet engine of the optimized profile is increased, and the relative increment is respectively 18.7% and 26.2%. The comparison result shows that the optimization effect of the hybrid penalty function method is better compared with the genetic algorithm.
TABLE 2 hybrid penalty function and genetic algorithm optimization results at design points versus reference values
Figure BDA0002838438210000112
Note: up ↓, down ↓, with respect to the reference value.
TABLE 3 throttle rates and their ratios for different profile fuel injection points at design points
Figure BDA0002838438210000113
Note: up ↓, down ↓, with respect to the reference value.
The fuel distribution tends to be different for different profiles, and therefore the above analysis is not sufficient to judge the rationality of the profile design. The heating rules from small to large total pressure loss are ordered into an equal-area heating rule, an isobaric heating rule, an isothermal heating rule and an equal-Mach number heating rule. Because the heating rule and the molded surface are in one-to-one correspondence, the molded surface optimization effect is analyzed from the view point of the throttling rate and the distribution ratio thereof. The throttle rates of fuel injection points of different profiles and the occupation ratios thereof are shown in table 3, from the aspect of the throttle rates, the mixed penalty function method optimized profile and the genetic algorithm optimized profile are relative to the reference profile, the throttle rate of the scramjet is improved by adjusting the profile angle, and the throttle rates are respectively increased by 38.03% and 37.45%, so that the thrust of the optimized scramjet is increased. From the angle analysis of the throttling ratio distribution ratio, the throttling ratio distribution ratio (the specific gravity is gradually reduced) of the optimized profile is sorted into an equal-area section, an equal-pressure section, an equal-temperature section and an equal Mach number by a mixed penalty function method, and the sorting is mutually consistent with the above-mentioned heating rule sorting, so that the optimized result is proved to improve the utilization efficiency of fuel oil. In addition, as can be seen from fig. 11, the axial parameters (temperature, pressure, mach number) of the optimized profile by the hybrid penalty function method are closer to the constraint boundary than the optimized result of the genetic algorithm, and the potential of the scramjet is exerted to the maximum extent, so that the thrust performance of the scramjet is improved. Based on the analysis, the performance of the combustion chamber can be improved after the genetic algorithm and the mixed penalty function algorithm are optimized, and the mixed penalty function has a better effect.

Claims (5)

1. A scramjet engine based on a combined combustion law is characterized in that a combustion chamber of the scramjet engine is a multistage combustion chamber formed by sequentially connecting four sections, namely an equal-area section, an isobaric section, an equal-Mach number section and an isothermal section, along the direction from an inlet to an outlet, wherein the equal-area section, the isobaric section, the equal-Mach number section and the isothermal section respectively use an equal-area heating law, an isobaric heating law, an equal-Mach number heating law and an isothermal heating law; a fuel injection point is provided at the inlet of each segment.
2. The scramjet engine based on the combined combustion law as claimed in claim 1, wherein the profile parameters of the multistage combustion chamber are obtained by optimization of an optimization algorithm under the condition that the constraints of temperature, Mach number and pressure are met and the thrust of the scramjet engine at the design point is maximum to achieve the optimization target.
3. The scramjet engine based on a combined combustion law as claimed in claim 2, wherein the profile parameters are horizontal included angle and throttle rate of each segment of the multistage combustion chamber.
4. The scramjet engine based on a combined combustion law as claimed in claim 2, wherein the optimization algorithm is a hybrid penalty function method.
5. The scramjet engine based on the combined combustion law as claimed in claim 1, wherein the equal area heating process of the equal area segment is described using the following model:
Figure FDA0002838438200000011
Figure FDA0002838438200000012
Figure FDA0002838438200000013
Figure FDA0002838438200000014
wherein σaThe total pressure recovery coefficient in the equal-area heating process,
Figure FDA0002838438200000015
static pressure drop for equal area heating process, cvSpecific heat at constant volume, Q as the heat of addition, M as Mach number, T as the static temperature, TtP is the static pressure and gamma is the specific heat ratio; subscript "3" is the equal area section inlet cross-section and subscript "4" is the equal area section outlet cross-section.
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