A method of assessing start risk for an oxygen-rich staged combustion cycle engine system

Abstract

The application provides a method for evaluating the starting risk of an oxygen-rich hypergolic cycle engine system, and aims at solving the technical problem that the existing engine system simulation process cannot effectively evaluate the risk caused by the ignition time lag of a thrust chamber. The application obtains the relationship between the fuel accumulation in the thrust chamber and time through the mathematical model of the engine thrust chamber based on the actual state before the starting of the engine, and further obtains the relationship between the chamber pressure of the thrust chamber and time, so as to obtain the starting risk of the engine system and make up for the defects of the prior art.

Description

Technical Field

[0001] This invention relates to an engine system evaluation method, and more particularly to a method for evaluating the starting risk of an oxygen-enriched staged combustion cycle engine system. Background Technology

[0002] In the thrust chamber of a bipropellant engine, the propellant that enters the thrust chamber later cannot immediately react chemically (combust) with the different propellants that enter earlier due to various reasons. It generally takes tens to hundreds of milliseconds for the propellant to reach the ignition conditions and then undergo a combustion reaction to produce hot gas, so that the thrust chamber can enter the working state. The time between the entry time of the propellant that enters the thrust chamber later and the time when the combustion reaction occurs is called the ignition delay.

[0003] During the ignition delay, propellant continues to enter the thrust chamber and cannot be immediately converted into hot combustion gases, causing the amount of propellant accumulated in the thrust chamber to increase continuously. When the ignition conditions are met, the accumulated propellant immediately combusts, producing a large amount of hot combustion gases. At this time, a pressure peak is very likely to occur. The risks posed by ignition delay during engine start-up include:

[0004] (1) The longer the ignition delay, the more propellant accumulates in the thrust chamber, the more hot gas is generated at the moment of ignition, and the higher the pressure peak. In extreme cases, the pressure peak may exceed the pressure bearing capacity of the thrust chamber, causing damage to the thrust chamber structure.

[0005] (2) During the start-up of an oxygen-rich staged combustion cycle rocket engine, the ignition and pressure build-up process in the thrust chamber is crucial for a successful start-up. This is because the ignition and pressure build-up process is not controlled by system regulating elements but primarily depends on the intense combustion process within the thrust chamber. If the ignition and pressure build-up rate is too fast, it can lead to a sharp drop in turbine pressure ratio, reduced turbine output power, and a decrease or even a negative residual power in the turbopump. Furthermore, the turbopump speed may fluctuate or even drop, causing significant fluctuations in system parameters and ultimately resulting in start-up failure. Among the factors affecting the ignition and pressure build-up rate, ignition time lag is a significant one. It is generally believed that the greater the ignition time lag, the higher the peak pressure at the moment of ignition in the thrust chamber, and the more prone the system anomaly.

[0006] In summary, before hot-fire testing of an engine, designers conduct system simulations based on the characteristics of each component to simulate the engine start-up process, identify potential risks in advance, and then take measures to mitigate them. Ignition delay can be considered a characteristic of the thrust chamber component; however, ignition delay is related not only to the propellant combination but also to factors such as the structural design of the thrust chamber injector, the ignition method, and the emulsion purge gas flow rate. It is difficult to establish a relevant mathematical model, thus making it impossible to quantitatively describe ignition delay. This results in the inability to effectively assess the system start-up risks caused by thrust chamber ignition delay in system simulations of the engine start-up process. Summary of the Invention

[0007] The purpose of this invention is to solve the technical problem that existing engine system simulation processes cannot effectively assess the risks caused by thrust chamber ignition delay, and to provide a method for assessing the starting risks of an oxygen-enriched staged combustion cycle engine system.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for assessing the start-up risk of an oxygen-enriched staged combustion cycle engine system, characterized by the following steps:

[0010] Step 1】Establish a mathematical model of the thrust chamber of the oxygen-enriched staged combustion cycle engine;

[0011] Step 2】Based on the actual state of the engine before starting, the fuel accumulation m in the thrust chamber is obtained through a mathematical model of the engine thrust chamber. 1f The relationship between time t and the following is:

[0012]

[0013]

[0014] In formulas (1) and (2), q mlfi and q mlfe q represents the flow rates of liquid fuel flowing into and out of the thrust chamber, respectively. mfg τ is the flow rate at which liquid fuel is converted into gas. f The time required for liquid fuel to convert to gaseous state; k represents the switching parameter for converting liquid fuel to gaseous fuel. When k=0, it means the switch is closed; when k=1, it means the switch is open; t0 represents the initial moment when liquid fuel enters the thrust chamber; Δt represents the ignition delay, which is given according to the design requirements; t0+Δt represents the moment when the ignition condition is met, i.e., the ignition delay ends.

[0015] Step 3】Based on the fuel accumulation m in the thrust chamber 1fThe relationship between time t and the chamber pressure p inside the thrust chamber is obtained. c The relationship between time t and the change of time t;

[0016] Step 4】Based on the chamber pressure p of the engine thrust chamber c Assess the starting risk of the engine system by evaluating the relationship between the engine system and time t.

[0017] Furthermore, in step 3], the thrust chamber pressure p c Relationship with time t It is expressed as follows:

[0018]

[0019] In formula (3), RT is the calorific value of the gas inside the thrust chamber, V is the volume of the thrust chamber, and ρ is the calorific value of the gas inside the thrust chamber. f The density of liquid fuel, m is the change in the mass of the gas inside the thrust chamber over time. g For the mass of the gas inside the thrust chamber, This represents the change in the calorific value of the gas over time. This represents the change in fuel reserves over time.

[0020] Furthermore, in step 3], the gas mass m in the thrust chamber g The relationship between time t and the relationship is as follows:

[0021]

[0022] In formula (4), q moi q represents the flow rate of gaseous oxidizer entering the thrust chamber. mfg q represents the flow rate at which liquid fuel is converted into gas. mge The flow rate of the gas flowing out of the thrust chamber.

[0023] Furthermore, in step 3], the relationship between the calorific value RT of the gas inside the thrust chamber and time t is as follows:

[0024]

[0025] In formula (5), τ g The residence time of the gas in the thrust chamber, and K g p is the propellant mixing ratio. c This refers to the pressure in the thrust chamber.

[0026] Furthermore, in step 3], the propellant mixing ratio K in the thrust chamber... g The relationship between time t and the relationship is as follows:

[0027]

[0028] In formula (6), K represents the propellant mixture ratio within the thrust chamber. g The change over time t.

[0029] Further, step 4 specifically involves determining the chamber pressure p of the engine thrust chamber at the ignition peak. c If the pressure is less than or equal to 10% of the steady-state chamber pressure, it indicates a low risk of engine system startup; otherwise, it indicates a high risk of engine system startup.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. The method of the present invention is based on the actual state of the engine before starting. Through the mathematical model of the engine thrust chamber, the relationship between the fuel accumulation in the thrust chamber and the time is obtained, and then the relationship between the chamber pressure and the time is obtained, so as to obtain the starting risk of the engine system and make up for the shortcomings of the prior art.

[0032] 2. The method of the present invention can effectively identify the system start-up risks caused by ignition delay, which helps designers take corresponding measures to reduce risks and improve the success rate of test runs. Attached Figure Description

[0033] Figure 1 This is a graph showing the change of thrust chamber pressure over time in an embodiment of the present invention.

[0034] Figure 2 This is a graph showing the change in turbine pump speed over time in an embodiment of the present invention.

[0035] Figure 3 This is a graph showing the change of generator chamber pressure over time in an embodiment of the present invention.

[0036] Figure 4 This is a graph showing the temperature of the generator changing over time in an embodiment of the present invention.

[0037] Figure 5 This is a graph showing the change of oxygen pump inlet pressure over time in an embodiment of the present invention. Detailed Implementation

[0038] The design principle of this invention is as follows: the fundamental cause of ignition delay is that the combustible mixture ratio is insufficient in the region supplying initial ignition energy, or there is insufficient ignition energy in the region where the combustible mixture ratio is met. Once the ignition conditions are met at a certain location in the thrust chamber, combustion rapidly spreads throughout the entire thrust chamber. However, it is difficult to describe with a clear mathematical model when the propellant can meet the ignition conditions. Addressing the problem of the inability to assess the risks caused by thrust chamber ignition delay in engine system simulation, this invention introduces a switching parameter related to the ignition delay time based on the existing thrust chamber mathematical model. Substituting this parameter into the overall engine start-up model allows for the acquisition of the impact of different ignition delays on system parameter changes, thereby achieving an effective assessment of the risks caused by ignition delay.

[0039] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] This invention provides a method for assessing the starting risk of an oxygen-enriched staged combustion cycle engine system, specifically including the following steps:

[0041] Step 1】Establish a mathematical model of the thrust chamber of an oxygen-enriched staged combustion cycle engine.

[0042] Step 2】Based on the actual state of the engine before starting, the fuel accumulation m in the thrust chamber is obtained through a mathematical model of the engine thrust chamber. 1f The relationship between time t and the expression.

[0043] Considering the actual physical phenomena of the ignition process in the thrust chamber of an oxygen-enriched staged combustion engine, the gaseous oxidizer enters the thrust chamber earlier than the fuel. During the ignition delay, liquid fuel continuously flows into the thrust chamber but cannot be converted into gas. As a result, the amount of liquid fuel accumulates more and more. When the ignition conditions are met, the accumulation reaches its peak. At the same time, the accumulated liquid fuel is rapidly converted into gas, and the chemical reaction begins. Parameters such as the gas mass, mixture ratio, and calorific value of the fuel gas in the thrust chamber change rapidly, and the chamber pressure rises sharply.

[0044] Based on the above physical processes, the ignition delay can be simulated by controlling the conversion process of liquid fuel. In this embodiment, the fuel accumulation in the thrust chamber is m. 1f The relationship between time t and the relationship is as follows:

[0045]

[0046]

[0047] In formulas (1) and (2), q mlfi and q mlfe q represents the flow rates of liquid fuel flowing into and out of the thrust chamber, respectively. mfgτ is the flow rate at which liquid fuel is converted into gas. f The time required for liquid fuel to convert to gaseous state; k represents the switching parameter for converting liquid fuel to gaseous fuel. When k=0, it means the switch is closed; when k=1, it means the switch is open; t0 represents the initial moment when liquid fuel enters the thrust chamber; Δt represents the ignition delay, which is given according to the design requirements; t0+Δt represents the moment when the ignition conditions are met, i.e., the ignition delay ends.

[0048] Step 3】Based on the fuel accumulation m in the thrust chamber 1f The relationship between the thrust chamber pressure p and time t is obtained. c The relationship between time t and the change of time t.

[0049] In this embodiment, the thrust chamber pressure p c The relationship between time t and the following formula is:

[0050]

[0051] In formula (3), RT is the calorific value of the gas inside the thrust chamber, V is the volume of the thrust chamber, and m³ is the volume of the gas inside the thrust chamber. lf ρ represents the amount of fuel stored in the thrust chamber. f The density of liquid fuel, m is the change in the mass of the gas inside the thrust chamber over time. g For the mass of the gas inside the thrust chamber, This represents the change in the calorific value of the gas over time. This represents the change in fuel reserves over time.

[0052] Among them, the gas mass m in the thrust chamber g The relationship between time t and the relationship is as follows:

[0053]

[0054] In formula (4), q moi q represents the flow rate of gaseous oxidizer entering the thrust chamber. mfg q represents the flow rate at which liquid fuel is converted into gas. mge The flow rate of the gas flowing out of the thrust chamber.

[0055] The relationship between the calorific value RT of the fuel gas in the thrust chamber and time t is as follows:

[0056]

[0057] In formula (5), τ g The residence time of the gas in the thrust chamber, and m g q represents the mass of the gas inside the thrust chamber. mgeTo determine the flow rate of the gas exiting the thrust chamber, K g p is the propellant mixing ratio. c This refers to the pressure in the thrust chamber.

[0058] The propellant mixing ratio K in the aforementioned thrust chamber g The relationship between time t and the relationship is as follows:

[0059]

[0060] In formula (6), m g q represents the mass of the gas inside the thrust chamber. m o i q represents the flow rate of gaseous oxidizer entering the thrust chamber. mge The flow rate of the gas flowing out of the thrust chamber.

[0061] Step 4】Based on the chamber pressure p of the engine thrust chamber c Assess the starting risk of the engine system by evaluating the relationship between the engine thrust chamber pressure p and time t. c If the pressure is less than or equal to 10% of the steady-state chamber pressure, it indicates that the engine system starts relatively smoothly and the starting risk is low; otherwise, it indicates that the starting risk of the engine system is high. The engine system can be re-simulated and evaluated by changing the ignition timing or adjusting specific parameters to ensure a smooth start.

[0062] Combination Figures 1 to 5 As shown, in the simulation of the start-up process of a certain oxygen-enriched afterburning engine, liquid fuel enters the thrust chamber in 1.4s, i.e. t0 = 1.4s. The ignition delay Δt is set to 0.1s, 0.2s and 0.3s respectively, and the state names are defined as follows.

[0063] Table 1 Status Naming

[0064] State 0 No ignition delay State 1 The ignition delay Δt is 0.1s. State 2 The ignition delay Δt is 0.2s. State 3 The ignition delay Δt is 0.3s.

[0065] The system parameter change curves corresponding to each state are as follows: Figures 1 to 5 As shown, in this embodiment, all parameters are dimensionless, and the steady-state value is set to 1.

[0066] Depend on Figure 1As can be seen, without ignition delay (state 0), the thrust chamber pressure rises steadily without a significant pressure peak. Considering ignition delay (states 1, 2, and 3), a significant pressure peak appears at the moment of ignition, and the longer the ignition delay, the larger the pressure peak. The pressure peak in state 3 even exceeds the steady-state chamber pressure. Furthermore, after the pressure peak occurs, the thrust chamber pressure exhibits a fluctuating upward trend. The longer the ignition delay, the more pronounced the fluctuation, which is more likely to cause instability in the thrust chamber operation, thereby reducing the reliability of the engine system.

[0067] Depend on Figure 2 It is evident that, without ignition delay (state 0), the turbopump speed climb process did not exhibit significant fluctuations; however, considering ignition delay (states 1, 2, and 3), the turbopump speed experienced varying degrees of drop at the thrust chamber ignition point, with the drop being more pronounced the longer the ignition delay. This is consistent with... Figure 1 The phenomena described correspond to these: the longer the ignition lag, the higher the thrust chamber pressure peak, the higher the turbine back pressure, the lower the turbine pressure ratio, and the more significant the reduction in turbopump residual power, thus causing a more pronounced drop in turbopump speed. Furthermore, after the speed drop occurs, the speed increases in a fluctuating manner; the longer the ignition lag, the more pronounced this fluctuation.

[0068] Depend on Figure 3 and Figure 4 It is evident that the longer the thrust chamber ignition delay, the more pronounced the fluctuations in generator chamber pressure and gas temperature. In state 3, the peak value of generator gas temperature fluctuation has significantly exceeded the steady-state value, and the corresponding generator chamber pressure has also approached the steady state. This is quite dangerous for the oxygen-enriched gas system (generator, turbine blades, gas ducts), and could potentially cause the engine system to be burned and damaged by oxygen enrichment.

[0069] Depend on Figure 5 It is evident that the longer the ignition delay in the thrust chamber, the lower the minimum inlet pressure of the oxygen pump, and the greater the possibility of cavitation in the oxygen pump, thus increasing the risk of engine system startup.

[0070] In summary, the method of the present invention can quantitatively assess the starting risk caused by thrust chamber ignition delay, and predict the maximum ignition delay that the engine system can withstand for reliable starting. Using the method of this embodiment, the system starting risk caused by ignition delay can be effectively identified, which is conducive to designers taking corresponding measures to reduce the risk and improve the test success rate.

[0071] Although embodiments of the present invention have been shown and described above, those skilled in the art should consider any variations and modifications of the above embodiments that fall within the scope of the present invention's spirit and essence to be within the protection scope of the present invention.

Claims

1. A method for assessing the starting risk of an oxygen-enriched staged combustion cycle engine system, characterized in that, Includes the following steps: Step 1】Establish a mathematical model of the thrust chamber of the oxygen-enriched staged combustion cycle engine; Step 2】Based on the actual state of the engine before starting, the fuel accumulation m in the thrust chamber is obtained through a mathematical model of the engine thrust chamber. 1f The relationship between time t and the following is: In formulas (1) and (2), q mlfi and q mlfe q represents the flow rates of liquid fuel flowing into and out of the thrust chamber, respectively. mfg τ is the flow rate at which liquid fuel is converted into gas. f The time required for liquid fuel to convert to gaseous state; k represents the switching parameter for converting liquid fuel to gaseous fuel. When k=0, it means the switch is closed; when k=1, it means the switch is open; t0 represents the initial moment when liquid fuel enters the thrust chamber; Δt represents the ignition delay; and t0+Δt represents the moment when the ignition condition is met, i.e., the ignition delay ends. Step 3】Based on the fuel accumulation m in the thrust chamber 1f The relationship between the thrust chamber pressure p and time t is obtained. c The relationship between time t and the change of time t; Step 4】Based on the chamber pressure p of the engine thrust chamber c Assess the starting risk of the engine system by evaluating the relationship between the engine system and time t.

2. The method for assessing the starting risk of an oxygen-enriched staged combustion cycle engine system according to claim 1, characterized in that: In step 3], the thrust chamber pressure p c Relationship with time t It is expressed as follows: In formula (3), RT is the calorific value of the gas inside the thrust chamber, V is the volume of the thrust chamber, and ρ is the calorific value of the gas inside the thrust chamber. f The density of liquid fuel, m is the change in the mass of the gas inside the thrust chamber over time. g For the mass of the gas inside the thrust chamber, This represents the change in the calorific value of the gas over time. This represents the change in fuel reserves over time.

3. The method for assessing the starting risk of an oxygen-enriched staged combustion cycle engine system according to claim 2, characterized in that: In step 3, the mass m of the gas inside the thrust chamber g The relationship between time t and the relationship is as follows: In formula (4), q moi q represents the flow rate of gaseous oxidizer entering the thrust chamber. mfg q represents the flow rate at which liquid fuel is converted into gas. mge The flow rate of the gas flowing out of the thrust chamber.

4. The method for assessing the starting risk of an oxygen-enriched staged combustion cycle engine system according to claim 3, characterized in that: In step 3], the relationship between the calorific value RT of the gas inside the thrust chamber and time t is: In formula (5), τ g The residence time of the gas in the thrust chamber, and K g p is the propellant mixing ratio. c This refers to the pressure in the thrust chamber.

5. The method for assessing the starting risk of an oxygen-enriched staged combustion cycle engine system according to claim 4, characterized in that: In step 3, the propellant mixing ratio K in the thrust chamber g The relationship between time t and the relationship is as follows: In formula (6), K represents the propellant mixture ratio within the thrust chamber. g The change over time t.

6. The method for assessing the starting risk of an oxygen-enriched staged combustion cycle engine system according to claim 5, characterized in that: Step 4】Specifically, if the engine thrust chamber pressure p at the ignition peak moment c If the pressure is less than or equal to 10% of the steady-state chamber pressure, it indicates a low risk of engine system startup. Otherwise, it indicates a higher risk of starting the engine system.

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