Propellant supply system of electric pump liquid rocket engine based on parallel connection of multiple pumps

Abstract

The application discloses a kind of electric pump liquid rocket engine propellant supply system based on the parallel connection of multiple pumps, belongs to liquid rocket engine propellant supply technical field.For the technical bottleneck that the existing electric pump cycle engine relies on single-pump high-power route, leading to the mass and cost of motor and battery pack super-linear growth with target thrust, and the power level cannot be expanded to medium and large rockets for a long time, based on the physical principle that "engine thrust depends only on propellant mass flow and exhaust velocity", the application proposes to use multiple small and medium power electric pump group units to maintain the same supply pressure and stack mass flow, realize the linear expansion of thrust;Each pump group unit is composed of a propellant pump, a driving motor, an independent battery pack and a unit controller, each unit is electrically isolated from each other, and the liquid circuit is connected in parallel through a busbar device, so that the output power and discharge rate of each battery pack do not increase with the increase of total thrust.

Description

Technical Field

[0001] This invention relates to the field of liquid rocket engine technology, specifically to a propellant supply system for a liquid rocket engine based on a multi-pump parallel electric pump, applicable to small to medium-sized liquid launch vehicles and their upper stages, landers, and other aerospace propulsion devices that use electric pump circulation as the power cycle. Background Technology

[0002] For a long time, gas turbopumps have been the mainstream solution for propellant supply systems in pump-fed liquid rocket engines. Turbopumps use high-temperature gas generated by a gas generator, staged combustion, or expansion cycle to drive a turbine, which in turn drives the propellant pump. They have high power density, but the system composition is complex: they require an additional gas generator (or pre-combustion chamber), complex start-up sequence, high-temperature turbine components, and a precise turbopump joint adjustment mechanism, resulting in long development cycles, high costs, multiple failure modes, and limited deep throttling and multiple start-up capabilities.

[0003] In recent years, with the advancement of lithium-ion batteries and high-power-density permanent magnet motor technologies, electric pump cycle (EPC) technology has gradually emerged. EPC uses batteries as its energy source and a motor directly drives the propellant pump, eliminating the need for a gas generator and turbine. It boasts advantages such as system simplicity, rapid start-up and shutdown, precise thrust adjustment, and high efficiency in energy conversion. Engineering practice, exemplified by a foreign EPC engine, has proven its feasibility for small launch vehicles: this engine has a sea-level thrust of approximately 24.9 kN, with each engine equipped with one fuel pump and one oxidizer pump, each driven by a brushless DC motor of approximately 37 kW. Domestically, EPC engines have also achieved a single-pump motor power of approximately 414.6 kW and a single-engine thrust of approximately 10 tons, representing the highest engineering level currently achieved in terms of single-pump power and single-engine thrust for EPC engines.

[0004] However, the industry has long held the view that electric pump cycle (EPC) engines are "unsuitable for medium and large rockets." The reason for this is that existing EPC engines invariably follow the single-pump centralized design paradigm originating from the turbopump era: only one pump is configured for each propellant, driven by one electric motor and powered by a centralized battery pack; when the target thrust increases, the power of this single pump, motor, and battery pack must be increased proportionally. This approach has the following inherent drawbacks: 1. Motor power bottleneck and the cost of superlinearity. Pump shaft power is directly proportional to mass flow rate. If the target thrust increases several times, the power of a single motor must also increase several times. Problems such as winding heat dissipation, rotor dynamics, bearing DN value, inverter capacity and insulation class of high-power motors are coupled, causing the specific power of the motor to decrease as the power of a single unit increases. The research and manufacturing cost increases superlinearly with power (approximately C∝P^k in engineering statistics, k≈1.3~1.5). Moreover, there are no mature off-the-shelf products for megawatt-class aerospace motors. Each thrust increase means a completely new high-risk development.

[0005] 2. Battery Pack Power Bottlenecks and Safety Issues. To output greater power from a single centralized battery pack, it is necessary to increase the discharge rate or connect more cells in series or parallel. High-rate discharge leads to a dramatic increase in internal resistance and heat generation, a significant reduction in usable specific power, and an increased risk of thermal runaway. Meanwhile, large-scale series and parallel cell connections introduce safety and reliability challenges such as equalization management and single-point short-circuit propagation. Calculations show that when the target thrust reaches the 1000 kN level, a centralized battery pack needs to continuously output approximately 8 MW of power, and its equivalent specific power will decrease from approximately 1.5 kW / kg to approximately 0.96 kW / kg. The battery pack's mass increases dramatically, becoming the largest structural dead weight component in the entire system.

[0006] 3. Single point of failure risk. The single pump, single motor, and single battery pack form a series reliability link. Failure of any link will lead to the failure of the entire engine, with no degraded operation capability.

[0007] 4. Pump hydraulic design constraints. The increase in single pump flow rate is constrained by specific speed, net positive suction head (NPSH), and impeller outlet linear velocity. The speed, size, and efficiency of high-flow-rate, high-head pumps are mutually restrictive, further exacerbating the difficulty of achieving high power output.

[0008] Existing patent literature concerning electric pump rocket engines has not resolved the aforementioned thrust expansion bottleneck problem: Patent CN109736971A (An Electric Pump-Pressure Liquid Rocket Engine, Xi'an Aerospace Propulsion Institute) discloses an electric pump-pressure engine system consisting of one oxidizer pump, one fuel pump, their drive motors, controllers, and power supplies. This patent belongs to a typical single-pump centralized architecture, with only one pump for each type of propellant. Its power supply is centralized, and it does not involve the concept of multiple pumps connected in parallel for the same propellant to increase thrust through flow superposition, nor does it have pump-stage redundancy or degraded operation capabilities.

[0009] Patent US6457306B1 (Electrical drive system for rocket engine propellant pumps) discloses an electric drive system for driving rocket propellant pumps with an electric motor. To address the problem of insufficient power from a single motor, it proposes using multiple motors to drive the same pump (including a counter-rotating motor pair arrangement). However, this solution still uses a single pump with a single flow path, essentially representing a technical approach that increases the power of a single pump. The pump's hydraulic bottlenecks, cavitation constraints, and single-point failure risks are not eliminated, and the rigid coupling of multiple motors to the same pump shaft cannot achieve fault isolation. This is fundamentally different from the technical approach of this invention, which involves "multiple pumps in parallel, flow superposition, and independent power supply."

[0010] Patent CN116025485A (A Launch Vehicle Attitude Control Propulsion System Based on an Electric Pump) applies an electric pump to the attitude control propulsion system. The power level is small and it does not involve the thrust expansion problem of the main propulsion supply system.

[0011] Patent WO2018051566A1 (Electric-assisted liquid fuel rocket propulsion system, IHI Corporation) adopts a hybrid architecture of electric motor-assisted turbopump, but still retains the gas turbine. The system complexity is not eliminated, and it does not involve a multi-pump parallel architecture.

[0012] Patent CN111654227A (A variable thrust liquid engine electric drive control propellant supply system, Jiangsu Shenlan Aerospace) achieves variable thrust by adjusting the speed of a single electric pump, which is still a single pump speed regulation route. The throttling depth is limited by the minimum stable flow of a single pump, and it cannot solve the problem of expanding the upper limit of thrust.

[0013] Patent CN121024797A (An Automatic Control System for an Electric Pump Rocket Engine, first filed by the inventor of this application) discloses a closed-loop automatic control method for an electric pump engine. It addresses the control accuracy problem of a single electric pump but does not involve the system architecture and thrust expansion method of multiple pumps in parallel.

[0014] Furthermore, while there are practices in engineering practice of increasing the total thrust of a rocket by connecting multiple small-thrust engines in parallel (such as nine electric pump engines in parallel on the first stage of a foreign rocket), parallel connection of the entire engine means that the entire set of components such as the thrust chamber, nozzle, valves, and frame are replicated many times over. The structural efficiency and cost are far inferior to the scheme of connecting only the pump unit in parallel within a single engine. Moreover, parallel connection of the entire engine is a general layout method and does not solve the thrust expansion bottleneck of the electric pump circulation supply system itself at the engine level.

[0015] In summary, the common limitation of existing technologies is that they all assume that "increasing the thrust of an electric pump engine requires increasing the power of a single pump," thus making the superlinear cost of the motor and battery an insurmountable obstacle. There is no existing technology that starts from the physical essence that "thrust depends only on the mass flow rate of the propellant" and decomposes the centralized high-power demand into multiple small and medium-power units by connecting multiple pumps in parallel inside the engine and equipping each pump with an independent battery pack, thereby eliminating the power bottleneck and realizing the economical expansion of electric pump cycles to medium and large thrust levels. Summary of the Invention

[0016] The purpose of this invention is to overcome the thrust expansion bottleneck of the existing single-pump centralized architecture of electric pump cycle engines, and to provide a propellant supply system for electric pump liquid rocket engines based on multi-pump parallel connection. This system enables the electric pump cycle to achieve linear, economical and reliable expansion to medium and large thrust levels with mature small and medium power components without relying on the development of high-power motors and high-rate, large-capacity battery packs.

[0017] The core innovation of this invention lies in proposing and demonstrating a flow parallel paradigm for thrust extension of an electric pump engine, which includes the following three aspects: (I) Reconstruction of the Thrust Extension Principle. The rocket engine thrust expression is as follows: F = ṁ·v_e + (p_e-p_a)·A_e ≈ ṁ·I_sp·g0 Where ṁ represents the total propellant mass flow rate, v_e is the equivalent exhaust velocity, I_sp is the specific impulse, and g0 is the standard gravitational acceleration. Under the condition that the combustion chamber pressure and mixture ratio remain constant (i.e., the supply pressure demand and specific impulse remain constant), the thrust is only proportional to the total mass flow rate ṁ. Therefore, increasing the thrust does not require increasing the head or power of any single pump; it only requires increasing the total flow rate while ensuring that the supply pressure (head) remains constant. According to the hydraulic characteristics of parallel centrifugal pumps, when n pumps with identical characteristics and equal heads are connected in parallel, the total flow rate is the sum of the flow rates of each pump. The total thrust then increases linearly with the number of parallel units n, while the load on each pump, each motor, and each battery pack remains constant.

[0018] (ii) Distributed independent battery pack power supply architecture. Each pump unit is equipped with an independent battery pack that supplies power only to its own unit, and the battery packs are electrically isolated and uncoupled from each other. As a result, regardless of the target thrust, the output power and discharge rate of each battery pack remain at a mature and safe medium level, thereby avoiding the power derating, thermal runaway risk and balance management problems of centralized large battery packs at high discharge rates; at the same time, the failure of any battery pack only affects its corresponding unit and does not affect the entire system.

[0019] (III) Thrust-to-mass gain ratio benefit criterion. This invention provides a quantitative criterion for the economic feasibility of parallel expansion: defining the thrust-to-mass gain ratio of a single pump unit. R = (F_unit / g0) / m_unit Where F_unit represents the thrust increment corresponding to the rated flow rate of the unit, and m_unit represents the total mass of the unit (pump + motor + independent battery pack + auxiliary pipeline valves). As long as R > 1, the thrust gain (equivalent to the supportable mass) obtained by each additional pump unit is always greater than its own mass cost, and parallel expansion is a positive benefit in terms of both energy and economy. Theoretical calculations show that under typical liquid oxygen / kerosene electric pump cycle parameters, the R value of units with power ratings of 50–400 kW reaches 11–13, which is much greater than the criterion line R = 1, indicating sufficient benefit margin.

[0020] The technical solution adopted in this invention is a propellant supply system for a liquid rocket engine based on a multi-pump parallel electric pump, including: a fuel supply branch and an oxidizer supply branch, wherein at least one branch (preferably both branches) is equipped with n≥2 parallel electric pump units (10); each electric pump unit (10) consists of a propellant pump (1), a drive motor (2), an independent battery pack (3), and a unit controller (4), which is a standardized and modular design; a one-way valve (5) and a manifold device (6), wherein the outlets of each pump are connected to the manifold device through the one-way valve to realize equal head parallel connection and liquid circuit isolation of faulty units; a common supply main pipe (7) to transport the propellant after the manifold to the thrust chamber (11); a main control module (8) to communicate with each unit controller (4) to perform speed coordination, phase-shifting operation, fault detection and isolation, degraded operation and deep throttling control; and a propellant tank (9) shared by each pump unit in the same branch.

[0021] Compared with existing patented technologies, the differences and inventiveness of this invention are reflected in: 1. Compared with CN109736971A: This patent only has one pump for each type of propellant, and the thrust amplification can only follow the single pump power amplification route; This invention sets up multiple parallel pump units for the same type of propellant, and uses the number of units instead of the unit power to match the target thrust. The thrust amplification cost changes from superlinear to linear, and for the first time, it obtains redundancy degradation capability at the pump stage.

[0022] 2. Compared with US6457306B1: This patent uses multiple motors to drive the same pump, and the pump and flow channel are still single, so the pump hydraulic bottleneck and single-point failure are still there; the present invention connects a complete "pump-motor-battery" unit in parallel, the flow channel is multiplied, the bottlenecks of the three levels of pump, motor and battery are eliminated at the same time, and each unit can be independently isolated, so the architecture is fundamentally different.

[0023] 3. Compared with WO2018051566A1: that patent retains the turbo pump and uses an electric motor for assistance, so the system complexity is not reduced; this invention is a pure electric pump cycle without any gas turbine components.

[0024] 4. Compared with CN111654227A: This patent relies on single-pump speed regulation and thrust variation, and the lower limit of throttling is constrained by the minimum stable flow of a single pump; This invention can achieve deep throttling far exceeding the speed regulation limit of a single pump by shutting down some units, while maintaining the operating unit at a high-efficiency operating point.

[0025] 5. Compared with the engineering approach of connecting multiple engines in parallel: This invention only connects the pump unit of the supply system in parallel, sharing the thrust chamber, nozzle and frame, avoiding the structural and cost costs of replicating the whole machine, and achieving thrust expansion within the engine at the lowest cost.

[0026] The beneficial effects of this invention are as follows: First, it breaks through the upper limit of thrust by replacing the development of a megawatt-level single engine with n mature power-level (50-500 kW) units in parallel. The electric power requirement of a single 240 kN-level engine is reduced from approximately 1953 kW to 488 kW (four-pump scheme). The 1000 kN-level engine does not require the development of an 8 MW-level motor and battery pack. For the first time, the electric pump cycle has a realistic engineering path to expand to medium and large thrust levels. Second, it reduces system mass. Distributed units avoid the power specific decay of high-power motors and the high-rate derating of batteries. The system mass of the 240 kN-level embodiment is reduced by approximately 10.8%, and that of the 1000 kN-level embodiment is reduced by approximately 23%. Third, it significantly reduces costs. The superlinear growth of unit costs with power is avoided. Standardized unit mass production enjoys the learning curve effect. The cost of the 240 kN-level embodiment is reduced by approximately 49%, and that of the 1000 kN-level embodiment is reduced by approximately 23%. Fourth, reliability is significantly improved. The parallel unit with n≥2 has the ability to isolate single pump failure and degrade operation. Under the condition of unit reliability of 0.99, the parallel connection of two pumps reduces the probability of supply system task failure from 10^-2 to the order of 10^-4. Fifth, deep throttling and pulsation suppression. Shutting down some units achieves a wide range of thrust adjustment. The staggered operation of each pump reduces the pressure pulsation of the supply main pipe and improves combustion stability. Sixth, modularization and industrialization. The same model of pump unit can be used in engines with different thrust levels, forming a modular and combined product series, shortening the development cycle and reducing the development cost per unit product. Attached Figure Description

[0027] Figure 1 The graph shows the linear relationship between engine thrust and total propellant mass flow rate. The graph marks the operating point corresponding to the number of units n when 500 kW pump units are connected in parallel. Figure 2 A comparison curve showing the change of total mass of the supply system as a function of target thrust between the single-pump centralized route and the multi-pump parallel distributed route of the present invention; Figure 3 A comparative graph showing the normalized cost of the supply system for the two technical routes as a function of target thrust; Figure 4 A bar chart showing the thrust-to-mass gain ratio R for pump units of different power levels (including the revenue criterion line R=1). Figure 5A comparative curve (semi-logarithmic coordinates) showing the change in the probability of system task failure with the reliability of a single pump unit under different numbers of parallel units. Figure 6 A bar chart comparing key parameters of the four-pump parallel scheme and the single-pump centralized scheme in the 240 kN-level embodiment; Figure 7 This is a schematic diagram of the propellant supply system of the present invention.

[0028] Figure 7 Explanation of reference numerals in the attached diagram: 1—Propellant pump; 2—Drive motor; 3—Independent battery pack; 4—Unit controller; 5—One-way valve; 6—Manifold; 7—Common supply main pipe; 8—Main control module; 9—Propellant tank; 10—Electric pump unit; 11—Thrust chamber. Detailed Implementation

[0029] The invention will be further described below with reference to the accompanying drawings, theoretical model, formula derivation, and embodiments. The following parameters and calculation results are used to illustrate the principles and benefits of the invention. In specific engineering implementation, they can be adjusted according to the propellant combination, thrust level, and component level. The parameters are for reference only.

[0030] (I) System Structure and Working Principle. For example... Figure 7 As shown, the propellant supply system in this embodiment uses a combination of liquid oxygen / kerosene propellant, including a fuel supply branch and an oxidizer supply branch. The fuel supply branch is equipped with two parallel fuel pump units, and the oxidizer supply branch is equipped with two parallel oxidizer pump units, for a total of four electric pump units (10). Each pump unit consists of a centrifugal propellant pump (1), a permanent magnet synchronous motor (2), an independent lithium battery pack (3), and a unit controller (4). The two pumps in the same branch draw propellant from a shared storage tank (9), and the pump outlets enter the confluence device (6) through check valves (5), and are connected in parallel with equal outlet pressure and head. After confluence, the propellant is transported to the thrust chamber (11) through a shared supply main pipe (7). Each independent battery pack (3) only supplies power to the motor of its own unit, and the four battery packs are electrically isolated from each other. The main control module (8) communicates with the four unit controllers (4) through a bus to perform speed coordination, phase-shifting operation, fault detection and isolation, and degraded operation control.

[0031] During operation, the main control module calculates the required total mass flow rate based on the thrust command and distributes it equally (or according to weight) to each pump unit in the same branch. Each unit controller adjusts the motor speed in a closed loop to ensure that the outlet pressure of each pump is consistent and the flow rate is superimposed according to the command. Since the total flow rate is the sum of the flow rates of each pump when centrifugal pumps are connected in parallel with equal head, the pressure in the main supply pipe remains unchanged at the design supply pressure, the combustion chamber pressure and specific impulse are not affected, and the engine thrust increases linearly with the total flow rate.

[0032] (II) Theoretical Model and Formula Derivation.

[0033] 1. The relationship between thrust and flow rate. Engine thrust is... F = ṁ·v_e, v_e = I_sp·g0 (Formula 1) Taking the specific impulse at sea level I_sp = 300 s, we get v_e ≈ 2942 m / s. Given the target thrust F, the required total mass flow rate is ṁ = F / v_e. Thrust and total mass flow rate are strictly linear ( Figure 1 This is the physical basis for the invention of "replacing power amplification with parallel flow".

[0034] 2. Pump power equation. The shaft power required by a single pump and its corresponding electrical power are: P_pump = ṁ_i·Δp / (ρ·η_p), P_e = P_pump / (η_m·η_inv) (Formula 2) Where ṁ_i is the pump mass flow rate, Δp is the total pump pressure rise, ρ is the propellant density, and η_p, η_m, and η_inv are the pump efficiency, motor efficiency, and inverter efficiency, respectively. In this embodiment, Δp = 15 MPa, equivalent density ρ = 1030 kg / m³, η_p = 0.66, η_m = 0.95, and η_inv = 0.97 are taken, and the total efficiency of the electric power chain η = η_p·η_m·η_inv ≈ 0.608. From equations (1) and (2), the relationship between total electric power and thrust can be obtained. P_e,total = F·Δp / (v_e·ρ·η) (Formula 3) That is, each kN of thrust requires approximately 8.14 kW of electrical power. A single 500 kW pump unit can provide a flow rate of approximately 20.9 kg / s and a thrust increment of approximately 61.4 kN.

[0035] 3. Parallel Hydraulic Characteristics. Assume the head-flow characteristic of a single pump is H = H0 - a·Q² (typical droop characteristic of a centrifugal pump). When n pumps with identical characteristics and equal heads are connected in parallel, the system characteristics are: H = H0 - a·(Q_total / n)² (Equation 4) That is, under the same head (same supply pressure), Q_total = n·Q_unit, and the total flow rate increases linearly with the number of pumps connected in parallel; the operating point of each pump remains unchanged, all within their high-efficiency zone. By using check valves to prevent backflow and combining devices to balance the resistance of each branch, stable parallel operation can be guaranteed. This is precisely the hydraulic realization of "increasing mass flow rate while ensuring supply pressure".

[0036] 4. Motor quality model. The specific power of the motor decreases as the power of the single unit increases. (The last part, "take...", seems to be a separate, unrelated statement.) p_m(P) = p_m0·(P / P_m0)^(-α), P>P_m0 (Formula 5) Where p_m0 = 5 kW / kg (a constant value is taken for p_m0 = 100 kW and below), and the attenuation index α = 0.15. The motor mass m_motor = P / p_m(P). In the single-pump centralized route, P is the total power, and the motor mass increases linearly with the thrust m ∝ P^(1+α); in this invention, the power of each motor is constant at P_unit, and the total motor mass increases linearly with the thrust.

[0037] 5. Battery Pack Mass Model. The mass of the battery pack is determined by the larger of the power constraint and the energy constraint: m_batt = max[P_e / p_b(P_e),P_e·t_burn / e_b] (Formula 6) Where the specific power p_b(P) = p_b0·(P / P_b0)^(-β) (p_b0=1.5 kW / kg, P_b0=200 kW and below takes a constant value, high-rate derating index β=0.12), specific energy e_b=200 Wh / kg, and working time t_burn=160 s. In the single-pump centralized route, the battery pack power is equal to the total power, and the specific power is dated to about 0.96 kW / kg at 8 MW; in this invention, the power of each independent battery pack is always on the order of P_unit / η_m / η_inv, always maintaining a rated specific power of about 1.5 kW / kg, without derating.

[0038] 6. Derivation of the thrust-mass gain ratio criterion. The thrust increment brought by adding a new pump unit is F_unit = ṁ_unit·v_e, and its mass cost is m_unit = m_pump + m_motor + m_batt + m_pipe. The thrust-mass gain ratio is defined. R = (F_unit / g0) / m_unit (Equation 7) The physical meaning of R is: the ratio of the mass that the unit thrust increment can support to the unit's own mass. When R > 1, the thrust increment generated by the newly added unit is greater than the gravity corresponding to its own mass, that is, the unit can still provide a net thrust gain for the rocket body after compensating for its own mass cost; it can be further proved by the rocket equation Δv = v_e·ln(m0 / m_f) that as long as R > 1 and the propellant in the tank increases proportionally to the flow rate, the thrust-to-weight ratio and carrying capacity of the entire stage are both improved. Substituting the units of the four power levels of 50, 100, 200, and 400 kW into equations (2), (5), and (6), the R values ​​are approximately 12.4, 12.4, 12.1, and 11.2, respectively. Figure 4 The value is much greater than the criterion line R=1, indicating that the parallel expansion has a positive revenue margin of about one order of magnitude; even if system-level costs such as structural installation and tank increments are taken into account, the criterion still holds firmly.

[0039] 7. Reliability Model. Treating the parallel supply system as a k-out-of-n voting system, allowing for degradation due to the failure of one unit, the system's reliability is: R_sys = r^n + n·(1-r)·r^(n-1) (Formula 8) Where r is the unit reliability of a single pump group. Taking r = 0.99: the failure probability of the single pump scheme is 1×10^-2; the failure probability of the dual pumps in parallel is reduced to 1×10^-4; and the failure probability of the four pumps in parallel is 5.9×10^-4; all of which are 1 to 2 orders of magnitude better than the single pump scheme. Figure 5 Furthermore, because each battery cell is electrically isolated from the others, electrical faults will not propagate across cells, thus blocking common cause failure paths.

[0040] 8. Cost Model. The research and manufacturing costs of high-power motors and their supporting batteries and inverters increase superlinearly with single-unit power, taking C∝P^1.4; the standardized unit of this invention is a mass-produced mature power product, using a learning curve with a 90% learning rate (unit cost decreases by 10% for every doubling of production volume). Calculation results are as follows. Figure 3 As shown: When the target thrust is 1000 kN, the normalized cost of the single-pump centralized route is about 473 (with the cost of a 100 kW unit as 1), while the cost of the route of this invention is only about 121, which is a cost reduction of about 74%.

[0041] (III) Calculation Verification and Multi-condition Comparison. The model described in equations (1) to (6) was applied to the thrust range of 25–1000 kN, and the results were obtained. Figure 2 The comparison of the total mass of the supply system shown is as follows: As the target thrust increases, the total mass of the single-pump centralized system increases faster than linearly due to the decrease in motor power density and the derating of the battery at high rates; the total mass of the multi-pump parallel system of this invention increases approximately linearly because each unit always operates in a mature power range without derating, and a mass gain zone with increasing thrust is formed between the two curves. At a target thrust of 1000 kN, the mass of the single-pump centralized system is approximately 12394 kg, while the mass of the system in this invention is approximately 9492 kg, a reduction of approximately 23%.

[0042] Table 1 shows a comparison of the component mass and power of the two schemes under different total power requirements (corresponding to different thrust levels). It can be seen that when the total power is 500 kW (approximately 61 kN thrust), the mass of the two schemes is basically the same (the multi-pump scheme is slightly heavier by 3% due to the combiner device), which is the critical point for the benefit of the parallel architecture. As the total power increases, the mass of the motor and battery in the single-pump centralized scheme increases superlinearly, and the battery specific power continuously decreases. However, the load and specific power of each unit and its independent battery pack in the scheme of this invention remain constant, and the mass saving increases from 4.1% at 1 MW to 22.9% at 8 MW, while the power requirement of a single unit remains at a mature level of 500 kW.

[0043]

[0044] Table 1 also reveals the applicable boundaries and selection guidelines of the present invention: when the total power corresponding to the target thrust does not exceed the mature power level of the unit (n=1), the parallel architecture has no benefit and the conventional single-pump scheme should be adopted; when the total power reaches twice or more of the unit power, the parallel architecture benefits simultaneously in terms of quality, cost and reliability, and the benefit increases monotonically with the thrust level - this is the quantitative basis for the present invention to realize the thrust level expansion of the electric pump cycle engine.

[0045] (iv) Example: 240 kN-class four-pump parallel supply system. Target sea-level thrust F = 240 kN, specific impulse 300s. From equation (1), the required total mass flow rate ṁ = 240000 / 2942 ≈ 81.6 kg / s; with a mixing ratio of 2.3, the oxidant flow rate is approximately 56.9 kg / s, and the fuel flow rate is approximately 24.7 kg / s. From equation (3), the total electric power of the supply system is approximately 1953 kW. If following the existing single-pump centralized route, it would require the development of a single motor, a single pump, and a single high-rate battery pack of approximately 2 MW, far exceeding the current highest engineering level of approximately 415 kW single-pump power for electric pump engines, resulting in extremely high development risks and costs.

[0046] The present invention employs a configuration of four units: two fuel pump units and two oxidizer pump units. Each unit has a power output of approximately 488 kW, placing it at a mature level that has been engineering-verified or is close to being verified in existing technologies. Each unit is powered by an independent battery pack, with a single pack output power also in the 488 kW range, and the discharge rate remains within the conventional safe range. (Calculation comparison...) Figure 6 The total mass of the four-pump parallel supply system is approximately 2239 kg, which is about 10.8% lower than the 2509 kg of the single-pump centralized system (approximately 270 kg, directly converted into carrying capacity); the normalized cost is approximately 32.7, which is about 49% lower than the 64.1 of the single-pump system; at the same time, it gains the ability to operate in a downgraded manner in case of single-pump failure—if any unit fails, the other unit in the same branch can increase its speed within the allowable range of the components to compensate for part of the flow, and coordinate with the synchronous adjustment of the opposite branch to maintain the mixture ratio, and the engine continues to work in a reduced thrust mode, while the single-pump centralized system will completely lose power under the same failure.

[0047] Control implementation method. The degraded operation control logic of the main control module (8) is as follows: after receiving the thrust command, the total flow command is calculated according to formula (1); the speed, current, outlet pressure and battery status of each unit are periodically detected to determine the health status of the unit; the one-way valve (5) of the faulty unit is closed to realize liquid circuit isolation, and the output of its independent battery pack (3) is cut off to realize electrical isolation; the total flow command is redistributed among the remaining healthy units, and each unit is subject to closed-loop speed regulation constrained by over-speed and cavitation limit; at the same time, the adjacent units are controlled to operate with a phase difference of 2π / n to reduce the pressure pulsation of the supply main pipe.

[0048] Deep throttling implementation method. When a wide range of thrust adjustment is required (such as during the recovery landing deceleration phase), the main control module can shut down some pump units in the same branch, leaving only one unit operating in its high-efficiency operating range: the theoretical throttling depth of the four-pump scheme can reach about 25% below the rated thrust. When combined with the speed regulation range of the operating unit itself, the total throttling depth is far superior to the single-pump speed regulation scheme, and each operating unit always operates near the operating point with optimal efficiency and stability.

[0049] The implementation differs from the comparative patent. Compared to the single-pump architecture of CN109736971A, this embodiment can generate a thrust spectrum from 61 kN (n=1) to 983 kN (n=16) by adding or removing standard units, without the need to redevelop any pumps, motors, or battery packs; compared to the multi-motor driven single-pump scheme of US6457306B1, any unit failure in this embodiment can be isolated by both hydraulic and electrical circuits, and there is no chain failure due to coaxial rigid coupling; compared to the single-pump speed regulation and thrust variation of CN111654227A, this embodiment achieves a deeper throttling depth through a two-stage method of "unit shutdown + unit speed regulation".

[0050] This invention is not limited to the specific technical details disclosed in the foregoing exemplary embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of this invention, including changes to the number of parallel units, unit power level, propellant combination, pump type and motor type, battery chemistry system and control strategy, shall still fall within the scope of the technical solution of this invention. Any modifications and alterations within the scope of the claims shall be included in the protection of this invention.

Claims

1. A propellant supply system for a liquid rocket engine with electrically driven pumps in parallel, characterized in that: It includes a fuel supply branch and an oxidizer supply branch, wherein at least one supply branch is equipped with n parallel electric pump unit (10), n≥2; each of the electric pump unit (10) includes a propellant pump (1), a drive motor (2), an independent battery pack (3) and a unit controller (4); each propellant pump (1) in the same supply branch draws the same type of propellant from a shared propellant tank (9), and its outlet is respectively connected to the shared supply main pipe (7) through a check valve (5) and a manifold device (6), and has an equal outlet. The pressure achieves parallel operation with equal head, so that the total mass flow rate of the supply branch is the sum of the mass flow rates of each pump unit; each independent battery pack (3) supplies power only to the drive motor (2) of its own unit, and the independent battery packs (3) are electrically isolated from each other and do not constitute load coupling, so that the output power and discharge rate of any battery pack do not increase with the increase of the total thrust of the engine; the system also includes a total control module (8), which is connected to the controllers (4) of each unit to coordinate the speed, start and stop and fault isolation of each pump unit.

2. Propellant supply system according to claim 1, characterized in that: The fuel supply branch is equipped with at least two parallel fuel pump units, and the oxidant supply branch is equipped with at least two parallel oxidant pump units, forming a dual-branch parallel architecture with no less than four pump units.

3. The propellant supply system of claim 1, wherein: The propellant pump (1) is a centrifugal pump, and the drive motor (2) is a permanent magnet synchronous motor or a brushless DC motor. The rated power of a single pump unit is selected within the mature power range of 50 kW to 500 kW. The target thrust is matched by increasing or decreasing the number of parallel units n rather than increasing the unit power.

4. The propellant supply system according to any one of claims 1 to 3, characterized in that: The selection of the pump unit satisfies the thrust-mass gain ratio criterion R=(F_unit / g0) / m_unit>1, where F_unit is the thrust increment corresponding to the rated mass flow rate of a single pump unit, g0 is the standard gravitational acceleration, and m_unit is the total mass of the pump unit including the propellant pump (1), drive motor (2), independent battery pack (3) and its auxiliary pipeline valves, so as to ensure that the thrust gain obtained by each additional pump unit is greater than its mass cost.

5. The propellant supply system according to claim 1, characterized in that: When any pump unit fails, the main control module (8) closes the one-way valve (5) of that unit and cuts off its independent battery pack (3) output to achieve dual fault isolation of the liquid circuit and electrical circuit. At the same time, it instructs the other pump units in the same branch to increase their speed, partially or completely compensate for the lost mass flow rate within the allowable range of the components, and realize the degraded operation of the supply system.

6. The propellant supply system according to claim 1, characterized in that: The main control module (8) achieves a wide range of deep throttling of the engine by shutting down some pump units and adjusting the speed of the remaining units; the lower limit of the throttling depth is determined by the minimum stable flow rate of a single pump unit.

7. The propellant supply system according to claim 1, characterized in that: The main control module (8) controls each propellant pump (1) in the same supply branch to operate with a set phase difference, so that the pressure pulsation at the outlet of each pump cancels each other in the confluence device (6), reducing the pressure pulsation amplitude in the common supply main pipe (7).

8. The propellant supply system according to claim 1, characterized in that: The electric pump unit (10) is a standardized and modular design. The same model of pump unit can be used in engines with different thrust levels, and the unit cost is reduced through mass production.

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