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CN-122021431-A - Performance prediction method for compact steam piston engine

CN122021431ACN 122021431 ACN122021431 ACN 122021431ACN-122021431-A

Abstract

The invention discloses a performance prediction method for a compact steam piston engine, which comprises the following steps of 1, constructing an engine zero-dimensional thermodynamic analysis model, calculating an engine indication performance parameter, 2, constructing an engine three-dimensional fluid dynamic CFD model, calculating an engine in-cylinder flow field detail parameter, 3, constructing a compact steam piston engine, obtaining an actual engine indication performance parameter, 4, comparing the actual engine indication performance parameter with the engine indication performance parameter, adjusting the zero-dimensional thermodynamic analysis model, and calculating to obtain an optimized indication performance parameter, and 5, predicting the performance of the compact steam piston engine according to the optimized indication performance parameter and the engine in-cylinder flow field detail parameter. The performance prediction method for the compact steam piston engine solves the problem that a single dimension model in the prior art cannot meet the design efficiency requirement while guaranteeing the prediction precision.

Inventors

  • LI DAIJIN
  • YANG HAO
  • QIN KAN
  • Wen Menggang
  • GUO QING
  • HUANG LI
  • HUANG CHUANG
  • XU HAIYU

Assignees

  • 西北工业大学

Dates

Publication Date
20260512
Application Date
20260129

Claims (10)

  1. 1. A performance prediction method for a compact steam piston engine, comprising the steps of: step 1, constructing an engine zero-dimensional thermodynamic analysis model, and calculating engine indication performance parameters through the model; Step 2, establishing a three-dimensional fluid dynamic CFD model of the engine, and calculating the detail parameters of the flow field in the engine cylinder according to the model; Step 3, constructing a compact steam piston engine, and testing the engine to obtain actual engine indication performance parameters; Step 4, comparing the actual engine indicating performance parameter with the engine indicating performance parameter, adjusting a zero-dimensional thermodynamic analysis model, and calculating to obtain an optimized indicating performance parameter; and 5, predicting the performance of the compact steam piston engine according to the optimization indicating performance parameter and the internal flow field detail parameter of the engine cylinder.
  2. 2. The method for predicting performance of a compact vapor piston engine as set forth in claim 1 wherein said step1 is specifically: Step 1.1, dividing the single-cylinder actual working cycle period of the engine into an air inlet process, an expansion process, an early exhaust process, an exhaust process, a compression process and an early air inlet process; step 1.2, dispersing a working cycle period based on an engine operation parameter, a thermodynamic law, an engine gas distribution phase and a piston kinematics rule, solving a piston equation simultaneously in each discrete time step, and iteratively calculating key point parameters in a cylinder at the moment of an air inlet process, an expansion process, an early exhaust process, an exhaust process, a compression process and an early air inlet process; the engine operating parameters include a clearance volume ratio Air intake ratio Expansion ratio of Ratio of preliminary exhaust gas Exhaust ratio Ratio of air to pressure Ratio of pre-charge Combustion chamber temperature Combustion chamber pressure Back pressure ; Step 1.3, integrating on a pressure-volume indicator diagram according to the key point parameters calculated in the step 1.2, and calculating to obtain single-cylinder indicator; and 1.4, calculating theoretical indicated power of the engine according to the single-cylinder indicated power, the engine speed and the cylinder number.
  3. 3. The method for predicting performance of a compact vapor piston engine according to claim 2, wherein said step 1.2 is specifically: step 1.2.1, calculating the key point pressure of the air inlet process according to the formula (1); (1); wherein P c is the combustion chamber pressure; Calculating a gas distribution angle in the gas inlet process according to the formula (2); (2); Wherein, the In order to be an air-intake ratio, The number of peaks and valleys of the piston; Calculating the key point pressure of the expansion process according to the formula (3); (3); Wherein, the Is the pressure drop coefficient; Calculating the distribution angle of the expansion process according to the formula (4); (4); calculating the key point pressure of the early exhaust process according to the formula (5); (5); Wherein, the In the form of a clearance volume ratio, In order to achieve the pre-exhaust ratio, Is the adiabatic index of the working medium, Calculating a gas distribution angle of an early exhaust process according to the formula (6); (6); Calculating a key point pressure of the exhaust process according to formula (7); (7); Wherein, the As a result of the back pressure, Calculating a gas distribution angle of the exhaust process according to formula (8); (8); calculating the key point pressure of the compression process according to the formula (9); (9); calculating a gas distribution angle in the compression process according to the formula (10); (10); calculating the key point pressure of the advanced air inlet process according to the formula (11); (11); calculating a distribution angle of an advanced air inlet process according to a formula (12); (12); Step 1.2.2, calculating the piston movement position according to formula (13); (13); Wherein S is the stroke of the piston, In order to obtain the number of peaks of the piston, In order to be the rotational speed, Time is; Step 1.2.3, calculating the volume according to formula (14); (14)。
  4. 4. The method of claim 2, wherein the single cylinder pilot work in step 1.3 is calculated as follows: calculating single-cylinder indication work according to formulas (15), (16) and (17); (15); (16); (17); Wherein, the Taking the efficiency factor of 0.9 as well as f as the fullness coefficient and 0.98 as well as the fullness coefficient; Is the effective volume of the piston; the theoretical indicated power in step 1.4 is calculated as follows: Calculating a theoretical indicated power according to equation (18); (18); In the formula, The number of the pistons is the number of the pistons, Is the rotational speed.
  5. 5. The method for predicting performance of a compact vapor piston engine of claim 2, wherein said step 2 is specifically: Step 2.1, based on the engine size parameters, establishing a fluid calculation domain model comprising the motion domains of the distributing valve, the cylinder and the piston, The engine dimensional parameters include the number of pistons z e , the cam peak number i e , the piston stroke S, the piston diameter d, An intake diameter d jq , an exhaust port diameter d pq , an intake process θ 1 , an expansion process θ 2 , a pre-exhaust process θ 3 , an exhaust process θ 4 , a compression process θ 5 , and a pre-intake process θ 6 ; Step 2.2, carrying out grid division on the fluid calculation domain model, setting boundary parameters, and establishing a simulation model; the boundary parameters comprise rotating speed, inlet temperature, inlet pressure and outlet pressure; Step 2.3, setting a multiphase flow model and a turbulence model, wherein the wall surface is a non-slip heat insulation wall surface, defining the rotation motion of an air distributing valve and the reciprocating motion rule of a piston, and adopting a movable grid technology for a piston motion area; and 2.4, selecting a solver, and performing transient calculation to obtain space-time distribution data of a pressure field, a temperature field and a speed field of the working medium in the cylinder, namely, the detail parameters of the flow field in the cylinder of the engine.
  6. 6. The method for predicting performance of a compact vapor piston engine of claim 5 wherein said multiphase flow model in step 2.3 is a VOF model, wherein said basic control equations of said VOF model include continuity equations, momentum equations and conservation of energy equations; the continuity equation is shown as a formula (19); (19); In the formula, The rate of change of fluid mass per unit volume over time; Mass flow rate as net outflow per unit volume; The momentum equation is shown as a formula (20); (20); In the formula, Rate of change of fluid momentum per unit volume over time; Is a convection term of momentum, showing momentum transport due to fluid flow; is a pressure gradient force; Is a viscous force; is a volume force; the energy conservation equation is shown as a formula (21); (21); In the formula, Is the satellite derivative of the total energy; is energy transport caused by heat conduction; Is energy transport caused by component diffusion; Is viscous dissipation work; is an external heat source; the turbulence model in the step 2.3 adopts an SST k-omega model, wherein the SST k-omega model comprises a turbulence energy k equation and a specific dissipation rate omega equation; The turbulence energy k equation is shown in formula (22); (22); In the formula, Is an unsteady term; Is a convection item; generating an item for turbulent energy; is a turbulent energy dissipation term; Is a turbulent energy diffusion term; The specific dissipation ratio omega equation is shown in formula (23); (23); In the formula, Is a transient term; Is a convection item; to generate items; Is a dissipative term; Are molecular and turbulent diffusion terms; Is a cross diffusion term; the rule of the rotation motion of the distributing valve and the reciprocating motion of the piston is specifically as follows: calculating the valve angular velocity according to formula (24); (24); In the formula, Is the rotation speed; calculating piston reciprocation according to equation (25); (25); The step 2.3 of adopting a movable grid technology for the piston movement area comprises the steps of defining a movement rule and a speed of the piston top surface changing along with time based on a cam molded line relation of the engine, loading the movement rule into simulation software through a user-defined function to drive the piston wall surface to move in a boundary mode, setting movable grid parameters, and automatically generating a new grid layer or combining original grid layers when the height change of the adjacent grid layers caused by the piston movement exceeds a preset proportion so as to keep the grid quality.
  7. 7. The method for predicting performance of a compact vapor piston engine of claim 5, wherein said step 2.4 is specifically: Step 2.4.1, setting a solver and an algorithm, namely selecting a pressure-based coupled solver and starting a transient computing mode, wherein the pressure-speed coupling algorithm adopts a SIMPLEC algorithm, gradient discrete adopts a least square method unit body format, pressure item discrete adopts a second-order format, and convection items of a momentum equation, an energy equation and a turbulence equation all adopt a second-order windward discrete format; step 2.4.2, time step and iteration setting according to engine speed Determining a time of the single duty cycle according to equation (26); (26); Wherein the method comprises the steps of Is the cam peak number; Will be Discrete into Fixed time step Calculated according to formula (27) ; (27); To ensure that each crank angle or cam angle step is not greater than 0.05 degrees; At each physical time step Setting 20 internal iterations, and monitoring that the key residual drops below 10-4 to ensure single-step convergence; Initializing and monitoring a flow field, namely initializing the whole calculation domain into static pressure outlet pressure and ambient temperature, and setting pressure, temperature and speed monitoring points in the cylinder, an air inlet and outlet passage and key areas of an air distribution valve; Step 2.4.4, executing transient calculation, namely starting a solver, and sequentially and iteratively calculating each time step; In each time step, the solver solves the continuity equation, the momentum equation, the energy equation and the turbulence model equation in sequence, and updates the dynamic grid; When the calculation is completed for at least 3 complete working cycles and the coincidence degree of the in-cylinder pressure indicator diagrams of the last two cycles is higher than 99%, judging that the transient calculation has reached periodical stability; Step 2.4.5, extracting data, namely extracting flow field data of all time steps from the last complete working cycle reaching periodical stability; the in-cylinder flow field detail parameters comprise an in-cylinder speed distribution cloud picture, an in-cylinder pressure distribution cloud picture and an in-cylinder temperature distribution cloud picture.
  8. 8. The method according to claim 5, wherein the testing in step 3 is specifically that a physical prototype is operated under given steam inlet temperature, inlet pressure and back pressure conditions, and the rotation speed and torque of an output shaft of the engine are synchronously measured; The actual engine indication performance parameter is calculated according to a formula (28) through the measured rotating speed and torque; (28); Wherein, the In order to be the rotational speed, Is torque.
  9. 9. The method for predicting performance of a compact steam piston engine according to claim 5, wherein in step 4, the actual engine indicating performance parameter is compared with the engine indicating performance parameter, and the adjusting the zero-dimensional thermodynamic analysis model is specifically to compare the indicating power calculated by the zero-dimensional model with the actual output power measured by the experiment, and by adjusting the efficiency factor, the flow loss coefficient or the heat loss coefficient in the zero-dimensional model, the error between the calculation result of the zero-dimensional model and the experimental data is smaller than a preset threshold.
  10. 10. The method for predicting performance of a compact vapor piston engine as set forth in claim 5 wherein said step 5 is specifically: The calibrated zero-dimensional model is utilized to rapidly calculate the output power and efficiency of the engine under different steam parameters and rotating speeds; And carrying out fine simulation on key or abnormal working conditions screened by the zero-dimensional model by utilizing the three-dimensional model, analyzing the flow uniformity, the vortex structure and the local heat transfer condition in the cylinder, evaluating the influence of the flow uniformity, the vortex structure and the local heat transfer condition on the performance and providing a basis for structure optimization.

Description

Performance prediction method for compact steam piston engine Technical Field The invention belongs to the technical field of heat engine design and performance simulation, and particularly relates to a performance prediction method for a compact steam piston engine. Background In the fields of small distributed energy sources and industrial waste heat recovery, the steam Rankine cycle SRC is one of potential technical paths. However, the design and performance prediction of compact, high power density piston expanders suitable for this scenario is challenging. The traditional method generally adopts a single zero-dimensional thermodynamic model or a three-dimensional computational fluid dynamics CFD simulation model to predict the performance, but has the following problems: The method has the advantages that the precision and the efficiency are difficult to achieve, the zero-dimensional model is fast in calculation, complicated non-uniform flow and heat transfer details in a cylinder cannot be revealed, the prediction precision is limited, the three-dimensional CFD model can reflect details, the calculation cost is extremely high, and the method is not suitable for multi-working-condition rapid analysis and optimization design. Model verification is insufficient, and the traditional research often lacks systematic comparison and verification with real prototype experimental data, and the reliability of the model is doubtful. The method lacks a collaborative framework, and the advantages of different dimension models can not be effectively integrated, so that an efficient closed-loop design verification tool from system-level rapid evaluation to component-level fine analysis is formed. Disclosure of Invention The invention aims to provide a performance prediction method for a compact steam piston engine, which solves the problem that a single dimension model in the prior art cannot meet the design efficiency requirement while guaranteeing the prediction precision. The technical scheme adopted by the invention is that the performance prediction method for the compact steam piston engine comprises the following steps: step 1, constructing an engine zero-dimensional thermodynamic analysis model, and calculating engine indication performance parameters through the model; Step 2, establishing a three-dimensional fluid dynamic CFD model of the engine, and calculating the detail parameters of the flow field in the engine cylinder according to the model; Step 3, constructing a compact steam piston engine, and testing the engine to obtain actual engine indication performance parameters; Step 4, comparing the actual engine indicating performance parameter with the engine indicating performance parameter, adjusting a zero-dimensional thermodynamic analysis model, and calculating to obtain an optimized indicating performance parameter; and 5, predicting the performance of the compact steam piston engine according to the optimization indicating performance parameter and the internal flow field detail parameter of the engine cylinder. The invention is also characterized in that: The step 1 specifically comprises the following steps: Step 1.1, dividing the single-cylinder actual working cycle period of the engine into an air inlet process, an expansion process, an early exhaust process, an exhaust process, a compression process and an early air inlet process; step 1.2, dispersing a working cycle period based on an engine operation parameter, a thermodynamic law, an engine gas distribution phase and a piston kinematics rule, solving a piston equation simultaneously in each discrete time step, and iteratively calculating key point parameters in a cylinder at the moment of an air inlet process, an expansion process, an early exhaust process, an exhaust process, a compression process and an early air inlet process; The engine operating parameters include a clearance volume ratio Air intake ratioExpansion ratio ofRatio of preliminary exhaust gasExhaust ratioRatio of air to pressureRatio of pre-chargeCombustion chamber temperatureCombustion chamber pressureBack pressure; Step 1.3, integrating on a pressure-volume indicator diagram according to the key point parameters calculated in the step 1.2, and calculating to obtain single-cylinder indicator; and 1.4, calculating theoretical indicated power of the engine according to the single-cylinder indicated power, the engine speed and the cylinder number. The step 1.2 specifically comprises the following steps: step 1.2.1, calculating the key point pressure of the air inlet process according to the formula (1); (1); wherein P c is the combustion chamber pressure; Calculating a gas distribution angle in the gas inlet process according to the formula (2); (2); Wherein, the In order to be an air-intake ratio,The number of peaks and valleys of the piston; Calculating the key point pressure of the expansion process according to the formula (3); (3); Wherein, the Is the pressure drop co