CN-121803367-B - Control method of methanol engine thermal management unit based on air compression thermal compensation and waste gas heat exchange

CN121803367BCN 121803367 BCN121803367 BCN 121803367BCN-121803367-B

Abstract

The invention belongs to the technical field of automatic control, and particularly relates to a control method of a methanol engine thermal management unit based on air-pressure thermal compensation and waste gas heat exchange, comprising the following steps of 1, uniformly modeling a heat transfer process and a fluid flow process in the methanol engine thermal management unit into a multi-physical-domain bonding graph model comprising a thermal domain and a fluid domain, and setting feature vectors comprising thermal domain features and fluid domain features for each node; and step 2, performing message transmission on the graph neural network, reading the thermal domain temperature characteristics of the corresponding node of the air inlet of the methanol engine as the predicted air inlet temperature, and step 3, enabling the air inlet temperature to reach the target air inlet temperature according to the comparison result of the predicted air inlet temperature and the target air inlet temperature by the PLC. According to the invention, through multi-physical domain coupling modeling and on-line iterative solution of the graph neural network, the defect that in the prior art, each heat exchange component is independently controlled and the system heat flow coupling relation is ignored is overcome.

Inventors

ZOU MIN
HUANG LIN
XIANG SHITAO
WU KUIHONG
CHEN BAICHUAN
WAN HONGJUN
JIA XIANGANG
HUI TAO
YANG YONG

Assignees

四川蓉腾自动化设备有限公司

Dates

Publication Date: 20260505
Application Date: 20260306

Claims (8)

1. The control method of the methanol engine thermal management unit based on air compression thermal compensation and waste gas heat exchange comprises a methanol engine, an air compressor, an electric heater, a first heat exchanger, a second heat exchanger, a three-way pipeline and a PLC controller, wherein the PLC controller is respectively connected with temperature sensors arranged at a first temperature monitoring point, a second temperature monitoring point and a third temperature monitoring point, the first temperature monitoring point is arranged at the outlet side of the first heat exchanger, the second temperature monitoring point is arranged at the outlet side of the second heat exchanger, the third temperature monitoring point is arranged at the air inlet of the methanol engine, the PLC is connected with the pressure signal interface of the air compressor, the cooling side of the first heat exchanger is provided with a cooling medium inlet temperature sensor, and the cooling medium inlet temperature sensor is connected with the PLC, and the control method is characterized by comprising the following steps: step 1, uniformly modeling a heat transfer process and a fluid flow process in a thermal management unit of a methanol engine into a multi-physical-domain bonding graph model comprising a thermal domain and a fluid domain, mapping each element in the multi-physical-domain bonding graph model into a node of a graph neural network, mapping each energy key into a directed edge of the graph neural network, and setting feature vectors comprising thermal domain features and fluid domain features for each node; Step 2, performing message transmission on the graph neural network, updating the self feature vector of each node according to the updating rule of the corresponding element type according to the feature transmitted by the directed edge of the adjacent node, performing pipe network flow modeling after completing 1 round of message transmission, solving the flow velocity value and the mass flow of each pipe section by taking the difference of the fluid domain pressure features of the nodes at the two ends of each pipe section as driving pressure difference, writing the mass flow back to the feature vector of the corresponding node of the graph neural network, alternately performing message transmission and pipe network flow modeling until convergence or reaching the preset maximum iteration round number, and reading the thermal domain temperature feature of the corresponding node of the air inlet of the methanol engine as the predicted air inlet temperature; Step 3, the PLC controls the electric heater or the first heat exchanger to work according to the comparison result of the predicted air inlet temperature and the target air inlet temperature when the methanol engine is not started, and controls the air compressor and the second heat exchanger to work cooperatively or controls the first heat exchanger to work after the methanol engine is started, so that the air inlet temperature reaches the target air inlet temperature; In the thermal domain, the methanol engine is set as a heat capacity element, the electric heater is set as a controllable thermal potential source element, the first heat exchanger is set as a first dual-port thermal resistance element, the second heat exchanger is set as a second dual-port thermal resistance element, and a cooling medium inlet on the cooling side of the first heat exchanger is set as a thermal domain boundary node; In the fluid domain, an air compressor is set as a fluid domain converter element, a pipe section connecting an air compressor outlet to a first heat exchanger inlet in an air inlet pipeline is set as a series combination of a first fluid inertia element and a first fluid resistance element, a pipe section connecting a second heat exchanger outlet to a methanol engine air inlet is set as a series combination of a second fluid inertia element and a second fluid resistance element, a three-way pipeline is set as a node 1, an inlet port of the node 1 receives waste gas heat generated by the methanol engine, 2 outlet ports of the node 1 are respectively connected to a second heat exchanger and an external heat dissipation pipeline, and a junction of the first heat exchanger outlet and the second heat exchanger outlet in the air inlet pipeline is set as a node 0.
2. The control method according to claim 1, wherein each node is provided with a 4-dimensional characteristic vector, the 1 st dimension is a heat domain temperature characteristic, the 2 nd dimension is a heat domain heat flow rate characteristic, the 3 rd dimension is a fluid domain pressure characteristic, the 4 th dimension is a fluid domain mass flow characteristic, the heat domain is connected with the fluid domain through a convection coupling element, the convection coupling element represents a transportation process of heat carried when the fluid flows through the heat exchanger, the PLC controller reads a real-time temperature value of a first temperature monitoring point temperature sensor and assigns the real-time temperature value to the heat domain temperature characteristic of a node corresponding to the first dual-port heat resistance element, reads a real-time temperature value of a second temperature monitoring point temperature sensor and assigns the real-time temperature value to the heat domain temperature characteristic of the node corresponding to the second dual-port heat resistance element, reads a real-time temperature value of a third temperature monitoring point temperature sensor and assigns the heat domain temperature characteristic of a node corresponding to an air inlet of the methanol engine, and assigns an outlet pressure of an air compressor to the fluid domain pressure characteristic of the node corresponding to the fluid domain converter element and a reading of a cooling medium inlet temperature sensor to the heat domain boundary node.
3. The control method according to claim 2, wherein for the node corresponding to node 1, the signed summation is performed after the heat flow rate characteristics of the heat domain transmitted by all the adjacent nodes of the entering side are marked with positive signs in the entering side direction and negative signs in the exiting side direction, and the summation result is distributed to each adjacent node downstream of the exiting side according to a pre-calibrated split ratio coefficient as an updated increment of the heat flow rate characteristics, wherein the split ratio coefficient is determined by the ratio of the equivalent heat conductance values of the second heat exchanger branch and the external heat dissipation pipeline.
4. A control method according to claim 3, wherein for the node corresponding to the 0 node, the fluid domain mass flow characteristics transmitted from all the adjacent nodes of the incoming side are signed and summed to satisfy the continuity after being signed according to the incoming side direction and the outgoing side direction, meanwhile, the thermal domain temperature characteristics and the fluid domain mass flow characteristics of the adjacent nodes of the incoming side are read, the mass flow characteristics of the branches and the corresponding thermal domain temperature characteristics are multiplied one by one and summed and divided by the sum of the mass flow characteristics of all the incoming branches, the mixed temperature is obtained and updated to the thermal domain temperature characteristics of the 0 node, and the thermal domain temperature characteristics are transmitted to the adjacent nodes downstream along the outgoing side.
5. The control method according to claim 4, wherein for the node corresponding to the first dual-port resistive element, the thermal domain temperature characteristics of the adjacent node on the intake side and the thermal domain boundary node of the first dual-port resistive element are respectively read, the difference between the temperature characteristics of the two ends is multiplied by the equivalent thermal conductance value pre-calibrated by the first heat exchanger to obtain the heat flow rate characteristics through the first heat exchanger, and for the node corresponding to the second dual-port resistive element, the thermal domain temperature characteristics of the adjacent node on the intake side and the adjacent node on the outlet side of the 1 node of the second dual-port resistive element are respectively read, and the difference between the temperature characteristics of the two ends is multiplied by the equivalent thermal conductance value pre-calibrated by the second heat exchanger to obtain the heat flow rate characteristics through the second heat exchanger.
6. The control method according to claim 5, wherein for the node corresponding to the fluid domain converter element, the fluid domain pressure characteristic of the adjacent node on the inlet side is read, scaled according to the compression ratio pre-calibrated by the air compressor, and updated to the fluid domain pressure characteristic on the outlet side, and meanwhile, the heat domain temperature characteristic of the adjacent node on the inlet side is read, the outlet temperature is checked according to the temperature rise map corresponding to the compression ratio pre-calibrated by the air compressor, and updated to the heat domain temperature characteristic, and when each round of message transmission is finished, the convection coupling element multiplies the fluid domain mass flow characteristic connected to the two ends of the convection coupling element by the heat domain temperature characteristic difference between the adjacent nodes and the pre-calibrated equivalent enthalpy coefficient to obtain the convection heat exchange quantity, and the sign of the convection heat exchange quantity is determined by the fluid flow direction.
7. The control method according to claim 1, wherein the convergence determination condition is that a thermal domain temperature characteristic variation of a node corresponding to an air inlet of the methanol engine in successive 2 iterations is smaller than a preset convergence threshold.
8. The control method according to claim 1, wherein in step 3, the PLC controller starts the corresponding heating device when the predicted intake air temperature is lower than the target intake air temperature minus the preset hysteresis deviation value, closes the corresponding heating device when the predicted intake air temperature reaches the target intake air temperature plus the preset hysteresis deviation value, compresses and heats air by the air compressor after the methanol engine is started and when the ambient temperature is lower than the preset low-temperature operation threshold value, and enters the second heat exchanger, the second heat exchanger continuously heats air by using the heat energy supplied by the exhaust gas heat generated by the methanol engine through the three-way pipeline and then sends the air into the methanol engine, and when the methanol engine is started and the ambient temperature is higher than the preset high-temperature operation threshold value, the air enters the first heat exchanger for heat exchange and cooling after the air enters the methanol engine after the air compressor is compressed, and the PLC controller performs locking of the preset minimum holding time after each operation mode switching.

Description

Control method of methanol engine thermal management unit based on air compression thermal compensation and waste gas heat exchange Technical Field The invention belongs to the technical field of automatic control, and particularly relates to a control method of a methanol engine thermal management unit based on air compression thermal compensation and waste gas heat exchange. Background The prior art approaches to engine intake air temperature regulation have mainly been as follows. The first is to directly heat the air in the air inlet pipeline by adopting the electric heating device, the structure is simple, the response speed is high, the air inlet temperature can be effectively improved in the cold start stage, the energy consumption of the electric heater is larger, the total energy consumption of the system can be obviously increased by still depending on the electric heater to maintain the air inlet temperature after the engine runs for a long time, and the comprehensive efficiency of the generator set is reduced. The second is to heat the intake air by using the engine coolant or exhaust waste heat, and this way can recover the waste heat generated by the engine operation to reduce the external energy consumption, but there is an inherent limitation that the coolant temperature and the exhaust temperature are low in the period when the engine is not started or just started, and the waste heat recovery system cannot provide enough heating capacity, so that the problem of insufficient intake air temperature in the cold start period cannot be solved. The third is to set up intercooler or heat exchanger in the air intake line and cool off the high temperature and intake, this kind of scheme has had wide application on the turbocharged engine, but traditional intercooler usually only designs to single cooling function, lacks the ability of reverse heating under low temperature environment, and applicable operating mode scope is limited. Most of the above existing solutions are designed for a specific temperature area or a specific working condition, and lack a unified thermal management architecture capable of covering both extreme low temperature and extreme high temperature environments. Some of the technical solutions attempt to combine electric heating with waste heat recovery, but there are still disadvantages in terms of switching control between different operating conditions. Conventional control schemes typically employ a simple threshold determination based on single temperature sensor feedback, i.e., activating the heating device when the intake air temperature is below a set point and activating the cooling device when it is above a set point. The control mode has two remarkable defects that firstly, the temperature feedback of a single sensor can only reflect the state of the air inlet temperature at the current moment, the variation trend of the air inlet temperature cannot be prejudged, the control action is always lagged behind the temperature variation, large overshoot or undershoot of the air inlet temperature easily occurs when the working condition is rapidly switched, secondly, the simple threshold judgment lacks a hysteresis mechanism and minimum holding time constraint, when the air inlet temperature fluctuates slightly near the threshold, the heating equipment and the cooling equipment are frequently and alternately started and stopped, the mechanical and electrical losses of the equipment are increased, the oscillation of the air inlet temperature with larger amplitude is possibly caused, and the combustion stability is deteriorated. Disclosure of Invention In view of the above, the main purpose of the invention is to provide a control method of a thermal management unit of a methanol engine based on air-pressure thermal compensation and waste gas heat exchange, which solves the defects of independent control of each heat exchange component and neglecting of the coupling relation of system heat flow in the prior art by multi-physical domain coupling modeling and on-line iterative solution of a graph neural network, realizes self-adaptive air inlet temperature control of the methanol engine in the whole environment temperature range, and effectively solves the problems of difficult cold start of the methanol engine and unstable combustion and easy knocking in the low-temperature environment. The technical scheme adopted by the invention is as follows: The control method comprises the following steps that the control method comprises the steps that the methanol engine thermal management unit comprises a methanol engine, an air compressor, an electric heater, a first heat exchanger, a second heat exchanger, a three-way pipeline and a PLC (programmable logic controller), wherein the PLC is respectively connected with temperature sensors arranged at a first temperature monitoring point, a second temperature monitoring point and a third temperature monitoring point, the first temperat