In the hall of the command and control center, Wang Yu, chief commander of the 921 rocket launch, Liu Xuesong, chief designer of the 921 rocket, Liu Yong, deputy director of the technical director of the 11th Institute of the Sixth Academy of Aerospace Science and Technology, who is mainly responsible for the 921 core stage and hydrogen-oxygen engines, Wu Chunmin, director of the Xi'an 11th Institute of the Sixth Academy of Aerospace Science and Technology, who is responsible for the development of liquid oxygen and kerosene engines, Li Yonghua of the 101st Institute of Aerospace Engineering, which is responsible for the ground test of the engine and provides liquid hydrogen fuel, and Gao Junlong, the aerospace professional department of the 54th Institute of the China Electric Power Science and Technology Co., Ltd., who is developing the ground safety remote control system, and a group of big bulls are discussing nervously.

Pang Xuelin and Tao Yongchang stood aside and listened.

Under normal circumstances, if the engine pre-cooling fails and the rocket body is overheated, it is not allowed to carry out the launch mission at all for this kind of cryogenic rocket powered by liquid oxygen kerosene and liquid hydrogen and liquid oxygen engine.

However, the effective launch time after cryogenic rocket fuel filling is only 24 hours, and considering the launch window, the time left for everyone to discuss is very limited.

Wang Yudao, the commander-in-chief of the launch, said: "The satellite has just sent a message that the launch window is from 17:30 to 19:00, and it can be postponed to 19:30 at the latest." It's 16:40, and we now have almost an hour left to fix the problem, taking into account the one hour left for the launch-related preparations before the launch. Lao Wu, the kerosene machine and the above circulating pre-cooling system are what you did, you can tell you about the situation transmitted back from the front. ”

Wu Chunmin nodded and said: "The data transmitted back by the sensor in front shows that after 2.5 hours of circulating pre-cooling, the total liquid consumption of circulating pre-cooling is 547.76kg, but the temperature of the pump casing is 15K higher than we expected, which is very abnormal." The temperature of the pump casing is an important parameter to measure the pre-cooling effect, and we usually take the temperature of the pump casing lower than a certain specified value as a sign of pre-cooling, and take this as the starting condition of the engine. This time, we used an improved version of the YF100K for the core-stage engine, which adopted the natural convection cycle pre-cooling mode. This mode is mainly to lead out a section of pipeline in front of the main valve of the engine and connect it to the storage tank, which we call the return pipe. At the beginning of pre-cooling, the propellant flows from the storage tank into the conveying pipeline, passes through the pump front valve and pump chamber, enters the return pipe, and then flows through the return valve from the return pipe to the storage tank. ”

Wu Chunmin paused and continued: "In this system, we do not have an external driving device, and the flow is only driven by the density difference between the propellant in the return pipe and the delivery pipe, so this is called natural convection circulation pre-cooling. The reason for the density difference is that due to the low temperature characteristics of the propellant, the ambient air forms a relatively high temperature heat source, and the propellant enters the pipeline and is heated and vaporized, and the density becomes smaller, resulting in reflux. In order to enhance the density difference between the propellant in the return pipe and the conveying line, make the circulation go smoothly, and ensure the full pre-cooling of the pump, a section of injection is usually added to the natural circulation pre-cooling. The pilot tube is connected from the return line, and helium is used as the injection gas source, and at the appropriate time, a short period of helium injection is carried out to enhance the circulation. ”

"Old Wu, is there any solution to that?"

Liu Xuesong said.

Wu Chunmin said: "I suggest organizing the operator of the first-level helium distribution table to return to the operation post, turn on the D7 blowing, and carry out helium injection for about half an hour to enhance the circulation and see if the temperature of the pump casing can be lowered." ”

Wang Yu looked around: "Everyone has no opinions, right?" ”

Everyone shook their heads.

Wang Yu said: "Okay, then operate according to Lao Wu's method first, and order the rescue personnel to be in place, if the pre-cooling is still not successful, the position will begin to prepare for the termination of the launch process." ”

"Yes."

Wang Yu's order was quickly issued.

On the large screen directly in front of the command center, the screen begins to switch to the scene inside the launch tower in front of it.

The entire command and control hall fell silent, and everyone waited patiently for news from the front.

Wang Yu, Liu Xuesong, Liu Yong, and Tao Yongchang whispered from time to time.

At this time, Pang Xuelin asked Wu Chunmin in a low voice: "Professor Wu, is it possible to reduce the temperature of the pump casing in this way?" ”

Wu Chunmin looked at Pang Xuelin, shook his head and said with a wry smile: "Not sure, the cyclic pre-cooling process is very complex, involving a variety of physical phenomena: pre-cooling begins, the pipeline system at room temperature forms a high-temperature heat source relative to the low-temperature medium, and the medium enters the pipeline and vaporizes sharply, and there will be pure liquid, different proportions of vapor-liquid two-phase, and pure gas flow along the pipeline. At the same time, the inner wall of the pipe is cooled by the cryogenic fluid, which will release heat and reduce the temperature of the pipe wall, while the air temperature will not change much, so that there is a temperature gradient between the pipe wall and the outside air, and thus a heat flow is transferred from the outside to the inside. With the pre-cooling, the temperature of the pipe wall gradually decreases, and the distribution of the fluid state in the pipe also changes continuously, until a certain point, the wall temperature no longer decreases, the heat flow from the outside world does not change, and the fluid state at each point on the pipeline does not change, and the pre-cooling will reach stability. In this regard, we are most concerned about the distribution of various parameters after the system is stabilized, especially the temperature of the pump casing. In the previous experiment, there was no problem with the circulating pre-cooling system, but I didn't expect a situation before launch, the key is that the liquid consumption of circulating pre-cooling is comparable to our theoretical calculation, but the temperature is 15K higher, there must be a problem. If the method of enhancing the circulation by helium injection is still not working, then this launch mission can only be cancelled and the relaunch can be re-launched after further improvement of the circulation pre-cooling system......"

Pang Xuelin thought for a while and said, "Do you have a design plan for the kerosene machine circulating pre-cooling system here, so it's convenient for me to show it?" ”

"Of course it's convenient!"

Wu Chunmin smiled and beckoned to a staff member to bring him the YF100K design manual.

Wang Yu and Liu Xuesong only looked at it twice, and they didn't care too much.

Although Pang Xuelin is very famous, most of his achievements are in the fields of mathematics and natural sciences, and they don't expect Pang Xuelin to help in a highly specialized field of applied engineering such as rockets.

Pang Xuelin didn't care, and directly found the theoretical calculation part of the circulating pre-cooling system through the catalog page of the design manual.

The theoretical calculation of the circulating pre-cooling system is mainly divided into two aspects, the first is the calculation of liquid consumption, and the other is the calculation of circulation.

Natural cycle pre-cooling is theoretically analyzed through a series of calculations, including numerical calculations of pre-cooling consumption and steady state. Judging from the results of numerical calculations, the oxygen system of the engine adopts natural circulation pre-cooling effect is good, and there is basically no major design problem, under normal circumstances, there should not be such a big mistake in the near launch stage.

Pang Xuelin's brows couldn't help frowning.