Chapter 1340 End Burning

"Wait a minute, wait a minute..."

Faced with such a dramatic change, the first person to be overwhelmed was Lin Chenggang himself:

"Academician Chang, please let me take my time..."

Compared with Shen Fangzhong who came from rocket dynamics and Li Jianqiang who came from air command, as a technician specializing in rocket propulsion and solid fuels, he was in a state of "understanding a little, but not completely understanding" theoretical chemistry.

It was precisely this state that prevented him from ignoring all the intermediate links and just listening to the results like a pure layman, nor from quickly and fully understanding the calculation process displayed on the computer.

After all, it involves quite complex knowledge of mathematics and physics, which is indeed a bit complicated for a traditional engineer.

The result was that before he could fully digest the part that pointed out the problems earlier, he heard Chang Haonan say that he had come up with three new ideas based on his own system.

If you don't have a broken heart, you can be considered mentally strong.

Fortunately, Chang Haonan also knew that his progress might be a bit fast, so after hearing Lin Chenggang call to stop, he waited patiently for a while.

However, there are some things that you just can't do.

If you don't understand it at first, it will be difficult to figure it out on your own in a short period of time.

So after a few minutes, Lin Chenggang's frown not only did not relax, but became even deeper.

Seeing that dragging it on like this was not a solution, Chang Haonan had no choice but to speak again, interrupting the other party's seemingly ineffective thinking:

"If there is anything you don't understand, you can ask me directly..."

Hearing this, a look of confusion flashed across Lin Chenggang's face.

Obviously, it was a system that he created, but no one else understands it better than him. This is a big blow to a technician.

But it wasn't the first time after all, so he was ready to excuse himself almost instantly.

"After all, he is Academician Chang, there is nothing to be ashamed of..."

After repeating it in his mind twice, he nodded calmly:

"When I designed the propellant system structure, I considered the thermal sensitivity and hydrolysis of polyvinyl alcohol. Not only did I test the individual components under laboratory conditions, I also processed them into propellants and conducted full-process combustion simulations. However, I did not find similar problems at the time..."

The results of the live-fire test are here, and they match Chang Haonan's calculations. Lin Chenggang must understand that he made a mistake.

But he couldn't figure out what was wrong for a while.

Due to the special structure of high molecular polymers, even different batches of products of the same brand sometimes show certain performance fluctuations, but at most there is a difference of a few percent at the numerical level, and it is impossible for the fluctuation to produce completely opposite properties.

"Because this is a type of reaction where individual differences are very obvious..."

Chang Haonan replied:

"Let alone the laboratory simulation, even in the previous test firing, weren't there 12 rounds out of the 10 rounds that were fired without problems?"

He turned back to the previous page of the calculation process and explained:

"Under normal circumstances, even if the slow burning method is used, the burning time of solid propellant will not exceed 5 minutes... In fact, let alone 5 minutes, even 50 minutes is not enough for the water elimination reaction to spread to the entire propellant column. At most, it will have some adverse effects on performance, and in terms of proportion, it can be basically ignored."

"That……"

This back and forth had already made Lin Chenggang's eyes a little dazed.

"So the key to the degradation of polyvinyl alcohol at high temperatures is not actually water."

Chang Haonan finally revealed the answer:

"The main product after water elimination is olefins, which form carbon-carbon double bonds in the residual structure of the polymer and migrate along the polymer chain to the next adjacent hydroxyl group, followed by a keto-enol isomerization reaction. Some polyvinyl alcohols with a relatively low degree of alcoholysis will retain a large number of acetate groups in the molecular chain structure, causing the decomposition process to produce a large amount of gaseous acetic acid and induce violent stretching vibrations of hydroxyl and carbonyl groups..."

"..."

After converting mathematical language into chemical language, Lin Chenggang finally understood.

"I see……"

However, whether it was mathematics or chemistry, it made no difference to the other two people listening nearby.

They were completely confused until this part finally ended. Shen Fangzhong quickly got to the point to prevent Lin Chenggang from continuing:

"Academician Chang, I don't know much about chemistry... but from the perspective of combustion dynamics, since the workflow can be fully controlled, can we abandon the traditional core combustion mode and directly adopt end combustion?"

"In this way, the cross-section of the charge can be made into a porous honeycomb, or even solid... Or even if the hollow charge remains unchanged, end-face combustion can improve the overall strength of the charge during operation and reduce the risk of failure."

In order to ensure uniform combustion, traditional solid propellants are made into a cylindrical shape, ignited from the top of the column hole, and then burned in layers from the inside to the outside.

The problem this brings is that the entire propellant column will become thinner and thinner as it burns, and its strength will become weaker and weaker.

In the past, solid propellants worked in a one-shot manner, with an explosion and a quick end, so the impact of this combustion method might not be significant.

However, the combustion of electronically controlled propellant occurs almost throughout the entire flight. Even if the initial strength of the grain is improved, problems may easily occur due to the huge lateral overload in the middle and end.

End face combustion burns the propellant column from bottom to top, making it shorter and shorter, and its ability to withstand overload becomes stronger and stronger, so there will be no concerns in this regard.

Chang Haonan was just interested in the propellant system developed by Lin Chenggang, so he came to check out the situation before the gliding hypersonic aircraft entered the critical stage of research and development. He did not consider things that were closer to the application level in advance, so he did not answer immediately after hearing this, but just lowered his head and thought for a moment.

"There is no problem with end-face combustion. At most, we can set up an expansion chamber between the charge and the nozzle. The key lies in the ignition method..."

As he spoke, he looked at Lin Chenggang, who was taking out a notebook and writing furiously.

As the designer of the CTK series of propellants, the other party must have considered this issue.

The latter just finished taking notes at this time, raised his head and replied:

"Unlike conventional propellants, the ignition of electronically controlled propellants relies on the contact between the electrode and the grain. And because multiple ignitions are required, the electrode must overcome the morphological changes caused by the combustion of the grain and always maintain contact with the combustion surface..."

"In this case, the core electrode is obviously the most intuitive way. The outer electrode can be directly integrated with the rocket shell, and the inner electrode can directly replace the original igniter. If the end face is burned, there will be problems with the electrode arrangement. At least one end needs to move with the charge to achieve continuous work."

Perhaps he felt that simply narrating it orally was a bit abstract, so he searched around for a while, then pulled over a whiteboard from the other end of the computer room.

"I have also considered the design of a ring-end electrode, with both electrodes fixed... This way, the heat generated by the electrical thermal effect can be concentrated mainly on the combustion end surface area, effectively reducing the melting of the propellant column, and the structure is relatively simple. The problem is that the contact performance between the propellant column and the ring electrode is unreliable. If an interference fit is used, there will be problems with the movement of the propellant column..."

"..."

For a moment, several people fell silent around the whiteboard.

"Perhaps... using coplanar electrodes?"

Chang Haonan has not done any special research in this area, so he is not very sure:

"Two identical electrodes are arranged on the same surface. Through gas pressure or hydraulic pressure, the grain is moved downward continuously as it burns to maintain contact. The current density of the grain is concentrated on the burning surface of the grain. The propellant on the surfaces of both electrodes burns. At the same time, it can overcome the defect of the grain being overheated and melted as a whole under the thermal effect of the current..."

He took the marker and made some minor changes to Lin Chenggang's drawing.

That's how it works sometimes.

The essence may not be complicated, but if the inspiration is not there, you may be stuck for a long time.

Therefore, Lin Chenggang understood almost immediately:

"And it is easier to lay out the mesh electrodes, ensuring that there is not too much additional resistance during the gas discharge process..."

Seeing that his idea was feasible, Chang Haonan threw the marker aside and continued:

"The only problem is that because the charge needs to be constantly moved by an external balancing force to achieve continuous contact between the electrode and the charge, the external balancing force of the moving charge should be able to change with the load, and the speed of the moving charge should be adapted to match the burning rate of the charge, which may be difficult for solid propellants."

"That's not a problem. I have enough burning rate-voltage matching data. It's easy to develop a new control logic..."