The military-industrial scientific research system of the academic master.

Chapter 1460 Endothermic Hydrocarbon Fuel

As the Mach number increases, the air flow speed in the combustion chamber continues to increase, and the pressure distribution diagram displayed on the main screen also begins to change. The shock wave angle gradually becomes steeper, and the high-temperature area slowly expands forward.

"The Mach number is stable at 3.0 and the combustion efficiency is 74%, slightly lower than expected, but still higher than the base value."

Xing Muchun turned to look at Chang Haonan,
"The temperature distribution is almost consistent with your numerical simulation."

The latter did not respond, but strode towards the temperature monitoring station and carefully observed the color image.

The red high-temperature area now occupies the rear third of the combustion chamber, and the front end presents an irregular wave shape - this is the characteristic formed by the interaction between shock waves and combustion.

"Third experiment, continue to increase to 5.0, pay attention to the pressure fluctuations in the isolation section."

Chang Haonan gave the order, but a hint of worry already appeared on his face.

He is not worried about the specific impulse problem caused by reduced combustion efficiency, but the significance of hydrocarbon fuel in scramjet engines is not just to provide thrust, but also cooling.

Mach number 5.0 is the upper limit of the subcombustion mode. As the speed approaches this critical point, the airflow in the combustion chamber becomes extremely unstable. The shock wave reflects back and forth in the narrow space, interacting with the flame front, producing complex pressure oscillations.

"The pressure fluctuation in the isolation section has increased, but it is still within the safe range."

The operator's voice was a little nervous.

Chang Haonan's eyes quickly switched between multiple monitoring screens. The combustion chamber performed better than he expected, but the real challenge was still to come - mode conversion.

"Prepare to switch to scramjet mode."

Chang Haonan issued the key instructions.

Mode conversion is one of the most dangerous stages of a dual-mode ramjet engine. Any slight carelessness may cause the combustion chamber to fail to start or thermal congestion and overflow.

It will also be the only process involving changes in the shape of the air intake.

Of course, today's test is just a simulated combustion, and there is not even a real intake duct.

"Switching fuel injection mode."

"Ignition system reconfiguration."

"..."

A series of operations were completed in a few seconds, and the data flow on the main screen suddenly became dense.

In the combustion chamber, the air flow speed has exceeded the speed of sound - the fuel must be mixed, ignited and burned in an extremely short time when the air flow passes through the combustion chamber at supersonic speed.

After three seconds of silence, the pressure curve suddenly stabilized.

"The scramjet mode has been established successfully!" An engineer almost jumped out of his seat:

"The combustion efficiency has exceeded 80.5% and continues to rise!"

After all, most of the flight time of Lingxiao-1 is still under hypersonic conditions, so the entire design is also limited to the scramjic mode. Coupled with the higher combustion chamber temperature, the combustion efficiency is bound to be higher than before.

Xing Muchun walked quickly to Chang Haonan and pointed at the temperature distribution map:
"Academician Chang, look at this shock wave structure. It is exactly the same as the numerical simulation in your report last year!"

On the screen, the high-temperature area presents a peculiar layered structure, as if it had been carefully arranged by invisible hands. This is the complex flow field formed by the coupling of the oblique shock wave system unique to the scramjet engine and the combustion heat release zone.

Chang Haonan's mouth curled up slightly, but he quickly returned to his serious tone:
"Continue to increase the Mach number, target 12.5."

As speeds increase further, the physics inside the combustion chamber become more extreme.

In supersonic airflow, the heat released by combustion is no longer evenly distributed, but is concentrated at the intersection of several oblique shock waves. These high-temperature hot spots move forward in the combustion chamber at an astonishing speed, posing a huge challenge to the cooling system.

"Mach number 8.0... the high temperature zone moves forward to the middle of the combustion chamber."

Each working cycle of the JF14 wind tunnel takes several hours. When the simulation test reaches Mach 8.0, the moon is already high outside the window.

"Mach number 10.0...there are signs of temperature increase at the inlet of the isolation section."

Chang Haonan noticed that on the temperature distribution diagram, the red area has occupied most of the space in the combustion chamber and clearly extends toward the air inlet. This is the key feature of the multi-point combustion chamber they designed - under different Mach numbers, the combustion will automatically stabilize at the optimal position.

As the total temperature and speed of the simulated airflow gradually approached the upper limit of the JF14 wind tunnel, the speed at which the numbers on the big screen jumped finally began to slow down, and the numbers in the simulated flow rate column climbed up with difficulty.
"Mach number 12.0...combustion chamber wall temperature reaches 85% of the critical value!"

Xing Muchun suddenly raised his voice.

Chang Haonan's gaze quickly turned to the temperature control console. Several sensors near the isolation section on the screen had turned a glaring red, and the values ​​were still rising.

"15 seconds left to reach target Mach number," the operator reported.

Chang Haonan's brain was working rapidly. Theoretically, the material should be able to last until the end of the test, but the temperature rise was about 7% faster than expected...

"The critical value of wall temperature is 92%!"

There was obvious worry in Xing Muchun's voice.

At this moment, a shrill alarm suddenly rang throughout the laboratory.

"Warning! The combustion chamber wall temperature exceeds the safety threshold! The cooling system is ineffective!"

A bright red warning box popped up on the main screen. The temperature curve was almost vertically rising, and the temperatures at several key points were approaching the limits of the nickel-based high-temperature alloy.

"Stop the test immediately! Shut off the fuel supply immediately!"

Chang Haonan gave the order without any hesitation and quickly pressed the emergency stop button.

After a millisecond reaction time, the fuel valve closed, the wind tunnel power system began to slow down, and the temperature curve on the main screen finally began to slowly decline after reaching a thrilling peak.

The lab was silent except for the hum of equipment cooling down.

Everyone stared at the numbers that were gradually falling, and only when they confirmed that there was no structural damage to the combustion chamber did someone breathe a sigh of relief. "When the test was terminated, the Mach number reached 12.3, close to the target value."

The operator reported softly, seemingly worried about being reprimanded by the big man in front of him.

Although the success or failure of the experiment has nothing to do with him, some comrades with hot tempers cannot help but lose control of their anger.

Fortunately, Chang Haonan didn't have any emotional fluctuations. He just raised his hand and rubbed his nose.

Although the test did not fully achieve its intended objectives, most of the key data was collected. More importantly, they avoided catastrophic consequences that could have caused equipment damage in a timely manner.

"Each team will immediately begin data analysis. I want to see a preliminary report within two hours."

Chang Haonan's voice returned to calm:
"Especially the reason why the cooling system failed."

Xing Muchun walked to Chang Haonan and whispered:

"Academician Chang, the performance of the mode conversion and scramjet stage is very outstanding, almost completely consistent with your theoretical prediction, except..."

Chang Haonan nodded:

"I know, let's look at the data first."

Two hours later, the team assembled in the conference room.

The projector displayed the preliminary analysis results of the test data. Chang Haonan stood in front with the laser pen pointing on a curve.

“That’s the problem.”

He points to a graph of the temperature gradients in the fuel cooling system:
“When the JP8 fuel passed through the cooling channel, the pyrolysis reaction did not reach the expected level. Analysis of the results showed that the fuel heat sink was about 12% lower than the design value.”

Xing Muchun frowned:
“But according to our previous calculations and tests, JP8’s chemical heat sink fully meets the requirements.”

"The upper limit of the Mach number for scaled-down testing is 8.0."

Chang Haonan explained:

“At higher speeds, the wall heat flux increases exponentially, while the residence time of the fuel in the cooling channel decreases… Pyrolysis takes time, which is limited by the chemical reaction kinetics.”

A low discussion suddenly broke out in the conference room.

After waiting for a few seconds, he continued:

"The good news is that the design of the combustion chamber itself has been proven to be feasible. The shock wave structure, combustion stability, and modal conversion efficiency have all met expectations. The biggest problem facing us is only the cooling problem."

"Switch to high heat sink fuel? Like JP7, or mix in some cyclohexane?"

A young engineer suggested.

"Cyclohexane is not suitable for our multi-mission needs, and there is probably no essential difference between JP7 and JP8."

Chang Haonan shook his head:
"I tend to do two things. One is to optimize the cooling channel geometry and increase the fuel residence time. This is the simplest solution, but if it is still not enough, I can only consider improving the fuel formulation and reducing the pyrolysis activation energy."

He turned to Xing Muchun:

"Old Xing, you are responsible for the first plan and lead the team to redesign the cooling channel..."

"..."

After the meeting, Chang Haonan returned to his office alone and looked at the simulation test results on the computer screen.

He recalled the exciting moments in the past dozen hours.

When the shock wave system was perfectly formed, when the scramjet mode was successfully established... in those moments, he could feel that hypersonic technology had taken a big step forward.

The red phone on the table suddenly rang. Chang Haonan took a look and saw that it was a call from the leader of the Industrial and Construction Committee.

He took a deep breath and answered the phone.

"Academician Chang, I heard that there were some problems with the test?"

Li Zhongyi's voice came from the other end of the phone.

“Yes, but overall it was a success.”

Chang Haonan replied:
“We validated the core concept of the multi-design-point combustion chamber, but the cooling system required some adjustments.”

“What support do you need?”

The other party went straight to the point.

Chang Haonan looked out the window at the gradually brightening sky:

"Not right now, but the petrochemical industry needs to be prepared. We may need to test a batch of hydrocarbon mixed fuels with relatively... special components."

Li Zhongyi originally came from the petrochemical system, so he naturally agreed to such a request immediately.

"By the way, there's one more thing."

Just as Chang Haonan was about to hang up the phone, the person on the other end changed the subject and interrupted him.

"what?"

"A little digression, we have seen some reports recently..."

Li Zhongyi's voice suddenly lowered, and his speech slowed down:
"Although it is impossible to be sure, there are many signs that the X51A hypersonic aircraft development project in the United States seems to have been seriously stagnant for some reason. It is said that the person in charge of research and development was involved in an intelligence security incident..."

(End of this chapter)