Chapter Forty-Eight: The Choice of Fuel

"Cease fuel injection, end the test."

With that command, the fuel supply was cut off, the combustion chamber stopped burning, and the searing air within the test center slowly cooled. A look of disappointment hung on their faces; though they had grown accustomed to failure after many trials, each new experiment brought a silent hope for success. Clearly, this attempt had ended in failure.

"It's a fuel issue. When we used propane just now, the phenomenon didn't occur. The trouble started when we switched to gasoline—gasoline simply isn't suitable for turbojet use."

The conclusion came easily, for the problem was plain to see. Anyone who had watched the entire test could recognize it.

"Let’s continue the experiment. For now, we’ll use propane and carry out the tests that aren’t related to fuel," Yang Hui considered, settling on the most reliable option he could think of. Time was pressing; the tests could not be halted.

Chief Wu nodded, agreeing with Yang Hui’s suggestion—it was the best course.

"Very well, we’ll proceed. You find a way to resolve the fuel issue. We need to identify a suitable fuel immediately."

Seeing the head of testing agree to his plan, Yang Hui motioned to Chief Wu, and the two walked out together. The journey was silent; their minds preoccupied with the fuel problem, which remained unsolved. They could only hope to devise a solution in time.

Back in the office, a mix of emotions washed over Yang Hui. The morning had progressed smoothly; the afternoon had barely begun when trouble started. The worst part was the lack of a reliable solution; his mood was beyond words.

By rights, as someone who had lived twice, Yang Hui’s resilience should have been formidable, yet the blow of seeing his carefully crafted design fail was not something rebirth could shield him from.

He pondered, sighed, and lamented, but in the end, he knew he had to stand up again. Problems would not solve themselves; only a practical solution would suffice.

He reviewed his thoughts—now was the time to act. The fuel had to be tested and proven. What he needed was a device to test the combustion properties of various fuels. Yang Hui already had a design in mind.

The method was simple: take a medical syringe, attach a plastic infusion tube between the syringe and the needle, and fix the needle in a vise. The fuel would be loaded into the syringe and pushed out at a steady rate; ignite the fuel as it emerged from the needle.

This would create a simple testing apparatus. Industrial design is sometimes just that straightforward—no need to complicate things or aim for grandeur. This, Yang Hui thought, was the most valuable lesson in the Republic’s industrialization.

Turning his idea into reality was easy. After explaining it to Chief Wu, Yang Hui soon procured a syringe, tubing, and needle from the medical office.

They found a spacious, windless spot. Lacking a vise, they improvised to secure the needle. The essential test apparatus was thus installed. It looked crude and primitive, but Yang Hui was confident it would meet the requirements. In his words: "Rough but effective." Sometimes, simple is best.

Regardless of the setup, the test began. They drew half a syringe of aviation kerosene, connected the tubing and needle, and pushed the fuel through until a jet of oil shot from the needle. Chief Wu, with a long match, moved closer to ignite the jet. As soon as the flame touched it, the fuel caught fire, forming a graceful arc from the needle to the ground, burning beautifully in midair.

Yet aviation kerosene could not be used for model turbojet fuel. It was too difficult to obtain, so they needed another solution.

There were only two common liquid fuels on the market: gasoline and diesel. Each had its merits, but for turbojets, gasoline alone was unsuitable—as seen during the earlier test. Gasoline ignites easily, but combustion is incomplete, causing intermittent burning.

Now it was time to try diesel. They expelled the kerosene from the syringe and filled it with diesel for the next test.

The needle sprayed a jet of diesel. Chief Wu brought the match close, but no matter how he tried, the fuel would not catch fire. This was the result of the diesel test—not promising.

Only one option remained: mix gasoline and diesel to see if they could be ignited together. Diesel, being less volatile, burns steadily but is hard to ignite directly, requiring compression for combustion in engines. Gasoline, in contrast, is highly volatile and can be ignited by a spark, though its combustion is less stable. Mixing the two might yield unexpected results.

To ensure ignition, they started with a 1:1 gasoline-diesel ratio. If ignition succeeded, they would increase the diesel proportion until they found the most stable mix. If it failed, they would boost the gasoline proportion to achieve combustion, then refine the ratio for optimal stability.

If neither could be made to burn reliably, they would be left with only propane or aviation kerosene—both inconvenient choices.

Drawing the gasoline and diesel into the syringe according to the ratio was made easier by the syringe’s graduated markings.

First, they tested the 1:1 mix. As the fuel jet shot out, it caught fire easily, and burned more steadily than pure gasoline, though there were still minor issues.

They increased the diesel ratio to 2:1. The burn was noticeably better. As more diesel was added, the flame stabilized further. At a 5:1 diesel-to-gasoline ratio, ignition became more difficult, but they had found a fuel mix that burned stably.

"Quick, write this down: mixed combustion of gasoline and diesel at a 4:1 ratio—diesel to gasoline—is the optimal mix. We finally found a solution."

Yang Hui set down the syringe, his joy apparent. It was a good day—so good that even the pungent smell of fuel seemed fragrant to him.

"Indeed, I didn’t expect a solution so quickly. Has it even been two hours?"

Chief Wu was also delighted. What pleased him most was not just finding the right fuel ratio, but solving this major problem in less than two hours.

"Pack up—we’re heading to the test center. I’ll only rest easy if the combustion chamber burns steadily." As he spoke, Yang Hui removed the syringe and needle, unconcerned whether they could ever be used medically again; his only concern was whether his combustion chamber would burn reliably.

"Ah, you’re back again. Is there something else?"

"No, we’ve found the right fuel. A 4:1 diesel-gasoline mix works best."

Hearing the solution had been found so quickly, the testing supervisor halted preparations for another experiment. He led Yang Hui to a fuel storehouse.

"This is mostly aviation kerosene, but we do have gasoline and diesel for our vehicles. We can mix your fuel right now." He opened the storehouse, where lubricating oil drums were stacked neatly. Gasoline, diesel, and kerosene were stored in underground tanks.

They found a large drum and measured out diesel and gasoline in the correct proportions. The two men lifted the heavy drum onto a handcart, and Chief Wu played the role of porter, wheeling it to the test center.

Once again, they conducted a combustion chamber ignition test. The fan supplied air, propane was introduced, and upon reaching the proper ratio, ignition succeeded. Preheating began. Since the fuel was a mix, its ignition point had changed; calculations suggested it was about 262 degrees. Playing it safe, Yang Hui waited until the chamber reached 280 degrees before giving the order.

"Inject liquid fuel—prepare."

"Ready. Fuel is being injected."

As the mixed fuel entered the combustion chamber, there was a faint sound; the color of the flame changed visibly, and the fire burned hotter.

Combustion was stable, the mixed fuel performed flawlessly, and sensors reported a peak temperature of 710 degrees Celsius in the combustion tube.

"No more fuel problems," Yang Hui remarked calmly, watching the steady rhythm of the flames.