Sword of Light: Humanoid Self-Propelled Artillery

Chapter 218 Fuel determines fighter jet performance
Of course, Wang Gensheng didn't care much about how Lao Zi dealt with the airport garrison commander, since he had already led his team away from Xuzhou Airport long ago.

However, at this moment, Li Xiu asked Wang Gensheng:
"Si Ling, do you think airplanes use the same kind of fuel as cars? If they do use gasoline, won't they use fuel meant for cars to fill airplanes?"

Wang Gensheng glanced at Li Xiu before speaking regarding Li Xiu's ammunition:
"Although both use gasoline, they are not the same type, so you don't need to worry!"

Wang Gensheng understood Li Xiu's lack of understanding, but he was too lazy to explain fuel grade and octane rating to her, since he himself only had a vague understanding of them.

They only knew that high-octane gasoline was one of the key factors that enabled the United States and the Allied powers to achieve air superiority in World War II, and that Doolittle was the inventor of high-octane gasoline.

It's important to know that in the early stages of World War II, the Spitfire's mediocre performance was underestimated by German pilots. Especially in the French theater of war in 1940, the German Bf-109 flew faster, higher, and had better acceleration than the British Spitfire and Hurricane.

However, when the pilots, carrying this sense of superiority, began to participate in the Battle of Britain, they were shocked to find that the Spitfire fighter was suddenly completely different!

German Messerschmitt Bf-109s typically flew over the English Channel at altitudes above 8,000 meters, at which German fighters consistently held a significant performance advantage. However, when Spitfires swooped in from even higher altitudes in large formations, the German pilots were taken aback.

Moreover, in the subsequent dogfight, the British fighters demonstrated faster dive and climb speeds, almost on par with Messerschmitt aircraft. The German Air Force, suffering heavy losses, unanimously concluded, "These are not the fighters we've encountered in the United States!" The key reason for this was that the British fighters were using fuel with an octane rating of 100 supplied by the United States.

Starting in the early 1940s, the United States began supplying high-octane gasoline with an octane rating of 100 to the United Kingdom, which significantly improved the fuel's anti-knock capability, thus matching the emergency boost function of the Merlin piston engine.

As a result, the Merlin III used in the Spitfire can increase its maximum power from 1,030 to 1,310 horsepower in five minutes, which increases its maximum speed at sea level by 40 kilometers per hour and its maximum speed at an altitude of 3,000 meters by 55 kilometers per hour, while greatly improving its climb performance at different altitudes.

Don't underestimate this seemingly small improvement of forty or fifty kilometers. This small improvement transformed the Spitfire from a mediocre fighter with decent low-altitude maneuverability into an almost all-around ace fighter! And this major change happened to coincide with the Battle of Britain.

This is the advantage of high-octane aviation fuel! In contrast, throughout the war, most German fighter planes only used fuel with an octane rating of 89, while Japanese aircraft never used fuel with an octane rating exceeding 87, thus greatly limiting the potential of German and Japanese engines.

Of course, even if the Japanese fighter jets were temporarily refueled with gasoline of 100 octane rating, their performance wouldn't necessarily improve immediately. This is because only by modifying a series of engine designs and increasing the compression ratio can the benefits of high-octane fuel be fully realized.

Therefore, the UK's "Greyback Falcon" engine and the US's high-octane gasoline are designed to work together to avoid the chicken-and-egg paradox.

The key figure who solved this paradox and created "high-octane gasoline" was the American aviation legend, Jimmy Doolittle.

And this Doolittle was the same Doolittle who later piloted a B-25 from an aircraft carrier to bomb East Asia. He also later achieved the "Palm Air Victory" in the North Philippines, turning the tide of the air war and pushing the Philippine Army to the brink of defeat. Doolittle's life was also legendary. In 1935, Doolittle, an officer in the U.S. Army Air Forces, temporarily left the military.

He also served as an aviation fuel manager at Shell Oil Company. Doolittle may be the first American to hold both the roles of aeronautical engineer and pilot, and he also holds a Bachelor of Science degree in Aeronautical Engineering from the Polytechnic University of Massachusetts, the first such degree ever awarded.

Shell, with its keen eye for talent, poached him from the US Army, tasking him with developing aviation fuels for both military and civilian use, and making him Shell's public face to the military. However, after joining Shell, Doolittle took the opportunity to solve a major problem that no one had ever realized before.

As a seasoned aviator, Doolittle wanted the United States to possess the world's fastest and highest-flying aircraft. He had visited Germany and witnessed the German Air Force's aircraft using Daimler and BMW fuel-injected engines, gaining an understanding of the crucial role technology plays in improving engine performance. He also identified one of the most critical aspects: high-octane gasoline.

The reason why the octane rating of aviation gasoline is important is related to the principle of internal combustion engines.

The higher the air-fuel compression ratio in an internal combustion engine, the higher the engine efficiency. However, excessively compressed fuel molecules can cause "knocking" due to friction, which increases engine wear and steals engine power.

Therefore, gasoline is mixed with additives such as tetramethyl ethyl lead to produce anti-knock gasoline. Ordinary 87-octane anti-knock gasoline can achieve a compression ratio of 8:1.

This is similar to the use of 92 and 98 octane gasoline. High-performance sports cars or luxury cars use 98 octane gasoline to prevent knocking and maximize the performance of their high-compression engines.

Doolittle also wanted to have a high-performance engine, so it needed to increase the engine's compression ratio as much as possible, ideally to 12:1. This required a fuel with lower volatility, namely aviation gasoline with an octane rating of 100.

At the time, both airplanes and cars used the same grade of gasoline. Due to its low price, both aircraft engine and vehicle engine designers only considered using ordinary anti-knock gasoline with an octane rating of 87.

After all, for the military, the use of the same fuel for aircraft and vehicles also simplifies transportation and supply chains.

However, this idea severely limits further improvements in aircraft performance in various aspects such as speed, climb rate, and maximum takeoff weight.

Therefore, Doolittle intuitively understood that the development of aircraft engines had encountered the chicken-and-egg paradox. Because high-octane gasoline and engines are a perfect match, research and development had to proceed simultaneously.

However, American engine manufacturers at the time, such as Allison and Pratt & Whitney, would not spend millions of dollars in advance to design and manufacture high-compression engines with better performance, when no one was producing high-octane fuel.

(End of this chapter)