In the previous installment, the jet engine was finally invented, but the reciprocating engine continued to evolve and develop significantly for civilian use.
Since I have the opportunity, I'd like to briefly introduce the current state of reciprocating gasoline engines, which is my area of expertise, but I'll indulge in a bit of my personal hobby.
This is purely my personal opinion, but I believe that the reciprocating engines used in WWII aircraft were, in a sense, the ultimate engines.
In my opinion, it would be extremely difficult (probably impossible) to recreate the same thing in modern times because the machine has become so complex.
Since I explained compressors last time, let's take a look at some WWII aircraft reciprocating engines, focusing on superchargers.
The basic form of the reciprocating engine for aircraft in WWII
At that time, aircraft performance was improving rapidly, and there was a growing demand for more powerful engines.
Therefore, the engine had to be made more efficient and larger.
However, reciprocating engines have a certain limit to the size of each cylinder, and to make them larger, it is necessary to arrange multiple cylinders together.
There are two main ways to arrange them, so I'll briefly explain them.
Air-cooled radial engine
The main difference lies in the cooling method, but let's start by introducing air-cooled engines.
As the name suggests, air-cooled engines are cooled by airflow, so the cylinders are positioned to allow as much airflow as possible to reach each one.
They are arranged radially as shown in the diagram.
However, this design limits the number of cylinders that can be increased, as they are arranged radially.
So the idea was to add two or three rows of cylinders to the back. Also, to allow for better airflow, the rear cylinders would be positioned at a different angle from the front row.
This is how they get bigger.
When viewed from the frontBecause it resembles a star and is cooled by air, this type of engine is called a radial air-cooled engine.
One advantage is that its structure is relatively simple.
On the other hand, a drawback is that the large surface area when viewed from the front results in significant air resistance, especially in the case of an airplane.
Water-cooled (liquid-cooled) V-type engine
The next configuration we will introduce is a V-shape.
First, when viewed from the front, the cylinders are arranged in a V-shape.
Then, you connect those V's vertically one after another to make them gigantic.
However, with a V-type engine, the airflow only hits the front, so the inner cylinders cannot be cooled.
Since it would be problematic if it couldn't be cooled, water (though it's not actually water) is used to cool the engine by running water passages through it.
Since the water naturally gets hot, it is cooled using a heat exchanger or cooler (radiator).
The type of this engineBecause it uses water for cooling and the engines are arranged in a V-shape, it is called a water-cooled (liquid-cooled) V-type engine.
One advantage of this is that, when viewed from the front, its surface area is quite small, which in the case of an airplane reduces air resistance and significantly improves performance.
On the other hand, because they use coolers and cooling water, their structure is relatively complex, making them difficult and troublesome to produce.
These were the main types of aircraft reciprocating engines of that era.
The most advanced engines of each country in WWII
Now, let's introduce the top-of-the-line engines from each country.
I once received a comment from a reader pointing out that it was strange to have a fuel injection system in front of the supercharger, but his argument was that it was impossible because mixing fuel before compressing the air with the supercharger would cause ignition due to the adiabatic compression effect, making it dangerous.
Unfortunately, gasoline doesn't burn that easily. The minimum ignition temperature for gasoline is 300°C, so it's not easy to ignite.
In the author's area of expertise, engines, specifically auto-ignition engines (those without spark plugs), gasoline needs to be compressed to approximately 15 times its original volume before ignition occurs through adiabatic compression (there are many other conditions as well).
In other words, a supercharger can only compress air to about 2 to 4 times its original pressure at best, so it won't ignite the gasoline.
High-octane gasoline, especially that used in wartime aircraft, is difficult to ignite.
I'd actually like to give a detailed explanation of the engine's internal workings, but I'll refrain from doing so and instead focus on the supercharger.
Japanese engine: Homare (Nakajima Aircraft)
First, let me introduce the Homare engine, a tragic engine that Japan is proud of.
Actually, I prefer the large-displacement engines of Mars, Venus, and Mamoru over Homare, but I'll go with Homare because it's famous.
Well, in my opinion, it can't be said that they succeeded in mass production, but it is a fact that it represented the pinnacle of Japanese engine technology at the time, so let's take a look.
This engine is extremely famous, so I think many people are familiar with it.
This one is an air-cooled star-shaped engine.
This engine was based on the 1000-horsepower class Sakae engine (air-cooled), but with the number of cylinders increased from 14 to 18, the displacement (while maintaining the two rows) increased, and further improvements were made to achieve a 2000-horsepower class with higher compression and higher rotation speeds.
Well, the engine details are well-known, so let's focus on the auxiliary equipment (superchargers).
While the engine did improve to some extent, the auxiliary components actually didn't improve as much.
The supercharger, a notable technology of this era, was a mechanically operated, single-stage, two-speed supercharger, the same as that used in the later models of the Sakae engine.
In my personal opinion, the lackluster evolution of this supercharger was a major contributing factor.
Now let's take a look at the layout (arrangement).
It might seem quite complicated, but other countries that are advanced in aviation were even more impressive.
However, pilots at that time must have had a very difficult time flying. In addition to controlling the aircraft's airframe, they also had to adjust the propulsion system, including the supercharger's gear ratio, fuel supply, engine speed, engine ignition timing, propeller gear ratio, and propeller pitch angle.
I'm extremely busy.
Although Japan had good fuel supply systems and air-cooled engine technology, its superchargers, electrical systems, and propellers were terribly behind, which was a major drawback (the poor quality of gasoline was also a significant problem).
I did increase the boost pressure from 0.5 atm to about 0.7 atm by increasing the impeller speed of the turbocharger, but I think this is the limit for a single-stage turbocharger.
The final step of installing the water-methanol injection system worked, but it was like a drop in the ocean.
Ultimately, the best performance figures were a takeoff power of 2000 horsepower at 0m altitude, 3000 rpm, and a boost of 0.7 atm (1.7 times atmospheric pressure) (35.8L displacement).
Looking at it again, 3000 rpm for something this size seems like an extremely high rotation speed and looks pretty dangerous.
The most famous aircraft adopted during the Greater East Asia War were the Ki-84 Ki-44 (Type 4 Fighter) for the Army and the Shiden-kai (Type 4 Fighter) for the Navy.
This is a bit of a boast, but for some reason, my company has a complete set of Sakae engines from a late-model Zero fighter that crashed off the coast of the Philippines, and I spent about half a day looking at them.
It was absolutely amazing.
Next, let's go to Germany.
German engine 801 (BMW)
When it comes to famous German reciprocating engines, I think the DB601 series of water-cooled (liquid-cooled) engines from Daimler-Benz comes to mind.
That's the engine that was installed in the BF109.
However, I'd like to introduce the BMW 801 (air-cooled engine), which played a significant role in the later stages of the war. This was the engine used in the Fw 190.
This engine was designed in a fairly conventional way, with two rows of seven cylinders each, resulting in 14 cylinders.
Because the design wasn't overly restrictive, its reliability and productivity were apparently quite high.
However, as you'd expect from Germany, the level of the engine's auxiliary components is simply too high.
Let's take a look at the BMW 801 D2, the most mass-produced model.
The supercharger is a conventional single-stage, two-speed mechanical supercharger.
Let's take a look at the layout (arrangement).
The engine and supercharger were conventional, but the control of each part of the propulsion system was optimized using an analog computer.
Furthermore, while fuel supply systems are usually called carburetors and use Bernoulli's principle to mix air and fuel (like a spray bottle), Germany used a mechanical pump to supply fuel to the air (mechanical injection).
Therefore, unlike in Japan, there is no need to adjust each device; the engine thrust lever (throttle lever) and control stick are used to control the aircraft so that it can fly optimally.
To put it bluntly, it's on the level of an out-of-place artifact.
What's even more amazing is that Germany has achieved the practical application of jet engines and rocket engines.
This engine was equipped with a water-ethanol injection system (though it's not actually that, it's an MW50) and had a takeoff power of 1600 horsepower at 0m altitude and 2700 rpm (41.8L displacement). The boost pressure is unknown, but it was probably around 0.7 atm (1.7 times atmospheric pressure), the same as in Japan.
While its raw specifications might be lower than the Homare, it likely excels in ease of use, productivity, and reliability.
Furthermore, towards the end of the war, the supercharger was upgraded to a 2-stage, 4-speed system, and it apparently produced around 2400 horsepower, so its basic capabilities were quite good.
Next, let's look at the UK.
British engine Merlin (Rolls-Royce)
I think the Rolls-Royce Merlin engine was perhaps the most successful engine of WWII (I personally like the Griffon and Napier Sabre).
After all, it was installed in famous aircraft such as the Spitfire, Mosquito, and Lancaster, and was later modified for ground use and renamed the Meteor engine, making it an incredibly versatile engine that was also installed in Cromwell cruiser tanks, Challenger cruiser tanks, Comet cruiser tanks, and Centurion tanks.
Furthermore, it was license-produced in the United States across the Atlantic and mounted on the ultimate fighter aircraft, the P-51D Mustang.
The design and mass production started very quickly, beginning in 1936. Although its performance wasn't particularly impressive at the time, the British, with their characteristic persistence and refusal to give up, steadily improved it, and fought through the competition almost entirely with this engine.
It's terrifying how the initial takeoff power was around 850 horsepower, but by the end of the war it had increased to 2000 horsepower.
The British are incredibly persistent and diligently work to improve things. In fact, from what I can see, they seem to have everything from the Merlin II to the Merlin 66.
There may be some gaps in the numbering, but this is an unusually high number of upgrades.
Now, speaking of the engine itself, it's my favorite liquid-cooled V12 engine. It's a little different from the Stars.
A 12-cylinder engine is the perfect reciprocating engine that everyone dreams of, with its arrangement perfectly harmonizing all vibrations in a reciprocating engine.
Well, there are many parts inside the engine that I'd like to introduce, but this time I'll hold back and take a look at the overall picture.
Let's take a look at the layout of the Rolls-Royce Merlin 66 from the later stages of WWII. The supercharger is mechanical, but it's the ultimate two-stage, two-speed type, linked to the fuel supply system and equipped with a compressed air cooler (intercooler).
It probably feels like things have suddenly become much more complicated. Even after simplifying it considerably, this is what it looks like.
I think this is one of the ultimate forms of mechanical superchargers. Moreover, it seems that the engine output lever (throttle lever) and the supercharger were linked, allowing for simple control.
This thing's performance is pretty amazing: at an altitude of 1600m, it has 2000 horsepower/3000 rpm/1.27 atm boost (2.27 times atmospheric pressure).
This engine has a displacement of only 27.4L, which is quite small.
It's astonishing that they're producing this much power with an engine displacement that's only 65% to 85% of Japan's 35.8L and Germany's 41.8L.
It's quite a monster.
Looking at the numbers alone, the performance difference between the two isn't that significant, but at higher altitudes, the Merlin 66 is vastly superior, to the point where there's no contest above 5000m.
The performance of the superchargers is just too different.
It's terrifying to think that these were mass-produced and mounted not only on many airplanes but also on tanks.
Furthermore, the fact that they were also developing jet engines is truly impressive.
Even after the war, the Merlin engine series remained very popular in the United States, particularly in air racing, a hobby for aviation enthusiasts.
Back in the day, it was apparently tuned to produce 3000 horsepower in races.
Let's take a look at America in the end.
American engine R-3350 Cyclone 18 (Wright Company)
Let's take a look at the American monster R-3350 Cyclone 18, a fitting finale.
This is an air-cooled radial engine.
This engine itself may not be very well-known, but it's the four-engine engine used in the B-29 bomber.
This is a large engine for bombers, so it's quite different from the engines from other countries that I've introduced so far. However, in my opinion, it's one of the ultimate forms of reciprocating engines that appeared in WWII, so I really wanted to introduce it.
This engine is no joke; it has two rows of nine cylinders, making a total of 18 cylinders, just like the Homare, but it's a massive engine with a displacement of 54.9L.
Moreover, it's a monster equipped with two exhaust gas-powered superchargers, the latest technology at the time.
Let's take a look at the layout (arrangement) right away.
It's incredibly complex.
I think this is one of the ultimate forms of reciprocating engines from the WWII era.
Moreover, it seems that reliability improved significantly after the fuel supply system was changed to a mechanical pump (mechanical injection) partway through production.
The output is also monstrous, with takeoff power at an altitude of 0m being 2200 horsepower/2800 rpm/boost pressure unknown.
What's even more astonishing is that even with a supercharger, power output usually drops somewhat as altitude increases, but this engine actually increases at an altitude of 10000m, producing 2500 horsepower at 2800 rpm with an unknown boost pressure.
I couldn't tell the exact boost pressure, but the output felt like it was at a level of around 2 atm (three times atmospheric pressure).
A B-29 with four of these is pretty amazing.
What's even more impressive is that they're managing to rev such a large 54.9L engine at 2800rpm.
These are some of the top-of-the-line engines from each country.
Summary of WWII reciprocating engines
We've looked at the top-of-the-line engines from each country at the time, but let's summarize them.
Before 1940, aircraft reciprocating engines had an output of less than 1000 horsepower, but in just about five years, that doubled to over 2000 horsepower (although horsepower alone isn't the only factor to consider).
I've never seen such a rapid pace of technological advancement in the field of machinery anywhere else.
Looking at it this way, Japan at the time was doing quite well in terms of engine specifications alone, but when you look at other figures, the situation was quite dire.
We will only compare the engines that were mentioned.
In terms of when production began, the order is Japan (1942) > America (1942) > Germany (1940) > Britain (1939).
Well, Merlin was constantly being updated, so comparing only the production dates isn't very meaningful, but the basic framework was established in 1939.
Looking at the number of units produced, it's not entirely accurate, but roughly speaking, it would be: UK (around 17 units) > Germany (around 6 units) > USA (around 3 units) > Japan (less than 1 units).
The difference will likely become even greater when we look at factors such as uptime and reliability.
Japan did its best, but the fundamental difference in industrial capacity made the situation quite difficult.
In any case, the fact that they were producing tens of thousands of these incredibly complex and expensive machines in just about five years is, in a sense, almost insane.
Well, it was an amazing era.
Typical turbocharger configuration
The engines I've introduced so far were truly top-of-the-line even back then, so the placement and shape of the superchargers are quite elaborate.
I feel like this will just end up explaining the complexity of the supercharger, so I'll introduce a more typical configuration.
The arrangement of those components was almost the same then as it is now in reciprocating engines.
Now let's look at the layout (arrangement).
It's quite simple: a centrifugal compressor for extracting driving force is placed on the exhaust side and connected to the centrifugal compressor on the intake side via a coaxial cable.
This causes the centrifugal compressor on the intake side to rotate and compress the intake air. The compressed air becomes hot, so it is cooled by a cooler (intercooler) before being put into the engine.
This is the typical supercharger system, which has remained unchanged from the past to the present.
To be precise, there are various variations, such as using two of these sets or modifying the shape of the compressor's scroll (cover) (twin-scroll turbo), but the basic principle remains the same.
People who drive what are known as turbocharged cars have this attached.
These superchargers have also advanced considerably. While engine durability is a major factor, about 20 years ago, the maximum compression was around 0.8 atm (1.8 times atmospheric pressure), but now in 2020, it's possible to compress to approximately 1.5 to 1.7 atm (2.5 to 2.7 times atmospheric pressure).
I'm looking forward to seeing how it evolves in the future.
Next time, we'll briefly explain modern reciprocating engines and then use engines as a topic to examine politics and technology.
It seems like I could go on and on about engines if I started explaining them, so I'll stop here. If there are any requests for explanations of military machinery (small arms, cannons, airplanes, tanks, logistics, etc. I'm not good at ships), which are my areas of expertise in machinery, engines, and production, I will introduce them in a separate, independent category.
By the way, I'd like to recommend a book I love: "The Romance of Engines," which describes the golden age of reciprocating engines. It's like a bible to me; I own three copies: one to read, one for safekeeping, and one spare. It's incredibly interesting if you're interested, and I think it would be very useful for current engine designers.
The Romance of Engines: Endless Scenes and Challenges in Technology, by Takashi Suzuki
The Romance of Engines: The Development of Ideas and the Struggles of Nurturing Them, by Takashi Suzuki
To those who found this article helpful in understanding design:
Since we're on the subject, I'd like to recommend a book that's essential for mechanical design.
To be honest, the content is extremely unhelpful, but it can be used like a dictionary when you forget the details. If you read this article, you should be able to understand the content and use it effectively. It also includes commonly used standards, making it quite useful.
If you don't already own one, I highly recommend getting one, even though it's a bit pricey. However, new ones are expensive, so if you're considering buying a used one, I strongly recommend checking that the surface roughness conforms to the new JIS standard.
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