Nakajima Homare

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Perhaps Calum could interject his thoughts on this: How come the Japanese, with inferior resources and fuels (to Germans) , were able to design an air-cooled radial of about 36 litres in the 2000 hp class while the BMW 801 was substantially larger and heavier, yet was slightly less powerful.

I have pondered that did the relatively small cylinder dimensions allow relatively high cylinder pressures without detonation...
 
Perhaps Calum could interject his thoughts on this: How come the Japanese, with inferior resources and fuels (to Germans) , were able to design an air-cooled radial of about 36 litres in the 2000 hp class while the BMW 801 was substantially larger and heavier, yet was slightly less powerful.

I have pondered that did the relatively small cylinder dimensions allow relatively high cylinder pressures without detonation...

Along the same line of questioning: what octane rating gasoline could Japan provide?
How consistent was quality control?
How consistent was gasoline supply mid-war?
We know that gasoline shortages crippled Japan by late WW2.
 
The 1,990 hp Nakajima NK9H Homare 21 engine was originally designed for the 91-octane fuel available in 1941, but by 1945 they had to work with 87 octanes (and it actually was able to only generate 1,800 hp.) or even sometimes mixed with a volatile oil extracted from pine tree roots that lowered the fuel to 85 octane. It was so contaminated with impurities that American Jeeps that used this fuel during occupation suffered engine failures.
 
Achieving 1800 hp with 87 octane would be remarkable for the BMW 801 to reach about 1700 hp required C3 fuel, i.e. much better than 87 octane.
 
Perhaps Calum could interject his thoughts on this: How come the Japanese, with inferior resources and fuels (to Germans) , were able to design an air-cooled radial of about 36 litres in the 2000 hp class while the BMW 801 was substantially larger and heavier, yet was slightly less powerful.

I have pondered that did the relatively small cylinder dimensions allow relatively high cylinder pressures without detonation...
The power/weight ratio, power/surface ratio, power/displacement ratio and absolute power that the japanese were able to extrapolate from their mid-late war air cooled radials using low octane fuel and without sleeve valves even obtaining acceptable reliability when supported by adequate logistics never cease to amaze me and stand in stark contrast with the inability of german industry to deliver aero engines over 2000 hp. However I've never understood why aircrafts with such a high power/weight and such a clean aerodynimics as the japanese figthers produced after 1943 were so slow in horizontal fligth
 
The German engines were, yet again, over-engineered masterpieces ? By comparison the Japanese went for an 'AK-47' ??
 
The Germans had their own problems of supply derived from the naval blockade.

The German industry was not able to produce the specially heat and stress resistant metallic alloys that were required. They lacked metals like the chromium and molybdenum that were essential to harden the steel. Germany had exhausted their stocks and could not import them during the war, as it has already happened previously with rubber and oil.

The chemists produced silicones to replace the rubber and synthetic oil of low quality from coal. But the ceramic materials for the compressor blades of the turbojets would not be ready on time and everyone knew it.

The lack of oil suffered by Germany, during the last year of the war, induced scientists and engineers to experiment with alternative fuels.

The most refined gasoline were used for conventional piston engines.

The BMW 003 turbojets worked with B.4 (87 octane petrol).

The J2 and K1 burnt by the Jumo 004 and Heinkel HeS 011 turbojets were heavy kerosenes.

The Argus pulsejet of the V-1 worked with crude oil.

The Peenemünde engineers designed a V-2 that worked with diesel oil and S-Stoff.

The Dr. Pabst, from the Gas Dynamics section of the Focke-Wulf Company, suggested that the ramjets of the future Triebflügel fighter burned even less volatile fuels at pitch oil or lignite tar.

To that purpose, they had to design a compact evaporating plant that could be installed onboard.

This situation affected specially to the conventional piston engines. Poor ratings of the 87 octane B4 fuel and poor quality of Schmiertoff lubricant, that obliged to run at high revolutions to deliver the required horsepower, were the cause of all the problem suffered. Rather deficient Kühlsotff (50% glycol, 50% water) cooling, vibration fractures and disintegration of bearings, due to shortage of tin during its manufacturing, caused corrosion and piston seizure.

To avoid these deficiencies, some engines were redesigned with bigger cylinders and twin (three speed) superchargers, due to the poor performance (just 30 minutes) of the one stage superchargers of first generation.

It was also tried to improve performances using two new power boost injection systems, the GM-1 (liquid nitrous oxide) for altitudes over 10,000 m. and the MW-50 (50% methanol, 49.5% water and 0.5% Schutzöl 39 anticorrosion fluid) for emergency power boost at medium altitude.

In spite of all these issues, the reliability of the new BMW 003 and Jumo 004 turbojets and the HWK 109 rocket engine was so low that the Oberkommando der Luftwaffe allowed the development of some piston engines to continue until February 1945!
 
The 1,990 hp Nakajima NK9H Homare 21 engine was originally designed for the 91-octane fuel available in 1941, but by 1945 they had to work with 87 octanes (and it actually was able to only generate 1,800 hp.) or even sometimes mixed with a volatile oil extracted from pine tree roots that lowered the fuel to 85 octane. It was so contaminated with impurities that American Jeeps that used this fuel during occupation suffered engine failures.
Perhaps Calum could interject his thoughts on this: How come the Japanese, with inferior resources and fuels (to Germans) , were able to design an air-cooled radial of about 36 litres in the 2000 hp class while the BMW 801 was substantially larger and heavier, yet was slightly less powerful.

I have pondered that did the relatively small cylinder dimensions allow relatively high cylinder pressures without detonation...
The Homare had smaller cylinders and could run at much higher rotational speeds.

The Japanese seemed to have a bit of a knack with air cooled engines. The Kasei was in production well before the BMW 801 was available in a usable form.

Both Germany and Japan had problems with the availability of high quality fuel, lubricants and alloys.
 
If I may, at the risk of stating the obvious, it looks as if the engineering team at Nakajima used the 14 cylinder Sakae engine as a starting point. The bore and stroke of the cylinders were the same on both engines for example. Increasing the number of cylinders, making the engine turn faster and increasing boost pressure (correct expression?) presumably went some way, if not a long way, toward achieving the required power.

One has to wonder if the Japanese intended to feed the Homare with 100 octane fuel but could not. As a result some or many versions of the engine may, I repeat may, have been fitted with a water methanol injection system.

A potentially delicate thought or two. Is it possible that the power levels attributed to the Homare were a tad exaggerated? In other words, is it possible that the wartime 2,000 hp ratings were obtained on specially made engines looked after like family heirlooms and fed 100 octane fuel? Is it also possible that the 2,000 hp ratings which became known were obtained after the war on engines tested by the Americans which were fed with 100 octane fuel?

Another tiny factor in the power issue might the type of horsepower used by the Japanese, Japan being a country which used the metric system. A rating of 2,000 metric hp, for example, is equivalent to almost 1,973 Imperial hp.
 
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