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The post WW2 US commission reports on Japanese aero engine manufacturers is interesting reading, Nakajima engineers said the JAAF engineers chose to work out the problems on the Homare themselves rather than come back to Nakajima, When asked about how good were the JAAF engineers the Nakajima engineers laughed a bit.....ouch!
Homare started as a 1800HP engine and later examples should have been able to achieve a 2000HP output... in theory. Homare was designed with 100 octane fuel in mind and, using the standard navy fuel of the time (92 octane), it could get past 1500hp only with a low pressure methanol/water injection system which sprayed the additive once a pressure hsensor detected that manifold pressure went above a certain threshold.Could it be that the Homare had much more upside potential than the Kasei? There were plans to boost output to 2400 hp or so I thought I read somewhere. What if the Kasei had reached its limit or close to it? Then 1850/1900 hp was all you were going to get.
There is not a lot of magic in basic engine calculations.
On the other side, one could argue that the smaller pistons, shorter rods and lighter reciprocating parts made it easier to spin it faster, as the inertia forces are lower. Gasoline engines also favor smaller pots due to the way the combustion starts.There is not a lot of magic in basic engine calculations.
Since the volume (not weight) of air to gasoline is something like 9000 to 1 an engines power is almost entirely related to the amount of air that goes through it per unit of time.
The Homare was a 2187 cu in engine (35.8 liters) so it needed either a lot of boost (more air per revolution of crankshaft) Like a 2240cu in Griffon and with Japanese gasoline that is not likely or it needs a lot of RPM, like the 2240 cu in Sabre. Likelihood
of a radial pulling much into the low 3000rpm range is?????
2 engines did it but both used a much lower boost than the Homare and both used a much shorter stroke.
A big problem with air cooled engines was the cooling. They were much more limited by cooling than liquid cooled engines.
Making power is one thing, surviving for more than seconds at a high power level is another.
On the other side, one could argue that the smaller pistons, shorter rods and lighter reciprocating parts made it easier to spin it faster, as the inertia forces are lower. Gasoline engines also favor smaller pots due to the way the combustion starts.
As you say, however, the Homare proved a bit too much for the alloys, oil and gas available to Japan at the time.
Nakajima 130x150 pot design went from 940 HP of the fist Sakae (33HP/L) to 1200 HP of the later variants (42 HP/L). If we consider the Homare pots/heads an evolution of the design employed in the Sakae, it debuted at 1800HP (50HP/L) and reached 2000 HP (55 HP/L) when development ceased.
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I think engine life must have been quite low. I remember reading that there was a shortage of Baabit metal and of good bearings due to the manufacturing plants being among the favourite targets of the US bombers.I have no idea how much the Japanese were trading engine life for power output.
Just so you know this thread is over 3 1/2 years old - I think a few members are still on here who may give you a response.Lots of good points here... Both the IJA and IJN would have been better off if they cooperated on installing and improving Kinsei and Kasei engines (instead of any other 14+ cylinder engines!) and then doing the same in 1942 for the Kinsei and Kasei 18-cylinder derivatives.... In other words, no Zuisei, Sakae, Mamoru, Ha-109, Homare (and especially not the Atsuta!)....
On the lack of cooperation: while the diffidence, bordering sometimes animosity, between IJN and IJA is often quoted as one of the factors contributing to the demise of Japan's war effort, it should be noted that, at the time, many nations still tended to give a certain independence to the various military branches because cooperation was seen as undermining the prestige, expertise and tradition of each of them.Lots of good points here... Both the IJA and IJN would have been better off if they cooperated on installing and improving Kinsei and Kasei engines (instead of any other 14+ cylinder engines!) and then doing the same in 1942 for the Kinsei and Kasei 18-cylinder derivatives.... In other words, no Zuisei, Sakae, Mamoru, Ha-109, Homare (and especially not the Atsuta!)....