Nakajama HA-45 Hamore engine

[Nikademus]

Hello,

I am looking for technical specifications for this series of engine. I am particularly interested in learning what type of av-gas it was designed for. There seems to be some confusion around this as I've seen some online sources say it was designed with 100 octane fuel in mind, others claim it was designed for 87 octane. Appreciate any light that can be shed on this.

Thx

 

[rinkol]

I have a reference written by the designer, Ryoichi Nakagawa, that I am sure says that the original design was intended for 100 octane fuel, but with the start of the war, the engine had to be modified to run off 92 octane fuel. The low quality of the available oil was another issue. Unfortunately, the document seems to be buried amonst others.

Robert

 

[davebender]

I wasn't aware that oil produced in Indonesia is of low quality. What is Indonesian crude refined into in the modern world?

 

[Ivan1GFP]

I believe just about all the Japanese wartime engines were designed for 91 or 92 octane.

Here is a good source for specifications:
NASM Research 4

- Ivan.

 

[davebender]

On whose octane scale?

I've read that German B4 fuel was equivalent to U.S. 92 octane and German C3 fuel was equivalent to U.S. 100 octane. However German octane numbers for these fuels were quite a bit lower.

 

[Shortround6]

octane ratings between countries were sort of nominal in the 30s. Octane ratings didn't even exist until the late 20s so it is little wonder that the world had yet to standardize the rating and/or test procedure about 10 years later.

octane ratings were obtained by testing the fuel in question against reference fuels in a test engine on the same day to equalize atmospheric conditions. Change make and model of test engine and results could/would differ. Octane ratings also change with the fuel air mixture even in the same engine on the same day.

 

[Ivan1GFP]

Shortround6 makes a good point. Octane ratings between different countries doesn't always translate.

These days, we typically see (R+M)/2 on the gas pump. R-for Research Octane typically gives higher numbers. M-for Motor Octane gives a bit lower.

I am guessing that the 92 octane Japanese fuel is probably a "Lean" rating.

Typical US aviation fuel was 100/115 for Lean and Rich ratings.
The C3 German fuel was typically listed as either 96 or 100 octane.
In US Testing of the FW 190G, the US equivalent to C3 fuel was 115/140 (or something along these lines)
It was noted as being superior to typical 100/115.

- Ivan.

 

[Ivan1GFP]

BTW, Does anyone know what the compression ratio was for the Homare? I believe I have seen it listed as 7.0:1 but am wondering if it was really 7.2:1 as it was on the Sakae from which it was derived.

- Ivan.

 

[Nikademus]

I have a reference written by the designer, Ryoichi Nakagawa, that I am sure says that the original design was intended for 100 octane fuel, but with the start of the war, the engine had to be modified to run off 92 octane fuel. The low quality of the available oil was another issue. Unfortunately, the document seems to be buried amonst others.

Robert

Thank you. Found what is probably the same reference online, for a fee. It appears the Homare was originally designed for 100 octane but had to be modified by IJA decree to take 87-92 octane fuel due to predicted wartime restrictions.

 

[Piper106]

Sounds like the Japanese assumed that fuel quality would improve over time, and design was started on that basis. They likely assumed that by the time the Homare would be entering service, 100 octane fuel would be available. The reality was not nearly as good.

Japanese aviation fuel early in the war (42-43) was "92 octane'. As others indicated this was the F3 'lean mixture' or motor octane number. Based on the low aromatic content (low amount of benzene, tolulene, xylene, etc.) and the low amount of synthetic 'alkalate' used in Japanese avaition fuel as decribed in documents posted some time ago by Micdrow, my educated guess is that this early war fuel (in Allied terms) would have been rated as about 92 / 100. By 1944, the allowable lean mixture number was relaxed from 92 to 91 octane to compensate for supply problems, and in the final year of the war, quality standards further dropped to 87 octane.

This compares with the standard Allied fuel of 100 / 130 (post 1942). The Allies had limited amounts of 100 / 150 fuel from late in 1944 in Europe, and some 115/145 fuel was available after V-E day. German C3 fuel was 96 / 115 in 1942, improving to about 96 / 130 by 1944.

Piper106

 

[wells]

92 octane Japanese fuel

USA specs ( From T2 technical manual )

Fuel AN-F-26 Grade 91/96
Alcohol spec AN-A-24 composed of half ethyl and half methyl alcohol

The alcohol was used with 50% water and was automatically injected at boost pressures above +180 mm ( 37" Hg )
Compression ratio was 8

 

[Ivan1GFP]

From the book "Genda's Blade", pilot accounts claim that their fuel was combined with aromatic pine oils for a result that was about 85 octane. Even so, their planes had enough performance to be easily superior to the Hellcats they encountered.

- Ivan.

 

[Shinpachi]

As a basic knowledge, av-gas Japan produced during the war was simply classified by each octane. They were
70, 80, 85, 87, 91 and 92. 95 was under development in 1945. Total quantity of the pine oil produced was only 500KL.

Octane more than 100 was imported from US before Pearl Harbor and mainly used for experimental planes and patrol planes.
Almost were consumed by 1944.

 

[Ivan1GFP]

Hello Shinpachi,

What was the standard for combat aircraft for operations?

- Ivan.

 

[Shinpachi]

As far as I have checked several operation manuals, 92 for the navy and 91 for the army but the actual fuel stock condition in the late war tells they seemed having more 87 or 80 than other octanes.

I need more detailed research by the base though.

Delivery list attached as an example here.

 

[Shinpachi]

Addition.

Av-gas stock in August, 1945
Location
Type/Q'tty

Atsugi Airbase, Kanagawa
91/180KL
87/1.2KL
85/9KL
80/7KL

Yokosuka Airbase, Kanagawa
120/60KL
91/3560KL
87/150KL
Experimental av-gas/300KL

Kisarazu Airbase, Chiba
Type unknown/84KL

Chitose Airbase, Hokkaido
70/23,200KL

 

[Aurum]

Addition...

Hi Shinpachi!
Do you have any other statistics of av-gas storages of other wartime periods?

Sounds like the Japanese assumed that fuel quality would improve over time, and design was started on that basis. They likely assumed that by the time the Homare would be entering service, 100 octane fuel would be available. The reality was not nearly as good.

Homare was began to design even before the war at Pacific started and as it was prolonged in 1942 finished in 1943 Japanese could assume that they could assert their outer defending perimeter. This became doubt only in the end of 1943

 

[krieghund]

Here is the engine specifications from the Middletown Depot Manual T2-301 dated 1946. This manual for for use by the personnel at the depot to keep the Ki-84 FE-301 in flying condition and has the appropriate pilot checklist, maintenance servicing procedures, inspection schedules, etc.

 

[Vincenzo]

Good docs, thanks.
This confirm japanese data.

 

[tomo pauk]

Gentlemen: was the WER achieved by ADI system?
Homare easily beats 2-stage B series R-2800, on far smaller displacement