Why C 3 fuel for the DB 605 AS ?

[Achi]

hello members and guests.
I dont know the reason why the DB 605 AS of the Me 109 G requires the C 3 fuel .There is no more power output and no higher boost.Later the K 4 was satisfied with the B 4 fuel.
Thank you for answer.

Regards,Achi

[Ratsel]

There was more then one version of the DB 605/AS engine used in the G-series.

DB 605/ASC(M) used C3 fuel and was rated at 2000PS
DB 605/ASB(M) used B4 fuel and was rated at 1800PS

[Achi]

I am relating to the version with 1.42 ata boost and without water-methanol injection .

[Ratsel]

if it didn't come with MW-50 then they used C3. think of it as a safety margin. however, ALL the DB 605's could run on either B4 or C3.

[Achi]

C3 fuel was rare,when an engine run on B4 this would be the choice.Safty margin could be the reason ,but than at great expenses.

[Ratsel]

From impression the stocks (fuel stocks in airfields in Northern Italy and Souther Germany it seems that the ratio of stocks was 50-50%, or perhaps 60-40% for C-3, so it appears that the 'roughly 2/3s of late avgas production was C-3' statement is definietely correct.

From early 1945 DB notes of meetings it appears that there was a tendency that fighter units in the East relied on B-4, and fighter units in the West relied on C-3, where possible (basically this means Bf 109G/Ks and the FW 190D, which could use either fuel, while the FW 190A/F types always needed C-3).

Basically by the start of 1944 all Bf 109s with methanol boost would use C-3 grade avgas as a rule. The reason for this was probably that in case of failure in the water injection system, C-3 had high enough octane rating to do without knocking, while B-4 would lead to engine damage in this case (though B-4 with methanol water injection allowed the same boost just as fine, so it was probably a safety measure).

The exception being the Bf 109G-10 and K-4 with the DB 605D engine which would need C-3 if they were to use of higher boost pressures; it would appear that they used both fuels.

[stona]

ALL the DB 605's could run on either B4 or C3.

Are you sure? I believe that use of either fuel only became possible with the DB 605 DB/DC and DB 605 ADB/ASC which didn't arrive until November 1944 and January 1945 respectively.
The DB 605 AS engine used the MW50 boost under the designation DB 605 ASM. It could only use C3 grade fuel.The MW50 system was developed in May 1944 and the first DB 605 ASM engines were produced in July of that year so there was a period where only one fuel was useable.
The Bf109G-6 AS/MW used the MW50 boost system in a slightly different way,by modification of the old GM-1 system,and also required C3 grade fuel.

Cheers
Steve

[Ratsel]

yeah, I'm sure.

[stona]

The information in my post comes from Daimler Benz documents.
Also In a meeting held at Rechlin on April 44, it was noted that GM-1 systems were being installed in the Bf109G with DB 605AS currently in production, in order to convert quickly to MW 50 use. In such cases, C3 would be mandatory.
See DB Aktennotiz Nr. 6127 v. 22.4.44

If you would like to tell me where you got the idea that all DB 605 engines could run on both grades I'm all ears.

Steve

[Ratsel]

If you would like to tell me where you got the idea that all DB 605 engines could run on both grades I'm all ears.

Steve

sure. http://kurfurst.org/Engine/Boostclea...DC_20-1-45.pdf. I'm sure you'll agree that any B4 fuel DB 605 can use C3. the link provided will tell you why a C3 fuel DB 605 can run on B4, including circumstances and directions.

[stona]

A DB 605 can run on B4 fuel and as those documents (with which I am familiar) show could run at a higher boost with C3 fuel,just as the British could run their Merlins at higher boost when 100 octane fuel arrived from the USA.
What a DB 605 engine could NOT do was run with the MW 50 system and B4 fuel. C3 fuel was MANDATORY on an engine with the MW 50 system fitted until the introduction of the versions introduced in late '44 and early '45. Remember that the MW 50 system was standard on the G-14AS.
It is probable that the red undercarriage legs seen on some G-5AS/MW was to indicate clearly,at least more obviously than the fuel triangle and from a distance,that these aircraft were to have C3 fuel only.
I refer you back to my posts above.
Cheers
Steve

[Ratsel]

refer me to what? did you not read the PDF I posted? boosts & mag settings.. its all their. anyways, I'm not going to argue this, but Bf109G-14/AS WNr.784765 used B4 fuel.

[stona]

You could increase the manifold pressure (boost from the supercharger) when using higher octane fuels in many engines. The documents you posted give the various limits for this in the DB 605 with different fuel types.
This is entirely different from the MW 50 system which injected essentially a water/methanol mixture into the supercharger. For this C3 fuel was mandatory.
That's me done. We'll let people reading the posts draw their own conclusions.
Cheers
Steve

[Achi]

Hello Steve,
Chris Starr writes :"...the first breed of methanol 605s used precious 96 -octane C3.However,the realities of fuel supplie in Germany meant that extreme pressure was applied to DB to develop further engines capable of using regular 87-oktane B4 and,when the firm introduced a final 605 family in late 1944 some were able to use B4 in conjunction with MW 50.Through further refinements of pistons design and the use of Bosch ...sparkplug,the DB 605DB was able to use B4 fuel at the 1850 PS/1.8 ata rating with MW 50." For the parallel DB 605A the same.
Hello Ratsel,
the C3 was in short supplie.The production of this in 1943 was less than 1/4 of the normal "Fliegerbenzin".

Regards,Achi

[stona]

the realities of fuel supplie in Germany meant that extreme pressure was applied to DB to develop further engines capable of using regular 87-oktane B4 and,when the firm introduced a final 605 family in late 1944 some were able to use B4 in conjunction with MW 50.
Regards,Achi

Hi Achi,he is correct. The DB 605 ADB/ASC arrived in January 1945 but that is splitting hairs as he refers to the DB 605 DB/DC series of engines which did indeed arrive in late 1944. As I originally wrote.

"use of either fuel only became possible with the DB 605 DB/DC and DB 605 ADB/ASC which didn't arrive until November 1944 and January 1945 respectively"

Until then the use of the MW 50 system mandated the use of C3 fuel in the DB 605 series engines.
Messerschmitt AG even devised a new stencil,a triangle divided vertically in red/yellow, applied near the MW 50 tank filler to denote the requirement of C3 fuel.

Cheers
Steve