Why C 3 fuel for the DB 605 AS ?

[razor1uk]

I can't help thinking that the red areas on U/C oleos was to indicate higher pressurised dampners (or it was the tyres..) needed for the extra weight of the boost system; there were some blow outs/accidents on post sortied landed/parked aircraft as the U/C was standard construction (with normal/accepted metalurgical defects) or to do with Czech made late model 109's IIRC - don't flame me, but I remember reading something to that effect a year or so ago onsite.

 

[Siegfried]

The temperature rise (in absolute degrees kelvin) air experiences when compressed is broadly a multiple of the degree to which it is compressed.

If air is compressed from ambient at sea level, this being 1.0 ata, till it reaches a pressure of 1.42 ata it has only been compressed by a factor of 1.42.

If air is compressed from 0.71 ata (the ambient at about 15,000ft) to 1.42 is has been compressed
by a factor of 2.0 and the temperature rise proportionately higher and this leads to greater risk of
preignition and detonation of the mixture (as opposed to deflageration which is a subsonic burn
on a flame front). The air at high altitude is cooler but not cool enough to keep the temperature
quite as low. Since the big DB603 supercharger mounted on to DB605 allows the DB605AS to support higher
pressure ratios temperature rise is slightly higher; so the Luftwaffe or Daimler Benz may have wanted a degree of extra safety margin or they genuinely wanted to introduce a new generation of engines optimized for C3 fuel.

Another factor may have been the state of spark plug development.

The original spark plug on the DB605A was the Bosch DW250ET 7 and this
sometimes caused pre-ignition at 1.42ata MAP for the DB605A meaning
the Me 109G frequently had to be restricted to 1.3 ata
(atmospheres or Barr of pressure) as fuel quality was also a problem.

New spark-plugs were needed to the end of the war for each increase in
manifold pressure.


1.42ata - Bosch DW250ET 7/1.
1.80ata - Bosch DW250ET 7/1A and 10/1.
1.98ata - Beru F280 E43. (Driving the DB605DCM and ASCM to 2000hp)


The 1.42ata capable DW250ET 7/1 sparkplug came in on the the summer of
1943 and helped raise boost from 1.3 ata to 1.42 ata (10%) and also Me 109G6
speed from 387mph to at least 397mph (almost catching up with the
1942 Me 109G2 which did 401mph)


The 1.98ata rating (from late 1944) on the Bosch DW250ET 7/1A and 10/1
was lowered to 1.9 ata due to engine failures until the said engines
burned out and were replaced with 1.98ata - Beru F280 E43 equiped
engines. Because the Luftwaffe mechanics were known to tinker and hot
rod engines they were threatened with 'severe punishment' for not
obeying the restriction.


The extra 200hp didn't increase max speed noticeably, only it could be
achieved at 5000ft lower altitude and improved climb.


It should be noted that better quality fuel probably would've alleviated the need for these spark plugs.

There were other ways of dealing with the issue of detonation: the ignition timing could
be retarded. The Daimler Benz engines were also known to use different compression ratios
about 7.4:1 for those optimized for B4 fuel and 8.4 for those optimized for C3. I
presume this was achieved by changing the crown of the piston or some similar method.

Also note that the formulation and knock rating of 'green dyed' C3 fuel seems to have been improved 3 times or so. The allies examined the fuel in crashed examples and noted a marked increase in green died fuel octane rating from about 92/115 to about 96/130 (from memory) around 1943.


As far as availability of C3 fuel it seems that in 1943 or so the Germans began
introducing new refineries to make the high octane additives via a process called
alkylation using byproduct gases from the hydrogenation plants.

Prior to that they been synthesizing iso-octane via polymerization. In this process
syn gas (from steam passed over coal) is converted to butanol over chromium catalysts.
The butanol is dehydrated to iso-buytylene and then polymerized to iso-octane.
C3 fuel was basically B4 fuel that had about 15-20% of this iso-octane added.

Unfortunately the butylene was also critical for the manufacture of Buna-N synthetic rubber and had to be rationed.

Hence C3 was reserved mainly for the BMW 801D engine of the FW 190A, while other engines had to use B4 fuel. I believe BMW 801 engines used on bombers may have been restricted in boost to use only B4 fuel as the early BMW 801C had. This contrasts with the allies who had sufficient supplies of 100/130 to use it on transports, bomber and fighters.

In the USA a process called catalytic cracking (as opposed to thermal cracking) using a regenerative catalyst (Houdry Process) had been developed and this allowed significant stocks of 100 octane fuel to be produced. In the UK exotic blends of fuel from SE asia and the Bahamas had initially been used to create 100/130 and by the time WW2 had started alkylation was used. Initial stocks of 100 octane fuel sent to the UK from the USA did not have the required 100/130 rich mixture response, it was about 100/125 due to the different manufacturing methods.

BMW tried to go a similar route on the BMW 802 but not by retuning the inlet duct but by adjusting exhaust valve timing.

Cracking apparently was not applicable to the German hydrogenation product, they seem to have been pre-occupied just making the huge investment in synthetic fuel plants and did not get alkylation plants in production 1943. The first months of 1944 marked the beginning of the allied oil plant bombing campaign, which attacked the oil plants just as they seemed to be gearing up for far greater production of C3 fuel. The production of iso-octane via the butanol/butylene route remained the dominant one in most plants.

It should also be noted that for a short time the Me 109F1 and F2 used C3 fuel for the DB601N engine. However when the DB601E was introduced a radical new technology came in that allowed the production of the same level of power on lower octane B4 fuel. The inlet and exhaust valve were given radical overlap timings (so that they would be simultaneously open)
while at the same time the inlet and exhaust duct lengths were tuned to resonate (like a wind instrument). This resonance scavenged the exhaust end gases out of the chamber and loaded in more air charge. The end gases tend to cause autoignition and displace useful air. This resonance tuning caused problems at low RPM so a variable length inlet duct was also introduced to re-tune the manifold. (this technology was transferred to the DB605). This kind of system only really works with the kind of direct in cylinder injection the Germans used.

 

[PWR4360-59B]

Siegfried, did they use TEL? If so how much? Also do you have the numbers on the radical overlap timing? Was is over 120 degrees?

 

[Siegfried]

Siegfried, did they use TEL? If so how much? Also do you have the numbers on the radical overlap timing? Was is over 120 degrees?

According to this link inlet versus exhaust valve overlap on the DB601E was 105 degrees. The DB605 series would be similar, perhaps more, as I assume there would be more experience.
IMPROVING THE MERCEDES
Performance Increase in the DB6xx/db601 Engine, circa 1940
by Jerry Wells, 2007
Daimler-Benz

The info on the spark plugs comes from May 2005 issue of Aeroplane magazine looks at the efforts of Daimler-Benz to increase the power of the engines installed in the Bf-109.

The Germans did indeed use a great deal of TEL about 5.5 milliliters TEL per Imperial gallon.

In the Hydrogenation plants hydrogen was produced from water gas via the water gas shift reaction. This was used to pressurize a coal/toluene slurry to 700 atmospheres pressure.
The resultant product was distilled to produce a fuel of about 71 RON (research octane number) which was upgraded to B4 (nominally 87 but really 91 RON) by TEL.

Toluene from the distillation was fed back to the next slurry mixture. The turbo compressors and metals to achieve 700 atmosphere pressure were quite a technical achievement.

You can see some British Intelligence analysis here:

http://www.fischer-tropsch.org/Tom Reels/Linked/A5464/A5464-0638-0654 Item 6A.pdf
Root directory is here
Fischer-Tropsch Archive

You will note that British Analysis picked up a big increase in the RON of the green dyed "C3" fuel in 1943 suggesting that the Germans were preparing to supply a new generation of engines.

Apparently the story is that in 1935 I.G.Farben swapped its patents for production of Synthetic rubber with Standard oils patents for TEL. It was a good deal for the Americans since the Germans didn't have cheap oil to produce cheap synthetic rubber.

There was another process called the fischer-tropsch process for producing gasoline; in this syngas is passed over catalysts of iron to produce gasoline: it was at the time of much lower quality and used only as 77 Octane Army Fuel if that. In general fischer-tropsch produces excellent diesel fuel (high cetane rating due to the favouring of long linear chains) but mediocre gasoline.

Sulphuric acid Alkylation was used to produce high octane alkalyte for upgrading fuel in addition to polymerization was used to make iso-octane.

 

[Achi]

Siegfried,
thank you for this informations.
In case of the TEL I know that there was a limit for normal fuel at about 87 octane.That means that even more TEL has no impact to the octan index.For higher octan you must add iso-octan or alkyl.

Regards,Achi

 

[kettbo]

Siegfried, Great post! Lots of technical ground covered here but pretty easy to follow!!!
Reducing timing helps an engine run on crappy fuel but the engine will not deliver full power.
Even my 454 cu in/ 7L engine in my El Camino loves more ignition timing (up to a point), 1 deg off can cost 40-50 horsepower
More overlap means less low rpm cyl pressure...good with poor fuel
less boost, less the octane requirement

 

[stona]

Tetra Ethyl Lead content in both C3 and B4 fuel was the same.
4.6 cc per U.S Gallon or 5.5 cc per Imp. Gallon
Not my mixed units! This equates to 1.2 cc per Litre.
Cheers
Steve

 

[Siegfried]

Siegfried,
thank you for this informations.
In case of the TEL I know that there was a limit for normal fuel at about 87 octane.That means that even more TEL has no impact to the octan index.For higher octan you must add iso-octan or alkyl.

Regards,Achi

There are surely diminishing returns with increased TEL. The other issue is spark plug and engine fouling. This is partially dealt with by adding 1,2-Dibromoethane as an anti fouling additive. On the He 177 there was some kind of special spark retardation that had to be applied every 2 hours to unfoul the spark plugs.

The British 100/150 fuel (which was really 110/150) had a lot of lead, supposedly built up in the exhaust stubs.

There was German research into using aniline as a knock additive and also triptan as there was also allied research.

One of the more interesting ideas the Germans had was the 'ring cycle' engine. Instead of troublesome spark plugs they proposed to
inject a special fluid to initiate compression ignition of the main mixture. This today would be refered to as a HCCI (homogeneous charge compression ignition engine) and is state of the art.

http://www.fischer-tropsch.org/Tom Reels/Linked/TOM 248/TOM-248-0116-0120 FD2866-46-Lt1.pdf
http://www.fischer-tropsch.org/Tom Reels/Linked/TOM 248/TOM-248-0153-0156 FD2866-46-Lt12.pdf

T.O.M. Microfilm Reel 248

 

[vanir]

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

The 605AS is just an A-1 of the late series (new piston crowns), with a DB-603A blower bolted on and a new gear. It is calibrated for 1.35-4 military and can be calibrated for up to 1.7 overboost but this requires the use of C3 and an induction coolant in the blower *exhaust* which is where Messer mounts theirs.
The type was a derivative of the channel front höhenstaffeln requirement which first produced the G-1 (the Gustav was originally a high alt interceptor version of the Friedrich), itself designed to operate in mixed formations with Fw-190A, which handled low alt intercepts whilst the G-1/GM-1 combination handled high alt.
With the formation of the Reich defence the DB-603 blower was bolted to the 605A-1 for a makeshift interceptor engine with a performance range of 6-9km altitude. The blower loses some efficiency at lower alt so performance is actually reduced under 5000 metres compared with other Gustavs.

It runs on B4. ZD500-B4 kraftstoff

It should be noted that this engine was historically unreliable under this condition, it preferred C3. These engines were sent almost exclusively to Reich defence in early 44 which operated in mixed formations with Antons, their airfields received C3 and might've actually had B4 shortages.
It is perfectly possible any given G-5 or G-6/AS might have run on C3 but they should have a B4 fuel card.

To overboost the AS motor you must have charge coolant and use C3. So the G-14/AS and any earlier model with MW50 kits fitted would also be C3 and have C3 fuel cards until Feb-Mar45 when several G-14/AS got B4 fuel cards and the new ASB motor.

The ASC/ASB motors are just D series updates for höhen staffeln. It's just a DB with a 603 blower, even the oil system is from the DB. The 603 blower actually has better cruise performance than the stock D series blower but the whole thing is a nomenclature issue, the operators of the AS Messers didn't even recognise which model Messer they were, it wasn't like that. Here's how it worked, they got pressurised Messers in 43 with GM-1 and in early 44 they got the new AS motor but Daimler was still having problems cracking 1.5ata with a 1.7 overboost on B4 in the 605 so a handful with MW50 kits and C3 to handle the pressures were delivered but these had a shocking engine life of only a few full throttle sorties before a piston burn-through. Everybody still waited for the D series motor.
In the meantime engine life in interceptor squadron had an even higher attrition rate than combat losses and many more were being created, as G-14/AS updates of the G-6/AS standardised the MW50 kit and 1.7ata overboost (1800PS on the bench and 1500PS at interception height), these all used C3 fuel.

It is well documented the RLM wanted all fighters if possible, to use B4 fuel and it has been noted as simply more realistic too. The D series updates and requirement to run on B4 fuel were added to the 1945 AS motor series production so that some G-14/AS started to receive the ASB motor when they requested a periodic engine replacement. These are almost identical to the DB motor in all specification and build, with the blower as the only change and cruise ratings as the only effect of the difference. It's an update for this very result. In 1945 G-14 were occasionally equal spec to G-10 and K-4 standard.


this ASC(M) ASB(M), DBM, DCM nomenclature is nonesense. All D series production derivatives were designed to use MW50 kits on any fuel. It is not stamped or a designation, it's just DB and DC, the latter just recognition of a factory tune setting change between fuels.
It is only stamped to A-1 and AS series engines destined for fitment in airframes with MW50 kits and C3 fuel cards, the fuel type was changed so they had to be stamped and designated. The ASB/ASC series just drops back to ASB or ASC designation and again both are designed to use MW50 out of the box so there's no need to specify and they don't.

The DB and analoguous ASB could interchangeably use both fuels. But if you changed boost calibration for C3 fuel only, you had to redesignate it. Same engine though.