wuzak
Captain
I get 71.5° with inlet of 24°C and 69.2 with inlet of 22°C.
Note that ADI/MW50 is a consumable.
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Well 2 degrees could be the difference between max power and catastrophic detonation. Lets say for example, if a supercharged engine is pushing 10 psi of boost at sea level (ambient pressure of 14.7 psi, ambient temperature of 24°C @ sea level, the temperature of the air after the supercharger will be 71.4 °C. At 22°C air after the supercharger is 64°C. Now if the detonation point was 69°C air after the supercharger, that 2°C just made the difference. All well in good on just the engine/supercharger, right? Now you have the 50%/50% water-methanol to throw into the equation.
I get 71.5° with inlet of 24°C and 69.2 with inlet of 22°C.
Note that ADI/MW50 is a consumable.
Well said. Those that advocate ADI and NO2 forget that it increases the weight of the plane and takes up volume (always very limited in a fighter). And of course doesn't last long. Plus you have the logistics issues, maintenance, et al.
But the greatest compliment paid by the Germans was by (in their own complicated way) copying the idea, at least by BMW.
C3 injection. They added fuel into .... the supercharger inlet, cooling the intake and allowing higher boost .. still had fuel injection to every cylinder
The simple answer as to why RR developed its engines (again, quite ingeniously considering their limits) the way it did was that it did not have either the time to develop a completely new engine in wartime in the 30-liter class (the "alternative" to further developing the existing Merlin was waiting for the Griffon until 1943/44..), nor the reliable domestic suppliers of DFI systems: they simply did not have access to Bosch AG products - AFAIK (and could be well wrong) the current DFI systems are essentially the same as the ones developed by Bosch right before WW2.
If the only thing you can mass produce is a 27 liter engine with a carburetor, then its going to be a 27 liter engine with a carburetor plus loads of explanations why this is really the superior way (while frantically developing your own 35 liter engine, the thing others have already done 5-10 years before). If you are stuck with a relatively small engine and trying to compete with big engines in output, you will have to rely on ever extreme amounts of supercharging. In that case you will probably inclined to keep the carburetor a bit longer, as even the minor, ultimately insufficient charge cooling bonus it provides can help to stay competitive. As I said, beggars can't be choosers, though they would probably like to argue that becoming a career beggar was a consciously made choice.
I wonder why aircraft like the Hellcat, Thunderbolt, Mustang H etc. bothered at all with ADI when they had all those wonderful, state of the art carburators...
I wonder why aircraft like the Hellcat, Thunderbolt, Mustang H etc. bothered at all with ADI when they had all those wonderful, state of the art carburators...
To claim that Rolls-Royce didn't go with direct injection because of their supposed "extreme conservatism" is the usual simplification and myth making of the ignorant
Luftwaffephile always like to describe the problems with fuel starvation during the Battle of Britain but don't seem to recognise that relatively small engineering changes eliminated the problem, which was then bypassed completely when the Bendix Stromberg direct injection carburettor was adopted.
The problem with such a pet theory is that it doesn't allow for the fact that ...
That Daimler Benz - via Bosch - and Junkers developed reliable DFI systems was a great achievement, but to use that in an attempt to damm the Merlin (with some faint praise) and other engines which did not adopt DFI is just ill-informed nonsense.
Tssk tsssk, such ignorance...
Yes, the air fuel mixture would be high for the draw through system (like that used in the Merlin).
But, it won't be as high as the air in a system where no fuel is added (ie direct injection, like DB 6).
It also highlights the different philosophies of the two engine manufacturers - Daimler-Benz opted for capacity, high compression and low boost (relatively). Rolls-Royce followed the path of the R engine - high boost, low compression ratio.
For the high boost route the fuel into the eye of the supercharger was invaluable in lowering induction temperatures.
What's the fascination with a capacity class? It is the power class that matters - and there the Merlin was a match for, or better than, the DB 601/605.
It was a concious decision on Rolls-Royce's part to use low compression ratios and high boost to achieve the power. It was Daimler-Benz's approach to use larger capacity and lower boost to achieve the power.
The Packard Merlin in the P-51H was the only type of Rolls-Royce engine, or derivative, that had ADI during the war. The reason was to screw even more boost out - from +25psi to +30psi.
1. Could it be, that the different design philosophies had to do with the quality of fuel and the knock resistance of the expected fuel?
From all I could read about german engine development, the engineers were well aware, that they were stuck basically on B4 fuel, also that the possibility to use and produce high grade B4 fuel wasn't given until 1936, as the IG Faben get the patent of lead tetraethy from Standard oil.
The germans had never the chance of the whole WWII to produce high grad fuel with/out of isooctane, because they don't have isooctane and don't know the development.
To my understanding this was one of the main reason they developed from the beginning to more capacity engines, because for higher boost (ata), you are in need for high grade fuel.
2. Also there was (Jumo 211, Jumo 213; compare to DB 601, DB 605, DB 603) a different design philosophy between the german engine factories Junkers and DB.
DB built it's engine from dry weight very light. The DB 601/DB 605 is at the same weight class of the Allison 1710 and RR Merlin with 33/35,9 Liter compare to 28 Liter engines, the DB 603 44 Liter at the same class as the RR Griffon and the Jumo 213 35/36 Liter engines.
At first sight to me, DB bought this "light weight" with relative low RPM's. After the development of the Jumo 213 out of the Jumo 211 with high pressure water cooling, Junkers was able drive the Jumo 213 with 500 rpm more then the Jumo 211. DB was not able to manage a much higher RPM at the DB 605 (100 RPM higher then the DB 601), although the DB 605 was converted also to a high pressure water cooling and sleeve bearings instead of roller bearings.
The DB 605 was next to the DB 603 compare to RR (Merlin, Griffon), Allison (V1710; Junkers (Jumo 213), the inline engine, that was driven with the lowest RPM.
I couldn't fathom this to the ground, but there must be different design philosophies.
Yes Junkers worked with 2 speed superchargers and not variable speed superchargers like DB, till the Jumo 213E, which had the first two stage 3 speed supercharger of any german engine in production.Did Junkers have 2 or 3 speed superchargers, rather than the variable speed superchargers of the DB series?
T2/T1 = (p2/p1) y-1/yWhere/how did you calculate those temperatures, using what assumptions.
In 1935-36 everybody had 87 octane fuel, they knew 100 octane was coming (Howard Hughes set the world speed record in 1935 using 100 octane) but they did not WHEN 100 octane was coming as a PRACTICAL fuel ( Howard's fuel cost 4.00 a gallon, many times normal aviation fuel). The basic decisions as to engine size, rpm and such were made at this time.
This is one reason for the British Rolls Royce Vulture, While they may KNOW the Merlin could STAND UP to 1600-1800hp they could not get that power from a service engine using service fuel.
A DB 601 was about 22% bigger than the Merlin in displacement but the early ones ran at about 20% slower so the actual air through the engine was within a few % of each other at similar boost levels. and the early engine weighed very close to each other and put out similar amounts of power.
Once production lines are established it becomes a question of how much power can be squeezed out of the existing design and here is where the British had an advantage in fuel. The British went through at least FOUR different fuel specifications/capabilities.
WHile they knew 100 octane fuel was coming NOBODY had any idea IF or WHEN such things as 100/130 or 100/150 would ever show up. It was almost science fiction in 1937-38.
Not quite; in 1937-1938 100 Octane fuel was being trialled on at least three RAF squadrons:
In September 1938 100 Octane was approved for use in Hurricanes and Spitfires:
Rolls-Royce were exhibiting 100 octane fueled Merlin Xs and quoting figures for Merlin IIs in December 1938:
while, at about the same time, the first deliveries of non-trail quantities to Fighter Command stations was underway: