Sorry for such a late reply, my oldtimer laptop needed some overhaul
The RR design approach on the Merlin and Griffon (low compression ratio, comparatively big supercharger, among other details on a V12 engine) was a carry over from the Kestrel. There was no 'indirect improvement of the power at altitude' due to any of the better fuels available, the ever better altitude performance was due to ever better superchargers (and intercoolers, once installed). Sure enough, the low compression ratio helped out with power under the rated altitude(s), with manifold pressures going to around 3 ata with 150 grade fuel and no water injection.
The job of the intercooler was not to 'cool back' the compressed air, but to make sure the temperature is within the, for engine, manageable limits. Eg. for the Merlin 61 in Spitfire VII, the 40% of intercooling was found to give the best results (per Morgan Shackledy, pg. 269), while the US standard was 50% of intercooling (at least for turbo engines). The high compression engine, like DB 605L,will need the intercooler even more. The max manifold pressure (on 605L) being limited to 1.75 ata with MW 50. Not just at 1.75 ata, but also for 1.43 ata (30 min power, 'Kampfleistung') required MW 50 injection.
1.75 ata is under 51 in Hg, or +10.2 psig; 1.43 ata is around 41 in Hg, or +5.5 psig; for comparison sake, another comparable non-intercooled 2-stage engine, V-1710 in P-63, will do 55 in Hg in military power, 60 in Hg in WER (5 min, no ADI) and 75 in Hg in 'WER wet' (ie. with ADI).
Manifold pressure is surely a factor for pre-ignition, itself being the function of many things connected to supercharging, intercooling, ADI yes or not etc.
The German C3 fuel was in the ballpark of what the Allies had when DB 605 was at the development phase. Increasing compression ratio, let alone increase of manifold pressure (and thus increase of power and stress generated) will induce even more reliability isues than encountered historically, that lasted more than a year.
The rate between C3 and MW 50 consumption was around 4:1 in the DB 605L. The MW 50 tank held 70 liters, consumption was 150 L/h for 1.75 ata and 75 L/h for 1.43 ata. Basically, whatever the compression ratio saves, gets offset and more by need to consume MW 50 mixture. Intercooler stays with the aircraft, and DB could've opted for air-to-air intercooler (20-30 kg?) like Jumo did for the 211J/P. Of course, intercooler and lower CR and ADI are not mutually exclusive and give best results, as we know when looking in many ww2 engines, including the Jumo 213E.
The MK 108 you mean?
The arithmetics in the bolded part are off by a large margin. Increase of compression ratio by 100% will not give 100% more fuel and do wonders on consumption:
So when we decrease the compression ratio by 13.33%, the power will go down by 3.3% for same RPM and manifold pressure. On the plus side, with CR of, say, 6.5:1, the 'Notleistung' regime (1.42 ata, 2800 rpm) might not be banned at all, instead for more than a year as it was, since the engine will be less stressed due to lower CR.
In order to cool the 3.3% increase of power? Not by a country mile.
LW needs a larger or a two stage supercharger, that will be well served by an intercooler. Otherwise the Allied aircraft with multi-stage superchargerd engines will kill the LW. As historically.
As for 'the engine and can no longer provide altitude compensation' - care to elaborate on this, how much this was important, preferably with some sources?
LW was sticking all things on the Bf 109 that managed, among the benefits, to slow down it. The air-to-air intercololer can be installed under the engine, with oil cooler relocated in MC 205 fashion. Same for water-to-air intercooler's radiator. Or, install a bit deeper radiator, as a part of main cooling system.
As for the DB 605A with greater CR: no, no - the reliabilty is lacking even on historical CR.
The 'simply provide 100/130 fuel to the Me 109' tidbit is a little hard to swallow, BTW
The RR design approach on the Merlin and Griffon (low compression ratio, comparatively big supercharger, among other details on a V12 engine) was a carry over from the Kestrel. There was no 'indirect improvement of the power at altitude' due to any of the better fuels available, the ever better altitude performance was due to ever better superchargers (and intercoolers, once installed). Sure enough, the low compression ratio helped out with power under the rated altitude(s), with manifold pressures going to around 3 ata with 150 grade fuel and no water injection.
The job of the intercooler was not to 'cool back' the compressed air, but to make sure the temperature is within the, for engine, manageable limits. Eg. for the Merlin 61 in Spitfire VII, the 40% of intercooling was found to give the best results (per Morgan Shackledy, pg. 269), while the US standard was 50% of intercooling (at least for turbo engines). The high compression engine, like DB 605L,will need the intercooler even more. The max manifold pressure (on 605L) being limited to 1.75 ata with MW 50. Not just at 1.75 ata, but also for 1.43 ata (30 min power, 'Kampfleistung') required MW 50 injection.
1.75 ata is under 51 in Hg, or +10.2 psig; 1.43 ata is around 41 in Hg, or +5.5 psig; for comparison sake, another comparable non-intercooled 2-stage engine, V-1710 in P-63, will do 55 in Hg in military power, 60 in Hg in WER (5 min, no ADI) and 75 in Hg in 'WER wet' (ie. with ADI).
Manifold pressure is surely a factor for pre-ignition, itself being the function of many things connected to supercharging, intercooling, ADI yes or not etc.
The German C3 fuel was in the ballpark of what the Allies had when DB 605 was at the development phase. Increasing compression ratio, let alone increase of manifold pressure (and thus increase of power and stress generated) will induce even more reliability isues than encountered historically, that lasted more than a year.
The rate between C3 and MW 50 consumption was around 4:1 in the DB 605L. The MW 50 tank held 70 liters, consumption was 150 L/h for 1.75 ata and 75 L/h for 1.43 ata. Basically, whatever the compression ratio saves, gets offset and more by need to consume MW 50 mixture. Intercooler stays with the aircraft, and DB could've opted for air-to-air intercooler (20-30 kg?) like Jumo did for the 211J/P. Of course, intercooler and lower CR and ADI are not mutually exclusive and give best results, as we know when looking in many ww2 engines, including the Jumo 213E.
The MK 108 you mean?
The arithmetics in the bolded part are off by a large margin. Increase of compression ratio by 100% will not give 100% more fuel and do wonders on consumption:
So when we decrease the compression ratio by 13.33%, the power will go down by 3.3% for same RPM and manifold pressure. On the plus side, with CR of, say, 6.5:1, the 'Notleistung' regime (1.42 ata, 2800 rpm) might not be banned at all, instead for more than a year as it was, since the engine will be less stressed due to lower CR.
In order to cool the 3.3% increase of power? Not by a country mile.
LW needs a larger or a two stage supercharger, that will be well served by an intercooler. Otherwise the Allied aircraft with multi-stage superchargerd engines will kill the LW. As historically.
As for 'the engine and can no longer provide altitude compensation' - care to elaborate on this, how much this was important, preferably with some sources?
LW was sticking all things on the Bf 109 that managed, among the benefits, to slow down it. The air-to-air intercololer can be installed under the engine, with oil cooler relocated in MC 205 fashion. Same for water-to-air intercooler's radiator. Or, install a bit deeper radiator, as a part of main cooling system.
As for the DB 605A with greater CR: no, no - the reliabilty is lacking even on historical CR.
The 'simply provide 100/130 fuel to the Me 109' tidbit is a little hard to swallow, BTW
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