Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
It's not high pressure effectively zero pressure, its cryogenic. N2O is weakly cryogenic.
... however there is a reference to the N2O system being made safe. It's a non inflamable liquid that could be protected by some kind of a self sealing system.
I would disagree with a fiar bit of what you've state about the DB600, Improvements in DB605 performance (aside from tuned scavenging and spark plugs) came about as a result of improvements in piston compression ratio and compressor fluid dynmamics, latter on still the supercharger was increased in size in the D and AS series engines but still remained a single stage. 1.98 ata boost, the maximum used by the 2000hp DB605DCM at CR of 8.5 is only 14 psig or 59 inches of mercury. To achieve somewhat lower power levels the Merlin needed 25psig (about 2.8 ata boost) for the same wieght and worse fuel consumption. Two stage compressors are not more efficient than single stage, they may draw less shaft power but this comes at the expense of intercooling which is basically throwing away energy into the intercooler for disposal by a bulky radiator of some kind.
Note I didn't say the DB605 with a single stage supercharger was better than engines with a two stage unit, I said it was far dependant on high supercharger compression ratios and provided sufficient performance; it clearly still faded away slightly earlier but not at all by much especially the latter englarged supercharger versions. The Merlin used its supercharger not to compensate for altitude but to overboost its engine while the DB605 did less so and it seems gained considerable fuel economy.
Improvements to the 605 over the 601 came from a number of things, 1. a 5.3% increase in displacement. 2. a 12-15% increase in rpm (2400-2500rpm to 2800rpm). 3. an 9% increase in boost (1.3 Ata to 1.42). Since some of these improvements compound it means that the increased valve overlap, increased compression ratio and improved compressor fluid dynamics are responsible for under 1/2 the improvement.
With the later versions it was mostly the increased boost as can be seen by comparing the percentage increase in boost to the percentage increase in power. It is not exactly the same but it is close. The fact that some times (certain models) of the 605 used "over boost" to reach their power levels is also evident by looking at some of the charts on Kurfurst's site. By over boost I mean using more boost than can be sustained to the critical height of the previous model.
Two stage compressors ARE more efficient than single stage compressors for a given level of boost. This was not new even in the late 30s, Mercedes used a two stage supercharger on their 1939 Grand Prix cars for that reason. comparing one supercharger to another at different levels of boost isn't really comparing the superchargers.
This line is a real hoot (joke) "at the expense of intercooling which is basically throwing away energy into the intercooler for disposal by a bulky radiator of some kind"
While true in a very theoretical sense regarding the whole system as a "heat engine" for ultimate fuel efficiency from a practical, real world sense the intercooler is a necessity to get high power output.
High fuel efficiency and high power from the size size/weight engine not really being possible at a given level of technology.
Charge cooling does at least three things for an engine. Since the power limitation comes from oxygen that can be moved through an engine per unit of time (mechanical strength being ignored) the more air means the more power.
There are figures around for the Merlin XX, it's supercharger in high gear heated the intake charge about 148 degrees C over the incoming air. when providing 9lb of boost. It had a pressure ratio of around 3.5 to 1. Higher pressure ratio superchargers are going to heat the intake charge much more (the Merlin 61 could compress the air 5.1 times at 23,500ft) and such high supercharger ratios at high altitude would have been unusable due to detonation problems without some form of charge cooling. Please note that the WER ratings on the P&W R-2800 were achieved using BOTH intercoolers and water/alcohol (MW/50) injection.
When assessing the supercharger set ups and what they achieved it is also good to remember in what order things happened and why.
When assessing the supercharger set ups and what they achieved it is also good to remember in what order things happened and why. When the Merlin 61 was developed and introduced it's purpose was to improve altitude performance.
Initial Boost was limited to 15lbs which was achievable with the single stage supercharger at low altitudes. Getting 15lbs of boost ( 60in manifold pressure) at 23,500 ft was NOT achievable with a single stage supercharger at that time.
Multiply the displacement increase by RPM increase by boost increase one barely gets a 36% increase.
An increase of compression ratio from 6.9 (DB601) to 8.5 (DB605DC) however figures prominently.
Valve overlap and multipoint fuel injection can get 10% to 15% more power.
The DB605 series has a quirky proportionality of boost levels at sea level and power increase however at full power height it was about 150hp more.
Two stage compressors are used when technology is inadaquet to produce the required compression in a single stage.
Of course it all gets down to detail design, but its clear the DDs engineering avoided dependance on high supercharger pressures and intercooling; so touting the Merlins intercooler supercharger setup rather ignores the point that it was in a way a fix to the limitations of carburation and throttle body injection.
Actually the high piston compression ratios prohibited the use of of high pressure ratio superchargers and without the high pressure ratio superchargers there was a lot less need for the inter coolers. Figure it out for yourself, Say you boost the piston compression ratio by 20%, you do not get 20% more power, you may get 5-10% more power but if you had kept the same piston compression ratio and increased the boost pressure by 20% you could burn 20% more fuel per power stroke. Even counting the extra power to drive the supercharger you come out ahead.From a practical point of view the DB series managed to operate high piston compression ratios and avoid the need for high pressure ratio superchargers and inter-coolers.
High compression ratios allow greater expansion of the hot gases and therefore more power and efficiency. There is more danger of pre ignition, however no energy is lost as in intercooling and while intercooling can clearly demonstate advantages it comes at a price as well.
The DB605DC managed 1850hp on C3 a 96/130 fuel without MW50 it weighed 745 kg.
The Merlin (66) seemed to need 100/150 fuel (really 110/150) to do the same it weighed 744kg.
For the high altitude Wellington, supposedly.
1.8 ata boost 11 psig
1.98 boost 14 psig.
The DB605 could get away with a single stage supercharger.
It is true. Modern gas turbines are renowned for reducing the number of stages as part of efficiency improvements.
Anti-Detonant Injection, OK SR beats meWhat's ADI?
The DB605DC managed 1850hp on C3 a 96/130 fuel without MW50 it weighed 745 kg.
The Merlin (66) seemed to need 100/150 fuel (really 110/150) to do the same it weighed 744kg.
In fact Merlin 66 produced appr 1980hp at sea level with 100/150 fuel and 25lb boost.
Juha
Higher power levels (eg Merlin 100) resorted to 100/150 plus ADI.
Thank you (both) since it means I've been able to confirm my suspicion that the Merlin 100-series didn't have it, they just had "standard" fuel injection, which did sufficient cooling on its own.
Thank you (both) since it means I've been able to confirm my suspicion that the Merlin 100-series didn't have it, they just had "standard" fuel injection, which did sufficient cooling on its own.
the energy LOST in the intercooler is pretty much theoretical as this energy is pretty much destructive to a high power engine. If you want to design a fuel economy special go ahead but the increased power from the denser charge has been proven over and over again (some German engines could pick up 4-5% in power just from using MW-50 WITH NO INCREASE IN BOOST). Speaking which doesn't MW-50 cause a loss of power as it reduces the heat (energy) in the intake charge? The Price of an inter cooler is weight, bulk and drag. But then lugging around 100-200liters if water/alcohol brings a few penalties too doesn't it?