109 e3b against spitfire II

[Crumpp]

If direct injection really was so great for piston aero-engines, the chances are that the Allies would have adopted it immediately post-war when all Axis technology was theirs for the taking.

The Allies did not have any direct injection engine technology to use.....

They could not make direct injection workable or practical using their fuel metering technology. Bosch's design, up until recently was the pinnacle of direct injection technology. It requires very high fuel pressures and the German system used a high pressure pump for each cylinder.

As already pointed out, post war, the turbine was supreme so why would any nation waste resources for a post war piston engine aircraft?????

[Crumpp]

Great Wartime article Viper. Thanks for posting that.

http://www.flightglobal.com/pdfarchi...0-%200569.html

http://www.flightglobal.com/pdfarchi...0-%200563.html

http://www.flightglobal.com/pdfarchi...0-%200562.html

An article definitely written to contain the public relations damage from intelligence on German fuel metering technology.

Rolls Royce's basic message is the German engines are not as efficient as they could be and only somewhat more efficient than the our engines.....

AND we can make a carburetor heat system that will overcome icing....

[Viper2000]

Originally Posted by Crumpp

The Allies did not have any direct injection engine technology to use.....

They could not make direct injection workable or practical using their fuel metering technology. Bosch's design, up until recently was the pinnacle of direct injection technology. It requires very high fuel pressures and the German system used a high pressure pump for each cylinder.

As already pointed out, post war, the turbine was supreme so why would any nation waste resources for a post war piston engine aircraft?????

Post WWII, it was perfectly within the Allies' rights to confiscate any and all German IP that they were interested in. So they could have made Bosch fuel injectors and put them into their engines at no great cost. They chose not to.

As for post-war engine development, the US government funded considerable development work on the R-3350 turbocompound, and indeed also upon the R-4360, both of which found their way into airline service.

Britain funded development of the Napier Nomad, which was a more ambitious take on the turbocompound idea (I strongly suspect that this engine was cancelled due to failure to meet its quoted performance; I modelled it in considerable detail a couple of years ago, and I could never make the quoted component efficiencies add up to the quoted SFC...).

Direct injection makes a lot of sense for naturally aspirated engines, compression ignition engines, or engines which operate over a wide power range. It's less attractive for a big aero-engine because if you're operating at fixed power with a reasonable amount of supercharge you should be able to attain excellent mixture distribution, and so the pragmatic solution is to have single point injection into the eye of the supercharger - which is basically what everybody ended up doing.

Of course, these days people aren't designing big piston aero-engines anymore, and they aren't supercharging*, so DI makes sense.

*and turbochargers tend to be bought from turbocharger companies, which means that injection into the eye of the turbo-supercharger impeller isn't really an option because it would be too much of a nightmare to organise the development effort - who pays for what etc?

[Viper2000]

Originally Posted by Crumpp

http://www.automobilemag.com/feature...ion/index.html

Single point injection has no advantages over direct fuel injection at all. The Supercharger is on a completely separate circuit and the engine still receives all the benefits of supercharging with the additional benefits of direct injection.

The supercharger is driven by the engine.

If you reduce the power consumed by the supercharger then you increase the brake horsepower and reduce the SFC.

Supercharger power consumption is just W*Cp*deltaT, ie W*deltaH.

Supercharger isentropic efficiency is

deltaH[actual]/deltaH[isentropic]

In the case of the Merlin, this figure was about 70%.

For isentropic, adiabatic compression,

T2 = T1(P2/P1)^(gamma/(gamma-1))

Hence it's trivial to calculate the isentropic deltaT, and deltaH.

DeltaT and deltaH both get smaller if we reduce T1.

Injecting fuel upstream of the supercharger reduces the temperature by about 25 K due to the latent heat of evaporation of the fuel.

This reduces the temperature rise across the supercharger, which is equivalent to increasing its adiabatic efficiency.

Clearly this confers an advantage to engines which inject fuel upstream of the supercharger. Given the considerable difficulty associated with increasing the aerodynamic efficiency of compressors, this advantage is not insignificant.

Mixture distribution is going to be very good provided that the charge temperature is sufficiently high for complete evaporation to be ensured. This will basically always be the case at high powers because deltaT is 100 K or more; indeed intercooling & aftercooling start to become necessary once you've got a lot of supercharge.

These advantages vanish at low non-dimensional power settings. Cars spend most of their time at very low non-dimensional power settings, and therefore DI wins hands down most of the time, especially if you go for CI, in which case it's almost no-contest.

In the end, the nature of all engineering trade studies is that the devil is in the detail. The optimum is a strong function of engine size and duty cycle, and we just don't build the sort of highly supercharged, high power spark ignition engines for which single point injection is attractive these days.

To use an analogy, old amplifiers used valves and therefore tended to have large transformers & rectifiers to produce the high DC voltages which allowed them to function. Most modern amplifiers are solid state, and they don't need those high voltages.

This doesn't mean that high DC voltages aren't still a good idea for valve amplifiers; I've got a pair of hundred watt half stacks sat next to me which run in excess of 400 V DC and sound great. But probably 99% of modern amplifiers for domestic use are solid state and so if you just ask "are high voltages a good idea for amplifiers" then the short answer is "probably not".

[Crumpp]

Originally Posted by Viper2000

The supercharger is driven by the engine.

If you reduce the power consumed by the supercharger then you increase the brake horsepower and reduce the SFC.

Supercharger power consumption is just W*Cp*deltaT, ie W*deltaH.

Supercharger isentropic efficiency is

deltaH[actual]/deltaH[isentropic]

In the case of the Merlin, this figure was about 70%.

For isentropic, adiabatic compression,

T2 = T1(P2/P1)^(gamma/(gamma-1))

Hence it's trivial to calculate the isentropic deltaT, and deltaH.

DeltaT and deltaH both get smaller if we reduce T1.

Injecting fuel upstream of the supercharger reduces the temperature by about 25 K due to the latent heat of evaporation of the fuel.

This reduces the temperature rise across the supercharger, which is equivalent to increasing its adiabatic efficiency.

Clearly this confers an advantage to engines which inject fuel upstream of the supercharger. Given the considerable difficulty associated with increasing the aerodynamic efficiency of compressors, this advantage is not insignificant.

Mixture distribution is going to be very good provided that the charge temperature is sufficiently high for complete evaporation to be ensured. This will basically always be the case at high powers because deltaT is 100 K or more; indeed intercooling & aftercooling start to become necessary once you've got a lot of supercharge.

These advantages vanish at low non-dimensional power settings. Cars spend most of their time at very low non-dimensional power settings, and therefore DI wins hands down most of the time, especially if you go for CI, in which case it's almost no-contest.

In the end, the nature of all engineering trade studies is that the devil is in the detail. The optimum is a strong function of engine size and duty cycle, and we just don't build the sort of highly supercharged, high power spark ignition engines for which single point injection is attractive these days.

To use an analogy, old amplifiers used valves and therefore tended to have large transformers & rectifiers to produce the high DC voltages which allowed them to function. Most modern amplifiers are solid state, and they don't need those high voltages.

This doesn't mean that high DC voltages aren't still a good idea for valve amplifiers; I've got a pair of hundred watt half stacks sat next to me which run in excess of 400 V DC and sound great. But probably 99% of modern amplifiers for domestic use are solid state and so if you just ask "are high voltages a good idea for amplifiers" then the short answer is "probably not".

Viper,

The basic premise you posted is entirely wrong for all practical purposes. Your math does not take into account the heat of the engine and heat transfer to the manifold.

The conclusion reached is incorrect when it comes to engines...

Injecting fuel upstream of the supercharger reduces the temperature by about 25 K due to the latent heat of evaporation of the fuel.

Injecting fuel into the intake raises the charge temperature. Liquid fuel transfers and has more heat capacity than air. That means the fuel allows the charge to absorb more of the intake manifold's heat and the over all effect is the charge temperature is higher which is therefore less dense.

You can confirm this with a copy of:

V.L. Maleev, Internal-Combustion Engines: Theory and Design, 2nd ed. (New York: McGraw-Hill Book Company, Inc., 1945).

http://books.google.com/books/about/...d=fgvHHgAACAAJ

So why does an IO-360 (fuel injected) have a higher peak power than a O-360 (carbureted)? The answer is that fuel injection reduces losses in the intake system. The first reason is that the venturi in the carburetor is another constriction in the flow, which manifests itself as a pressure drop in the intake manifold. This pressure drop is eliminated with a fuel injection system, thus allowing a higher pressure to reach the cylinders, and thus a larger amount of fuel/air charge to enter the cylinder.

The second reason is that the fuel/air charge is colder, and thus denser when it reaches the cylinder, again allowing a larger amount of fuel/air charge to enter the cylinder. Just like when you add carb heat, the density of the fuel/air charge is reduced when it is heated. So you're asking "Why would it be heated?" In some carbureted engines, the intake manifold is heated to assist distribution. Even without intake manifold heating, the intake manifold will be hotter than the ambient air simply because it is attached to the engine. Heat transfer studies have shown that the liquid fuel on the walls on the intake manifold increases the rate of heat transfer. (Ref 1) Thus, in a carbureted engine, the small drops of fuel in the fuel/air charge cause the charge to heat up more passing through the intake manifold than dry air would passing through the same intake manifold. Therefore, the density of the fuel/air charge is decreased, reducing the amount of charge entering the cylinder. Experiments have shown that volumetric efficiency may be increased by 10% by direct injection of the fuel into the cylinders. This also prevents loss of fuel because of valve overlap. Fuel injection into the intake port (just outside the intake valve) shows a smaller, but appreciable improvement. (Ref 1)

http://www.eaa1000.av.org/technicl/e...htm#References

[TomcatViP]

Originally Posted by Viper2000

If direct injection really was so great for piston aero-engines, the chances are that the Allies would have adopted it immediately post-war when all Axis technology was theirs for the taking. The fact that they didn't do so speaks volumes.

Sry but you are bypassing economics realities : the Industrial war machine was in such a strain at the end of WWII that minimal change in production were made where there was not strategical importance in order to downsize the level of investments. Many non-allied advanced tech were simply rejected in face of this.

Civil Aviation (the only one still interested in piston engine at the time) loose for long Injected eng, Fadec (without D and E ), canards foreplane etc.. Some of the very much "advanced" tech that was rushed back on the GA shelves as "new" products in the late 80's and 90's.

The conclusions you give does not convince me - Sry I am duplicating earlier comments of very good quality