109 e3b against spitfire II

[Viper2000]

Originally Posted by Crumpp

There is no such thing as a direct injection aircraft engine in General Aviation. All fuel injection is single point injection much like the Allied designs of WWII.

Actually pairs of these things fly over my head every day...

Originally Posted by Crumpp

In a direct injection engine, there is almost no variation in CHT or EGT between the cylinders.

CHT is dominated by cooling; EGT is dominated by stoichiometry. CHT variations are an inevitably fact of life for air-cooled engines.

Originally Posted by Crumpp

It is that temperature variation that robs a single point fuel metering system of power.

A perfectly reasonable statement if and only if you are comparing identical intake conditions.

[CaptainDoggles]

Originally Posted by Viper2000

CHT is dominated by cooling; EGT is dominated by stoichiometry. CHT variations are an inevitably fact of life for air-cooled engines

He's not saying that EGT and CHT are equal, he's saying that across the cylinders CHT won't vary much, and neither will EGT.

[Viper2000]

Originally Posted by CaptainDoggles

He's not saying that EGT and CHT are equal, he's saying that across the cylinders CHT won't vary much, and neither will EGT.

I was responding to this:

If you have flown an aircraft with individual Exhaust Gas Temperature Gauges and Cylinder Head Temperature gauges you would know their is a wide variance in the temperatures with any fuel metering system that introduces fuel to the intake.

...

[Crumpp]

He's not saying that EGT and CHT are equal, he's saying that across the cylinders CHT won't vary much, and neither will EGT.

Correct. Thank you.

What I am saying is obvious for anyone who has flown a piston engine aircraft with individual CHT/EGT. You can see the power robbing temperature differences of introducing fuel anywhere in the intake system.

Only by metering fuel with a direct injection system will the cylinders have equal EGT's and CHT's across the engine.

Actually pairs of these things fly over my head every day...

I did not know the DA-42 diesels were direct injection. It figures, diesel is the easiest type of engine to direct inject.

[Crumpp]

I was responding to this:

You misunderstood it.

Of course EGT is not going to equal CHT in an individual cylinder, that is a silly concept. Only in direct injection will the EGT and CHT be equal across the cylinders of your engine.

Fuel introduced in the intake will cause the cylinders to draw different mixture ratios as the firing order is cycled. The different fuel mixture ratio will cause each cylinder to have a different CHT and EGT from the other cylinders in the engine. This is a very common known fact for pilots as you see it every time you fly so you don't get worried when one cylinder has a temperature 100 degrees lower than another cylinder. That is just a by product of introducing fuel into the intake system instead of directly injecting it in the cylinders so the mixture can precisely metered.

[Viper2000]

Originally Posted by Crumpp

I did not know the DA-42 diesels were direct injection. It figures, diesel is the easiest type of engine to direct inject.

In many ways it's tougher because the pressures are higher. However, the alternatives are worse, so injection becomes the route of least resistance sooner.

[Crumpp]

In many ways it's tougher because the pressures are higher.

Diesels are some the first engines to be successfully directly injected. DI eliminated the need for a complicated pre-mix chamber and the mechanical gearing required to control the mixture.

You don't have to worry about getting fuel and spark to the chamber at the right time, just the fuel.

[Crumpp]

if you are comparing identical intake conditions.

Any fuel metering system that introduces fuel into the intake system cuts down on the efficiency of that intake just by being there.

Sure the fuel cools the charge but the airflow volume is restricted by the fuel metering device. Carburetors, whether float, SU, or TBI restrict the airflow volume.

With Direct Injection, the intake can be designed free from the volume and flow obstruction of a fuel metering system component.

[catito14]

It was not solved in the "Spitfire II" the problem of negative G?

[catito14]

Oh, i see. Thanks for the clarification cheesehawk!

Regards