yr right - By hymomics, I presume you mean harmonics. What adverse harmonics does a CI engine possess, that a SI doesn't?

Every driven a desiel and then a petrol car what's the difference. The rattle is the firing which give the proplem. They not a smooth engine on firing.

Which leads to something I just thought of. When we balance props we use accelerometers. These pick up the bad vibes in the engine. Not sure they will work on theses engines but

The Austro Engine is certified to run on EITHER JetA1 (plus 2 dozen or so equivalents depending on your countries preference) alongside pump diesel. Add to that the economy you get from them, plus the longevity of the core engines and you've got the undeniable future for all light aircraft applications.

The V1 twin turbo diesel Diamond does 190 kts at 28000 feet burning a total of 36 litres per hour. or 18 litres per hour per side. (Coming from the mouth of Austro/Diamonds ferry pilot himself) Although the airframe is only certified to something like 18000 feet.

Austro are aiming for a 5000 hour TBO and are projecting an unlimited TBO into the future as their condition is constantly monitored via oil sampling at every service by the manufacturer.

They are also working on a number of larger applications in the 350 hp range which may already be in use by the US military in drone applications.

I've flown a couple of different diesel models on a number of occasions and I can say I was quite impressed with them. As for "ry igrht" comment re vibration I can confirm they are light years ahead of their opposite number in Lycoming. I can't comment on TCM as I've never flown a 4 cylinder 180-200 horse TCM.

In the Diamond twin (diesel), you can have the canopy open with both engines running and still have a conversation with your headsets off. They are that quiet and smooth.

Can't wait for more diesels like the V8 mentioned here are certified and STCable or fitted to production aircraft. Bring em on!

This would have to be the biggest piece of misinformation I have come across lately The rattle is the firing which give the proplem. They not a smooth engine on firing.


An Audi A8 V8 twin turbo diesel at idle is quitter than the petrol equivalent it uses Piezo Injectors that control the flame front with up to 8 fuel pulses and is just delightful to drive I owned one for a time, great car Euro 5 compliant without using Blue Goo.

T28D
SO what are the harmonics from if not the firing pulses?
The Vision 350 innovation allows the fitting of an aluminium propellor, previous diesels could only be fittted with composite blades. Are you refering to flame lift off length, after initial autoignition? As you would know the flame in a CI engine propagates quite differently to that of an SI engine.

YUP As you would know the flame in a CI engine propagates but it is still a predictable flame front or she wont go !!!!!

That takes me back to diesel theory: Lift off, diffusion flame, cool flame soot, oxidisation etc etc. But it also makes that noise or rattle that Yr Right spoke of.
By the use of modern fuels, with better matching cetane number for swirl chambers and cylinder head design, CI engines can now be produced almost vibration free. Note almost, they all seem to have a frequency that resonates, a car can be geared to avoid that RPM

the diesel noise is caused by the ignition delay of the fuel and depends on the amount of fuel injected before actual ignition. If you can get a lot in before it begins to burn, you'll get a rapid pressure rise as it all suddenly goes off together, which is the cause of the knocking/rattling sound.

pilot injections, rate-shaping, or whatever-you-want-to-call-it that the electronically controlled injectors do are all designed to limit the amount of fuel injected prior to ignition.

Having said that, not much of this has anything to do with torsional harmonics, hymomics or any other imagined figment that the propeller sees. It's the compression ratio that pretty much dictates the torque amplitude for a given load/power level

AndyRR Would you like to explain why?

Hard to explain without waving my hands in the air drawing imaginary diagrams, but...

...in simple terms, the net work done is the sum of the (positive) expansion work and the (negative) compression work. If you increase the compression work by increasing the compression ratio (negative torque pulse) you also increase the expansion work (positive torque pulse). The net work done is the same (more-or-less) but the difference between the two (torque pulses) is the amplitude. Hence higher CR >> higher torque amplitude.

Why not go back to radial diesels?

From the link Radial engine - Wikipedia, the free encyclopedia

A new Piper or Cessna would look awesome with a radial up front :ok:

Have you ever seen the engine mounts in a modern diesel car. They huge and not only that they also electronically controlled to smooth out the nvh. this is hard to over come in an aircraft when its fitted with a prop.
And as I recall now I may been wrong but don't they fire via compression, hence the rattle. Now the rattle is the problem as it sets up the harmonics though the whole of the airframe, as I said earlier a TB 10 or 20 was fitted with one and it blew the tail off it as it taxyed back after its first and only test fight, then you have the problem of a prop. Now as I understand they also fitted with a cushion rubber drive to take the pluses out.
In a modern car this is not so much as a problem as weight is not such a primary concern but in an aircraft it is.
Also as I said earlier im not sure you be able to do a prop balance on the airframe with one of these engines,


Cheers

The vibration through the crankshaft would not vary as the pulses stay in balance, unless of course it is a single cylinder.

I read recently that a diesels natural combustion properties mean it runs in constant detonation, hence the traditional clatter sound a diesel makes.

Modern diesel engines have eliminated this clatter by using a pilot injection that comes before the main injection pulse, as well as pulses of fuel injection after combustion has started.

I do no it's mandatory line replacement if you have to crack one open. $$$$$

I just watched that video and while the noise level has drop a hell of a lot you can still hear it with still means bad vibes

That might be true on a multi-cylinder engine with an infinitely stiff crankshaft, however no-one's invented an infinitely stiff crankshaft yet. A radial engine is a close approximation though.

The diesel knock/rattle is in the 5-15kHz range and the engine mounts are not very well coupled at that frequency at all. It's like trying to remove the tail of your TB20 by repeatedly hitting the crankcase with a hammer...

yr right - You're confusing sounds (hearing a diesel clatter) with vibration (torsional and longitudinal crankshaft whip).
Vibration will lead to airframe cracking, noise from the combustion process won't.

The fancy engine mounts in current diesel cars and light commercials are designed to prevent the diesel clatter noise from transferring to the chassis and body via amplification through the engine block, the chassis, and the body.

A CI engine has a longer duration power stroke than an SI engine. The power stroke from an SI engine is relatively short.
This accounts for the much higher torque production from a diesel engine.
The much higher torque level of an aircraft diesel is possibly more of a concern with regard to prop damage/life, than anything else.

The considerably higher compression ratio of a CI engine is what produces the larger rotational impulses as compared to a SI engine.
Most diesels are 16 to 18:1 compression ratio. The much lower compression ratios of SI engines produce much lower rotational impulses.
However, a misfiring SI engine (an exceptionally rare event in CI engines) would produce far greater rotational impulses, than a CI engine ever would.