Engine technology free-for-all

[roon]

Speaking of Napiers...



Note the nutation of the connecting rod and bushing.

And some very pleasant Bristol clockwork:

[amho]

A question:
does increasing compression ratio increases engine noise? by increasing cr, mixture pressure increase and combustion product pressure goes higher too, does it affects engine noise?

Not necessarily. It depends on the pressure & temperature of the exhaust gas when the exhaust valves open. That is determined by many things including the expansion ratio, ignition timing, and air-to-fuel ratio, along with the compression ratio. The geometry of the exhaust pathways (runners, pipes, mufflers, etc.) also play a big part.

But that is only to speak of exhaust noise. Combustion noise during compression ignition can be heard as pinging, ticking, or growling in diesel engines, or when gasoline fueled engines experience knock. Which again has something to do with compression ratios, but not only.

yes I know that many factors as you mentioned affects engine noise but imagine all parameters are same in engine A and B in exception of higher cr in engine B then is there any higher combustion noise in engine B necessarily? consider situation that combustion is normal I mean no knocks or any abnormality...
I want to know about combustion noise and not about exhaust noise.

[roon]

My guess is: as compression ratio rises, all other things being equal including the size of the fuel charge, and assuming a gasoline SI engine, the temperature and pressure of the charge air will continuously increase. There will be a transition from spark ignition, to auto ignition, to failure of the piston or cylinder. So I guess you could say that combustion noise, as heard from outside the engine on a muffled vehicle, or as detected with a knock sensor, increases as CR rises until engine failure. Within a narrow set of assumptions. There is a variable compression ratio engine on the market from Nissan currently, so your question is akin to asking what happens if there is a failure or fault of the CR controls of such an engine.

[J.A.W.]

Frankly, the question is simplistic.. there are multi-factorial aspects to causation of engine sounds, let alone "noise".

As an example, Bristol sleeve-valve radials were noted to be quieter than rival poppet valve equivalents..
(inspite of running higher comp-ratios), with some "noise" reduction - from more complete combustion,
due to volumetric efficency advantages ( visibly evidenced - by an overt lack of exhaust flames, at night),
plus mechanically, by having far fewer recip' components ( pushrods/rockers/valves) hammering up & down..

This C.I. 2T mill ( Napier Nomad) was also fairly quiet.. but as per current F1 - the exhaust energy was
compounded via turbine, rather than simply/crudely - blasted out of efflux nozzles - for basic thrust..

[Tommy Cookers]

exhaust thrust benefits from systems that preserve the individual exhaust pulses (as does car turbocharging)
J.A.W has shown this from the Flight archive re RR and the DH Hornet

in this Merlin 1940-style 'ejector' exhaust was somewhat less than ideal (though far better than Bristol 'collector' systems)
as V12 adjacent cylinders' exhaust phases are 120 deg apart (ie not ideal 240 deg interval as in car twin-turbo V6s)
imo this explains why the 12 individual stub exhaust was used from 1941
on TV 617 Squadron Lancs in 1945 had 12 flat-tailed (non-stubby) pipes paired mechanically but functionally seperate

(Gunston wrote that Bristol Hercules bomber 'collector' exhaust tail pipe had many small exits before a closed end)
radials including Bristol went to multiple pipes after the 190 and (many or all ?) had fan-assisted cooling airflow
the multiple pipe systems all had many individual pipes and some 2 into 1

postwar Convair had a lavish augmentor system on the successful 240 airliners helping cooling (without fan) and thrust
mixing cooling air and exhaust it gained a 'free' 13% power at quite low speeds
(see Flight archive of 11 November 1948 issue - can't post the link)

[J.A.W.]

T-C, this 'Flight' article compares aerodynamic drag findings for various power-cooling installations
fitted to the aerodynamically clean Hawker Tempest - which utilized both liquid & air-cooled engines.

Notably, BMW's use of fan-cooling for the FW 190 is rejected as needless complexity - for fighter operations,
but careful flow design still brings the radial drag penalty* closer to that of liquid-cooled radiator set-ups..

http://www.flightglobal.com/pdfarchive/ ... 01441.html

*Albeit the tests were 'cold' - & so, absent 'Meredith effect' dynamic flows - derived from rejected 'waste' heat?

[Tommy Cookers]

it doesn't compare aero drag in flight - it is comparing aero drag at zero lift

the 180 lb weight penalty of the annular radiator creates a lift-dependent drag penalty proportionate to that 180 lb (and worse)
the performance prediction ignores this

simply .....
the annular aircraft would likely be better at chasing V-1s or kamikazes
but no better or maybe worse in fighter vs fighter activity


the space needs of efficient wing radiator seems a good point ie what's right in a Mosquito isn't right in single-engined planes
and we know the underslung radiator is relatively better on 2 or 4 engined planes than on single engined

[roon]

Notably, BMW's use of fan-cooling for the FW 190...

I see the fan has its own drivetrain. Why the fork shaped exhaust tips in the drawing below?

[roon]

Three pipes exit the inlet horn, aft of the air filter. What could these be for? The central pipe could feed the compressor. The two pipes either side could be routing air into the metal shroud they are connected to, for cooling the compressor housing. I suppose one could be a BOV return. Or maybe they have a unique compressor design with three inlets.

If it's for cooling the intake air path may be: roof scoop>air filter>airbox beneath air filter>side pipe>compressor shroud>side pipe>air box beneath air filter>center pipe>compressor inlet.

[Tommy Cookers]

[quote=roon] .....Why the fork shaped exhaust tips in the drawing ? ....[/quote]
good question ! (note as J.A.W says later the dwg is not a 190 arrangement - and the forks are sets of 5 fishtail nozzles)
suggestions ....
entrainment of slipstream and cooling air by exhaust gas ?
exhaust gas is sliced into jets to increase area under shear
thrust is increased due to less loss from KE as gas-mix's velocity is much lower than exhaust's
cooling is helped

did it work ? Gunston says it gave a modest propulsive thrust and sucked air through the cowling
was it copied ? surely yes eg developed Zero developed Corsair La-5 etc etc

and mixing to cool gas in various ways and reduce flame/glow ? (note as above -it's a bomber and needs flame damping)

[J.A.W.]

Roon, the cutaway pic BMW you posted is a power-egg bomber unit such as powered the Do 217/Ju 88 & etc..
The BMW powered FW 190 grouped its exhaust pipes outlets.. the Bomber types were 'flame damped'.. per T-C..

[J.A.W.]

T-C, Rolls-Royce & Napier both developed annular radiator set-ups on the Hawker fighters..
Hawker however preferred its own solution, via the wing leading-edge location, but the Air Min kyboshed them..

Here is the Hawker Fury prototype LA 610, which was originally slated as a Griffon Tempest, but eventually
received the 3,000+ hp Sabre VII & Hawker's wing leading edge radiators..

[Tommy Cookers]

the Deltic on UK rails gained disproportionate fame due to its high power when the real benefit was better power continuity

competitors had large low-rpm 4 stroke engines with less power and were much heavier eg 130-140 tons (and 16 wheels)
greater weight was often useful - giving critically more braking (against expectations most freight wagons remained unbraked)
but one UK railway procured high rpm 4 stroke diesel-hydraulic German designs (reduced to UK 10" narrower 16" lower max)
most were 8 wheel unitary construction to keep weight to about 80 tons - the smaller size complicated the transmission
but a low-tech non-unitary version had a heavy 'chassis' frame - this requiring 6 axles so weighed about 120 tons
the 120 ton job was more useful because of its better braking
final diesel-hydraulics had 2700 motor hp but at speed only 56% (1520 wheel hp) due to transmission mismatch and losses

diesel-electrics efficiency fell just below 70% at high speed
eg Deltic locos got 2250-2750 hp to the wheels (best generator efficiency 89% and similar motor/gearing losses)
and tractive effort was eg 'only' 30500 lb at 32.5 mph - worse than a big steam loco's (freight or MT)
(the diesel has constant power ie TE falls with speed - short-term steam power to some extent increases with speed)
the TE above was after Deltic gearing was raised - before which armature winding burst was possible at high speed
close to 120 mph then became possible - one 1974 schedule London-Retford (to emulate HSTs) was 91 mph average

[roon]

Finally some views of a new DTM four-cylinder. Cam gears seem to be at the rear of the engine. The large cover over the front end of the crankshaft--flywheel? Timing wheel?

Where the previous V8s peaked at over 500hp, the new inline-fours will start their careers with over 600hp... With a maximum capacity of 2.0-litres, the new turbocharged engines feature a 30hp ‘push-to-pass’ feature along with anti-lag and a shift point of 9,500RPM. It will achieve these figures running 102RON pump fuel, roughly equivalent to 95-octane in the US. Mounted longitudinally, the cars remain rear wheel drive. The previous V8s weighed 148kgs (326lbs) but the new motors weigh just 85kgs (187lbs)...

http://www.speedhunters.com/2019/03/goo ... -cylinder/

[Zynerji]

Single scroll turbo? Surprising...