Engine technology free-for-all

[J.A.W.]

.......As BMW found & Bristol belatedly confirmed, radial engines - with their inherently problematic mixture distribution, did gain significant benefit from direct injection.
& Bristol had found that sleeve-valve merits included ( as Ricardo predicted) certain flow dynamics,
which enabled aspects of improved port injection performance, too..

charge distribution problems can be worse with DI or PI than with carburation or similar at the throttle body
(for the best current appreciation of the practicalities the appropriate forums can be googled)

DI helps in low boost engines by enabling the raising of CR .....
it loses in high boost engines the large saving in supercharger work etc of fuel-evaporation cooling

T-C, the Germans did utilize 'hot cams' with higher overlap, along with higher static comp-ratios in their mills,
- which was only efficiently practicable with DI, & worth - in their view, the loss of latent-heat charge-cooling.

& of course, the Bristol sleeve valve cylinder offered yet a greater level of options..

Re: DI &/or PI injector placements, being sans poppet valve-heads to crowd the combustion chamber/plug location,
or obtund the inlet ports..

& by allowing elegant pipe routing for efficacious exhaust efflux vectors - useful both for air-cooling flow, & thrust..


'Flight' shows how well Bristol got its 'power-egg' Hercules set-up sorted, even for their utility 'carthorse' Freighter;

http://www.flightglobal.com/pdfarchive/ ... 00239.html

[Tommy Cookers]

well this is quite interesting re the emerging recognition of 'thrust HP' ....but
it reminds us how aircooled engines had less scope for reducing 'cooling drag' or getting 'free' thrust
the Convair 240 was maybe the high point in this

btw your Hornet link seems to imply the reason the famous Merlin 'ejector' exhaust systems were suddenly outmoded ...
better preserving the exhaust pulses via individual stubs presumably gave more thrust (RR saying more than expected)

[J.A.W.]

T-C, in mid `44, R-R were test-running their V12's on high-boost (+25lb using 150 grade avgas) for all-out low-level speed,
to enable interception of Nazi V1 cruise-missiles - which were soon to be bombarding long-suffering Londoners.

One problem they encountered - with increased exhaust efflux, under high-boost - was blowing the folded 'fishtail'
type of 'ejector stubs' apart.. & a new exhaust nozzle design was needed, as shown below:



For the high-boost Sabre, Napier went to individual ejector stubs, 12 per dual bank - rather than the previous paired type:



The Allison V12 also developed an individual ejector stub per exhaust port, & with 12 per bank too,
since - unlike the siamesed port R-R mills - the Allison head utilized a full port, per exhaust valve:

[wuzak]

The Allison V12 also developed an individual ejector stub per exhaust port, & with 12 per bank too,
since - unlike the siamesed port R-R mills - the Allison head utilized a full port, per exhaust valve:

http://s1.e-monsite.com/2009/03/18/09/6 ... ra-jpg.jpg

That solution was unique to Bell.

The reason is that Allison did not actually develop ejector exhausts - they supplied flange plates to which the airframe manufacturers would attach their take on the ejector exhausts.

[J.A.W.]

Allison sure tested 'em.. the early V-1710 P-39/P-40/P-51 made do with pairs, but later Bell-birds & the F-82, ran 1 per..

& check how a V-1710 turbo manifold set-up looks..

[Tommy Cookers]

on a 'turbocharged' (mechanical stage + turbocharged stage of course) 3420
for/from what ?

[J.A.W.]

Flown with XP-75 & XB-39 (X4) prototypes.. P-38 was usual service user turbo V12 (X2)..

[wuzak]

Flown with XP-75 & XB-39 (X4) prototypes.. P-38 was usual service user turbo V12 (X2)..

And XB-19, where it was being tested as an alternative to the R-3350 for the B-29 program.



https://en.wikipedia.org/wiki/Douglas_XB-19

Some more info
https://forum.warthunder.com/index.php? ... vy-bomber/

[wuzak]

Also used in the Lockheed XP-58





https://en.wikipedia.org/wiki/Lockheed_ ... _Lightning

Also proposed for several other projects, including a variant of the Martin B-26 and considered as a replacement option for the sleeve valve X-1800/XH-2600, which was dropped by Pratt and Whitney and the USAAF. Was alo one engine option of the McDonnell Model 1 proposal, with engine buried in the fuselage driving wing mounted pusher props via extension shafts.

[J.A.W.]

& here is the German 'double-twelve' equivalent, the DB 610, which - although put into service, powering the
Heinkel He 177 heavy bomber - also suffered a number of difficulties, ranging from issues with the core
DB 605 V12's, through various airframe installation problems..
- yet the coupling system itself - was fairly trouble-free, while turning a huge 4-blade propeller.. AFAIR.

[wuzak]

& here is the German 'double-twelve' equivalent, the DB 610, which - although put into service, powering the
Heinkel He 177 heavy bomber - also suffered a number of difficulties, ranging from issues with the core
DB 605 V12's, through various airframe installation problems..
- yet the coupling system itself - was fairly trouble-free, while turning a huge 4-blade propeller.. AFAIR.

http://www.b-domke.de/Aviationimages/De ... 0_7430.jpg

Certainly more reliable than the earlier 606.

Differed from the V-3420 in that the two halves were self contained engines, which were joined at a common gearbox. Each half could be disconnected from driving the prop by a clutch, and could be shut down.

One side was a mirror image of the other - since the supercharger was side mounted.

[J.A.W.]

For sure W, that individual function capability was a useful feature, & contributed materially to the operational record of the big Heinkel when penetrating the dangerous night skies over London in 1944, while suffering a similar loss rate
( ~10%) - as the British 'Heavies' attacking Berlin at the time - which was IMO, fairly creditable..

Interestingly, the B-29's Wright R-3350's also suffered from over-heating failures on ops..
& the XB-39, though it never got a production order ( insufficient available Allison mills?) offered higher performance..

I'm guessing though, that USAAF technical branch didn't really like the 'cobbled together' approach to aero-engines..
albeit - they did buy the mammoth P & W R-4340 - 'Corncob' - which was a kind of doubled twin row radial..

& unlike the British with their like effort - the R-R Vulture - the USAAF did persevere & make it work in service post-war,
- even if it was a 'maintainer's nightmare' & remained mostly unwanted - by civil aviation operators..

[J.A.W.]

Interesting dissertation on Napier ICE developments here.. http://www.newcomen.com/wp-content/uplo ... Vessey.pdf

John Cobb's Napier Lion-powered Railton.. not only collected the outright Brooklands lap record..
but then went over to Bonneville, & duly collected the 24hr speed record.. via an average speed of 150 mph..

[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?

[roon]

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.