If recips were made nowadays

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Ceramics get hot, they just don't melt as easy

We have been being promised ceramic engine parts for over 40 years, yet they don't seem to show up in actual service engines (reciprocating, they do show up in turbines sometimes) except for certain applications. We have had ceramic insulators in spark plugs for decades
beats the heck out of mica.

One account claims an experimental engine with ceramic cylinder had trouble with pre-ignition at 12 to 1 compression ratio. Which tends to limit it's usefulness on a supercharged engine.
 
True S/R but there is little incentive with modern engines, they already last longer than the cars they are in in road cars, in top motorsport most of the regs are to restrict the power output and the costs for each team. Given an unlimited budget big strides would be made possibly equalling the performance of the early meteors lol
 
PWR4360-59B said:
I guess though in a plane the battery master would shut it off, well and the engine as well.
Click to expand...

I am not positive but I would very much doubt that turning off the battery would affect FADEC on aircraft as that would kill the engine and therefore I would doubt that any regulatory authority would approve it.

Remember magnetos are used on pistons rather than the lighter, simpler and more reliable distributor and coil because the magneto is self contained and therefore not affected by battery or generator or any general wiring failures. Turbines of coarse do not use ignition except for start and relight.
 
MiTasol said:
I am not positive but I would very much doubt that turning off the battery would affect FADEC on aircraft as that would kill the engine and therefore I would doubt that any regulatory authority would approve it.
Click to expand...

Correct.
There are aftermarket CDI ignition systems available which could replace the old magnetos. They utilise a separate generator to provide power. I'd expect that FADEC units would have at the least a battery back-up to allow diversion to an alternate airfield.

FAA Certification standards for FADEC:

 
Ceramic engine parts have been sucesfully made for many many years, valves being the most sucessful.

However they are quite astonishingly expensive to produce reliably, and so unless you are in Formula One (who now cant do it
either because of the regulations) , you wouldnt bother - as modern super-alloys are "good-enough". Ceramics are now
used generally as the basis for heat resistant coatings, which is the modern approach.

The biggest change in engine design since WW2 is really the understanding of how to lay out a proper combustion chamber,
which enables really good boosted engines now to run 14:1 compression ratio with 4Bar boost pressure. This enables
you to drastically downsize the requried swept volume for a given output, which in turn makes it far easier to
stick the revs up - which in turn for a given cylinder pressure obviously increases power dramatically. It is
of course slightly more difficult as an aero engine has a different duty cycle to an automotive race engine,
however, racing series like Indy-car on oval tracks are in fact ALMOST 100% throttle the whole time,
so it is not that much of a stretch to apply that to aero-engine duty cycles.

Now to put some actual maths behind all that, if you asked me to make you a water cooled V-layout
engine for a Spitfire, one set of actual calculated performance figures that my software spits out are:

Bore 92mm
Stroke 80mm
RPM 8000
Swept Vol of Engine = 6.38 Litres
N. Cylinders = 12
Cylinder CR = 14:1
Compressor CR = 4.2:1
Air Density after Intercooler = 3.6kg/m^3
Mass Flow into Cylinders = 1.46kg/sec
BMEP = 35Bar (about 60% of that of a modern F1 engine)
Brake Output = 1665 Bhp at the propellor

(This is assuming a VERY average value for thermal efficiency, if you were willing
to go to compounding, the above 1665bhp can probably head north of 2000bhp -
but with lots a lots of extra bits and money needed ).

I think it will be hard to increase that on normal fuels, the next step is more cylinders; my own personal
favourite means would be the Jumo222 style layout (but with 4valve heads of course). Bore is about
maxed out for sensible high-speed combustion and stroke cant really go up much whilst keeping
mean piston speed managable, and 8000rpm is already getting tricky for a constant-duty engine.

So basically I reckon you can just about make a "Merlin" about four times smaller if I did one now. This
would not be a cheap engine though !
 
Internal Engine Coatings
And one of many services. I guess you haven't kept up with the performance world, this is all old school now. And many turbine hot section parts are also coated to protect the metal parts.
 
Just so we have a benchmark a Merlin XX at 20,000ft in a Hurricane was .

Bore 137mm
Stroke 152mm
RPM 3020 (as listed in the test)
Swept Vol of Engine = 27 Litres
N. Cylinders = 12
Cylinder CR = 6:1
Compressor CR = 1.6:1 manifold pressure
......................= 3.5:1 over ambient air pressure, both include RAM.
Air Density after Intercooler = unknown, no intercooler.
Mass Flow into Cylinders = 1.09kg/sec (includes fuel)
BMEP = 14.23Bar
Brake Output = 1073Bhp at the propellor (225hp was being used to drive the supercharger)

BMEP was figured at 1298 crankshaft HP.
powerplant was also getting 113HP from the ejector exhaust at a forward speed of 335mph.

The real question is not if you can make a modern engine 4 times smaller in displacement but if you can make it 4 times smaller in weight?

Now I have no doubt that modern engines using modern materials can show vast improvements over WW II or post WW II piston engines.
However the market has also changed. Around 2000 hours of engine life seems to be a common goal for the newer engines. This is an area where modern materials and manufacturing techniques can make huge differences over the older engines.
I would however be a bit cautious about improving power and engine life in large amounts. Both can show large improvements over the older engines but not max improvements in both at the same time.

The Rotax company for example (with 175,000 engines built) is offering a range of 4-5 flat four engine engines with four of them sharing a common displacement of 1.2l and offering carbs to a turbo setup and from 80-115hp, all claim a 2000hr engine life. The 1.35l turbo 141hp version is offered at 1200hrs (work may be ongoing to extend that?) Now the strain on the engine is a bit more than it appears at first glance because they are offering full take-off power to 15,000ft.(subject to time limits).
A modern engine can get more power and more life than the old engines but pushing the performance will cost some of the possible engine life.

A big problem with trying to build modern high power (500hp and up) engines is that the commercial market (not sport or racing flyers) will want engines that work at higher altitudes (crop dusters and bush pilots excepted) and the piston engines have to have suitable supercharger systems. A lot has been learned about superchargers and turbochargers over the years and these too will show vast improvements.
Are these improvements enough to challenge the gas turbines?
 
The challenge to turbines will be that a recip can work on a greater variety of fuels, I mentioned NOx at one point and how all a combustion enhancer will do to a turbine is cause more heat stress, a literal melt down.
Oh and to see jet engine fuel consumption just watch this, and remember it is one of many fuel injectors on the engine an not running to max capacity.
View: https://www.youtube.com/watch?v=5fRBOkXvAK0

This guy is great for learning more about turbines and jets.
 

Recips work on a narrow range of fuels at a time without some pretty funky fuel management systems. And for aircraft you are pretty much restricted to gasoline or jet fuel/kerosene or a blend. Reciprocating aircraft engines should NOT be run on automobile fuel unless it is a dire emergency and the flight is low and short. AIrcraft fuel has higher vapor pressures and such to prevent vapor lock.

There is no reason to use NOx in a turbine engine as most turbines are pushing more air through the engine than they need for combustion.

So what if jets use a lot of fuel, they make a lot of power. Engine that used the nozzles in the video passes 49kg of air through the engine every second compared to the Merlin XX 1.09kg/sec and Snowygrouch's hypothetical V-12s 1.49kg/sec.

Two of the Orenda engines could power the CF 100

to 550mph. Want to estimate what kind and how many reciprocating engines it would take to do that? or what the fuel burn would be?

The Orenda engine was also a product of it's time, a first generation axial flow turbojet with a 6.1:1 pressure ratio. It weighed 2430lbs.
By the mid 60s you had low by pass turbofans of similar diameter and weight with much more power, pressure ratios 3 times as high and fuel consumption of 2/3rds the Orenda.
By the 80s jets and turbo fans had gotten lighter, more powerful and more economical.
 
For me, if jets were not a possibility then the start point for recips must be what was in service at the end of WW2 and under development. With all the technology introduced in F1 much of which has been banned, I see no reason why a water cooled multi cylinder H or X format could produce 8-10,000HP
 
Where is the dividing line between technically possible and commercially feasible?

From a website: "a Formula One powertrain, a supposed 1,000 horsepower and an engine that revs to 11,000 RPM. But guess what! For the mere $3 million it costs, the engine will only last 31,000 miles."

Or that you lease a Formula I engine for the season at 900,000 to 1 million dollars?
How many hours in the season?

And what happens when you take the Formula I engine to 20,000ft (or 30,000ft?)
 
Piston engines use NOx because they can't get enough air into the engine to burn the amount of fuel needed to make the desired power.
Since air is only about 21% oxygen even small quantities of supplemental oxygen will allow much more fuel to be burned.
Germans used NOx to increase the performance at altitude instead of building 2 stage superchargers.

Jets on the other had are pushing way more air through the engine than they are using for combustion. It may be needed for cooling. In any case, they don't need more air/oxygen from supplemental sources. If more power is needed from a given engine they stick a big burner can on the back end and squirt fuel into the exhaust stream where it combines with the excess air in the jet exhaust. This is called an afterburner. No new airscoops (except for cooling) or chemical tanks needed.

Jets work just fine (combustion wise) at high altitude unlike piston engines because of this excess airflow. Or perhaps it is better to say their performance doesn't fall off as badly.

Claiming jets have something wrong with them because they can't/don't use NOx it a total misdirection.
 

Gas turbines can burn quite a variety of fuels: hydrogen, methane, propane, gasoline (preferably unleaded), kerosene, Jet-A, Jet-B, diesel, marine diesel (although they can be a trifle hard to start on that without design changes), producer gas, powdered coal, and peat (when I worked at Lycoming, there was an LTC-4 [commercial variant of T55] running on peat in Scotland]).
 
Engineering an air craft power plant like any other thing in engineering, is to find that little special thing that will for sure give the recip a huge edge over the turbines. Say for argument sake there was a recip that would burn a fuel that costs nothing. That alone would instantly give it an advantage over the turbine, all the airlines would be begging to have recips back on the wing yesterday. Costs? Do you know how much an engine for say the 787 costs? And then how much fuel it will guzzle in its life time? Its a world where everyone worries about how much fuel is used. Not how fast or high it goes.
 
Since there is no magic fuel that a reciprocating engine can use that a turbine cannot use that argument is rather pointless.

You keep missing the point about how much power is produced per unit of power made or per passenger/lb of cargo moved. Not the consumption per minute or per hour. SOme modern turbo fans are just as efficient as any piston engine. Electrical generating stations are using gas turbines and not reciprocating engines

power plant in my old home town. Been there for around 30 years, runs on natural gas (from pipeline) Each 'unit' was around 25,000hp if I remember right. Brick building on the right is the remains of the old coal fired plant.
How many reciprocating engines are you going to need?

Reciprocating engines have their places, turbines don't scale all that well down to small sizes. But making big power is not the place for reciprocating engines.

Banning (severely restricting) air travel and air cargo would save a lot of fuel but also cause economic havoc. Reciprocating powered aircraft would not only fly slower and lower but carry fewer passengers/less cargo. Longer (and rougher) flights would discourage long distance flights (transatlantic was barely practical at the end of the piston powered airliner era), Trains aren't really that fuel efficient when it comes to people, they are moving hundreds of tons of rail car compared to only few score of tons of passengers. They are great at heavy freight/cargo. People with 2 week vacations are not going to go to Europe by ship from the US.
And Ships are also not a fuel efficient way to move people if time is any consideration. Cruise Ships/large liners can burn thousands of gallons per hour when moving in the 25mph range. Yes they hold thousands of people but if they take 5-6 days to cross the Atlantic what does that do the passenger miles per gallon calculation (granted they are burning bunker C or something close to it)

And if you want air travel at 25,000ft and 300-400mph that is the realm of the turboprop.
 
What no-one has mentioned is that yes, it may technically be possible to push a recip to 8-10,000 hp, what sort of reliability are you going to get, compared to a turbine? If you want thousands of horsepower for thousands of hours then it's turbines.
The forces involved within a piston powerplant mean that there are extremes of forces with pistons changing directions, cams hitting tappets that will cause failure. Extracting more power simply increases these forces. What's the design life of the F1 engine that people here are using as an example of what is possible?
It is possible to get 10,000 hp (calculated) from 500 CI, but that'll only last for a few seconds...
 
I was purely discussing from a standpoint that for some reason unknown to physics jet engines didn't work. Without jet engines huge resouces would be pushed into reciprocating engines, two stroke four stroke and diesel.
 
Huge resources can be pushed into them but they have laws of physics (or at least chemistry and combustion) that they have to obey too.

I would note that Formula I racing engines in the 1930s weren't doing too badly. Mercedes ended with a 3 liter V-12 making 480hp at 7500rpm using 305psi BMEP (21 bar) and 2.31 Atm in the manifold for two roots superchargers running in series (two stage) which allowed 7% more power while using 10% less manifold pressure than the single stage supercharger setup. The competing Auto Union engine made 485hp at 7000rpm with 335 psi BMEP (23 bar) and higher cylinder compression and 2.66 Atm. Also used a two stage roots blower set up.
Granted they were not using gasoline for fuel

Engine designers of the late 30s and early 40s got into some of the monstrosities that failed to make the war (or mass production) because they were trying to get around the limits that existed at the time.


Now please note that since this engine was designed with 14 cylinder "modules" there was no continuous crankshaft. Granted this meant crankshaft design was much simplified but is also means that those green shafts in the drawing were geared to the 3 individual crankshafts and they brought the power both to the rear auxiliary section and to the front propeller drive gear section. The lay shafts turned at over 12,000rpm. 84 spark plugs and 84 valves, 7 valve/cam covers each held on with 50 lock wired fasteners.
Or the Big Lycoming.

36 cylinders, each with about 1/4 in more bore but 1/8in less stroke than a R-1820.
It is an R-7775. Obviously cylinder size had reached a limit so more power is out using that method.

The add more cylinders gets a bit tricky too, perhaps a lot easier these days with computers and much more knowledge about vibrations but adding cylinders tended to multiply the vibration problems by a factor well above the percentage of added cylinders.

Raising RPM has troubles of it's own as the number of possible harmonic vibrations goes up. Iam not saying the last two cannot be solved but they are going to suck up a fair amount of the money effort. Please note that P & W spent 8 million bring the R-2800 to production status. They used 25 million to get the R-4350 to production status and some would say it still needed more work. Those are WWII dollars. The R-2800 had 3500 hours of test running before it passed it;s type test. The R-4360 used 23 engines and had 15,000 hours before it became reliable.

Modern materials and computer aided design and analysis can help with these numbers but large, high power reciprocating engines are not easy to design/build.

BTW the 1939 Mercedes Grand Prix engine weighed 603 lbs. (no coolant or radiator?)
A 1939 P & W Wasp Junior (R-985) could make 450hp for take-off and cruise as long as the fuel held out at 400hp/2200rpm at 5000ft on 91 octane fuel
for 668lbs.
 

So that performance is at sea level?

At 20,000ft your compressor needs to give twice the PR to get the same performance.

And if your compressor can deliver a PR of 8:1, that's a problem at lower altitudes.

Unless you use a turbo to compensate for altitude.
 
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