21 replies to this topic

[Yelnats]

I go way back and can recall when F1 engines had about 125 HP per litre. Now they are approaching 300 bhp per litre. Is there a theoretical limit for a naturally inducted engine? Perhaps something to do with the speed of sound and velolocities in the intake tracts?

Propeller driven aircraft ran into a wall at about 450 mph due to sonic effects. Could there be a similar limit for the piston internal combustion engine?

[Ray Bell]

F1 has been pushing those thresholds remarkably for years. The Cosworth DFV was a milestone when it was built, yet kept on improving over its long life. The turbo era put a stop to things for a while, but now we see more incredible progress.
Maybe there is a limit, and there's one thing for sure: F1 will find it!
On the subject of propellor-driven aircraft - Don't Lear make one that goes to pretty much sonic speeds? And I'm sure the Russians had a big (four engined) aircraft that flew at comparable speeds to 707s. Where's the Observers' Book of Aircraft?

[Art]

There was a TV program on the Russian bomber. It had counter rotating props and it was sound proofed inside. American jet fighter pilots flying next to it said that the sound of the props made them naziated if they stayed close very long. Was it called the Bear???

Art NX3L

[Tarnik]

Yes, the Tupolev "Bear". It had four turboprops but didn't go supersonic-only about 500 mph.

[Yelnats]

The piston engine has had a remarkable lifespan and forms a part of most hybrid designs. For a while in the early sixties the future of the piston engine looked dim with the gas turbine and Wankle recieving all the attention. But developments like turbo-charging, multi-valve designs, polution restrictions and lightweight aluminium castings have kept the piston engine more than competative.

I suppose a small constant speed gas turbine in an electric/hydrogen hybrid would give the piston engine a run but the reciprocating engine has such a huge knowledge base manufacturers tend to stick with the well tried.

The fuel cell seems the only sensible electric source as it is not burdened with several hundred pounds of dead weight batteries with a limited life-span and high replacment cost. But as long a fuel costs stay low in the USA (though rising lately) these the expensive hybrids stand little chance of competeing against monster SUV's and Pickups.

[desmo]

It's an interesting question. How volumetrically efficient can a conventional unblown piston engine be? The energy content of the fuel one can pull through the engine at stochiometric ratio seems the only limit I can think of.

[Nathan]

Im going to get a lot of slack and critisism for what Im about to say...but what the hell. From my knowledge a normally aspirated engine can only produce 85 ft./lbs of torque per liter of capacity. There is no solid proof of this however, but research will demonstrate that...So that means in theory a F1 engine can get a max 255 ft./lbs of toruqe. Now if you use this and calculate HP assuming the engine can maintain maximum volumetirc efficency all the way to redline, at 18,000-rpm and F1 engine can make a max 874hp. If F1 passes the 17000 rpm limit, the max HP to be made would be 825-hp. Again this is all theory, but the numbers do make sence when compoared to F1 rumour. HP is Torque times RPM divide by 5252. REMEMBER THIS ALL THEORY. Dont bash me too bad guys and gals...

[Yelnats]

Yes Nathan, tourque per unit of displacement has been remarkably constant over the years and is a limit imposed by volumetric efficiency or the effectivness of a design in completely filling the cylinder with a charge of Air/fuel.

With the limit imposed by volumetric efficiency, increased RPM's has been the path to more power since turbocharging was banned. Ram chargeing techniques using variable length intake paths offer a way to exceed these theoretical limits when combined with variable valve timing. These relativly unexplored options are looking very attractive when the ban on Berylium and other exotic materials goes into effect and a top limit to rpm's can be seen.

[This message has been edited by Yelnats (edited 03-05-2000).]

[tak]

Nathan-
You've got my attention! I'm curious about the theory--where did you see/hear this. Any references would be appreciated.

Tak

[davo]

Tak not so much a theory as thermo. Yelnats comments are spot on. With an air limit there is a limit to how much fuel you can burn and how much gross energy can be made from the engine.

Then - and I am aware of what I am saying here - we make some assumptions (or we are lucky enought to be inside the industry and have lots of fun toys and access to lots of hard data - not me ) on thermal efficiency of the motor...

And have a limit of "X"Nm per litre. The limit being soft rather than hard.

"Tuning for Speed" one of the old standards on playing with engines says there are only three things to work on. (None of what it says has been "out dated" as such.)

- reducing frictional losses
- reducing waste heat
- increasing breathing efficiency (outright or with more revs)

How these three things are achieved is far from simple of course.

In another thread I put up a formula which had been given to me (rather than thought up by me) of HP/L/1000revs which is a slightly different perspective on Nathan's comments

Genuinely innovative approaches to internal combustion engines may move the goal posts but they haven't moved far over the history of F1.

Yelnats comment on inlet air velocities would seem to be a very much top end limit. As port diameters increase there is a real limit created from the bore diameter of the engine.

One of the advantages of direct injection is that the fuel does not need to be carried into the combustion chamber and as such does not reduce the breathing efficiency of the engine. Its not much but then thats what F1 plays with - lots of "not much"s separate McLaren from Minardi.

I hazard a forecast that it is direct injection which will be the next engine step - other than the ongoing more revs, more revs.


[This message has been edited by davo (edited 03-04-2000).]

[Yelnats]

Direct injection could offer improvements specific output but what are the odds that the FIA would ban any development in that direction on the basis that it violates the FIA rule that atmospheric induction of the fuel/air mixture is the only method permitted under the current formula?

[This message has been edited by Yelnats (edited 03-05-2000).]

[desmo]

I couldn't find anything in the 2000 technical regs that would, IMO, make direct injection illegal. In fact:


1.12 Supercharging :


The injection of fuel under pressure is not considered to be supercharging.

If the improvement in performance was significant it would probably be banned though, as that seems to be the way that the FIA works.

[Billy Gunn]

Hey Desmo,
Currently it has to be assumed that the biggest problem facing F1 Engine engineers is to convert fuel from the liquid state to the gasseous state - assuming relative fuel consumption for engine power levels, this requires something approaching 3.3Kw of energy to vapourise the fuel per cylinder. Not very easily done when running at 18,000 rpm - this gives a time limit of around 3.33millisecs for the vapourisation phase. Higher revs and hence higher power can be achieved by going to smaller cylinders - hence the rumoured move of some engine suppliers to be looking at V12's again (especially after the discovery that the narrow track cars worked better with longer wheelbases - one of the arguments against the V12 disappeared, namely that the V10 was the best compromise due to it being narrower than a V8, and shorter than a V12). Remember Honda have probably forgotten more about high speed engines than the rest of the F1 engine suppliers know! Their motorcycle race engines in the SIXTIES were running 5 cyl. 125's at 18,000rpm, and a prototype 3 cyl 50cc racer ran at the Dutch GP in practice (but never raced) was reputed to rev to 25,000rpm and produce near to 30 bhp! But I digress - direct injection has the same basic problem of the fuel vapour phase transition, it is emminently suited to low speed passenger cars, rather similar to the diesel concept from which it comes. I think that any benefits from direct injection will have been well researched by all the F1 engine suppliers - and promptly put on the back shelf for the time being.
The issue that strikes me as being the next big development leap forward is the electronic actuation of the valves, this would have devastating effects on previous thinking about SI engines. Instant VVT, and with throttling ability you can throw away the throttle butterflies (or barrels). All this saved weight (no cams or cam drives needed) from an area the engineers die to save weight from - the top of an engine. Here's to the sound of the first 20,000+ rpm V12. I bet it will sound almost as good as a Napier Sabre!!!!

Gudonyall Billy G

[Yelnats]

Thanks Desmo, Good to see that direct Injection is specifically included. This will make it slightly harder for the FIA to ban it after some manufacturer spends millions developing it.

Billy Gunn, I derived great pleasure reading about the exploits of Honda in designing these jewels of engines in the sixties. The piston speeds were kept under control by the multi-cylinder designs and the miniscule strokes involved and may not scale up well.

By the look of the BAR contenders mediocer results so far Honda has a bit to learn yet before it becomes a contender in F1. There may be a considerable reserve of power left in the BAR/Honda design because the bulletproof reliability displayed to date indicates they may have something up there sleeve yet.

[Billy Gunn]

Hi Yelnats,
Glad you liked to learn a little of Honda's past exploits. Like I said don't underestimate them! Just because the BAR has so far appeared slow (and I believe it is slow) don't blame the engine. The chassis has far more effect on the pace of a car than the 'mere' power of the engine. Over the last couple of years there have been some noticeable turn arounds in teams performances - these have generally been accredited to new engine designs or change of supplier; but this is not always as it seems - it may benefit the team to let the punters out in the wide world 'think' that the reason they have gone quicker was a change of engine. Remember Arrows and Damon Hill in Hungary '97 - that chassis was perfectly suited to the circuit and they nearly caused the biggest upset to the form book ever. All that was done with the 'under powered, unreliable' Yamaha engine!
Others I can think of, the way the Stewart cars went last year - don't tell me the new Cosworth found all that much power - look at the way the Minardi's went towards the tail end of last year with Stewart's '98 engines.
I once heard tell the story of a driver who when told by the team race director that "all will be well when we get the next engine revision, it will have another 20 hp", the driver exclaimed "what am I going to do with another 20 hp, I can't get the existing power I've got down onto the track!" Remember also Renault in the mid '80's they had their own team, but were roundly beaten by every team they customer supplied their engine to, another case of a bad chassis?
The lengths that teams are now going to improve aero performance are staggering. Little has been thought by the general punters as to why the Ferrari has the top pod exit exhausts. Not for engine benefits thats for sure - more like the theory of entrained air at low speed over the rear wing but destroying the airflow at high speed - giving a veritable 'variable wing effect', no need for a flexy wing here which can fail a FIA scrutineering test!

Donchajusluvit!!
Billy G

[Yelnats]

Sorry my previos post wasn't clear. I ment to say I derived great pleasure in reading about the exploits of the Honda engines of the sixties AT THE TIME they were racing (I'm quite ancient) though I enjoyed yours also. If I recall correctly these engines were in competition with Yamaha two strokes and proved to be dead ends because of the intrinsic advantages of the two stroke engines in racing applications.

[Billy Gunn]

Hey Yelnets,

Two points:-

1. Two strokes are banned from F1 (as are Wankels, 5 strokes, barrel engines, clapper engines, and anything other than a good old 'suck,squeeze,bang,blower' reciprocator)

2. Two strokes should have been penalised by capacity/2 when they first appeared by the FIM. The argument for this is that the piston works simultaeneously above and below itself, whereas in a four stroke only the topside of the piston performs any work.

To their credit the FIM did get it correct when the Wankel rotaries came on the race scene; they applied a 2/3 swept capacity formulae. The reason for this was that the piston in a Wankel works on all 3 sides simultaeneously, but the output shaft runs at 1/2 rotor speed!

Yacantpolishaturd!

Billy G

[Ray Bell]

Billy G -
reminds me of the Austin Healey driver who spent a fortune getting the first alloy head ever seen in Australian for his 3000, which was dominant in productions sports.
When they were down 10hp on the dyno he nearly cried - but on the circuit he picked up two full seconds a lap at Warwick farm with the loss of about 50lbs high over the front axle.

------------------
Life and love are mixed with pain...

[Yelnats]

Billy Gunn, Yes, two strokes are prohibited (did I imply they weren't?) as is almost every other variation of power types. Now that they have got down to limiting the number of cylinders to 10, we can be sure any other innovations will meet the same fate.

[Nathan]

Dear Tak,

Sorry for this late reply. By chance to you work for STL in Japan??? My theory comes from studying Normally Aspirated race cars. I belive the Ferrari 333SP and a few others I forget makes 85 ft./lbs of Torque per liter. I have never seen any other go beyond that. I have no technically backing only years of reading and calcualting expericance.

[DEVO]

ART... The "Bear" was known for it's incredible range. I forgot the range but I thought it was 18,000 miles. Anybody?

[Art]

Power limitations.

With this question we have to say to hell with the rules! With DFI and direct air injection and rotory shaft exhaust. The only limit on power is the strength of the metals in the reciprocating mass.

Art NX3L