30 replies to this topic

[Gerald Ryan]

I remember seeing a summary of some Japanese research papers some years back. The most interesting one was a Honda paper regarding experiments and research into ultra-high rpm engines, but they were not the only people doing such research.

Honda was looking into engines operating up into the 20,000 rpm region and even above that (as high as 36,000rpm at peak power). The experimenters seemed to be thinking along the lines that they could eventually apply this technology in racing to prove it and place it into production subsequently. They wanted to get small engines of compact size powerful enough for road use and good performance (big rpm when power demand high) while maintaining good (reasonable) economy/fuel consumption (modest rpm when power demand low). Broadly the results were as one would expect; lots of small cylinders, short strokes, multiple valves etc. I imagine they'd have needed some interesting multi-speed transmissions to get the scheme to work out well.

What really interests me now (and how I wish I'd written down the references and author names at the time) are some of the comments at the end of their summation. There was discussion of a suggestion that the piston rings could be done away with. Friction could be reduced. They indiciated that careful shaping of the piston with voids and cavities could trap vortexes etc to provide a gas sealing function. It seems they were interested in using fluidics to control blow-by. I suspect they were thinking that they could do this as the cycle times were low (high enough rpm) and the time for gas to leak away was reduced. The big news was a suggestion that they may be able to use fluidics for a VVT function, even leaving the poppet valve partially open (when normally it shouldn't be) or disposing of it altogether.

Perhaps that would be possible if one were to put some sort of reed valve block in the inlet port (Alfa experimented with that idea at one stage, but they were operating it at conventional rpm levels). Unfortunately this was not elaborated on.

I am aware of people who have run two-stroke engines in karts without rings. The comment were unanimously that high rpm performance is improved, the low end is weak and that the slower you go the worse it gets. Also those engines were very difficult to start. Given that they were push started, I guess that makes sense. It'd need a really fast push-off to get enough rpm to have a hope of accelerating into an appropriate rpm range. I recall that those pistons were conventional in every sense except that the rings were not fitted. On the other hand, Honda et al would have been experimenting with some interesting shapes...

Since it now appears that F-1 engines are not going to be headed into the +20k rpm territory, we are not going to be finding out about how to make an ultra-high rpm engine survive and operate efficiently there; at least, not in F-1 anyway. Still, I'm interested in this topic. If you were to build an ultra high rpm piston engine (no limit on piston count or materials or valves etc), how would you do it? What would you do to eliminate the rings and to sort out the breathing losses? Do you eliminate the poppets or if not, how do you modify them in form or function? I'd be interested in your comments.

BTW does anyone know whether Honda published in open literature and if so where? I have searched around and although I know the papers exist I don't know where. Is there much available on ultra-high rpm engines at all?

Regards

Gerald Ryan

[Greg Locock]

I remember reading something like that 25 or 30 years ago - not much help for you.

Ha

http://www.sae.org/t...l/papers/700122

1970.

http://www.sae.org/t...cal/books/PT-53 looks like better value for money

Cheap bastards http://www.bevelheav.../combustion.htm

[Bill Sherwood]

I'd be ditching the poppet valves and going to rotary valves.
I'd still be using rings, but only one single thin ring.
Naturally a very short stroke.
Small diameter crank pins & journals, etc.

And a big re-think on oil & bearings - Do we need them in their current form?

[NRoshier]

there is a long standing precedent in model aircraft engines which have not run rings (except in 4 stroke form) in engines that have revved to 30,000rpm for a long time. The relevance of this to the current topic is somewhat limited however...though they are essentially a diesel.

[cheapracer]

Originally posted by Bill Sherwood
I'd be ditching the poppet valves and going to rotary valves.
I'd still be using rings, but only one single thin ring.
Naturally a very short stroke.
Small diameter crank pins & journals, etc.

And a big re-think on oil & bearings - Do we need them in their current form?

Well your first bunch is what F1 do except they still used poppet valves - all day long at 20,000.

I am interested to hear more, oil lube means 2 parts dont touch each other and if rollers were better, they could make 'em lighter and no skidding, dont you think they would? So whats the secret you want to share?

[cheapracer]

Originally posted by NRoshier
there is a long standing precedent in model aircraft engines which have not run rings (except in 4 stroke form) in engines that have revved to 30,000rpm for a long time. The relevance of this to the current topic is somewhat limited however...though they are essentially a diesel.

It is irrelevent because they are miniscule unlike a number of Jap bikes that run to 20,000 rpm or more with 12,000 kms major service intervals.

Mind you at 250cc (4 cyl, 42 hp) they arent so big either but at least they carry people!

[McGuire]

Originally posted by Greg Locock
I remember reading something like that 25 or 30 years ago - not much help for you.

Ha

http://www.sae.org/t...l/papers/700122

1970.

http://www.sae.org/t...cal/books/PT-53 looks like better value for money

Cheap bastards http://www.bevelheav.../combustion.htm

Good old PT-53. Includes #700122 and the other Honda paper along those lines, #640664, "The Small High Speed, High Performance Gasoline Engine." Also the Ford Indy and GT papers and a classic, "The Coventry Climax Racing Engine 1960 - 1965" by Walter Hassan, starring the Climax H16. Great stuff.

[Gerald Ryan]

Greg

Thanks for that. I remember the paper. I think Honda kept researching into higher & higher rpm for some time after that. The summary I recall seeing was in the early/mid '90s. It included some other references (other than Honda) as well. How I wish I'd kept it (never, never discard or thow technical stuff out- you'll live to regret it).

One of Hondas high(ish) rpm engines that escaped the lab was the oval piston NR500 and the later NR750. There was also a turbocharged version which was discussed at the time but never revealed. These got into the low 20k rpm range but, as far as I know, no higher. I understand that Honda persevered in their rev-hunt and got well into the 30k region.

If you were researching in this area what modifications would you make to the pistons to eliminate rings to rely on gas dynamics for sealing. Similarly with valves. What would you suspect these researchers did?

Best Wishes for a Happy and Prosperous New Year

Gerald

[Gerald Ryan]

Bill

I know of two Sydney, Australia based organisations that were researching rotary valves for internal combustion engines. One of them built a rotary valve engine for investigation into a F-1 application. The rpm was certainly available. It appears that engine's main advantages over the V-10s of the time was its superior combustion chamber form and reduced surface temperatures throughout the chamber and head. The researchers found that such were the pace of developments in F-1 that no sooner had they achieved their breakthrough, they needed to improve their engine's performance considerably to get ahead again. Ultimately they prevailed but by then the rules had changed and their engine was rendered un-necessary by the politics and rules of F-1. I heard this engine screaming its guts out on several occasions as they tested it on the dyno. The whole project was run in careful security and no-one was supposed to talk about it or about who the customers and applications were. I viewed an early design rotor valve sample and can confirm that at one point they did have some lubrication issues. I gather those were solved. The project ran for several years (as the patent record demonstrates). As for the second organisation, all I know about them is that they built engine/s and parts to test.

Australia has a solid history of innovative engineers. I'd be pleased to go back and work there there again one day. Still, the difficulties of the rotary valve for internal combustion engine can't be underestimated or over-stated. It really is a vexatious and mighty tough challenge. It has been attempted several times and as far as I know, success was achieved on at least one occasion. I guess the leson is to choose your final application with great care.

The earliest attempt to build a RV engine in Australia I know about was a fellow called Dunstan. He built a rotary valve head for the Holden six. Anyone know more about this?

Retuning to my original question about ultra-rpm engines; the summary paper I read did not mention rotary valves. It was all engines with poppet valves or cunning modifications thereof. I was interested to find out how they proposed to hang the poppets open longer than what we do now (to give the actuation mechanism an easier time of it I guess). It was specifically stated that the valve/s were open into parts of the cycle where it was not normal for that to occur and that fluidic and vortex means were employed to make everything behave. They even suggested the possibility of leaving the valves out altogether! I looked up what I could find about unusual valve timimg events and the only (slightly relevant) record I found was in regards to a highly turbocharged Oldsmobile Quad engine project by Feuling in the USA (where the exhaust valves were opened a few thou for a few degrees during the power stoke and then opened fully at the conventional point in the cycle after that- they wanted to activate the extractor prior to the exhaust event). So I'm trying to find out what tricks were tried by the high rpm research people or what might work if it were tried.

Regards

Gerald

[Gerald Ryan]

Bill

BTW can you elaborate about oil and bearings. I'd be keen to read more.

Regards

Gerald

[Ray Bell]

Originally posted by McGuire
.....and a classic, "The Coventry Climax Racing Engine 1960 - 1965" by Walter Hassan, starring the Climax H16. Great stuff.

Maybe 'flat 16'?

[cheapracer]

Originally posted by Ray Bell


Maybe 'flat 16'?

mAYBE THINKING OF THE brm OF COURSE.

i THINK CAPS LOCK IS ON, DARN IT.

[malbear]

I think that a style of motor shorter than a flat 16 would be in the style of the napier saber H24
2.4 ltre bore 60 mm stroke 35mm sleve valve or beare head. The central power output shaft could be geared down to reduce friction and revs that the gearbox has to cope with.


http://www.khulsey.c...pier_sabre.html

[McGuire]

Originally posted by Ray Bell


Maybe 'flat 16'?

Quite right, flat 16. The BRM was the H16. Thanks for the correction.

[TDIMeister]

For all the reasons proponents advocate such high-revving engines, for example offering good performance and good fuel efficiency, in actuality the opposite effects are realised in practise.

A high-revving engine necessitates a short stroke to maintain a reasonable mean piston speed for durability. A short stroke with large bore (like F1 engine practise) doesn't give a very good combustion chamber shape with high crevice- and surface-to-volume ratios. For a series production street car, controlling HC emissions in light of today's legislated limits and getting good indicated efficiencies would be tough.

Second, friction at such high RPMs on an engine with large cylinder counts and small bore/stroke dimensions, even on a downsized concept, would be very high. In general, an engine with similar layout and technology will show FMEP inversely proportional to per cylinder swept volume. All else being equal, a 5L 8-cylinder engine will have lower FMEP than a 4L with the same cylinder count and base engine design (but be careful, a lower FMEP, as a function of displacement, doesn't imply gross friction is lower in the larger engine), but a 4L 6-cylinder would likely have lower FMEP than either. Inertial- and friction forces scale exponentially with RPM, such that a doubling- or tripling of operating RPM increases friction and inertial forces by much more, and the latter of which needs to be addressed with larger, higher friction bearings and/or lighter and presumably lower safety factor components when cost is set as a constraint.

If an engine operates up to, say, 20000 RPM with a mean piston speed of 20 m/s at that speed, at 10000 RPM, it's at 10 m/s and at 3000 RPM only 3 m/s. So many engine performance and gas-flow parameters scale with mean piston speed, and when you get down to such low values, it follows that performance at 3000 RPM, the RPM range where most people would be operating most frequently, would correspondingly be very poor. If optimum performance is said to be achieved within 75% of the peak mean cylinder pressure (I define optimum performance as that band between peak torque and peak power for a typical engine), that means an engine running at up to 20000 has a useful operating band between 16000-20000 RPM. In contrast, a more conventional engine which operates to 6000 RPM with the same maximum 20 m/s mean piston speed has a useful operating range from 4500 RPM to 6000 RPM, a more "accessible" range in everyday driving.

Also, driving at normal highway-legal speeds with such a high-revving engine would mean necessitating very short, very closely-spaced gearing and lots of speeds. High transmission ratios result in high inertias, as they get multiplied by the gear ratio squared. It is for this reason that unloaded trucks can often accelerate quicker from second gear rather than from first -- or the so-called crawler -- gear.

Additionally, when designing an engine to operate over a far wider operating range, extra effort must be concentrated so that structural resonance frequencies are avoided, particularly of the most damaging low-orders. Clearing resonances even to 8000 RPM is one thing; a first-order eigenfrequency is of 133 Hz is not a big problem, but at 20-30k RPM, try designing a crankcase for 500 Hz!!

Originally posted by Gerald Ryan
I remember seeing a summary of some Japanese research papers some years back. The most interesting one was a Honda paper regarding experiments and research into ultra-high rpm engines, but they were not the only people doing such research.

Honda was looking into engines operating up into the 20,000 rpm region and even above that (as high as 36,000rpm at peak power). The experimenters seemed to be thinking along the lines that they could eventually apply this technology in racing to prove it and place it into production subsequently. They wanted to get small engines of compact size powerful enough for road use and good performance (big rpm when power demand high) while maintaining good (reasonable) economy/fuel consumption (modest rpm when power demand low). Broadly the results were as one would expect; lots of small cylinders, short strokes, multiple valves etc. I imagine they'd have needed some interesting multi-speed transmissions to get the scheme to work out well.

What really interests me now (and how I wish I'd written down the references and author names at the time) are some of the comments at the end of their summation. There was discussion of a suggestion that the piston rings could be done away with. Friction could be reduced. They indiciated that careful shaping of the piston with voids and cavities could trap vortexes etc to provide a gas sealing function. It seems they were interested in using fluidics to control blow-by. I suspect they were thinking that they could do this as the cycle times were low (high enough rpm) and the time for gas to leak away was reduced. The big news was a suggestion that they may be able to use fluidics for a VVT function, even leaving the poppet valve partially open (when normally it shouldn't be) or disposing of it altogether.

Perhaps that would be possible if one were to put some sort of reed valve block in the inlet port (Alfa experimented with that idea at one stage, but they were operating it at conventional rpm levels). Unfortunately this was not elaborated on.

I am aware of people who have run two-stroke engines in karts without rings. The comment were unanimously that high rpm performance is improved, the low end is weak and that the slower you go the worse it gets. Also those engines were very difficult to start. Given that they were push started, I guess that makes sense. It'd need a really fast push-off to get enough rpm to have a hope of accelerating into an appropriate rpm range. I recall that those pistons were conventional in every sense except that the rings were not fitted. On the other hand, Honda et al would have been experimenting with some interesting shapes...

Since it now appears that F-1 engines are not going to be headed into the +20k rpm territory, we are not going to be finding out about how to make an ultra-high rpm engine survive and operate efficiently there; at least, not in F-1 anyway. Still, I'm interested in this topic. If you were to build an ultra high rpm piston engine (no limit on piston count or materials or valves etc), how would you do it? What would you do to eliminate the rings and to sort out the breathing losses? Do you eliminate the poppets or if not, how do you modify them in form or function? I'd be interested in your comments.

BTW does anyone know whether Honda published in open literature and if so where? I have searched around and although I know the papers exist I don't know where. Is there much available on ultra-high rpm engines at all?

Regards

Gerald Ryan

[OfficeLinebacker]

Originally posted by TDIMeister
Clearing resonances even to 8000 RPM is one thing; a first-order eigenfrequency is of 133 Hz is not a big problem, but at 20-30k RPM, try designing a crankcase for 500 Hz!!

Seriously.

[Greg Locock]

I doubt anyone is suggetsing that a very high rpm engine is likely to be better for efficiency, or, probably durability.

It may however be better for power/installed volume, or power/weight, both of which are perfectly sensible measures in some cases.

[Engineguy]

Originally posted by Greg Locock
I doubt anyone is suggetsing that a very high rpm engine is likely to be better for efficiency, or, probably durability.

It may however be better for power/installed volume, or power/weight, both of which are perfectly sensible measures in some cases.

... like a light, compact, "limp home" engine, say 250cc, for a plug-in EV maybe? Still, extreme RPM has a diminishing returns factor that makes it unattractive in the real world. There is very little package size and weight penalty for replacing that screaming 250 with a conventional (i.e. sub-10K) 400cc generating the same power.

[Gerald Ryan]

NRoshier

Model aircraft engines are relevant. After reading your post I went off and did some investigating to find out some more about them. I pulled one of these little engines apart. Sure enough, no piston rings. The owner confirmed 36,000 rpm and 2.5 - 3 bhp. The engine was all of 3cc. So he has 1hp per cc. Impressive result for a piston engine.

It would be interesting to know about the bmep and thermal efficiency. Has anyone got any data about this aspect?

Regards

Gerald

[Engineguy]

Originally posted by Gerald Ryan
Model aircraft engines... 36,000 rpm and 2.5 - 3 bhp. The engine was all of 3cc. So he has 1hp per cc. Impressive result for a piston engine.

Perhaps. Really just a reminder that output doesn't scale up. With tens (hundreds?) of million$ development over decades, the 125cc per cylinder 2-stroke racing bike engines (125, 250, 500GP) are at less than half that output (i.e. 55hp @ 13,000, 110hp @ 13,000, 220hp @13,000); around 0.44hp/cc.
.

[Greg Locock]

It was a 30 cc engine. Still 100 hp/litre. On that somewhat arbitrary measure the best I've seen is say 120 .

Typically 35% of the fuel goes straight out the exhaust. Heywood has some nice studies showing the tradeoff between blowthrough, mixing, scavenging, power and so on.

[Engineguy]

Actually, Greg, there are R/C car engines with the output level Gerald mentioned.

I didn't do an exhaustive search, but at 3.5cc and 2.5 hp @ 33,000 RPM, the following is in that ballpark...

http://www.osengines...s/osmg2068.html

... and of course there may be others better.

The point stands though, that you can't drive it to the office unless you're a really little guy... with a big supply of nitromethane. Speaking of which, doesn't the use of nitromethane (effectively an oxygen adder or providing its own oxygen or however you want to look at it) make power output comparisons to normally-aspirated engines a little invalid?
.

[Greg Locock]

wow

Good point about the nitro

ah here's where the factor of 8 comes from http://en.wikipedia....ki/Nitromethane

[cheapracer]

Originally posted by Gerald Ryan
. Sure enough, no piston rings.

Gerald

Rule of thumb - 0.001 per 1" piston clearance required.

You work it out.

[Bill Sherwood]

Originally posted by Gerald Ryan
NRoshier

Model aircraft engines are relevant. After reading your post I went off and did some investigating to find out some more about them. I pulled one of these little engines apart. Sure enough, no piston rings. The owner confirmed 36,000 rpm and 2.5 - 3 bhp. The engine was all of 3cc. So he has 1hp per cc. Impressive result for a piston engine.

It would be interesting to know about the bmep and thermal efficiency. Has anyone got any data about this aspect?

Regards

Gerald

Factor in something like 50% nitro methane as well.
Not really practical for a road or even race car.

[McGuire]

Originally posted by Engineguy
Speaking of which, doesn't the use of nitromethane (effectively an oxygen adder or providing its own oxygen or however you want to look at it) make power output comparisons to normally-aspirated engines a little invalid?

I would think so, considering nitromethane has a stoichiometric ratio of 1.7:1-ish. A 500ci Top Fuel/Funny Car engine will burn approximately one gallon of fuel per second.

[McGuire]

Originally posted by Gerald Ryan
NRoshier

Model aircraft engines are relevant. After reading your post I went off and did some investigating to find out some more about them. I pulled one of these little engines apart. Sure enough, no piston rings. The owner confirmed 36,000 rpm and 2.5 - 3 bhp. The engine was all of 3cc. So he has 1hp per cc. Impressive result for a piston engine.

It would be interesting to know about the bmep and thermal efficiency. Has anyone got any data about this aspect?

Regards

Gerald

Easy enough enough to calculate BMEP if you know bhp and displacement...

BMEP in PSI = (BHP x 792,000) / (Cubic inch displacement x RPM)

However, BSFC and thermal efficiency will be horrifying for these little dears as the exhaust is typically a cloud of fuel (and oil) vapor.

[Gerald Ryan]

This has become very interesting.

If you were able to avoid the usual 2-stroke fuel short-circuiting problem (and there are ways to do that), then would such tiny engines be able to power a micro-car? For example, what about a multicylinder (a 36 bhp V-12 say or a 24 cylinder 72 bhp) engine of super compact size in a single seater? The powertrain is now tiny enough that the vast majority of the car is available space for payload.

Regards

Gerald

[Greg Locock]

"If you were able to avoid the usual 2-stroke fuel short-circuiting problem (and there are ways to do that), "

Not really. The tradeoff is well described in the literature. You can have lots of power, and lousy fuel economy and emissions, or reasonable power, and moderately lousy fuel economy and emissions.

To get good power and good economy and good emissions requires direct injection, and a blower. =money.

This is all ancient history.

[McGuire]

Originally posted by Gerald Ryan
This has become very interesting.

If you were able to avoid the usual 2-stroke fuel short-circuiting problem (and there are ways to do that), then would such tiny engines be able to power a micro-car? For example, what about a multicylinder (a 36 bhp V-12 say or a 24 cylinder 72 bhp) engine of super compact size in a single seater? The powertrain is now tiny enough that the vast majority of the car is available space for payload.

Regards

Gerald

Two-strokes cannot possibly meet the emissions and fuel efficiency requirements.

Also, cost is a first-order consideration in microcars. What is the component count and unit cost of a 36 bhp V12? Roughly speaking you have 3x the parts to manufacture and assemble compared to a four-banger.

[kikiturbo2]

Originally posted by Greg Locock
"If you were able to avoid the usual 2-stroke fuel short-circuiting problem (and there are ways to do that), "

Not really. The tradeoff is well described in the literature. You can have lots of power, and lousy fuel economy and emissions, or reasonable power, and moderately lousy fuel economy and emissions.

To get good power and good economy and good emissions requires direct injection, and a blower. =money.

This is all ancient history.

I would just like to add that outboard marine engine manufacturers went trough all of that 2 stroke business in the past 10 years, and the only, IMHO, cost effective solution for 2 stroke fuel economy and emissions problems was Ficht direct fuel injection, used by Johnson... that one had no blower, and the direct injection used a very simple combined high pressure/injector unit.... the solution was very elegant but unfortunately, they had other construction issues, like short plug life etc (IIRC).... so outboard marine engines, surprise, switched to 4 stroke technology....

in all honesty, while a really big time RPM engine, like a small multicylinder 2 stroke might look interesting, I just do not see the point... on my desk at the moment is a production suzuki GSX-r 1000 engine... which with the gearbox and intake weighs somewhere around 65 KG... while producing 175 HP.... I just do not see the point in going for anything smaller..