44 replies to this topic

[GSX-R]

Hello,

I've already talked about this subject on a French forum and would like to ask you about this question.

At the beginning we've talked a lot about the pre-burning time and the real burning time. After many exchanges we've almost stated that the RPM limitation was due to the gasoil (diesel fuel) burning time. The question was also quite difficult to confirm because it's difficult to find injection cartography (confidentiality) and especially the injectors flow.

I use to make simulation using Lotus engine simulator and in the help, they talk about formula about the burning rate. Some (depend of the fuel) are dependent of the RPM (gasoline for example), some are not. And diesel fuel is not.

This is the formula extracted from the soft help :

0-100%(deg) = 30 + ( 50 / ( trapped AFR x 0,06691 x 0,7))

And this is reenforced by a comment of "Enginead" on another forum http://www.eng-tips.....cfm?qid=126059

and further by an old comments of a perkins consultant :

http://www.perkins.c...0020408,00.html


The diesel RPM would be more limited by injectors flow, engine solidity. It could be so possible that the MPS would be more critical in current diesel cars (12-14 m/s) that the real gasoil burning rate.

Any thoughts ?

Regards

[Wuzak]

As the rpm rises, doesn't the ignition need to be advanced to compensate for the burn speed of the fuel?

Something that spark ignition engines can and do take advantage of, whilst the compression ignition engine cannot.

[GSX-R]

Yes the diesel injection advances time before TDC regarding load and RPM. But they cannot do this as much as SI engines. only a few degrees. The conditions before are not optimal to initiate the combustion and, i think if we inject too early there's also the risk to get a too much violent bulk combustion before TDC, dangerous for the engine health, and combustion smoothness and control become out of control.

[J. Edlund]

A diesel doesn't operate with a flame front as a SI (spark ignition) engine!

In a diesel engine the liquid fuel is injected by high pressure into the cylinder which contains hot compressed air. The fuel atomizes and forms small droplets. When in contact to the hot air the fuel will start to vaporise so that the liquid fuel in the droplets will be surrounded by fuel vapor. When fuel comes in contact with air reactions will start to occur (oxidation), and the speed of such reaction will depend on basicly the temperature. At a certain temperature (reaction speed) the heat energy released by the reaction will be greater than the heat energy transfered away and this will cause the speed of reaction to increase, which increase the temperature and the cycle goes on. This temperature is known as the "autoignition temperature" and is for diesel about 250 degC.

So when the fuel is injected, droplets form, fuel vaporises and then after a short delay the vaporised fuel start to burn as it comes into contact with the oxygen. This means that the cylinder will be full of small droplets with liquid fuel in the in the centre of the droplet, surrounded by fuel vapor and flames (burning fuel).

In a diesel the injection starts somewhat before TDC and continues to somewhat after TDC and with modern diesel engines the injection duration, startpoint, endpoint and fuelmass injected can be controlled by an electronic unit much like fuel injection and ignition is controlled on a SI engine.

When the piston has reached about half the stroke during the combustion phase the flame will go out due to quenching. Also, at this point the combustion will be inefficient when it comes to torque production this means that the combustion must be done before a certain point.

To get a fast combustion one can say that there are two problems, one being that fuel must be injected fast and be finely atomized and distributed. The second problem is that to burn the fuel it must come into contact with air and this is basicly the same problem seen in gasoline engines but without a flame front (the flame in a diesel engine is called a diffusion flame). So to increase the speed of a diesel one must design an engine that can inject finely atomized fuel into the cylinder and during the combustion fuel vapor is helped to come into contact with oxygen by using turbulence.

A diesel can't knock, so the fuel is not given an octane number, instead it's given a cetane number. The cetane number depends on how easy the fuel will ignite, affecting for example the delay before the fuel self ignite. Using a high speed engine the fuel must have a cetane number that allows it to ignite fast. This can somewhat be compensated for by using higher compression ratios, inject the fuel earlier or some some sort of ignition help (an addetive to the gasoline, a spark plug in the cylinder and so on).

When the fuel in a diesel engine ignites it does so violently, and this causes the knocking sound. Infact it ignites so violently that at the first ignition test the pressure indicator was blown out if the test engine almost hitting Dr. Diesel himself.

The torque output of a turbodiesel is generally limited by at low speed exhaust emissions (since the engine is run a bit richer), and and mid range cylinder pressures (which can damage the engine) and at high speed turbocharger speed and exhaust gas temperature. The reason for running the diesel richer at low speeds is to produce extra torque where the turbocharger won't give that much boost.

[McGuire]

Piggybacking on J. Edlund's excellent post... another important difference between diesel and SI combustion: the diesel has no throttle; speed and output are regulated by varying the fuel volume. (As a point of interest, with direct injection an SI engine does not require a throttle either, at least in principle.) When the diesel is at idle, fuel delivery is miniscule and the extra air is simply pumped on through the engine. At max load/speed fuel delivery goes into the stoichiometric range for the full air volume and the engine into full cackle-and-black-smoke mode. This whole deal is key to noise and emissions (particulate and NOx) management; or, why modern EFI technology means even more for diesels than it did for SI engines.

Along those lines...if some portion of the fuel volume can be delivered and lit off early in the cycle (even BTDC) the situation is helped considerably, as Edlund noted. This is sometimes known as "pilot injection," as in the Powerstroke engines (analagous to a pilot light on a stove I guess). The idea is to fill out the indicator card, if you will, with a serial progression of fuel delivery and combustion, instead of one big squirt and one big combustion pressure spike. As this technology is perfected diesels can be made smoother, quieter, and cleaner. And lighter and higher-revving too, with the extreme pressure loadings averaged out and under better control, allowing lighter cylinder blocks and reciprocating components, and lower inertia loads.

Who knows, maybe one day they can even make an acceptable car engine out of the thing.

I don't believe there is a 4500 rpm speed limit for diesels. There are higher pressure loadings and thermal gradients resulting in heavier components and greater inertial loadings, that whole vicious cycle, and with electric injectors you are always dealing with the inertia of their solenoid cores. But these are matters of progressive development just as with SI engines, not absolute ceilings by any means. Ricardo says its Judd V10-based diesel racing engine develops max torque at 6500 rpm, and is capable of 10,000 rpm with its inlet restrictors removed.

[Wuzak]

Originally posted by McGuire
As a point of interest, with direct injection an SI engine does not require a throttle either, at least in principle

Don't some of BMW's petrol engines go without throttles? I believe they control engine speed with valve control, and don't have direct injection.

[McGuire]

BMW Valvetronic engines still employ throttling, but without throttle blades. The intake valve lift is manipulated to perform the throttling function.

This is actually a very old idea but with a new twist. On some of the earliest automotive engines there was no throttle plate in the carburetor. The throttle was a lever or foot pedal operating a mechanical linkage which controlled the maximum lift of the intake valve. BMW does this one better as its mechanism is fly-by-wire: the CPU uses the driver's "gas pedal" and other inputs to command a stepper motor which operates the variable-lift mechanism on the camshaft.

On the other hand, diesels typically employ no throttling at all: they run at 100% air capacity all the time. Speed and output are regulated by fuel delivery. This is also possible with GDI on spark-ignition engines, at least in principle.

[GSX-R]

Thank you for these answers, even if I've already read those behaviours before.

In the "reving" problems, it's not easy to talk about the max RPM if we talk about turbocharged diesel. I know that nowadays, each diesel engine, except the last VW SDI, are turbo charged.
Every turbo (SI and CI) have a defined interesting effeiciency range, even if today with sequential charging it will be enlarged.

So let's talk about about diesel excluding the constrainst linked to the charging system. Let's talk about an engine with a perfect turbo (or no turbo) and also that would have a perfect volumetric efficiency.

Is it more the injectors flow and efficiency that limits the RPM, more the Pmax (nowadays 180-200 bars) for the cylinder head and pistons, or more the MPS, the pumping force to create swirl, or the fourth ?

Does the Mean Piston Speed fixes a limit at 13-14m/s like a common SI engine is generally limited at 18m/s ?

[McGuire]

I don't believe there is any 18 m/s limit on mean piston speed for SI engines, so naturally I have a similar opinion about a parallel speed limit for diesels.

I have been something of a Johnny One Note on the subject of piston speed here, so I will spare everyone another harangue. With the board search function on the menu above, I am sure you can find several examples of my droning on at length on the subject...should you be that curious to know what I think.

[GSX-R]

Sure there is a correct MPS to make the engine reliable to roll x * 100.000 km.

The max MPS are for F1 at 26 m/s. Honda S2000 and BMW M3, high cost cars go 23-24 m/s

For mass production cars, 18-20 m/s is a common value for SI mass production cars.

Sure the limit is higher to broke the part bu you need as stated above reliability.

Most of CI cars piston go 13-14 m/s. Does the MPS count as much as for SI cars, that's whay i would like to know from an CI automotive engeneer. Or the piston/rod shaft are more sensitive and design to support the limiting factor that is Pmax and so on the instant torque.

[McGuire]

Originally posted by GSX-R
Sure there is a correct MPS to make the engine reliable to roll x * 100.000 km.

The max MPS are for F1 at 26 m/s. Honda S2000 and BMW M3, high cost cars go 23-24 m/s

For mass production cars, 18-20 m/s is a common value for SI mass production cars.

Sure the limit is higher to broke the part bu you need as stated above reliability.

Most of CI cars piston go 13-14 m/s. Does the MPS count as much as for SI cars, that's whay i would like to know from an CI automotive engeneer. Or the piston/rod shaft are more sensitive and design to support the limiting factor that is Pmax and so on the instant torque.

If the mean piston speed "limit" is infinitely variable for different engines and applications, it's not much of a limit, is it?

Let's say there really is a 18 m/s limit on piston speed and you have built your engine to it. Now what if you increase the CR 1.5 points? Or if you increase the mass of the piston and rod assembly 10%? Or if you shorten the connecting rod 15%? You haven't changed the piston speed one bit but you have changed the pressure and/or inertial loadings significantly. So what does mean piston speed tell you about the actual loadings, really? Not much. You still have to do your sums. Diesels are no different.

[ciaoduc1]

If a direct injected SI engine didn't have a throttle, wouldn't that have an EXTREMELY lean mixture at all but WOT (or whatever you want to call it)?

How can diesels get away with it? Does diesel fuel "burn" cooler?

[GSX-R]

Engines are different, some comp ratio are 17, other 18.
I've reported many engines here in europe. Almost diesel engines at their max power run beetween 11-13 m/s

So, my question is still : do the diesel engines mainly not go over 4.500 RPM because of realiability of the mecanics parts or is there any injection flow, gasoil combustion rate limitation that prevents them to go further ?

My guess to the answer is more the seconde option but i would like to check with some of experts.

[GSX-R]

Originally posted by ciaoduc1
If a direct injected SI engine didn't have a throttle, wouldn't that have an EXTREMELY lean mixture at all but WOT (or whatever you want to call it)?

How can diesels get away with it? Does diesel fuel "burn" cooler?

Don't understand the first part of your question

2) Start of combustion on diesel is hotter than SI but combustion and end of combustion is cooler than SI engine due mainly to big difference in compression ratio burning.

[McGuire]

Originally posted by GSX-R
Engines are different, some comp ratio are 17, other 18.
I've reported many engines here in europe. Almost diesel engines at their max power run beetween 11-13 m/s

So, my question is still : do the diesel engines mainly not go over 4.500 RPM because of realiability of the mecanics parts or is there any injection flow, gasoil combustion rate limitation that prevents them to go further ?

My guess to the answer is more the seconde option but i would like to check with some of experts.

I believe Edlund already supplied the answer.

[McGuire]

Originally posted by ciaoduc1
If a direct injected SI engine didn't have a throttle, wouldn't that have an EXTREMELY lean mixture at all but WOT (or whatever you want to call it)?

How can diesels get away with it? Does diesel fuel "burn" cooler?

Yep, diesels can run very lean off peak load, like over 50:1. In terms of heat rejection the diesel is simply a different animal. I am not sure we can say they "get away" with anything, however. Traditionally, NOx emissions have always been a problem. Interesting development in recent diesels: EGR.

With SI engines using throttleless GDI the strategy is to use GDI's charge stratification capablility and clever chamber turbulence to burn local areas of fuel at near-stoichiometry and let the excess air pump right on through more or less unscathed. Here too, A/F ratios in the range of 50:1 to 100:1 are possible. However, that kind of talk (as well as terms like "lean burn") can be kinda misleading. The portion of the charge that is actually combusting is nowhere near that lean.

[GSX-R]

Originally posted by McGuire


I believe Edlund already supplied the answer.

Edlungs has correctly exposed the diesel behaviour and some of the constrainsts but didn't discuss about the main contrainst that limit the RPM, and did not mention the MPS.

[J. Edlund]

Mean piston velocity isn't really such a big limiting factor (it probably affect friction loss, wear and perhaps also ring sealing but not more than that), piston acceleration is more the limiting factor. Still, the piston acceleration isn't what limits the diesel engine. Even though its internal components are heavier they aren't that much heavier unless it's an industrial engine made for reliablity and efficiency.

Turbocharging a diesel is quite different than from turbocharging a SI engine. Since there will be no knock limit compression ratio doesn't need to be reduced. Also boosting the engine allow the use of leaner mixtures (even at full load) without sacrificing power output so exhaust emissions will be lower while efficiency will be higher (effect of the lean mixture). Since the engine adjust fuel independently of air the range of which over the turbocharger can work will be wider, and the cooler exhaust allow the use of variable geometry turbines. To produce extra power low down where the turbocharger can't work a richer mixture can simply be used at teh cost of some fuel and emissions.

The reason why most diesels doesn't operate at higher engine speeds is probably not because operating at such speeds isn't possible, its just that operating at higher speeds won't be as efficient as lower engine speeds with current injectors and combustion chambers. Since we can create the power we need using boost or a larger displacement higher speeds are simply not an effective option. Using higher engine speeds will also increase the rpm range making the engines more difficult to turbocharge and tune. If diesels were used in racing with limitations on displacement there may have been a different story though.

Cylinder pressures is a more limiting factor than one may believe. In diesels it's common to use much stronger pistons, rods, blocks, heads and larger bearing diameters. In truck diesels, at least on the high power units, it's also common to use pistons of steel with a skirt of aluminum to increase strength and cylinder heads are always made of cast iron rather than aluminum as the latter would simply fail due to fatigue caused by the cylinder pressure. On some larger diesels the cylinderhead is sealed to the block by other means than a gasket due to the pressures.

[GSX-R]

Ok, so according to you, the RPM is not limited by MPS (and thus piston acceleration that is linked to RPM², stroke and the rod length/stroke). It's not linked to the combustion process itself but more by the injection system, turbo efficiency range, inlet acoustics, swirl etc.. ? That's it ?

That was my first thougth i would like to confirm because i had no mecanical evidence that the 12-14m/s (and the according piston acceleration especially at TDC) could be critical for reliability.

Thank you.

[McGuire]

The question might be rather like asking why there is say a 8000 rpm limit on gasoline production engines. There really isn't one technical limitation, but rather a convergence of factors that impose an informal constraint on higher rpm.

[mmmcurry]

Ok, this ain't technical as such, but:

I remember Martin Brundle saying a couple of years ago when the BMW engine first got to 19K rpm that Ken Tyrell had once gone into a lengthy explanation as to why F1 engine's would never go above 8.5K. He did not go into any detail as to what the reasons were though (I think internal friction was one).

Is there any reason why the current rpm issues could not be solved or surcumvented as they were for petrol engine's or are we into a 'I canna change the laws of physics' (with bad Scotish accent) moment?

Steve.

[GSX-R]

Yes.
My question was more, what is the present main(s) factor(s) that limits the RPM ?

[clSD139]

The industry gives a good estimation of rpm factors:
-8V hot hatch: original max hp around 5000 rpm.
-16V GTI etc.: some more horses around 6000 rpm.
-VTEC, Valvetronic,...: redline a bit over 8000 rpm.

Maybe you have too look for the increase of Nm.

[GSX-R]

This thread is about .. diesel

[llmaurice]

Surely the massive compression ratio employed on modern diesels ,thereby requiring hefty pistons ,rods , flywheel/clutch etc have a fair bearing on this , as well as bore/stroke ratios.
Anyway ,who needs revs with the low speed torque available from diesels.
At the end of the day , anything with valves can't rev like a stroker !

[marcus123]

That was a very interesting post from J. Edlund. I was wandering if he could give a similar description for an SI engine ( or point me in the right direction ).

I have been trying to find out for a while why petrol is better suited to a SI engine and deisel better suited to compression ignition.

[J. Edlund]

Some interresting quotes regarding Schricks Hurricane DID 600 turbodiesel:

"While the engine is tuned for a maximum speed of 6000 rpm, Schrick reports that it is still actually burning the charge when running to 8500 rpm albeit with reduced power output. Beyond that sort of crankshaft speed useful combustion is indeed lost..."

"It can run up to 10,000 rpm when motored by the propeller, as it is when the aircraft is in a dive, which is a very high speed for compression-ignition operation."

"In view of the relatively high crankshaft operating speed the compression ratio is relatively low for a diesel engine at 14:1. To go higher would call for excessive strengthening to cope with the higher cylinder pressure and high operating speed."

I have been trying to find out for a while why petrol is better suited to a SI engine and deisel better suited to compression ignition.

Petrol has a high octane, low cetane, boiling range of 25-215 degC and an ignition temperature of 300 degC (regular), 400 degC (premium). Aviation gasoline (avgas) has a boing range of 40-180 degC, an ignition temperature of 500 degC and consist of basicly alkylate blended with aromatics such as toluene, xylene and so on. Avgas contains organic lead compounds and alkylates is known to respond very well on them (unlike aromatics or alcohols).

Diesel has a low octane, high cetane, boing range of 180-360 degC and an ignition temperature of 250 degC. Diesel has a slightly lower energy content, its higher density does however more than compensate for that.

This means that if one tries to run a SI engine on diesel, the fuel would be difficult to vaporise as it does not boil until 180 degC. Cold starting would basicly be impossible and even starting a warm engine will probably not be easy. When the engine is running the fuel can cause pre-ignition and detonation and thereby damage the engine or preventing any higher power output.

If one tries to run a CI engine on gasoline the fuel will easily varporise, perhaps to easy causing warm start problems (as the fuel boils inside the injection system). As the ignition temperature is high, and the cetane low the engine will have difficulty burning the fuel. One must likely raise the compression ratio or add large amounts of ignition improvers to get the engine working like it should. Without addetives the gasoline will likely also cause injection pump damage as it doesn't have the lubricating properties of diesel (the same problem have been seen with diesel/ethanol blends and clean low sulfur diesels).

[GSX-R]

Originally posted by J. Edlund
Some interresting quotes regarding Schricks Hurricane DID 600 turbodiesel:
...

Thank you for this example, where can i find additionnal informations about this engine i didn't know?

[J. Edlund]

Originally posted by GSX-R


Thank you for this example, where can i find additionnal informations about this engine i didn't know?

This info was taken from the latest issue of "Race Engine Technology", no. 009 that is.
The company has a website, www.schrick.com but there isn't any info there. The engine was designed for the military for use in an unmanned small spyplane or something like that.

[desmo]

Did anything come of the VW/Cosworth V10 CI engine slated for Le Mans? Just before I got details on this one my source got sent an NDA, so no official news since.

[kit]

I'd like to 'stick my oar in' with this question: Is it somehow possible to use a diesel engines superior torque over that of a gas engine to create some sort of transmission that uses the torque advantage to convert it into excelleration and top end speed? Just wondering.

[Greg Locock]

Yes there is. We techies call it a gearbox.

[hydra]

[Slumberer]

"Excelleration"

What a fabulous word! I shall be using that a lot from now on and will see how many people notice!

[Dynojet]

GSX-R

I'll give my contribution to the topic, as I've already had the same questions, and could learn a lot by working for a 4x4 diesel vehicles manufacturer.

First of all, the "limit" of the manufacturers can be somewhat higher, as the engines we use have the fuel cut at 5500 rpm.

The main reason was explained rightly by Edlund, is the burn rate of fuel that mainly limits the diesel rpm. There were several technological advances like the turbulence inducers, pilot injection, fine spray injectors, etc. that increased the rate of fuel burn, and is pushing this limit.

This could make the engine manufacturers adequate the engine geometry to anchieve those rpms (r/l ratio, stroke lenght, cam timing, etc), and make engines with more power.

Unlike pal Mcguire states (I remember a earlier discuss about that) really there is a limit of mean piston velocity, as it implies directly in the accelerations stand by the con rods, and also as he mentioned friction wear. And is about 25 m/s for race engines.

A con rod have to cope with about 1000 G's of acceleration with a 24 m/s MPV.

As you mentioned, the manufacturers are aproaching this limit. It may increase with advances in material technology, but I don't think it will go to far.

[McGuire]

Originally posted by Dynojet
Unlike pal Mcguire states (I remember a earlier discuss about that) really there is a limit of mean piston velocity, as it implies directly in the accelerations stand by the con rods, and also as he mentioned friction wear. And is about 25 m/s for race engines.

only on message boards and suchlike. On real engines you have to do your sums, calculate the actual loadings.

[McGuire]

Originally posted by Dynojet


A con rod have to cope with about 1000 G's of acceleration with a 24 m/s MPV.

You need one more zero, approximately.

[McGuire]

Originally posted by Slumberer
"Excelleration"

What a fabulous word! I shall be using that a lot from now on and will see how many people notice!

I used to work with a guy (Bill Byers, RIP) who, due to his midwestern accent and manner of speech, always spoke of "exhilaration" rates etc. I liked that.

[shaun979]

Originally posted by Dynojet
[B] there is a limit of mean piston velocity, as it implies directly in the accelerations stand by the con rods

Mean piston velocity, stroke, RPM - any two of these allow you to find the third. You might as well calculate the loads directly rather than go by mean piston speed of 25m/s. An engine with half the stroke of another engine, operating at twice the RPM of the other engine, will have around 70-80% higher peak acceleration at TDC (tension). At BDC, roughly over 120%-150%. Both engines have the same mean piston speed, but accelerations are much different and not only that, they occur at a much different rate consuming limited cycle life (racing).

A con rod have to cope with about 1000 G's of acceleration with a 24 m/s MPV.

It average road going MPV will be between 3000 and 5000 G assuming 24m/s. 1000 G is very low. 10000 G is very high and is closer to F1.

[clSD139]

Another diesel discussion (the 7000 is just my search term);

http://forums.atlasf...&highlight=7000

I informed my source: the diesel bike can not just do 9000 rpm, it has still torque!

The rather exeptional redline eliminates excessive gearing, the engineer said.

[Dynojet]

Mean piston velocity, stroke, RPM - any two of these allow you to find the third. You might as well calculate the loads directly rather than go by mean piston speed of 25m/s. An engine with half the stroke of another engine, operating at twice the RPM of the other engine, will have around 70-80% higher peak acceleration at TDC (tension). At BDC, roughly over 120%-150%. Both engines have the same mean piston speed, but accelerations are much different and not only that, they occur at a much different rate consuming limited cycle life (racing).

Shaun979, you are correct, but you are always searching for power in a race engine, and it's proportional to RPM. The max acceleration is function of engine speed squared, stroke. The minimum stroke has a fisical limit, the limitation ends to be the piston velocity.

Gmax = ((N^2*L)/2189) * (1 +1/2*A))
MPV = .166*L*N

A = con rod length to stroke ratio
N = RPM
L = stroke

clsd139

I have heard som about a racing diesel engine, but think it has a 7000 rpm redline, or something like that... 9000 rpm is impressive to me.

[shaun979]

Originally posted by Dynojet
Shaun979, you are correct, but you are always searching for power in a race engine, and it's proportional to RPM.

Thanks for the explanation, but I still do not see why you do not want to calculate the actual value rather than take piston speed and work in proportion to that.

The minimum stroke has a fisical limit, the limitation ends to be the piston velocity.

If I'm reading this correct you mean "The minimum stroke has a physical limit, which tends to be the piston velocity." I see how there can be a limit to maximum stroke, but I don't see a limit on minimum stroke. Would you be so kind as to explain a little further? If I took a F1 engine and halved its stroke to say 0.8 inches, and turned it 40,000 RPM, the piston speeds would be about the same, but piston accleration would be a lot higher and that would be limit, wouldn't it?

[J. Edlund]

Originally posted by shaun979


Thanks for the explanation, but I still do not see why you do not want to calculate the actual value rather than take piston speed and work in proportion to that.



If I'm reading this correct you mean "The minimum stroke has a physical limit, which tends to be the piston velocity." I see how there can be a limit to maximum stroke, but I don't see a limit on minimum stroke. Would you be so kind as to explain a little further? If I took a F1 engine and halved its stroke to say 0.8 inches, and turned it 40,000 RPM, the piston speeds would be about the same, but piston accleration would be a lot higher and that would be limit, wouldn't it?

Half the stroke at 40,000 rpm would mean that the piston velocities will be equal, the maximum piston acceleration would however be twice as high at around 20000 G. There would also be very diffucult to get an efficient combustion at that speed since the we have the same flame path but now only half the time to do it. The frequency will also be twice that of the current engines which most likely will cause some difficulties with resonances and harmonics.

[shaun979]

Thanks J, Yes I raised the example only for illustration that accelerations can be very different even at similar mean piston speeds.

You have a PM

[clSD139]

Thé diesel bike, military approved, among others:

http://journeytofore...esel_bikes.html

It seems even that with a diesel pyrotechnic, or explosion wave speed considerations are not the main problem. Maybe nothing on itself is the limit, what is the future demand?