2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Gruntguru.

It works the opposite way.

Given the real maximum speed, one can calculate the real overall resistance at the specific point (because he has, at that point, the "engine force" that pushes forwards the bike-rider).

Then he can use this for the calculation of the accelerations, the best points for changing gear ratios, etc.


An interesting option of the RoadLoad program is that it has the "hard use of clutch" mode wherein the driver, burning a lot of friction disk material in the clutch, can keep the engine permanently at the maximum torque point at all speeds below the speed corresponding to the peak torque rpm for the specific gear ratio in the gearbox.

In such a case, it is like having a constant torque engine (constant until the point of the maximum torque), and the performance data become the best possible.

Thanks
Manolis Pattakos

[Tommy Cookers]

the 2 stroke torque curve I was looking for
http://www.automobile-catalog.com/curve ... f_102.html
and the last DKW produced http://www.automobile-catalog.com/curve ... f_914.html
to ask - are they artifacts of retro-processing ie based on insufficient real data ?
RETRO-EDIT - see my previous and later posts

Tom Donney shows the Saab 96 sporty full disc crank impedes flow and a hybrid (part-standard) crank is better at most rpm
http://www.tomdonneymotors.com/wp-conte ... h-Text.pdf

some Jaguar curves from a gem of a source (uselessly for comparison not the XK'E')
http://www.jagweb.com/aj6eng/v12_archives.php

this SAE paper seems to show 4 stroke CI aero engines with reduction function via the camshaft are better than 2 strokes at reduction
http://papers.sae.org/2017-01-1808/

[Pinger]

A couple of points on torque curves.
Basically, the flatness (or otherwise) is determined by the exhaust system and at this point as the exhaust is the determining factor in Blair's three 2T categorisations it might be worth a quick revisit. His categorisations are by BMEP and as are follows.

4 bar BMEP. In this category are simple 2Ts eg chainsaws, strimmers etc. Low BMEP as the exhaust used is for compact silencing and adds nothing to gas flow capability. Specific power output circa 75hp/litre courtesy of the relatively high (9500) rpm.

8 bar BMEP. In this category are simple 2Ts but with cylinders in multiples of three or four, they employ a compact branch exhaust manifold and an expansion cone to the benefit of better breathing hence higher BMEP. The expansion cone (in outboards at least) is short supplying an early returned -ve pulse. Whether this is by choice or lack of space in the mid section I do not know. Typical max power rpm is 5-6000rpm and 75hp/ litre is the norm. The compact branch exhaust manifold providing cross-charging is effective over a wide speed range.

11-12 bar BMEP. In this category are full performance 2Ts where maximum power takes precedence. High BMEP due to the highly beneficial effects of individual pipes per cylinder and high power due to that and the high rpm potential.

Only engines in the first two categories are capable of delivering a torque curve that could be considered at all useful as propulsion for a vehicle as heavy as a car. The 11-12 bar unit is too peaky (though 'power valves' offer a lot in terms of civilising them). The 4bar unit without revving to 9500 would be lacking in power so only one 'type' is remotely suited to car propulsion.And that is the 8bar unit - as has largely been the type hitherto employed (SAAB, DKW, etc).
(It is by the above categorisations that I would like to see Manolis pitch his designs).

Which brings me to my second point.
In order to achieve anything resembling fuel efficiency with a 4T throttling losses must be avoided. Thus the current trend with SI 4T is to cruise at low rpm at a throttle opening which effectively equates to unthrottled running at that rpm. If more is required of the engine simply pressing the pedal achieves nothing as the engine is already getting all the air it can consume. Which means a downshift to higher rpm is required, which in turn requires driver input or a flexible (automated) transmission.

The 2T's fuel efficiency conversely is not hampered by throttling but aided by it. Thus the savage rpm restriction imposed on the 4t is not required and the 2T will respond to more 'pedal' - making it a highly responsive engine to drive and considerably easing the driver or transmission's task. What's not to like?

[J.A.W.]

I was looking...to ask - are they artifacts of retro-processing ie based on insufficient real data ?
...this SAE paper seems to show 4 stroke CI aero engines with reduction function via the camshaft are better than 2 strokes at reduction.
http://papers.sae.org/2017-01-1808/

T-C, I'd reckon that SAE paper is a prime example of theoretical fancy - not based on real data..

Indeed its a classic 'apples & oranges' case.. esp' with reduction drive/PTO via the camshaft - deemed best!
The 'piston-port' 2Ts that were considered, wont have a camshaft, & OHC being current 'best practice' 4T-wise..

[J.A.W.]

A couple of points on torque curves...

11-12 bar BMEP. In this category are full performance 2Ts where maximum power takes precedence. High BMEP due to the highly beneficial effects of individual pipes per cylinder and high power due to that and the high rpm potential.

Only engines in the first two categories are capable of delivering a torque curve that could be considered at all useful as propulsion for a vehicle as heavy as a car. The 11-12 bar unit is too peaky (though 'power valves' offer a lot in terms of civilising them). The 4bar unit without revving to 9500 would be lacking in power so only one 'type' is remotely suited to car propulsion.And that is the 8bar unit - as has largely been the type hitherto employed (SAAB, DKW, etc).
(It is by the above categorisations that I would like to see Manolis pitch his designs)...

In point of fact P, a dedicated 'formula' racing car could easily accommodate the most highly tuned 2T..

Since actual empirical experience shows that such high output 2T engines were able to be sufficiently modulated by skilled riders in G.P. racing, with a minimum of ECU override, but conversely, when 4T engines derived directly from F1 were tried ( viz: Aprilia RS 'Cube') - they proved far too savage..

& so current 4T Moto GP is now reliant on many electronic 'fixes' to provide that necessary power 'finesse'..
..while still far below the specific output of the - sadly, now banned - 'pukka' 2T G.P. machines..

[Pinger]

In point of fact P, a dedicated 'formula' racing car could easily accommodate the most highly tuned 2T..

I should have been clearer that I was referring to road cars - the porky brutes that they have become.

[gruntguru]

Hello Gruntguru.
It works the opposite way.
Given the real maximum speed, one can calculate the real overall resistance at the specific point (because he has, at that point, the "engine force" that pushes forwards the bike-rider)..

I was talking about the absolute maximum speed - the highest speed possible with optimum gearing.

An interesting option of the RoadLoad program is that it has the "hard use of clutch" mode wherein the driver, burning a lot of friction disk material in the clutch, can keep the engine permanently at the maximum torque point at all speeds below the speed corresponding to the peak torque rpm for the specific gear ratio in the gearbox.

In such a case, it is like having a constant torque engine (constant until the point of the maximum torque), and the performance data become the best possible.

That is exactly how a top-fuel dragster works! Would only be an advantage in 1'st gear for most vehicles (optimum upshifts usually land the engine above the peak-torque-rpm).

[gruntguru]

the 2 stroke torque curve I was looking for
http://www.automobile-catalog.com/curve ... f_102.html
and the last DKW produced http://www.automobile-catalog.com/curve ... f_914.html
to ask - are they artifacts of retro-processing ie based on insufficient real data ?

"The Horspower / Torque Curve below was generated by the ProfessCars™ software, based on the factory data:"

[manolis]

Hello Gruntguru.

You write:
“I was talking about the absolute maximum speed - the highest speed possible with optimum gearing.”


Even if we know the real speed the motorcycle achieves with its actual gearing (and not the highest speed it would achieve with the optimum gearing), we have the required information for the calculation of the aerodynamic and rolling resistance at a specific known point.

For instance, if with the 26PS of the Kawasaki the highest speed possible (with the ideal gearing, I mean) is 150Km/h, however with its actual gearbox (a gearbox with longer gear ratios than the motorcycle of the drawing, but not the optimum gear ratios for achieving the top speed) its top speed is only 135Km/h at 11,000rpm (i.e. below the allowed rev limit of the engine, which in the power / torque plot is 12,000rpm), then we know that at 135Km/h and 11,000rpm (wherein the engine makes 19PS at most) the sum of the aerodynamic and rolling resistances is 19PS.

The problem is when the maximum speed of the motorcycle is limited by the revving capability of the engine (as in the Kawasaki KX of the drawing: at 105Km/h of its maximum speed with the longest gear in the gearbox, the engine operates at 12,000rpm).
In such a case you can’t know (and is difficult to calculate), how many of the 14PS the engine can provide at 12,000rpm, are actually provided.


On the other hand, even this way (i.e. to accept that the maximum speed is limited at 105Km/h not by the gearing but by the aerodynamic and rolling resistance) the error, the mistake in the calculations is small if you think that with 14PS a motorcycle can’t go significantly above 105Km/h.





You also write:
“That is exactly how a top-fuel dragster works! Would only be an advantage in 1'st gear for most vehicles (optimum upshifts usually land the engine above the peak-torque-rpm).”


Exactly.

With the exception of the quite peaky engines, like the Kawasaki KX of the drawing, wherein for the best acceleration / performance it is required a lot of clutch slipping / burning after every gear shift, as this drawing (RoadLoad program, same data as before, but with "hard use" of clutch) shows:

.


Only few people can get how, consuming a lot of clutch friction material, they can bridge the gaps of the “accelerating force” and so improve the performance of a motorcycle or car having peaky torque curve.

With the proper use of the clutch it is like turning their “peaky torque” engine into an engine having, from zero rpm to the rpm wherein the maximum torque is provided, constantly the maximum torque.

Thanks
Manolis Pattakos

[Tommy Cookers]

proper use of the clutch - means holding the engine WOT at constant (peak engine torque) rpm
they do this (once per 2 mile lap) at Oliver's Mount ?? (but don't in the TT - they just avoid stalling ie save the clutch ??)
if the clutch was to slip automatically/naturally at this peak engine torque it would be easier and have more credibility

(iirc we check the helicopter clutch does this below peak torque so torque-protecting the transmission at all times)

@gg
2 bits of manufacturer's data are the usual - peak power/peak power rpm and peak torque/peak torque rpm
superficially plausible but artificial power and torque curves could be synthesized from these
my implied question was - do people think the DKW curves given are true measurement or synthesized ?
(their Jag E type plot seems synthetic and clearly pessimistic at lower end wrt real XK150S figures in Campbell's book 'The Sportscar' - see earlier post)
@J.A.W
Continental made the Tiara engines (combined cam drive and prop drive) from 1965 to 1980
so running to 4000 rpm (allowing more power) not the usual eg 2500 or 2800
but their economy was not good enough for the 1970s 'energy crisis' fuel prices

[J.A.W.]

Hi Manolis..

I think you maybe forget that the KX 125 is an MX race-bike, for use on dirt tracks..
..it is easier to spin the rear tyre loose on such surfaces.

& the 125 G.P. race bike equivalent - even with perhaps twice the max hp - still made do
with a 6-speed gearbox, & while perhaps a bit hard on the clutch in starts, generally had no
clutch "burning" issues" - over the course of a G.P. race distance..

[J.A.W.]

@J.A.W
Continental made the Tiara engines (combined cam drive and prop drive) from 1965 to 1980
so running to 4000 rpm (allowing more power) not the usual eg 2500 or 2800

Yes T-C, I gathered that the idea was to utilize the 1/2 engine speed cam-drive ratio as a defacto reduction gear..

Hardly a suitable prospect for an OHC design though..

[Tommy Cookers]

real-world aircraft engines sooner or later fail compression checks on one cylinder and so go out of service
this is fixed in 1 day or less with the universality of pushrod valves and individually-detachable cylinders
a good reason why the market doesn't want OHC aircraft engines

[J.A.W.]

real-world aircraft engines sooner or later fail compression checks on one cylinder and so go out of service
this is fixed in 1 day or less with the universality of pushrod valves and individually-detachable cylinders
a good reason why the market doesn't want OHC aircraft engines

I think you'll find that its more a matter of perceived legal liability issues T-C..
.. just look up the sorry story of the Porsche & Subaru engines in aero applications..

Meanwhile here's another 'synthetic' performance graph site of possible interest:
http://www.motorcycleperformanceanalyze ... d-350-1987

[Pinger]

A quick question that some of you aero engine gurus should be capable of helping me with.
On those big radials where there is a cylinder pointing towards the ground - how is it prevented from being flooded with oil in the way a conventional sump is?
And while I'm asking questions, following on from one of the linked threads (pilot's forum) there was much talk of the lowest cylinder being the hardest to work on. Why so?