2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

As to why a 2T would not necessarily be such an advantage under the current rules is that:

• The maximum capacity is set (can be no more than 1,600cc)
• The minimum capacity is set (can be no less than 1,590cc)
  [*}The fuel flow is restricted (100kg/hr maximum) and thus the amount of air that can be pumped is restricted
• Minimum dimensions for mounting faces to the tub and gearbox are set.
• Minimum weight and CoG limitations
  [*}Only poppet valve engines are permitted (you could make a 2 stroke with poppet valves) - the engine must have 2 inlet and 2 exhaust valves.

[/list]

Thus, while the maximum operating speed of a current F1 engine is ~12-13,000rpm, we could expect that the 2T would be no more than 6-7,000rpm operating condition, where the fuel flow is much less (59.5-68.5kg/hr).

So, in short, the normal 2 stroke advantages of lower weight and compactness are gone. A lower capacity to allow the 2 x BMEP "advantage" and maintain the rpm to a level where the full fuel flow allowance can be accessed is not permitted, nor can the configuration be changed to a 3 cylinder.

The 2 stroke would be as much, if not more, constrained by the rules than current 4 strokes.

Actually W, the primary F1 rule restraint on 2Ts - is in fact - the explicit ban..

Notwithstanding your debatable/unfounded speculation on perceived loss of fundamental 2T attributes..

Why do you imagine the ban is there.. front & centre?

Edit: Typo..

[J.A.W.]

Hello J.A.W.

You write:
“Manolis, I'd be interested to see your design shown stat above in metal “

A functional prototype is the normal way to proceed.

Yet, it is more challenging the theoretical “evaluation” / analysis of the “24 / 7 breathing” of the above “tuned exhaust at high revs” PatTwo Harmonic (that needs neither reed valves, nor rotary / drum valves).

For instance:
With the control-valve wide open,
the “crankcase-volume” appears as infinite (and the “primary compression ratio” as 1).
With the control-valve closed, the “crankcase volume” can be smaller than in any conventional 2-stroke.

Thanks
Manolis Pattakos

Thanks Manolis, & best wishes with successful trials..

[wuzak]

Actually W, the primary F1 rule restraint on 2Ts - is in fact - the explicit ban..

Notwithstanding your debatable/unfounded speculation on perceived loss of fundamental 2T attributes..

Why do you imagine the ban is there.. front & centre?

Edit: Typo..

The ban is there because none of the manufacturers involved in F1 have ever used 2 stroke in production cars. Unless Honda have, of that I am unaware.

More specifically, it is there to stop someone coming in with a 2 stroke and winning (however likely or unlikely that is) and forcing the others to develop 2 strokes which are of little relevence to their production cars.

My point remains. You could take out the one line that expressly forbids 2 strokes, and teh rest still stands.

The ICE has to be a V6 of 90° bank angle, between 1590cc and 1600cc, bore 80mm ±0.1mm, weigh at least 145kg (with all the ERS bits specified), crankshaft centreline 90mm ±0.5mm above the reference plan and on the car centreline, the mounting faces must be 480mm apart and have mounting studs in the specified locations, the CoG height must lie a minimum of 200mm above the reference plane, and the fuel flow shall be no more than (0.009 x RPM + 5.5)kg/hr between 0 and 10,500rpm and and 100kg/hr from 10,500rpm to 15,000rpm.

The rules also stipulate that there shall be 2 inlet and 2 exhaust poppet valves per cyclinder. Which would not be the favoured method in 2 strokes. So lets ignore that one too.

It still comes down to the fact that the 2 stroke will be fuel limited because it won't be able to run to 10,500rpm with the fuel flow restriction. If you could, it would be at some astronomical AFR.

The 2 x BMEP advantage you keep on about is simply that the 2 stroke pumps approximately twice as much air per rev than the 4 stroke, and hence uses approximately twice the fuel and making approximately twice the power.

Tightly limit the capacity, configuration and fuel flow then the pumping advantage becomes a hinderence. You won't be able to access the full fuel flow limit.

[J.A.W.]

More study needed W..
What is the technical 'fiction' of BMEP % by 1/2 - as applied to 2Ts in engineering text books - about?
&..
Obviously the closely circumscribed/technically retarded F1 rules currently in force are severely limiting..
..especially those slow moving, flow-obtunding poppets..
Yet..
Have any of those manufacturers sold turbo-compound-electro-hybrids in showroom standard cars?
No, AFAIK..
Nor are the emissions objectives in line with road vehicle standards.. ..more technical 'fiction' perhaps?

Your speculative values applied to putative 2T working fluid functional limitations are seemingly sans foundation..
..what about the efficiency lost to needless pumping work done by 4Ts?

Is your view - as to why 2T are specifically banned.. ..just a guess?

So W, are you au fait with what an M-B race mill lease costs?

[wuzak]

I doubt if Mercedes built 2 strokes (and they were allowed) that a lease would cost any less. The major costs are in R&D (which they would likely need to spend more, not being experts in 2 strokes) and the ERS systems.

So what is wrong with my thought process JAW?

• The two stroke has one intake and one exhaust event per revolution
• The four stroke as one intake and one exhaust event for every two revolutions
• ergo, the two stroke has twice as many intake and exhaust events per revolution than the four stroke
• thus the two stroke pumps twice as much air as the four stroke
• meaning the two stroke needs twice as much fuel at a given rpm as the four stroke, assuming the same AFR, TE and VE
• which means for the same fuel flow rate the two stroke either has to run at half the rpm or have half the capacity
• but since the capacity is fixed it must use half the rpm, which means a lower fuel flow rate than the maximum
• which means less power

[wuzak]

Have any of those manufacturers sold turbo-compound-electro-hybrids in showroom standard cars?

No, but that is not to say they won't.

The core of the engine is a small capacity turbo 4 stroke. Which they do make by the thousand.

[J.A.W.]

W, your 4T output scheme is inversely developed..
The wasted strokes involve pumping/frictional inefficiencies..
Air is not limited, but fuel is, so that given superior 2T BSFC.. ..more power..

& most engine design is virtually realised via cyber-works - long before being committed to metal nowadays, isn't it?

[wuzak]

W, your 4T output scheme is inversely developed..
The wasted strokes involve pumping/frictional inefficiencies..
Air is not limited, but fuel is, so that given superior 2T BSFC..

& most engine design is virtually realised via cyber-works - long before being committed to metal nowadays, isn't it?

Superior 2 stroke BSFC is an assumption.

To access the 100kg/hr fuel flow limit at 10,500rpm the 2 stroke would have to run an AFR ~2 x that of teh 4 stroke. Does that sound practical to you?

[Blanchimont]

From page 30 of this thread: http://www.provenion.de/65-1-FFI.html

The bottom picture shows a min bsfc of ~235g/kWh up to 41kW of power output, although it's not clear if these data are only simulated or measured on a real engine. What could the big companies like Mercedes or Renault achieve with higher budgets and more R&D?

[Andres125sx]

The purpose of any engine is transforming energy (fuel) into movement, or technically speaking, work

If an engine use double energy, it will obviously produce around double work. Does that mean it´s more efficient? Obviously no, it´s just using more energy


Then there are many different parameters to classify ICEs, and on some of them 2t are better than 4t (simplicity, size, hp/litre), so depending on the application 2t may be better than 4t, for example for personal helicopters where weight is critical

But generally speaking main engine purpose is transforming energy into work to move vehicles and/or people, so you can´t ignore how much energy it´s using and then saying it produce more work as a proof of its superiority, sorry but that´s absurd.

For a fair comparison they must start with same initial conditions, so when talking about engines that´s using same energy/fuel to see wich of them make the most of it.

That´s for a general comparison, if it´s for an specific application then you can take the most interesting parameters for you, like weight for a helicopter, simplicity/reliability for an everyday transport.... but you can´t ignore energy used if trying to claim an overall winner

[Blanchimont]

In a true racing car without minimum weight limits on car or engine, what is the best engine?
The one that achieves the minimum lap time, not necessarily the strongest one!

Therefore it should
- have a small overall weight(including cooling, charging components)
- have a small volume
- have a high power output
- little fuel consumption(smaller tank)

I think two strokes and rotary engines have shown in the past to achieve the first three points, the only thing what today they need to prove is low bsfc. If similar to a 4T, everyone would use 2T or rotary engines, if allowed, even in a fuel limited series.

Is there currently any racing series, where 2Ts are allowed and where big manufacturers are involved?

[Richard]

It made "sense" to directly compare them for decades, as it still does in showrooms today R.. so why not?

Most people cope just fine with different engine sizes for different configurations, ie NA versus turbo and petrol v diesel.

Buyers simply look at the 0-60 mph and mpg (or metric equivalents) data when comparing engines in their cars. Geeks also look at BHP and kW.

You wouldn't compare a 2 litre diesel with 2 litre petrol, so why insist on fixed volume when comparing 2T v 4T?

[J.A.W.]

Because of the metric system?
I certainly do compare a 2 litre to a 2 litre, & the makers do too, diesel fuelled or not.
Diesel powered sports-racing cars are allowed, but are they allowed to operate as 2Ts?

Funny that one of the terms used t describe 4Ts by 2T fans is 'diesel' - due to certain similarities..

[J.A.W.]

The purpose of any engine is transforming energy (fuel) into movement, or technically speaking...
transforming energy into work to move vehicles and/or people, so you can´t ignore how much energy it´s using and then saying it produce more work as a proof of its superiority, if trying to claim an overall winner

& A-125.. if you read the posts showing links to BSFC in this thread ( inc' B's above), you would see this is happening too..

As regards helicopters, if you refer back to page 5, & read the NASA-Garrett 2T helo-mill ( turbo-compound-diesel)
proposal, you will see that the efficiency/work potential - is superior to gas turbine power in that case..

Yet, it hasn't made it to the sky - ~20 years later..

Why? Due to powerful vested interests, which is also clearly, the reason 2Ts are banned in F1/Moto GP..

[gruntguru]

I don't think 2T would have much if any advantage in the current formula. The best reason for banning them is road-relevance (lack of).

Road cars generally have not embraced 2T:
1. Traditionally due to oil burning, HC emissions, uneven idle and cruise etc.
2. Modern 2T tech has fixed all the above problems but not the issues of excess air, NOx and reduction catalyst incompatibility.

Funnily, the lean-burn nature of current F1 makes the engines less road relevant for the same reason!

The primary reason 2Ts are banned in F1 is the fundamental thermodynamic advantage of X2 BMEP..

The main advantage of 2T is airflow per engine displacement, weight and size. Under current F1 rules a 2T could not use its airflow advantage - the 4T 1.6 is already capably of flowing more air than required for the 100kg/hr fuel allowance. I think I have said elsewhere that the 2T would have operate with approximately half the MAP to acchieve the correct airflow. This may have a negative impact on TE and therefore power due to reduced surplus turbine power at the lower PR.

The only thermodynamic advantage of the 2T is reduced friction due to fewer strokes/cycle. This would be very slight in the F1 context.