2 stroke thread (with occasional F1 relevance!)

[Tommy Cookers]

a few days ago someone PM'd me saying his inside info says F1 uses near stoichiometric mixture
my reaction is at 4 bar induction pressure the mixture must be very lean unless the valve timing is most unconventional

but if there's Prius-style abnormally late IV closure or Fiat-style abnormally early IV closure the VE is not as expected
ie in F1 we could have eg 4 bar induction pressure producing far less air massflow than expected ie near-stoichiometry

simple questions -
is the work done by the compressor proportionate to the induction pressure regardless of the delivery ? or ..
is the work done by the compressor proportionate to the induction pressure multiplied by the delivery ? or ..
to something else ?

this aspect is analogous to the 2 stroke case
and is important to boosted and compounded 2 strokes


regarding 2 stroke true diesels aka slow-speed diesels
the crosshead Wartsila went to very low rpm and very large displacement, for direct drive of ever larger propellors
the other crosheadhead true diesel maker went to higher rpm etc
but passenger ships have no room for crosshead engines
their trunk piston engines now have very high powers with very good efficiency - ship people would call them medium-speed

surely there is something to be learned from products other than Wartsila's ?


btw regarding the efficiency of air propellors
the exhaust thrust of aircraft engines substantially increases propulsive force (thrust) at conventional speeds
eg 20% at 400 mph and 30% at 500 mph
so propulsive efficiency approaches or exceeds 100% of crankshaft power
(and coolant heat can be applied to suitable aerodynamic ducts to increase 'free' thrust further)

[manolis]

Hello Pinger.

You write:
“VW's new system behaves as Fiats - to avoid patent infringement while still exploiting a Miller/Atkinson cycle?”


If you mean this VVA of VW:



it is a simple two step VVA.

Honda’s V-TEC does (or can do) the same and is some 30 years older.
The V-TEC drives each valve either by a wild cam lobe, or by a mild cam lobe, with the selection based on hydraulically displaced locking pins (as VW’s VVA) .

In some of their models, the VW-group uses the above VVA to deactivate the valves of some cylinders, in some other models VW uses it to run the engine in one of two different modes (typically: sport mode and economy mode).


The MultiAir / TwinAir of FIAT, Alfa Romeo, Chrysler is a way more sophisticated (and at the same time “mechanically” simpler) VVA (Variable Valve Actuation system) wherein there are available infinite valve lift profiles (continuously variable, from full deactivation of some valves, to full lift - full duration).

The hydraulic MultiAir / TwinAir system of FIAT has true electronic control, based among others, and on the feed back from the exhaust; it needs neither a throttle valve nor VVT (Variable Valve Timing):



The PatAir (the outgoing air control):





adds an infinity of additional (and more efficient) modes of operation (unlimited Atkinson Miller cycle) to the MultiAir / TwinAir of FIAT.



You also write:
"Why does it take 1000hp to displace the air at 400km/h then?"

The 400Km/h is anything but a small speed: it is the 1/3 of the sound velocity in the air; and the frontal area of the Veiron is about two square meters.

Thanks
Manolis Pattakos

[manolis]

Hello Johnny comelately

You write:
"btw regarding the efficiency of air propellors
the exhaust thrust of aircraft engines substantially increases propulsive force (thrust) at conventional speeds
eg 20% at 400 mph and 30% at 500 mph
so propulsive efficiency approaches or exceeds 100% of crankshaft power
(and coolant heat can be applied to suitable aerodynamic ducts to increase 'free' thrust further)"


"Crankshaft power" denotes a reciprocating piston engine.

Sorry, but I can't get it.

Thanks
Manolis Pattakos

[J.A.W.]

Hi Manolis, I think you meant Tommy, not Johnny.

& Tommy was making the point that besides 'shaft horsepower' driving the prop,
a significant net propulsive benefit can be gained from proper attention to venting hot gas 'waste'..

Both from exhaust nozzle thrust - either direct from combustion processes, or indirect from coolant exchange.

[johnny comelately]

Hi Manolis, I think you meant Tommy, not Johnny.

& Tommy was making the point that besides 'shaft horsepower' driving the prop,
a significant net propulsive benefit can be gained from proper attention to venting hot gas 'waste'..

Both from exhaust nozzle thrust - either direct from combustion processes, or indirect from coolant exchange.

Coanda effect.
thanks for that, i'm going to get back to this as soon as my head stops hurting
I got baffled by science there for a minute

[J.A.W.]

Some Coanda effect may be involved for duct efficiency - Johnny..

But most thrust - is primarily from vector direction of the energetic 'waste' hot-gas - via 'jet' nozzles,
& at a higher speed than the airframe..

Just like a toy 'bottle rocket'.

[Pinger]

Hello Pinger.

You write:
“VW's new system behaves as Fiats - to avoid patent infringement while still exploiting a Miller/Atkinson cycle?”


If you mean this VVA of VW:

https://www.youtube.com/watch?v=r4J8OLbGcD4

it is a simple two step VVA.

This >> https://www.youtube.com/watch?v=JjM14JBPdBI&vl=en

[johnny comelately]

Some Coanda effect may be involved for duct efficiency - Johnny..

But most thrust - is primarily from vector direction of the energetic 'waste' hot-gas - via 'jet' nozzles,
& at a higher speed than the airframe..

Just like a toy 'bottle rocket'.

Yes Coanda was mentioned re Tommys "(and coolant heat can be applied to suitable aerodynamic ducts to increase 'free' thrust further)

[J.A.W.]

Sure it wasn't the 'Meredith effect' - that T-C was actually posting about, Johnny?

[johnny comelately]

Sure it wasn't the 'Meredith effect' - that T-C was actually posting about, Johnny?

No, I'm not sure at all.
We have done some work on getting rid of the tyre air wedge and have "energised" the ducting with exhaust, indirect i know.
We have to get booted off this thread for this graffiti

[johnny comelately]

Sure it wasn't the 'Meredith effect' - that T-C was actually posting about, Johnny?

How very interesting!

[johnny comelately]

To Manolis Pattakos regarding your reply to me about BSFC and two strokes. (and as I have stated before, I havent got enough science to bite me)
The deflection of the discussion about BSFC from an energy efficiency measurement to a thermal measurement is a moot point because the Kw are net (after heat and everything else losses are subtracted), so in effect we are talking the same apples, me Johnathon, you Granny Smith.
So my only point was firing twice as often as the equivalent 4 stroke they have an advantage in relation to time which is power density in my book.
Two stoke losses relating to thermal efficiency is another matter, I think they have an inherent advantage IF you can get the gas exchange cleanly done, something that the slow revving marine diesels have time to do.
Their drawback is the huge volumes, ok masses, they have to move, so valving and charging or whatever is critical.
Showing my ignorance here, but do those large diesels have any kind of expansion chamber effect from anything?
Burn time is another interesting area and i see you have a novel approach to that, do you have a running engine? (apologies if that is an old question already answered)
Is the initiation in the smaller chamber?
as i understand it HCCI ignites the lot at once, does yours do that or is there some delay or inhibition?
does it have NVH problems?
is there a problem with HCCI in that it is too quick a combustion?

is there a drawback on emissions with a complicated shape causing unburnts? (new word)

[johnny comelately]

simple questions -
is the work done by the compressor proportionate to the induction pressure regardless of the delivery ? or ..
is the work done by the compressor proportionate to the induction pressure multiplied by the delivery ? or ..
to something else ?

this aspect is analogous to the 2 stroke case
and is important to boosted and compounded 2 strokes

Is this regarding pumping losses?

[Tommy Cookers]

yes, something like that ...or ...
when is a pumping loss not a pumping loss ?

ie we might think the Wartsila's breathing is a struggle
but they don't care how much compressor work is needed as they are not compounding (significantly) from the turbine

any CI engine is to a greater or lesser extent a heat dilution engine

somehow there must be a unified way of viewing the range of possibilities

[Pinger]

'Air work' is Ricardo's term.
With a 4T he lumps all the mechanical friction with air work on the basis that that friction is encountered emptying and filling the cylinders.

Re HCCI.
Yes, very high rate of combustion creates mechanical problems. I've yet to hear of HCCI utilising more than 40% of the air. So substantially more air required for the same power output (which inevitably means boosted, bigger or faster) and if a symmetrically ported 2T then charge loss will be no better than with Lambda = unity.
Trapped charge in the crevices (behind valves, in ring lands, etc) can fail to combust as quenched in the crevices and when released has missed the main (fast) combustion so misses the cut and appears in the exhaust as UBHC. At higher levels of air utilisation HCCI creates NOx.

HCCI has (IMO) been put on a pedestal as the unobtainable holy grail with one single virtue. All it can do now is fall from that pedestal.