2 stroke thread (with occasional F1 relevance!)

[J.A.W.]

.......More likely, it is as an anti-detonant injection method utilizing the latent heat ( absent in DI) , for hard running, at WOT.
( & that is something BMW did for its DI aero-engines, 70+ years ago, by injecting extra av-gas into the supercharger eye).

extra fuel upstream of the supercharger (like MW/ADI fluid) is a 'free' charge cooler......
reducing compression work (supercharger power consumption per massflow) and charge temperature (and engine temperature overall)
though when were BMW doing this without either MW or GM (nitrous) kits that anyway required more fuel ?
most of the numerous non-compound Wright R-3350s used ADI and fuelling upstream of the supercharger and had none of the compound's DI

the benefits are far less in an NA engine, as here today

the time element may act against DI, the fuel needs some 'charge preparation' time to evaporate enough for rapid and full combustion
so PFI may be necessary at the high rpm needed for full power

though PFI displaces charge by evaporation volume of fuel etc and DI (after valve closure) does not

Bear in mind that such 2T mills are running resonance-wise at WOT max-output states, whereby the pulse tuning
means that fuel is shot back into the combustion chamber from the exhaust port.

As noted by KC in the linked article such crankcase breathing 2Ts run best & hardest at quite low temperatures, ( ~50`C)
so that charge cooling is considered to be worthwhile.

As a matter of interest, I have a ~45 year old set of Kawasaki factory graphs for their very basic H2 piston port 2T triple,
- one of which shows specific fuel consumption in grams/hp/hour.
It gives its best efficiency of ~300 gm/hp/hr @ peak power,( ~7,000 rpm), when its simple tuning parameters chime together,
for a modest ~100hp/ltr.


As regards the BMW , it was for wartime emergency hard running, introduced on FW 190 fighter-bombers of the type
that were making 'tip & run' attacks over the English Channel, & which were liable to being 'coursed' by the even harder
running Napier Sabre powered Typhoon interceptors at nought feet over the sea.

The BMW required C3 ( German 'hi-test') petrol, so any extra shot into the supercharger eye, was available from main supply.
& it was the German V12s using lesser grade B4 fuel, which used MW 50 as emergency boost ADI, from a discreet tank.

[J.A.W.]

@ Manolis, have you seen this ? http://www.greencarcongress.com/2016/08 ... tribo.html

This may obviate some of the durability concerns of 2Ts having port windows cut through the cylinder wall,
& if it means total loss lubricant oil consumption can also be reduced, then HC emissions are likewise lower.

[Brian Coat]

TWO STROKE PFI+DI INJECTION

I finally got my head around the fact that the main reason they need DI is to deal with emissions in the presence of the very high residuals and short circuit at low speed and light loads.

To pass emissions, this requires very late, very precise injection to run some sort of stratified combustion and prevent short circuit.

The load points in the 5-Mode Snowmobile emissions test are 59% weighted to <1/3 load, so this is important, I guess.

But you look at the 2T DIs without a secondary injector, they still run homogeneous early injection at higher speeds and loads, for reasons of fuel flow amount (pulse width) and homogeneous charge prep.

A similar DI set up is on this unit from Evinrude - same owners as Rotax, who power Skidoo.

http://publications.lib.chalmers.se/rec ... 149154.pdf

The high fuel flow homogeneous mode is just giving the DI injector designer more headaches in terms of low flow precision at the bottom end.

Injector precision is important enough for them to use fancy voice coil injectors anyway, so they must be up against it.

So why not let a PFI injector handle most of the high speed / high load homogeneous fuel flow and have a more precise DI injector to enable better emissions.

It is no better / worse than a PFI 2T for high duty emissions but then nor is early injection homogeneous DI any better.

PFI does also offer the potential for high duty lubrication benefits. I noticed AC use a special piston window to allow the PFI injector to lubricate the big end. Not sure what Rotax do here.

These engines still have HC emissions far worse than their 4T counterparts and it may only be a matter of time before they follow the same path as the dirt bikes?

[J.A.W.]

As you know B-C, 'emissions' regs are as much a political call as technical, & its 'swings & roundabouts' as far as
which parameters are deemed worse, HC residues or noxious gasses, some of which - the 4T produces more of.

As for 'dirt bikes', here : http://www.ktm.com/enduro/300-exc-1/

This is the newly revised for 2017, dual-purpose/enduro 2T from KTM, which is road-compliant in many markets.

Note though, it is not yet using FI, even though KTM purchased Husqvarna a few years back - for its BMW
developed DFI 2T system - which Husqvarna had ready to market.

KTM are still sitting on this.: http://www.cycleworld.com/2012/08/13/tw ... surrection
It appears that KTM are holding back for marketing reasons, rather than technical, since their 4Ts are FI equipped.

[manolis]

Hello J.A.W.

Thanks for the DLC related link.
A DLC protection film created (by its own) between sliding surfaces (and automatically regenerated when damaged) would change many things, not only in the 2-stroke engines.


Regarding the KTM300exc 2017, which uses a carburetor:

How does it manage to comply with the emission standards?
I read it goes to the customer with “restrictions” in the exhaust and in the intake. Those restrictions are immediately removed by the customer / rider.

It sounds like a “cheap” trick to bypass regulations without dealing with, and solving, the real problem.

Do I miss something?

Thanks
Manolis Pattakos

[manolis]

Hello Brian Coat.

You write:
“So why not let a PFI injector handle most of the high speed / high load homogeneous fuel flow and have a more precise DI injector to enable better emissions.”

Two injectors are required per cylinder, the one inside the combustion chamber (DFI), the other outside (PFI).

The simplicity advantage and the low cost advantage of the two-stroke vanish.

And the emissions problem is not really solved.
It is more a way to comply with the current rules and regulations.

The article http://www.reuters.com/article/us-autos ... SKBN12E11K shows a similar “solution” (how to comply with the rules in the lab tests, being more (or way more) pollutant in practice, i.e. where it really matters).


The DFI is problematic at high revs. As in the Diesels, the fuel has not the required time to evaporate and get mixed with the air.

The PFI is problematic in the 2-strokes because a part of the fuel is lost unburned to the exhaust.


The PatATeco solves the problem of the PFI by not allowing fuel to exit from the cylinder before participating in a combustion.



From another viewpoint, the PatATeco operates as a directly injected two stroke, without the limitations of a DFI .
After the closing of the exhaust port, a quantity of prepared fuel-air mixture is “injected” into the cylinder (the asymmetric transfer port operates as a huge injector running at low pressure).
The final gust of air cleans the passageways.
With the closing of the asymmetric transfer port, the already prepared (when it was at the backside of the piston crown) rich fuel-air mixture is pushed into the cylinder wherein it has the time to mix with the existing air (this air was trapped into the cylinder with the closing of the exhaust port).

Thanks
Manolis Pattakos

[J.A.W.]

Hello J.A.W.

Thanks for the DLC related link.
A DLC protection film created (by its own) between sliding surfaces (and automatically regenerated when damaged) would change many things, not only in the 2-stroke engines.


Regarding the KTM300exc 2017, which uses a carburetor:

How does it manage to comply with the emission standards?
I read it goes to the customer with “restrictions” in the exhaust and in the intake. Those restrictions are immediately removed by the customer / rider.

It sounds like a “cheap” trick to bypass regulations without dealing with, and solving, the real problem.

Do I miss something?

Thanks

Manolis Pattakos

Yes Manolis,


To be sure the basic carb-tech is cheap, & is well understood, for tuning purposes.

Different markets have different rules, & esp' for such competition oriented machines..

& not many road-side cops have emissions control equipment on hand, so unless they have an established power vis a vis
'probable cause' to impound an otherwise lawful rider's machine on the stop, the best they can do is order a tech-inspection..

..by which time 'The cheap trick" parts can be re-installed to meet EPA norms..

& to be fair, even with injectors - "the two stoke advantage" does not "vanish", since with the advent
of powerful ECU & DI injector tech, if anything, it has clearly increased.. politics/marketing notwithstanding..

[Brian Coat]

Manolis: I understand and agree with the DI/DFI/Both pros and cons you list. I am not an advocate of this dual system, I was just trying to figure out the engine makers' rationale because a few of them use it.

Although it is an "costly emissions-test-focused" implementation of a 2T it still has power density benefits, which are important for the snowmobile.

Your mechanical proposal would have pros and cons vs. DI, of course. e.g. the effect of stratification vs homogeneous

Did you build and test one? If so, how were the HC emissions?

What do the main engine makers say about your concept?

[J.A.W.]

Manolis: I understand and agree with the DI/DFI/Both pros and cons you list. I am not an advocate of this dual system, I was just trying to figure out the engine makers' rationale because a few of them use it.

Although it is an "costly emissions-test-focused" implementation of a 2T it still has power density benefits, which are important for the snowmobile.

Your mechanical proposal would have pros and cons vs. DI, of course. e.g. the effect of stratification vs homogeneous

Did you build and test one? If so, how were the HC emissions?

What do the main engine makers say about your concept?

Not only "snowmobile" B-C, but any high-performance 'personal' machine, on land, air or water..

[FW17]

The DFI is problematic at high revs. As in the Diesels, the fuel has not the required time to evaporate and get mixed with the air.

Didn't orbital come out with the air assisted fuel injector to resolve this problem?

How does F1 engines manage to prepare the air fuel mixture in the short periods of time than a 2 stroke at high revs ?

[Tommy Cookers]

How does F1 engines manage to prepare the air fuel mixture in the short periods of time than a 2 stroke at high revs ?

my guess ....
because they inject at about 5 times the pressure that was allowed even in 18000 rpm NA F1
because they spent millions on designing and producing special fuel for this property (as well as other special properties)

[Brian Coat]

The DFI is problematic at high revs. As in the Diesels, the fuel has not the required time to evaporate and get mixed with the air.

Didn't orbital come out with the air assisted fuel injector to resolve this problem?

How does F1 engines manage to prepare the air fuel mixture in the short periods of time than a 2 stroke at high revs ?

I guess F1 uses very high fuel pressures coupled with injectors which are optimised for performance, with no regard to emissions regulations, idle quality ...

[J.A.W.]

The DFI is problematic at high revs. As in the Diesels, the fuel has not the required time to evaporate and get mixed with the air.

Didn't orbital come out with the air assisted fuel injector to resolve this problem?

How does F1 engines manage to prepare the air fuel mixture in the short periods of time than a 2 stroke at high revs ?

DI 2T makers use systems which differ greatly, & for example the E-TEC 'voice coil' injectors as used by BRP
(& noted in the research link kindly added above by B-C) are self pumping ( no high pressure rail) a feature
which BRP notes allows function in their 2T machines up to 10,000 rpm .

This would be equivalent to a 4T doing 20,000 rpm, which is of course well above the current F1 limit.

Other 2T DI makers use staged pumps for very high pressures ( Yamaha) or air blast method ( Orbital).

Now F1 V6 turbo-compound engines do run very high cylinder pressures, & while their DI is rules constrained by number , location & fuel delivery of injectors, they are obviously running a sophisticated set-up.


Even 60+ years ago mechanical DI systems were operating with the "peak delivery pressure of around 2,000 lb/sq/in",
as shown below.

http://www.flightglobal.com/pdfarchive/ ... 01631.html

[manolis]

Hello all.

At http://www.brp.com/sites/default/files/ ... ounder.pdf
it is a brief presentation of the various subsystems of the E-TEC technology of Rotax.
The fuel is injected at a pressure of 35 bar.


Brian Coat wrote:
“Did you build and test one? If so, how were the HC emissions?”

Not yet.
It is a “fresh” project based on the PatAT / PatATi (GB2,528,748 patent) for which an 800cc “proof of concept” Opposed Piston prototype:



has been made (youtube video: https://www.youtube.com/watch?v=aXvRaVqiHxs )



Brian Coat also wrote:
“What do the main engine makers say about your concept?”

Their standard policy is not to respond.
When you get the time try to ask them to see how it works (or rather: how it does not work).



FW17 wrote:
“Didn't orbital come out with the air assisted fuel injector to resolve this problem?”

Yes. Several years ago.
A few 50cc 2-stroke scooters were in production (Piaggio, Aprilia, Peugeot) around 2000.
Thousands of articles were written about the great advantages of the Orbital 2-strokes.
Several millions were invested.
The “Great Expectation” proved not so great in practice and the investors’ money were lost.



Stihl in their 2-stroke chainsaw (youtube video: https://www.youtube.com/watch?v=ycaWg8bz93o ) uses stratified charge:

“In the stratified charge system, a fuel-free cushion of air is inserted between the burnt charge in the combustion chamber and the fresh charge in the crankcase. This cushion reduces the fuel-ladden exhaust. The result: more performance with lower weight, up to 20% lower fuel consumption when compared to 2-stroke engines without 2-MIX Technology as well as significantly reduced exhaust emissions.”

The problem with the stratified charge is that the exhaust port closes several crankshaft degrees after the end of the transfer; the mixture in the cylinder has plenty of time to pass unburned to the exhaust.
No doubt, things are improved as compared to the conventional 2-strokes. But the problem is still not really solved.

Thanks
Manolis Pattakos

[Brian Coat]

Brian:
“What do the main engine makers say about your concept?”

Manolis:
"Their standard policy is not to respond.
When you get the time try to ask them to see how it works (or rather: how it does not work)."

In my experience, an engine maker will usually take notice of a credible and useful proposal presented in a professional manner, to the right person.