2 stroke thread (with occasional F1 relevance!)

[Pinger]

Hello J.A.W.

With the direct injection of the BRP / Rotax spark ignition 2-strokes rated up to 10.000rpm, a reasonable question is whether (and how efficiently) the air fuel mixing and the combustion can really cope with such rhythms.

Mixing is easy, atomisation less so. Mixture passing through a hot crankcase cannot not atomise!

Hello Pinger.

To heat the fuel before the injection (for the sake of atomization) doesn’t sound as a problem (there is a red-hot exhaust that can “cook”, for “free”, anything).

Now meter the vapour....

The real question is:

Why didn’t they put, so far, one of their 2-stroke engines (say, the Evinrude E-TEC 250 G2 HO) in a car to pass all tests (emissions, fuel efficiency, durability, etc) and prove its superiority at all conditions?

Different horse for a different course.

[J.A.W.]

But, atomisation was what held DI back as back in the 1980s when first tried using mechanical injector pumps the required (small) droplet size was unobtainable. Sophisticated injectors amplifying the pressure and/or air blast is what made DI possible.
Still it is hampered by short available injection time at high loads (if charge loss to the exhaust port is to be avoided) and the technology is complex - relative to IDI or carbs.

Actually P, mechanical DI featured in all standard use, big capacity Nazi-era German 4T aero-engines..

The problem for small 2Ts was of course - speed.. the injection event had to keep time with every piston upstroke..
..& the fraction when the piston had closed off the exhaust port .. we had to wait for 'Moore's law' - to facilitate that..

[manolis]

Hello J.A.W.

I asked again and again the same thing:


“Why didn’t they put, so far, one of their 2-stroke engines (say, the Evinrude E-TEC 250 G2 HO) in a car to pass all tests (emissions, fuel efficiency, durability, etc) and prove its superiority at all conditions?”


because the answers don’t seem really convincing.


It will cost them almost nothing (the engines are already in production).

Even if they fear to risk their “good name”, they could create another brand dealing with the opportunities of the 2-strokes in the cars / motorcycles (say like: “under the license of BRP / Evinrude”)..


To leave unexploited such a huge opportunity (2-stroke car engines) is not justified by the “risk”.


Thanks
Manolis Pattakos

[J.A.W.]

Mixing is easy, atomisation less so. Mixture passing through a hot crankcase cannot not atomise!
Now meter the vapour....

You have this all wrong P..
In fact, DI 2Ts suffer from lack of lost 'latent heat of evaporation' previously utilized by through crankcase fuelling..
..& must have added coolant compensation via specific crankcase coolant galleries..

The always hot 2T piston serves as evaporation heat source in DI 2Ts.. albeit the hard-run performance sleds now
use an auxiliary TBI supplement for WFO use, when the calibrated delivery capacity of the DI system - is exceeded..

[J.A.W.]

Hello J.A.W.

I asked again and again the same thing:


“Why didn’t they put, so far, one of their 2-stroke engines (say, the Evinrude E-TEC 250 G2 HO) in a car to pass all tests (emissions, fuel efficiency, durability, etc) and prove its superiority at all conditions?”


because the answers don’t seem really convincing.


It will cost them almost nothing (the engines are already in production).

Even if they fear to risk their “good name”, they could create another brand dealing with the opportunities of the 2-strokes in the cars / motorcycles (say like: “under the license of BRP / Evinrude”)..


To leave unexploited such a huge opportunity (2-stroke car engines) is not justified by the “risk”.


Thanks
Manolis Pattakos

Sadly Manolis, I think you fail to comprehend the actual, & very 'Machiavellian' way - the 'market' is operated..
Rational considerations as you & I see.. are deemed 'noisy outliers' - & I've even had Kevin Cameron confirm this..

[Pinger]

Manolis: Orbital did exactly what you are proposing Evinrude should. The results were good, the acceptance not.
Small Fords fitted with Orbital's triple were even trialled by a UK police force and while they enjoyed the performance they disliked some aspects - the size of the tail pipe IIRC was one of their (petty) concerns.
Then there was Jaguar's dalliance with the V6 (that I'm still keen to hear more of) that went nowhere and proved nothing other than the veracity of the maxim which states 'the 4T guy will screw up the 2T'.

[Pinger]

You have this all wrong P..
In fact, DI 2Ts suffer from lack of lost 'latent heat of evaporation' previously utilized by through crankcase fuelling..
..& must have added coolant compensation via specific crankcase coolant galleries..

The other side of the same coin.
The cooling effect to the crankcase from the fuel passing through it is exactly what atomised the fuel thoroughly. It is well known that final fuel atomisation in a 4T is courtesy of the heat from the piston crown. But just look how long there is available for that - induction and compression strokes combined. DI in a 2T to avoid charge loss is post exhaust port closure and before spark. A mere fraction even at the same rpm. You already have proved this by mentioning how course atomisation could be made to work in WW2 4Ts - when the same kit on a 2T could not. (Solenoids developed for ABS were the first step in changing this - see Chrysler's mid 1980's 2T development programme).

The always hot 2T piston serves as evaporation heat source in DI 2Ts.. albeit the hard-run performance sleds now
use an auxiliary TBI supplement for WFO use, when the calibrated delivery capacity of the DI system - is exceeded..

Two things at play there I suspect.
At full load the choice is to directly inject before exhaust port closure to get all the fuel into the cylinder and accept some charge loss, or acknowledging charge will be lost by doing so, employ less direct fuelling and enjoy the cooling and atomistaion benefits. A good strategy but more complicated to execute.

[J.A.W.]

You have this all wrong P..
In fact, DI 2Ts suffer from lack of lost 'latent heat of evaporation' previously utilized by through crankcase fuelling..
..& must have added coolant compensation via specific crankcase coolant galleries..

The other side of the same coin.
The cooling effect to the crankcase from the fuel passing through it is exactly what atomised the fuel thoroughly. It is well known that final fuel atomisation in a 4T is courtesy of the heat from the piston crown. But just look how long there is available for that - induction and compression strokes combined. DI in a 2T to avoid charge loss is post exhaust port closure and before spark. A mere fraction even at the same rpm. You already have proved this by mentioning how course atomisation could be made to work in WW2 4Ts - when the same kit on a 2T could not. (Solenoids developed for ABS were the first step in changing this - see Chrysler's mid 1980's 2T development programme).

The always hot 2T piston serves as evaporation heat source in DI 2Ts.. albeit the hard-run performance sleds now
use an auxiliary TBI supplement for WFO use, when the calibrated delivery capacity of the DI system - is exceeded..

Two things at play there I suspect.
At full load the choice is to directly inject before exhaust port closure to get all the fuel into the cylinder and accept some charge loss, or acknowledging charge will be lost by doing so, employ less direct fuelling and enjoy the cooling and atomistaion benefits. A good strategy but more complicated to execute.

Not quite P, those WW2 aero-engines were huge - for SI, & were usually employed in hot-boost, steady rpm operation..
& since crankcase 2Ts make best power at ~50`C, that cooling fuel charge is needed when sudden WFO operation
is demanded for hard running , esp' since the regular operation is lean & on the proverbial 'sniff of an oily rag', lube-wise..

[Pinger]

Not quite P, those WW2 aero-engines were huge - for SI, & were usually employed in hot-boost, steady rpm operation..

As in any 4T, the fuel can (and will) be administered as soon as the exhaust stroke has finished. Ample time and heat there for atomisation.

& since crankcase 2Ts make best power at ~50`C, that cooling fuel charge is needed when sudden WFO operation
is demanded for hard running , esp' since the regular operation is lean & on the proverbial 'sniff of an oily rag', lube-wise..

Not entirely true. The small(ish) units for sleds etc running to high rpm may well employ additional to DI fuelling measures but larger (eg, OBs, Orbital's auto angine, etc) rely on DI alone - no matter the load. Their fuel efficiency does suffer as a consequence at full load though. They may well employ a degree of cooling to the CC provided by the main cooling system (though I've never heard directly of it) but they are content to dispense with any fuel cooling of the CC. (They will, of course, be running a metered oiling system).

I query ''regular operation is lean'' - on the basis that (short of employing the pumping capability of expansion chambers - and when they are used, high specific output being the aim and hence no tendency toward lean is acceptable) as 2T pumping losses increase with air requirement, there is no justification to go lean. Compression at any load will commence with a full quota of gas (unlike the 4T) even if exhaust products are less thermodynamically ideal than air.

[J.A.W.]

Not quite P, those WW2 aero-engines were huge - for SI, & were usually employed in hot-boost, steady rpm operation..

As in any 4T, the fuel can (and will) be administered as soon as the exhaust stroke has finished. Ample time and heat there for atomisation.

& since crankcase 2Ts make best power at ~50`C, that cooling fuel charge is needed when sudden WFO operation
is demanded for hard running , esp' since the regular operation is lean & on the proverbial 'sniff of an oily rag', lube-wise..

Not entirely true. The small(ish) units for sleds etc running to high rpm may well employ additional to DI fuelling measures but larger (eg, OBs, Orbital's auto angine, etc) rely on DI alone - no matter the load. Their fuel efficiency does suffer as a consequence at full load though. They may well employ a degree of cooling to the CC provided by the main cooling system (though I've never heard directly of it) but they are content to dispense with any fuel cooling of the CC. (They will, of course, be running a metered oiling system).

I query ''regular operation is lean'' - on the basis that (short of employing the pumping capability of expansion chambers - and when they are used, high specific output being the aim and hence no tendency toward lean is acceptable) as 2T pumping losses increase with air requirement, there is no justification to go lean. Compression at any load will commence with a full quota of gas (unlike the 4T) even if exhaust products are less thermodynamically ideal than air.

No P, if it wasn't needful, BRP/Rotax would not have performed the sled mill redesign with its extra complexity..

& FYI, the BMW 801 used in the wartime FW 190 also utilized just such an extra injector for hard running as ADI..
..aimed direct into the supercharger inlet eye..

Those E-TEC Ski-Doo's are hi-po mills & do use an expansion chamber exhaust system.. & the lean condition is an
eco-cruise deal, for fuel/emissions advantage.. & instant response - hard running, has different requirements..

Marine engines are more likely to be run on steady settings - for high torque - as aero-engines are..

&,

Back to the Orbital 2T car engine trials.. the major G.M. 'marketing' objection was due to the potential/proposed buyer being focussed on an 'econobox' & probably of 'aged/female' demographic & they would be 'unnerved' by the
standard 2T 'sporty' - quick - 'throttle response', 'torque hit', & lack of engine braking..
(After all, if so many 'bikers' are put off 2Ts for these reasons, what chance does an 'old duck'stand?)

..Never-the less - they're all aspects - which would today - be tamed in cars by CVT & regenerative braking..

[Pinger]

& FYI, the BMW 801 used in the wartime FW 190 also utilized just such an extra injector for hard running as ADI..
..aimed direct into the supercharger inlet eye..

Fuel cooling for 4Ts is as old as the 4T is. Americans for decades supplied large main jets rather than radiator capacity. Well, the jets were a fraction of the brass needed for rads... (Perhaps they should have saved the brass from the larger hole in the jet...)

No P, if it wasn't needful, BRP/Rotax would not have performed the sled mill redesign with its extra complexity..

Those E-TEC Ski-Doo's are hi-po mills & do use an expansion chamber exhaust system.. & the lean condition is an
eco-cruise deal, for fuel/emissions advantage.. & instant response - hard running, has different requirements..

Lean, in that context means stratified charge by DI I think. Which, incidentally, pretty much requires an indentation pocket in the piston crown - just the sort of heat absorbing additional area that cross flow pistons are castigated for! That, may have been a factor which pushed them back toward fuel cooling the CC.

Marine engines are more likely to be run on steady settings - for high torque - as aero-engines are..
&,

Low down torque for the 'hole shot' then throttled back high rpm - for the rest of the day is their thing I think. Bogging them is what kills them - so yes, different operational conditions.

Back to the Orbital 2T car engine trials.. the major G.M. 'marketing' objection was due to the potential/proposed buyer being focussed on an 'econobox' & probably of 'aged/female' demographic & they would be 'unnerved' by the
standard 2T 'sporty' - quick - 'throttle response', 'torque hit', & lack of engine braking..
(After all, if so many 'bikers' are put off 2Ts for these reasons, what chance does an 'old duck'stand?)

..Never-the less - they're all aspects - which would today - be tamed in cars by CVT & regenerative braking..

Yep - ironically - the 'sportiness' was an objection! And yes, entirely tameable.
Lack of engine braking I never minded on a 2T bike. What bikers appreciate in their early days is a broad torque range so that they know the engine will pick up when they give it gas at the corner apex. A peaky 2T can be difficult in that regard. They don't have to be peaky though.

Anyone with any info on the Jaguar/Thornhill(?) V6?
One snippet I heard was that Jaguar thought it needed EGR so plumbed some in from downstream in the exhaust system... Maybe it's better I don't find out anymore.

[J.A.W.]

No, P, got nothing on the Jag 2T.. but I'd suspect that like the other major car makers, they were trying to make
a silk purse (pukka 2T) out of a sow's ear ( great lump of a poor breathing ex-4T), & failed..

Again I think you've gone skew-if on the marine usage, the 'punchy' 2T torque hit to get 'up on the plane' - is useful,
of course, but the relentless wet-hull drag - even when 'out of the hole' - requires that big 2T mid-rpm torque-rise too..

What is the biggest capacity 2T bike you've taken for a ride P?
See if you can blag a ride on a well tuned 750 Kawasaki.. I've got a road-legal 750/3 in an RDLC Yamaha chassis..
..& its FUN.. big/light enough to hack it - if you want to be lazy & leave it in top gear, & if you want to ZAP!.. downshift..

[manolis]

Hello Pinger.

You write:
“Orbital did exactly what you are proposing Evinrude should. The results were good, the acceptance not.”


At

http://www.4x4brasil.com.br/forum/attac ... ngines.pdf

(“A High Mileage Extended Duration Fleet Trial of Orbital's Direct . . .”)

is available the presentation of Orbital, at Engine Expo 1999 Hamburg Germany, wherein they give some results (field measurements) for a fleet of small cars equipped with 2-stroke Orbital direct injection engines.



According the above plot of Orbital, the average fuel consumption was 7.2l/100Km, while the average lubricant consumption was 5.3l/10,000Km (i.e. 0.053l/100Km).

This means a 136:1 fuel/oil ratio, which is better relative to the conventional 2-strokes, but not really good.

The step piston of Hooper was better with 200:1 fuel/oil ratio.

The Achates Power side-camshaft Opposed Piston is even better (at least 440:1 fuel/air ratio (565:1 average fuel/oil ratio) according their data).


The real problem is not the oil itself, but the spoiling of the combustion it causes (more at http://www.pattakon.com/tempman/Lubrica ... Diesel.pdf )


Worth to mention:
While in the 2-strokes the lubricant is lost (air pollution), in the good 4-stroke the used lubricant can be recycled and used again.

On the other hand, with a more than 300:1 fuel/oil ratio, a 2-stroke can play strongly the 4-strokes.

Thanks
Manolis Pattakos

[Pinger]

No, P, got nothing on the Jag 2T.. but I'd suspect that like the other major car makers, they were trying to make
a silk purse (pukka 2T) out of a sow's ear ( great lump of a poor breathing ex-4T), & failed..

Everything I've heard suggests they just did not understand what they had.

Again I think you've gone skew-if on the marine usage, the 'punchy' 2T torque hit to get 'up on the plane' - is useful,
of course, but the relentless wet-hull drag - even when 'out of the hole' - requires that big 2T mid-rpm torque-rise too..

Seems that they have a quite flat torque curve across half their rpm range placed smack in the middle and above that (rpm wise) the power curve flattens. Suggesting plenty 'back-up' torque if the rpm drops back. Are they restricted carb size wise to reduce delivery ratio and give better fuel economy at high rpm cruise? Exhaust tuning appears to suggest plugging pulses occur in the mid range rpm and suction pulses arrive very early (though that could be a consequence of the available length in the leg).

What is the biggest capacity 2T bike you've taken for a ride P?
See if you can blag a ride on a well tuned 750 Kawasaki.. I've got a road-legal 750/3 in an RDLC Yamaha chassis..
..& its FUN.. big/light enough to hack it - if you want to be lazy & leave it in top gear, & if you want to ZAP!.. downshift..

Nothing bigger than a 250 (that I can remember) but they have ranged from the torquiest trials motors to the peakiest of road going - the Mk1 RG250. My mate's later (Stan Stephen's tweaked) RGV250 was a revelation next to it.
Your 750 RDLC sounds a proper blast. Alas, here in the UK all the early 80's Japanese stuff has been bought up by those whose mortgages are paid and are reliving their youth - though what exactly is youthful about parking a bike in a garage as an ornament escapes me. Ho hum..
There is a KTM 500 in my shed - but alas, nowhere to run it. A proper torquefest that one!

[Pinger]

This means a 136:1 fuel/oil ratio, which is better relative to the conventional 2-strokes, but not really good.




The real problem is not the oil itself, but the spoiling of the combustion it causes (more at http://www.pattakon.com/tempman/Lubrica ... Diesel.pdf )

There is more that can be done. Why, for example run main bearings in the crankcase when they can be placed outside, sealed from the CC, and fed oil which can be reused?

More freedom with 2T re combustion chamber shape to mitigate against any loss in octane due to oil involved in combustion.
And the oil used (the cause of particulates) in the diesel study was never formulated with a view to being burned.

Incidentally, when the big clampdown on 2T outboards occurred... it was then that they found that all the trucks using auto greasing systems on their chassis were contributing to water way pollution. The expelled grease had to go somewhere - and washed down the drains it ended up in rivers etc.