2 stroke thread (with occasional F1 relevance!)

[olefud]

i'm sorry but are ricardo out of there minds? do they seriouslt think an engine will evacuate exhaust gas when the piston is traveling downwards? the "concept" above is not only usless as far as actually being ablt to have two sets of differeing cam's but the bloody thing will be as efficiant as painting your house with a tooth brush!

Four-cycle engines need to have the power stoke pressure down to near ambient by BDC. The exhaust valve opens during the power stroke to allow blow down that avoids energy losses that would result from residual cylinder pressure during the exhaust stroke. At high RPMs the exhaust has to open rather early to accomplish this.

[Tommy Cookers]

conclusion is that there are "powers" thats wants 4 stroker..more than 2 stroker dispite the powergains for the trostroke engines..Sad but true!..

about 25 years ago the EU funded 2 stroke research (eg at Lotus) because the emission of NOx was inherently low with the 2 stroke (also with the RC/Wankel), so it would need only a 2-way catalyst

then we all went in 1992 to the 3-way catalyst (more expensive and less fuel-efficient) because certain European car makers who were heavy exporters to the USA and Japan had already standardised their whole production this way (by getting their governments to pay the extra cost to home-market buyers, against EU rules)

[321apex]

Old thread, but I will throw in my 3 cents.

Major auto manufacturers spent a lot of time and money in early 90's to explore the highly "modernized" version of a 2 stroke engine technology proposed by Orbital Corp. which come up with direct in-cylinder fuel/air injection and held several other key patents. In spite of the collective work across all continents, nothing commercial for passenger car use came off of it.

Basic problems could not be resolved, and they were:
- durability of pistons and rings due to piston port design feature
- inability to pass tightening, long term emissions - in US the OEM's had to warranty emissions for 100k miles
- fuel consumption - still inferior to 4 stroke due to inherent pumping losses

Since 2 stroke never made it into passenger cars, there really was no technical incentive to scrap the whole eco-system of industrial means and know-how already producing 4 stroke racing engines - forcing the money making Cosworths, Ilmors and others into strange technology with no valves. Del West a major US company in racing would have lost significant part of their sales volume.

[Foyle]

2-stroke F1 would actually make a huge amount of sense now.

The game changer is 500bar gasoline direct injection pressures now available (as used on current F1 engines). That means that high speed DI 2-stroke can have efficiency comparable to 4-strokes as they no longer blow un-burnt fuel through the exhaust. (In my previous engine development job I've seen DI 2-strokes that had higher efficiency than competing 4-strokes)

A 1.5-2L 2-stoke V6 with DI and 15000rpm max speed would sound awesome - more like the old 3L V10's while costing probably only 20-30% of even the old 2.4 V8's. It would also cut their size and weight dramatically with hugely reduced complexity and component count. Not to mention elimination of lots of external systems.

Could likely be made even cheaper and maybe more efficient/cleaner by mandating a specified roots or fixed ratio belt driven centrifugal scavenging supercharger + intercooler rather than crankcase scavenging to allow better scavenging, higher compression ratios and reduced need for tricksy lubrication and air flow solutions in the crankcase and reed valves etc.

Emissions would be no worse than 2.4L V8's. Efficiency could be made much higher if capacity was not limited, but rather fuel-flow restricted (say max fuel flow at 13000-15000rpm).

The engine designs would be simple enough that we wouldn't need the participation of big auto companies as development is orders of magnitude cheaper than with high speed 4-stroke valve trains. They would be cheap and easy to rebuild, and would greatly reduce necessary head count both at races and at home bases. Eliminating arguments for long life engines.

All in all it would be hugely beneficial to getting F1 costs down, and simplifying the cars, while taking us back to the much loved high frequency exhaust noise.

The same arguments applies to other forms of motorsport. DI 2-stroke should be the standard for high performance and low cost with good efficiency. It also has more relevance to a world that wants hybrids and range-extenders.

[Abarth]

[....]DI 2-stroke should be the standard for high performance and low cost with good efficiency. It also has more relevance to a world that wants hybrids and range-extenders.

Very good post foyle!

Yes DI 2 Strokes would have been really an interesting way to go. DI and forced scavenging are the (in these times easy) tools to avoid burning oil and outputting unburnt fuel.
One power cycle per cylinder and rev leads to lower rpm at comparable power, and there is no need for the valve train. Both will result in better mechanical efficiency.

Also for a small range extender, with a more or less stationary operating point (constant rpm and max load) a 2 Stroke DI makes much more sense than the Audi approach with a wankel, which is inherently inefficient due to huge surface heat losses.

THAT would have been really a step forward in many aspects, not the least being costs.

[tok-tokkie]

Your post, Foyle, makes me wonder if 500 bar DI will not have the consequence of exactly the type of engine you suggest being developed for regular commercial use anyway. The huge reduction in complexity, mass & bulk and cost will surely entice engine manufacturers to develop them. But what about laws banning 2-strokes because of pollution rather than the pollution itself - does this not make any 2-stroke (no matter how clean) illegal?
I know Evinrude did a direct injection 2-stroke outboard motor some years ago.

[Tommy Cookers]

there were 2 stroke DI cars in the 40s/50s (Gutbrod & Lloyd) and DI 4 stroke cars
the Ford Ka was designed for a supercharged DI 2 stroke (that's why it went to the old pushrod engine, the engine bay was so small)

500 bar is presumably about enabing super high CR in boosted road and race engines by super-late injection
but DI accesses the benefit to 2 stroke pollution without needing anywhere near 500 bar ?
some 2 stroke scooters (and outboards as the previous post) still currently use DI ?? (at lower pressures)

[Abarth]

I recall the company Orbital which did quite some work in the field of DI 2 Stroke, anyone recalls the "Orbital Engine"?
Here are many papers available:
http://www.orbeng.com.au/technical-publications.html

[Foyle]

Orbital do low pressure compressed air based fuel injection. They present an easy low-tech solution that is not bad, but ultimately not the same level of efficiency as is possible as with as high pressure DI gasoline.

High pressure DI permits higher compression ratios, cooling of charge due to evaporation, and multiple injections to create stratified charge (areas of increased richness in the combustion space to allow easy ignition of an overall lean mixture)

Until recently I worked in car IC Engine development (principally high performance turbos). Gasoline emissions regulations have not gone beyond the point of delivering additional health or environmental benefits to the world a decade ago, and their increasing stringency now is purely a political sop for the green vote, as well as serving as a massive barrier to entry to prevent any new competition for existing car makers (which they are only too pleased about). Emissions related equip on car engines now amounts to as much as 30% of the engine cost. That said diesel particulates are probably the one area that is worth regulating more carefully.

Emission regs basically prevent operation at anything other than stoichiometric (not rich not lean) for gasoline - which automatically increases fuel consumption above the more efficient lean burn solutions in order to keep the 3-way catalysts working to eliminate NOx. But the impact on the world is that we are burning far more gasoline than we need to if we were a bit more sensible about prioritising efficiency over ridiculously low levels of emissions.

It is very difficult to operate a 2-stroke at stoichiometric conditions owing to nature of loop-scavenging. Will always be some excess air, or slightly rich or lean exhaust due to imperfect mixing - and 3-way cats can't handle that unless you have a big plenum to allow exhaust to mix an homogenise before the cat. So 2-strokes won't be making a mass market comeback, except possibly in diesels that operate at much lower temps with far less NOx formation.

Car makers are very happy to make extremely complex engines when regulations prevent simpler solutions from undercutting them.

[Tommy Cookers]

Orbital do low pressure compressed air based fuel injection. They present an easy low-tech solution that is not bad, but ultimately not the same level of efficiency as is possible as with as high pressure DI gasoline.

High pressure DI permits higher compression ratios, cooling of charge due to evaporation, and multiple injections to create stratified charge (areas of increased richness in the combustion space to allow easy ignition of an overall lean mixture)

Until recently I worked in car IC Engine development (principally high performance turbos). Gasoline emissions regulations have not gone beyond the point of delivering additional health or environmental benefits to the world a decade ago, and their increasing stringency now is purely a political sop for the green vote, as well as serving as a massive barrier to entry to prevent any new competition for existing car makers (which they are only too pleased about). Emissions related equip on car engines now amounts to as much as 30% of the engine cost. That said diesel particulates are probably the one area that is worth regulating more carefully.

Emission regs basically prevent operation at anything other than stoichiometric (not rich not lean) for gasoline - which automatically increases fuel consumption above the more efficient lean burn solutions in order to keep the 3-way catalysts working to eliminate NOx. But the impact on the world is that we are burning far more gasoline than we need to if we were a bit more sensible about prioritising efficiency over ridiculously low levels of emissions.

It is very difficult to operate a 2-stroke at stoichiometric conditions owing to nature of loop-scavenging. Will always be some excess air, or slightly rich or lean exhaust due to imperfect mixing - and 3-way cats can't handle that unless you have a big plenum to allow exhaust to mix an homogenise before the cat. So 2-strokes won't be making a mass market comeback, except possibly in diesels that operate at much lower temps with far less NOx formation.

Car makers are very happy to make extremely complex engines when regulations prevent simpler solutions from undercutting them.

Your every word is a gem, Sir !!

regarding F1 2 stroke potential
4s NA gained hugely from very high bore:stroke ratios (in relative valve/port area, helped by throttle maps and slick gearboxes)
2 strokes cannot use high b:s ratios, they run out of port area as the port height decreases with stroke

[FW17]

F1 regulations are quiet restrictive but are AOC rules permit for a 2 stroke in LMP1?

If there were benefits to it i am sure atleast a garage 56 entry with 2 stoke would have been tried

Then again with costs so high in lower categories, a 2 stroke engine might be a good idea ensure greater competition

[Foyle]

Yamaha make high pressure direct injected 2-strokes for outboard motors. They get a somewhat bad reliability rep entirely due to issues with fuel quality (and high pressure injectors + pumps need clean fuel to survive).
http://www.yamahaoutboards.com/outboard ... ifications

Emissions and efficiency wise they are apparently great. But still only 45 bar injection pressure compared to 500bar of F1 and 120-200bar frequently used in GDI road cars.

Bombadier makes all sorts of low pressure DI 2-strokes.

There is enough anger/frustration amongst motocross and motorbike racers over high overhaul costs of 4-strokes to perhaps eventually get 2-strokes back - most likely would be with DI. Or might see it adopted in Karting to improve emissions. That would provide probably the only realistic means for ever getting 2-strokes back into motorsport, but if it did happen then as benefits were more widely seen it would give at least a possiblity of extending to other classes.

[Abarth]

Yes 2 Stroke has problems in maintaining Lambda = 1 for proper three way catalyst function. OTOH, this issue can be overcome with lean operation and "storage catalysts" which store NOx, as they are already used.

But I see much more potential in a stationery operation at full load, constant rpm, in a rage extender use.
In a road car, charging constantly the batteries with say 40kW in an optimized operating point will yield a very good over all efficiency.

What is the mean power in todays F1 over a lap?

[Foyle]

What is the mean power in todays F1 over a lap?

100kg fuel in 100 minutes. 17grams per second. for 44MJ/kg fuel and 35% efficiency that is 260kW (345hp) average.

[langwadt]

Yes 2 Stroke has problems in maintaining Lambda = 1 for proper three way catalyst function. OTOH, this issue can be overcome with lean operation and "storage catalysts" which store NOx, as they are already used.

But I see much more potential in a stationery operation at full load, constant rpm, in a rage extender use.
In a road car, charging constantly the batteries with say 40kW in an optimized operating point will yield a very good over all efficiency.

40kW is high, you can probably maintain highway speeds in a standard car with half that