This months Bike magazine

<div class='quotetop'>QUOTE (BarryMachine @ Feb 12 2008, 12:09 AM) <{POST_SNAPBACK}><div class='quotemain'>oh dear now you are even going against what the designers and users of DI are saying!!

it may be "exact amounts" but the fact is the "Exact amounts" for highest power, out of say a gp two stroke, is occuring when all the previous burned gases are gone and the combustion chamber is full of air/fuel at the optimum mix ratio. This only ever is nearly approached when some of the new charge goes out the exhaust port .... therefore s wasted .... even on a DI engine.
Ah, you have some mis-understandings where DI is concerned.

Hopefully this picture will help.
2792:2_stroke.jpg]

As you can see, in a conventional 2-stroke engine, the combustion products from the previous cycle are forced from the cylinder with a new air/fuel charge. This charge is compressed in the crankcase by the underside of the piston and then enters the cylinder when the piston uncovers the transfer port. Unfortunately, the exhaust port is open during the entire time that the transfer port is open – allowing part of the air/fuel mixture to “short circuit” through the cylinder during the scavenging process.

In a DI 2-stroke engine, the fuel is injected into the cylinder late in the cycle, as the piston is returning. This means that the exhaust port is covered and the air is already being compressed. The time available for vaporization and mixing is short, so the fuel must be atomized into very fine droplets to allow the fuel to vaporize for combustion.

Crankcase-scavenged two-stroke cycle engines use a waste lubrication system. Some of the oil is deposited on the appropriate components (crank bearings, rod bearings, cylinder walls) while the mixture is in the crankcase. The remaining oil then travels with the air/fuel mixture into the cylinder where it is either short-circuited or trapped in the cylinder. The short-circuited oil contributes to the emissions, mostly as smoke.

Direct-injected two-stroke engines still use a waste lubrication system. However, since
the oil is not dissolved in the fuel, it deposits more effectively on the walls and bearings where it is needed. This reduces the oil migration into the combustion chamber, which dramatically minimizes the smoke caused by combustion of the lubricating oil.

<div class='quotetop'>QUOTE (Babelfish @ Feb 12 2008, 11:35 AM) <{POST_SNAPBACK}><div class='quotemain'>What make these things work now and not then is the different materials, alloys, CAD and machining presition. This enable low cost, durable solutions to things invented almost a century ago.
10 years ago Honda said they were at the limit of possible bore (> 100mm) for a high reving engine with the VTR. Today Ducati run a 1200 with almot 10 mm wider bore with the max hp 1300rpm higher. (street version)
That is made possible by improvements in the injection, inlet channels and combustion chamber.
FYI, big bore engines have a similar problem with compete combustion because of the large area the fuel has to spread over in a short time and lack of fuel on the edges means burnt pistons and piston rings.

Hmmm ..... You know I was going to "poo poo" this but then you got me wondering ok yes I can't see them making valve trains work twice as fast ... but who knows maybe they will .... then when they apply some of the valved ship engine 2 stroke technology to smaller engines then we could see them comepete on efficiecy.


<div class='quotetop'>QUOTE (Babelfish @ Feb 12 2008, 11:35 AM) <{POST_SNAPBACK}><div class='quotemain'>You have earlier suggested that 4-strokes are close to completly developed, electonics are they only part that have any real potential left. The above is just a small part of how very untrue this is. The problem with the 2 stroke is not that it has reached it's end of development but that very few are willing to invest in that development.


Yes but Mat oxley was selling DI as a cure, a burning method cure, they've been tried and are used where fit ..... none suit a motogp engine ...... anyhow these things of which you speak are not DI.


I'm glad you brought up the electronics ...... are you getting a sense that without exploring what electronics can do, and using what is found ... future development will be limited?

<div class='quotetop'>QUOTE (yamaka46 @ Feb 12 2008, 11:47 AM) <{POST_SNAPBACK}><div class='quotemain'>Ah, you have some mis-understandings where DI is concerned.

Hopefully this picture will help.
2792:2_stroke.jpg]

As you can see, in a conventional 2-stroke engine, the combustion products from the previous cycle are forced from the cylinder with a new air/fuel charge. This charge is compressed in the crankcase by the underside of the piston and then enters the cylinder when the piston uncovers the transfer port. Unfortunately, the exhaust port is open during the entire time that the transfer port is open – allowing part of the air/fuel mixture to “short circuit” through the cylinder during the scavenging process.

In a DI 2-stroke engine, the fuel is injected into the cylinder late in the cycle, as the piston is returning. This means that the exhaust port is covered and the air is already being compressed. The time available for vaporization and mixing is short, so the fuel must be atomized into very fine droplets to allow the fuel to vaporize for combustion.

Crankcase-scavenged two-stroke cycle engines use a waste lubrication system. Some of the oil is deposited on the appropriate components (crank bearings, rod bearings, cylinder walls) while the mixture is in the crankcase. The remaining oil then travels with the air/fuel mixture into the cylinder where it is either short-circuited or trapped in the cylinder. The short-circuited oil contributes to the emissions, mostly as smoke.

Direct-injected two-stroke engines still use a waste lubrication system. However, since
the oil is not dissolved in the fuel, it deposits more effectively on the walls and bearings where it is needed. This reduces the oil migration into the combustion chamber, which dramatically minimizes the smoke caused by combustion of the lubricating oil.

I have absolutely no misunderstandings on what DI does.... I know you do now after posting that picture .....

Thats all still in the realms of a "plonker engine", surely you can see the difference when operating at the sort of charge flows of a GP 2 stroke?. These aren't "lawnmowers", pehaps even turbine engine technology is the nearest thing

Here's a quick one ... go out and work out what it takes to build an expansion chamber .... there's a few little calc's there that from ememory fill you in on the gas flow and what can be manipulated.

<div class='quotetop'>QUOTE (BarryMachine @ Feb 12 2008, 01:54 AM) <{POST_SNAPBACK}><div class='quotemain'>Hmmm ..... You know I was going to "poo poo" this but then you got me wondering ok yes I can't see them making valve trains work twice as fast ... but who knows maybe they will .... then when they apply some of the valved ship engine 2 stroke technology to smaller engines then we could see them comepete on efficiecy.
Well, the valve train solution is your fixation, i'm not saying the solution will be valves, just that history has shown that what was nothing but a nice drawing and a good idea many years ago now is common property.
<div class='quotetop'>QUOTE <div class='quotemain'>Yes but Mat oxley was selling DI as a cure, a burning method cure, they've been tried and are used where fit ..... none suit a motogp engine ...... anyhow these things of which you speak are not DI.
No, but they are farily recent improvements that work now but didn't 10 to 40 years ago. Based on that, I'm not the one to rule out a solution for 2 stroke engines.
Excuse my ignorance but I thought they actually used DI in the new 125 aprilias in '07? Two or four of the aprilias were using a new engine and I thought that was DI. Surly not a 100% success, just ask Pasini (at a point last year I think he had 6 poles and no finishes), but non the less the fastest bike out there when it worked (for a lap or three)

<div class='quotetop'>QUOTE <div class='quotemain'>I'm glad you brought up the electronics ...... are you getting a sense that without exploring what electronics can do, and using what is found ... future development will be limited?

Well, limited yes, but then again there has allways been limits on the engine, why not on the electronics as well. Look at the cars where there has been limits for a long time and still electronics in consumer cars are exploding these days. There is no reason why the same shouldn't happen with motorbikes.
I'm not against electronics, hell I'm an electronics engineer, but I'm against devices that take over the control of the bike when the we come to racing. Control shuld be with the rider, not with "devices". That kind of thing suits the comuter not the racer.

<div class='quotetop'>QUOTE (BarryMachine @ Feb 12 2008, 12:42 AM) <{POST_SNAPBACK}><div class='quotemain'>But I assure you I loved two strokes, I stil have around 2o various 2 strokes in my garage at home .... but I do accept scientific reason.
Now there you had me thinking that you'd actually bother reading and understand my post (with pictures ) of why the fuel doesn't end up out of the exhaust port before being burned with DI.

<div class='quotetop'>QUOTE (BarryMachine @ Feb 12 2008, 01:00 AM) <{POST_SNAPBACK}><div class='quotemain'>Thats all still in the realms of a "plonker engine", surely you can see the difference when operating at the sort of charge flows of a GP 2 stroke?. These aren't "lawnmowers", pehaps even turbine engine technology is the nearest thing
Sadly, you have dashed my hopes.

WTF have lawnmowers got to do with it.

The fuel is fully burnt because it is directly injected into the combustion chamber as the piston is coming up. The amount of air charge is not limited, nor is the fuel charge, so there is no problem with using it on a GP 2-stroke.

DI does not mean you inject small amounts of fuel, rather that you inject exact amounts at a precise time. The timing and quantity of the air and fuel injection are controlled separately. At light loads, fuel is injected relatively late to create a stratified charge with a richer mixture around the spark plug than in the rest of the cylinder. At higher loads, the fuel is injected earlier to allow greater penetration and a more homogeneous mixture in the cylinder.

Oh well, I guess it was too much to expect that you'd agree with this "scientific reasoning" given that a huge proportion of your arguments against DI seem to hinge on the "fact" that some of fuel injected ends up out of the exhaust port before being burnt.

<div class='quotetop'>QUOTE (yamaka46 @ Feb 12 2008, 12:06 AM) <{POST_SNAPBACK}><div class='quotemain'>Actually, the noise is one thing that DI can't remove, and whilst people like you and I think that's a great thing (I love the riiiiing diing diiing diiiing and the smell of Castrol-R, come to that ) the fact that the sound is at the frequency of speech gives it a higher decibel reading than a 4-stroke. Given the whinging of people living near race tracks about noise these days, I think that that in itself is enough of a death knell for the remaining 2-strokes.
The whinging of people who live near race tracks is something that really gets my goat too. There was a great racetrack in Sydney at the warwick farm horse racing track which also had the advantage when I was a kid that you could get there on the train. I saw some great car racing there including tasman series open wheeler racing with some of the then current F1 guys. It had operated for 50 years or so, with motor racing only 2 weekends per year, and there probably wasn't a house within miles when it started but resident complaints got it shut down. Another track at amaroo park which wasn't so great was specifically built miles away from houses but had similar problems as suburban sydney approached it, although I guess the land would have become too valuable for housing in the end anyway.

"Not in my backyard" is bad enough in the first place, let alone when you know what is there when you buy your house.

<div class='quotetop'>QUOTE (BarryMachine @ Feb 12 2008, 01:00 AM) <{POST_SNAPBACK}><div class='quotemain'>I have absolutely no misunderstandings on what DI does.... I know you do now after posting that picture .....

Thats all still in the realms of a "plonker engine", surely you can see the difference when operating at the sort of charge flows of a GP 2 stroke?. These aren't "lawnmowers", pehaps even turbine engine technology is the nearest thing

Here's a quick one ... go out and work out what it takes to build an expansion chamber .... there's a few little calc's there that from ememory fill you in on the gas flow and what can be manipulated.
Ooh, you edited that post whilst I was replying

What bit of that picture is wrong? Where is my misunderstanding?

The expansion chamber (an improperly named device) utilizes sonic energy contained in the initial sharp pulse of exhaust gas exiting the cylinder to supercharge the cylinder with fresh mixture. As the fuel is directly injected this is not required.

<div class='quotetop'>QUOTE (michaelm @ Feb 12 2008, 01:21 AM) <{POST_SNAPBACK}><div class='quotemain'>The whinging of people who live near race tracks is something that really gets my goat too. There was a great racetrack in Sydney at the warwick farm horse racing track which also had the advantage when I was a kid that you could get there on the train. I saw some great car racing there including tasman series open wheeler racing with some of the then current F1 guys. It had operated for 50 years or so, with motor racing only 2 weekends per year, and there probably wasn't a house within miles when it started but resident complaints got it shut down. Another track at amaroo park which wasn't so great was specifically built miles away from houses but had similar problems as suburban sydney approached it, although I guess the land would have become too valuable for housing in the end anyway.

"Not in my backyard" is bad enough in the first place, let alone when you know what is there when you buy your house.
Tell me about it. Here in Boonah we have a grass airstrip. People have built houses at one end of the strip on a hill. When the wind direction deems we take off that way we are clearing the hill and hence the houses by about 500ft. With the wind in the opposite direction we clear the hill by even less on final (though we do do "glide" approaches, ie at idle).

The airstrip was there first, yet they complain about the noise.

<div class='quotetop'>QUOTE (Babelfish @ Feb 12 2008, 12:09 PM) <{POST_SNAPBACK}><div class='quotemain'>No, but they are farily recent improvements that work now but didn't 10 to 40 years ago. Based on that, I'm not the one to rule out a solution for 2 stroke engines.
Excuse my ignorance but I thought they actually used DI in the new 125 aprilias in '07? Two or four of the aprilias were using a new engine and I thought that was DI. Surly not a 100% success, just ask Pasini (at a point last year I think he had 6 poles and no finishes), but non the less the fastest bike out there when it worked (for a lap or three)

And how is his fuel economy ?? great improvements ?

DI works, I don't deny that, its just another method of putting fuel into the cylinder. But to suggest it competes with 4 strokes on efficiency is wrong.

Again, DI competes with 4 stroke only up to a certain performance level, whereafter the benefits dissapear. Motogp bikes operate at levels whereby the power required demands that a 2 stroke is operating in a non-fuel-efficient fuel zone. On 4 strokes with DI that zone is extended.

<div class='quotetop'>QUOTE (yamaka46 @ Feb 12 2008, 12:24 PM) <{POST_SNAPBACK}><div class='quotemain'>Ooh, you edited that post whilst I was replying

What bit of that picture is wrong? Where is my misunderstanding?

The expansion chamber (an improperly named device) utilizes sonic energy contained in the initial sharp pulse of exhaust gas exiting the cylinder to supercharge the cylinder with fresh mixture. As the fuel is directly injected this is not required.

added not changed ... but nonetheless read the bit in the post there as to why the picture is not much use at all.

Its like posting a picture of a nail and saying doesn't your new house look good

<div class='quotetop'>QUOTE (yamaka46 @ Feb 12 2008, 12:24 PM) <{POST_SNAPBACK}><div class='quotemain'>The expansion chamber (an improperly named device) utilizes sonic energy contained in the initial sharp pulse of exhaust gas exiting the cylinder to supercharge the cylinder with fresh mixture. As the fuel is directly injected this is not required.

well refer back to Babels post about DI currently being used ..... bet Pasinis Aprillia had a chamber .... love to see how it went without it.


PS. I didn't edit this in my last post as I spotted it after the fact, hence separate post since you require it

<div class='quotetop'>QUOTE (yamaka46 @ Feb 12 2008, 12:18 PM) <{POST_SNAPBACK}><div class='quotemain'>The fuel is fully burnt because it is directly injected into the combustion chamber as the piston is coming up. The amount of air charge is not limited, nor is the fuel charge, so there is no problem with using it on a GP 2-stroke.

Again ..... yes I know .... but are you saying the fuel efficiency at that performance level is comparable to a like powered 4 stroke?

<div class='quotetop'>QUOTE (yamaka46 @ Feb 12 2008, 12:24 PM) <{POST_SNAPBACK}><div class='quotemain'>The expansion chamber (an improperly named device) utilizes sonic energy contained in the initial sharp pulse of exhaust gas exiting the cylinder to supercharge the cylinder with fresh mixture. As the fuel is directly injected this is not required.

Back to this bit again ... its too simple ... does not include much and it is a bit hmmmm incongruent....

Explanation:

The expanding cone part of the chamber, nearest the exhaust port, causes a neagtive pressure which helps pull out the burned gases as weel as the following new charge. So it really helps scavenging, but it sets up a flow with a bit of momentum that tends to draw out too much of the new charge .....

To get that new charge, that was lost out the exhaust, back in where it will do good, the rear cone ( the convergent one ) reflects a positive pressure wave that at a tuned rpm ( tuned by the length from the exhaust port to the cone effective distance ) approaches the exhaust port hence effectively "batting" back in some of the wasted charge...... its a real winner of a device!! ......

The crank pressure seems more of a "supercharger" however with the fitting of a well tuned pipe this phenomena greatly improves at a narrow band of rpm.

So I'd say with DI the pipe must be tuned to suit it but it would be awfully close.

<div class='quotetop'>QUOTE (BarryMachine @ Feb 12 2008, 02:22 AM) <{POST_SNAPBACK}><div class='quotemain'>Explanation:

The expanding cone part of the chamber, nearest the exhaust port, causes a neagtive pressure which helps pull out the burned gases as weel as the following new charge. So it really helps scavenging, but it sets up a flow with a bit of momentum that tends to draw out too much of the new charge .....

To get that new charge, that was lost out the exhaust, back in where it will do good, the rear cone ( the convergent one ) reflects a positive pressure wave that at a tuned rpm ( tuned by the length from the exhaust port to the cone effective distance ) approaches the exhaust port hence effectively "batting" back in some of the wasted charge...... its a real winner of a device!! ......

The crank pressure seems more of a "supercharger" however with the fitting of a well tuned pipe this phenomena greatly improves at a narrow band of rpm.

So I'd say with DI the pipe must be tuned to suit it but it would be awfully close.
Nope, you still don't get it. With DI you do not lose the fuel out of the exhaust port because the piston is blocking it when the fuel is injected - it is not sucked in - so what use would an expansion chamber be?

There is no wasted charge. The only stuff coming in through the inlet port is air and oil. DI scavenges the cylinders with pure air containing no fuel at all, so no need to reflect the exhaust gasses back into the cylinder - it's just burnt gasses and air, no lost fuel, so no need for expansion chambers.

As far as the pictures I posted, I read the bit in your post as to "why the picture is not much use at all" and it seemed to be about lawnmowers. I replied to it in post #105, so again I repeat my questions :

What bit of the picture is wrong? Where is my misunderstanding?

Here you go Yamaka I saw this some time ago ... finally found it again ..... its the simplest pictorial explanation I have found ... its a real gem.

http://www.vf750fd.com/blurbs/stroke.html

It tells more of the story than that picture you posted.

<div class='quotetop'>QUOTE (BarryMachine @ Feb 12 2008, 09:36 AM) <{POST_SNAPBACK}><div class='quotemain'>Here you go Yamaka I saw this some time ago ... finally found it again ..... its the simplest pictorial explanation I have found ... its a real gem.

http://www.vf750fd.com/blurbs/stroke.html

It tells more of the story than that picture you posted.
Yes, the animation in the link you posted is lovely and shows exactly how conventional 2-strokes work, but there is no DI going on there.

I understand how a conventional 2-stroke works (and obviously you do too from previous posts). My point is that you fail to understand how a DI 2-stroke is different.

The two pictures I posted show how a direct injection 2-stroke engine is different from a conventional carburetted crankcase-scavenged 2-stroke engine.

<div class='quotetop'>QUOTE (yamaka46 @ Feb 12 2008, 08:25 PM) <{POST_SNAPBACK}><div class='quotemain'>Yes, the animation in the link you posted is lovely and shows exactly how conventional 2-strokes work, but there is no DI going on there.

I understand how a conventional 2-stroke works (and obviously you do too from previous posts). My point is that you fail to understand how a DI 2-stroke is different.

The two pictures I posted show how a direct injection 2-stroke engine is different from a conventional carburetted crankcase-scavenged 2-stroke engine.

Yes I know its diferent ..... but we are on the subject of irrespective of the differences .... DI does not solve the problems with fuel efficiency in 2 strokes, especially when higher performance is called for.

I hope you read that article .... interesting bit in that the government vehicle trial of the orbital engined vehicles being more inefficient than the engines they replaced. Interesting comments there, theywold really interest Rog. ( what with him studying Performance Engineering at Kingston Uni and all ) Seems like everyone there finds the same problem ..... when you want power.... its inefficient.

<div class='quotetop'>QUOTE (BarryMachine @ Feb 12 2008, 10:43 AM) <{POST_SNAPBACK}><div class='quotemain'>Yes I know its diferent ..... but we are on the subject of irrespective of the differences .... DI does not solve the problems with fuel efficiency in 2 strokes, especially when higher performance is called for.
The problem I have is that you keep referring to the lack of fuel efficiency and then blame it on the fuel being lost down the exhaust port which cannot happen with DI.

You keep stating that DI can't give a fuel-efficient high-performance solution, but don't back this up with any facts other than stuff about conventional engines (irrelevant).

<div class='quotetop'>QUOTE (BarryMachine @ Feb 12 2008, 10:43 AM) <{POST_SNAPBACK}><div class='quotemain'>I hope you read that article .... interesting bit in that the government vehicle trial of the orbital engined vehicles being more inefficient than the engines they replaced. Interesting comments there, seems like everyone there finds the same problem ..... when you want power.... its inefficient.
Those comments are unedited replies, therefore rather like posts on a forum. Anyone can post/reply, regardless of their knowledge or lack thereof. Also the motorcycledaily article and hence the comments are from late 2001. Engineering development does not stay still over 6+ years.

BTW, this was one of the replies in the article you linked to:

<div class='quotetop'>QUOTE <div class='quotemain'>Honda, and maybe others, have developed clean two strokes in house. Honda's system is called Active Radical Combustion (ARC). ARC is simpler, lighter, cheaper and has fewer problems than Orbital's system and was used both on race bikes (Paris-Dakar) and street bikes (a Japan only 250 DP bike). I had the great pleasure of speaking to Kevin Cameron (along with Erv Kanamoto one of my life long heroes) about ARC. Kevin had been allowed to read the Honda research and testing documents and was very impressed.