2 Stroke Tech.

[2T_vs_4T]

I'm looking for a web site or forum that has the latest 2 Stroke Tech. Fuel injection or direct injection.
This may be old hat, but, with the direction injection of fuel into a 2 stroke engine once the exhaust port has closed, is an expansion chamber of such an elaborate design, say as used on the new Ossa 300i enduro, really necessary. As the theory behind the sound waves and back pressure has become unnecessary as no fuel is lost out of the exhaust port, with direct injection after it has closed. When you look at the Yamahe 2 stroke outboard engines there is no such elaborate expansion chamber.
Any Tech people out there with their thoughts.
2T_vs_4T.

[David Lahey]

tuned exhausts are for creating pressure waves to help the engine breathe so yes they are a benefit for a 2 stroke with direct or indirect fuel injection
If there is no tuned exhaust on a modern Yamaha 2 stroke outboard motor, I would say it is for the same reason that they were not fitted to run-of-the-mill carburetted 2 stroke outboards (expansion chambers wont fit in the space available)

[2T_vs_4T]

Ok, so the expansion chamber helps remove the exhaust gases. Then why is there no expansion chamber on a Yamaha 2 Stroke outboard with HPDI?

[mustanggrahame]

An expansion chamber on a carburetted 2 stroke puts back fuel and air into the cylinder. On a fuel injected 2 stroke you would still use an expansion chamber to put air back into the cylinder. More air allows more fuel to be added top get more power. Injected or carby same theory with pipe design.
Grahame

[Lozza]

I'm looking for a web site or forum that has the latest 2 Stroke Tech. Fuel injection or direct injection.
This may be old hat, but, with the direction injection of fuel into a 2 stroke engine once the exhaust port has closed, is an expansion chamber of such an elaborate design, say as used on the new Ossa 300i enduro, really necessary. As the theory behind the sound waves and back pressure has become unnecessary as no fuel is lost out of the exhaust port, with direct injection after it has closed. When you look at the Yamahe 2 stroke outboard engines there is no such elaborate expansion chamber.
Any Tech people out there with their thoughts.
2T_vs_4T.

Outboards are different animals the only thing they have in common is they are 2 T engines. The EFI does the fuel the pipe makes the HP it is the over riding influence on an engine.

[2T_vs_4T]

Have any of you seen a 2 stroke diesel motor with a blower. Without a a cut out in the air intake these motors would rev to destruction. I experienced this a a young guy, they rev.

[2T_vs_4T]

So what about a small blower on a 2 Stroke motor for forced induction and direct injection.

[gordon67]

try a search for a commer ts 3 diesel from the 1960s .....cheers

[Mike52]

try a search for a commer ts 3 diesel from the 1960s .....cheers

Try driving one 
Mate , match the sound of a screaming 2/stroke with a supercharger and you've hoon heaven.

tuned exhausts are for creating pressure waves to help the engine breathe so yes they are a benefit for a 2 stroke with direct or indirect fuel injection
If there is no tuned exhaust on a modern Yamaha 2 stroke outboard motor, I would say it is for the same reason that they were not fitted to run-of-the-mill carburetted 2 stroke outboards (expansion chambers wont fit in the space available)

The scavenging/supercharging effect would still work.

[gordon67]

Hi Mike,
I did in the 60s, performance not bad but no engine braking= bad to stop

[Mike52]

Hi Mike,
I did in the 60s, performance not bad but no engine braking= bad to stop

Do you still remember the sound.
Brilliant.
I used to double d clutch and split the diff just to hear it.

[gordon67]

Its something you never forget,....... i still wake up and hear it now after all those years,

[John Orchard]

An expansion chamber create's both positive and negative pulses back at the exhaust port.  You want a negative  (vacuum) pulse at the exhaust port just as it is opening; the quick evacuation of the exhaust gases and the resulting negative pressure in the combustion chamber also aids the fuel coming up the transfer ports, rather than just having crankcase compression doing the job.

Although, with direct injection, there will be no fuel going out the exhaust port, with a positive pulse arriving back at the port just as the piston is closing, a mild form of 'supercharging' effect is a result by pushing some air back into the chamber; hopefully without any of the previously spent exhaust gases.

[pancho]

I'm looking for a web site or forum that has the latest 2 Stroke Tech. Fuel injection or direct injection.
This may be old hat, but, with the direction injection of fuel into a 2 stroke engine once the exhaust port has closed, is an expansion chamber of such an elaborate design, say as used on the new Ossa 300i enduro, really necessary. As the theory behind the sound waves and back pressure has become unnecessary as no fuel is lost out of the exhaust port, with direct injection after it has closed. When you look at the Yamahe 2 stroke outboard engines there is no such elaborate expansion chamber.
Any Tech people out there with their thoughts.
2T_vs_4T.

if you check the inside of the outboard motor leg, guess what you find? an expansion chamber cast into the inner shape of the leg.
pancho

[Lozza]

An expansion chamber create's both positive and negative pulses back at the exhaust port.  You want a negative  (vacuum) pulse at the exhaust port just as it is opening; the quick evacuation of the exhaust gases and the resulting negative pressure in the combustion chamber also aids the fuel coming up the transfer ports, rather than just having crankcase compression doing the job.

Although, with direct injection, there will be no fuel going out the exhaust port, with a positive pulse arriving back at the port just as the piston is closing, a mild form of 'supercharging' effect is a result by pushing some air back into the chamber; hopefully without any of the previously spent exhaust gases.

Erm not really. When the exhaust port opens to the pipe you have a hot high pressure wave, following the high pressure outbound wave is a trough lower than atmospheric pressure. That trough/depression stays there until BDC when that is the lowest pressure in the engine and when most bulk flow happens.After this is when the reflection from the baffle cone arrives to push most of the intake charge back into the cylinder. There never is any 'pushing' through the transfers by the decending piston, there is never any negative pressure in the combustion chamber. You still want the pipe for these reasons.

Correct panch and outboards also use water to vary the diameter of the stinger outlet.

[Montynut]

Erm not really. When the exhaust port opens to the pipe you have a hot high pressure wave, following the high pressure outbound wave is a trough lower than atmospheric pressure. That trough/depression stays there until BDC when that is the lowest pressure in the engine and when most bulk flow happens.After this is when the reflection from the baffle cone arrives to push most of the intake charge back into the cylinder. There never is any 'pushing' through the transfers by the decending piston, there is never any negative pressure in the combustion chamber. You still want the pipe for these reasons.

Correct panch and outboards also use water to vary the diameter of the stinger outlet.

Surely Lozza the "trough lower than atmospheric pressure" is a negative pressure although that is on the scale of gauge pressure not absolute pressure of course. A fuel/air mixture or just air can only flow from an area of higher pressure to an area or lower relative pressure. The difficult thing for people to understand is the idea of relative pressure as opposed to absolute or gauge (atmospheric) pressure. The pressure may always be more positive than the atmosphere but be negative or positive relative to the pressure in the cylinder or crankcase area. I think that is the concept that most people struggle with.

It is a bit the same as how we breathe by expanding the chest volume creating a relative low pressure in the chest cavity causing the lungs to take in air until equilibrium is reached. The low pressure is only relative. That is why the air supply pressure in scuba gear increases to the diver as their depth increases to maintain that relative pressure relationship.

Or am I just crapping on

[maico police]

Just showing off (again).......

[Mike52]

Erm not really. When the exhaust port opens to the pipe you have a hot high pressure wave, following the high pressure outbound wave is a trough lower than atmospheric pressure. That trough/depression stays there until BDC when that is the lowest pressure in the engine and when most bulk flow happens.After this is when the reflection from the baffle cone arrives to push most of the intake charge back into the cylinder. There never is any 'pushing' through the transfers by the decending piston, there is never any negative pressure in the combustion chamber. You still want the pipe for these reasons.

Correct panch and outboards also use water to vary the diameter of the stinger outlet.

Surely Lozza the "trough lower than atmospheric pressure" is a negative pressure although that is on the scale of gauge pressure not absolute pressure of course. A fuel/air mixture or just air can only flow from an area of higher pressure to an area or lower relative pressure. The difficult thing for people to understand is the idea of relative pressure as opposed to absolute or gauge (atmospheric) pressure. The pressure may always be more positive than the atmosphere but be negative or positive relative to the pressure in the cylinder or crankcase area. I think that is the concept that most people struggle with.

I

Are you guys saying that the pipe would help increase volumetric efficiency ?

[pancho]

to my mind that is the guts of it.

[Lozza]

Surely Lozza the "trough lower than atmospheric pressure" is a negative pressure although that is on the scale of gauge pressure not absolute pressure of course. A fuel/air mixture or just air can only flow from an area of higher pressure to an area or lower relative pressure. The difficult thing for people to understand is the idea of relative pressure as opposed to absolute or gauge (atmospheric) pressure. The pressure may always be more positive than the atmosphere but be negative or positive relative to the pressure in the cylinder or crankcase area. I think that is the concept that most people struggle with.

It is a bit the same as how we breathe by expanding the chest volume creating a relative low pressure in the chest cavity causing the lungs to take in air until equilibrium is reached. The low pressure is only relative. That is why the air supply pressure in scuba gear increases to the diver as their depth increases to maintain that relative pressure relationship.

Or am I just crapping on

Pipe pressure goes lower than atmospheric, same as your lungs, as I'm pretty confident when I breathe I am breathing air at 1.00 atmospheres.Same as I'm confident the air a engine intakes is at atmospheric(disregarding any ram air boxes).If the pressure in the header pipe was not less than atmospheric nothing would flow toward it at BDC. Prof Robert Fleck at QUB has a excellent SAE paper in this.

[Montynut]

Surely Lozza the "trough lower than atmospheric pressure" is a negative pressure although that is on the scale of gauge pressure not absolute pressure of course. A fuel/air mixture or just air can only flow from an area of higher pressure to an area or lower relative pressure. The difficult thing for people to understand is the idea of relative pressure as opposed to absolute or gauge (atmospheric) pressure. The pressure may always be more positive than the atmosphere but be negative or positive relative to the pressure in the cylinder or crankcase area. I think that is the concept that most people struggle with.

It is a bit the same as how we breathe by expanding the chest volume creating a relative low pressure in the chest cavity causing the lungs to take in air until equilibrium is reached. The low pressure is only relative. That is why the air supply pressure in scuba gear increases to the diver as their depth increases to maintain that relative pressure relationship.

Or am I just crapping on

Pipe pressure goes lower than atmospheric, same as your lungs, as I'm pretty confident when I breathe I am breathing air at 1.00 atmospheres.Same as I'm confident the air a engine intakes is at atmospheric(disregarding any ram air boxes).If the pressure in the header pipe was not less than atmospheric nothing would flow toward it at BDC. Prof Robert Fleck at QUB has a excellent SAE paper in this.

I'm not an engine expert but pressure and measurement of pressure is an area I'm familiar with. Atmospheric pressure is a very variable value as you know from tuning. It is also a variable that is taken out of measurements of closed cycles such as steam condensers by using absolute values. Typical pressures in this instance would be 6Kpa absolute (0Kpa Absolute being a perfect vacuum) or nominally -100Kpa gauge.

If you are breathing at the top of a 2000m mountain you are not breathing at one atmosphere you are breathe at some value less than 1bar absolute (nominally 106Kpa absolute). Even though this is the case the pressure differential across your lungs is the same as that at sea level (1 atmosphere). That is why you suffer oxygen deprivation at high altitudes due to the lower atmospheric pressure but your lungs take in the same volume of air which is now lower in pressure and hence less dense therefore less oxygen leading to, well, eventually death.

What causes air to flow into or out of an engine or any other vessel or system is a pressure differential the only time these laws do not apply is when some form of mechanical pumping is applied (ram air effect or mechanical/turbo supercharging). People commonly discussing pressure it is taken as gauge pressure where atmospheric pressure is considered to be zero.

I think we are saying the same thing but the atmospheric pressure versus pressure differential thing is confusing the issue.

[Lozza]

I think so too.