7 ms·

Rehabilitating the image of the two-stroke engine (1990)

28 points by camtarn 8y ago

slededit 8y ago
The simple problem with the two stroke is its almost impossible to prevent some gas from leaking out via the exhaust since the inhalation and exhalation happen simultaneously. Environmental standards are so stringent that this is a non-starter, even though it could achieve much better gas mileage. Even if you solved that problem you'd still have to burn the oil used for lubrication.
- swimfar 8y ago
  There are other options. If you have forced induction and direct injection you fix both those problems. You no longer use the crankcase for pressurizing the intake so the bottom end can be lubricated like a 4-stroke engine instead of adding oil to the fuel. With forced induction you can blow clean air through the ports expelling all the exhaust without wasting any fuel. This obviously adds quite a bit of complexity to the design, though. It may not be economical in the end. And that's assuming you can get it to meet emission regulations.
  - anticensor 8y ago
    Uniflow forced-induction directly-injected engines also burn oil. Example of a such 2-stroke engine: https://en.wikipedia.org/wiki/EMD_567 https://en.wikipedia.org/wiki/EMD_567
  - cup-of-tea 8y ago
    I believe that's how diesel two-strokes work. Can it work with petrol? Burning diesel is still undesirable.
    - kazinator 8y ago
      The diesel cycle as such can work with gasoline, but actual diesel engine implementations not designed for gasoline won't take it very well due to multiple issues. The timing of the injection of diesel is not right for gasoline, and perhaps the compression ratio isn't also. Gasoline is thin and volatile, lacking lubricant properties.
- deleted 8y ago
  [deleted]
jhoechtl 8y ago
At least in Europe two stroke gardening machinery in the range between 20 to 50ccm is getting quickly replaced by current-powerd engines. When you use them, the accu is empty and after two winters out in the barn they are dead. But because gas powered two stroke engines are getting so quickly replaced they have become so cheap. Sometimes I think replacing them with current powered engines serves as a testbed to improve storage technology and to drive manufacturing costs down for the car accumulator producers.
- Maakuth 8y ago
  One related positive trend is that the vendors of these machines are using the same battery across their range of devices. Then they cut down costs by unbundling the battery from the equipment so that you only need to buy batteries when you really need more. That way you end up having less of these batteries just waiting for their expiration in the garden shed.
- aequitas 8y ago
  4 stroke engines are doing well in this area nowadays. We have a few machanised garden tools with 4 stroke and they are not that expensive. They are not dirty cheap like the electric ones but that depends on the quality range you buy as well I guess. Added benefit of the 4 stroke is they run a lot quieter.
- chrisseaton 8y ago
  What is a ‘current-powered engine’? Do you mean an electric motor? Is there some significance to the unusual term you’re using?
  - stan_rogers 8y ago
    The use of the word "accu" (short for some variation on "accumulator") rather than "battery" suggests that English is not the poster's native language. Here on HN, that should not be a surprising state of affairs.
ncmncm 8y ago
So, what happened? And why are we seeing this again now? Especially, when internal combustion is about obsolete?
- owenversteeg 8y ago
  Because there are a lot of applications where you've just got to have an internal combustion engine, and that will remain the case for many years. Everything from aerospace to long-distance to simply low-cost applications usually require ICEs and the high fuel density that comes along with them.
  - zrobotics 8y ago
    Another point is easily refuelable. Chainsaws are by and large 2 stroke due to weight, and while electric saws do exist they have a short runtime. Hauling enough batteries into the woods for a day of firewood cutting isn't an option when 1.5gal of fuel will more than suffice.
    - dsfyu404ed 8y ago
      >while electric saws do exist they have a short runtime. It doesn't help that they're all flimsy consumer models that break if you even think about doing real work with them.
- AmVess 8y ago
  This article is almost 30 years old. No one pursued it because there's not a cheap and simple way of getting 2-stroke engine emissions down to an acceptable level. ICE are far from obsolete, and will be in demand until the day we wring the last drop of petrol from this Earth.
  - joecool1029 8y ago
    Pretty much sums it up. Anyways there's better directions for research now like HCCI that should bring petrol engines efficiencies up: https://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition https://en.wikipedia.org/wiki/Homogeneous_charge_compression...
blutack 8y ago
KTM (large Austrian motorcycle manufacturer) have a EURO-4 emissions compliant 2 stroke by using fuel injection and metering the lubrication oil. https://enduro21.com/index.php/40-general/2184-first-look-2018-ktm-250-300-exc-tpi-2-stroke-enduro https://enduro21.com/index.php/40-general/2184-first-look-20...
cromulent 8y ago
The article talks about the innovative injection technology from the Orbital Engine Company. Here's an article about that companies history and why it never caught on apart from existing 2 stroke markets (outboard motors etc). https://www.carmrades-blog.com/all-articles/2017/11/24/failure-to-launch-the-orbital-engine-company https://www.carmrades-blog.com/all-articles/2017/11/24/failu...

28 points by camtarn 8y ago

The simple problem with the two stroke is its almost impossible to prevent some gas from leaking out via the exhaust since the inhalation and exhalation happen simultaneously. Environmental standards are so stringent that this is a non-starter, even though it could achieve much better gas mileage. Even if you solved that problem you'd still have to burn the oil used for lubrication.

swimfar 8y ago
There are other options. If you have forced induction and direct injection you fix both those problems. You no longer use the crankcase for pressurizing the intake so the bottom end can be lubricated like a 4-stroke engine instead of adding oil to the fuel. With forced induction you can blow clean air through the ports expelling all the exhaust without wasting any fuel. This obviously adds quite a bit of complexity to the design, though. It may not be economical in the end. And that's assuming you can get it to meet emission regulations.
- anticensor 8y ago
  Uniflow forced-induction directly-injected engines also burn oil. Example of a such 2-stroke engine: https://en.wikipedia.org/wiki/EMD_567 https://en.wikipedia.org/wiki/EMD_567
- cup-of-tea 8y ago
  I believe that's how diesel two-strokes work. Can it work with petrol? Burning diesel is still undesirable.
  - kazinator 8y ago
    The diesel cycle as such can work with gasoline, but actual diesel engine implementations not designed for gasoline won't take it very well due to multiple issues. The timing of the injection of diesel is not right for gasoline, and perhaps the compression ratio isn't also. Gasoline is thin and volatile, lacking lubricant properties.
deleted 8y ago
[deleted]

jhoechtl 8y ago

At least in Europe two stroke gardening machinery in the range between 20 to 50ccm is getting quickly replaced by current-powerd engines. When you use them, the accu is empty and after two winters out in the barn they are dead. But because gas powered two stroke engines are getting so quickly replaced they have become so cheap. Sometimes I think replacing them with current powered engines serves as a testbed to improve storage technology and to drive manufacturing costs down for the car accumulator producers.

Maakuth 8y ago
One related positive trend is that the vendors of these machines are using the same battery across their range of devices. Then they cut down costs by unbundling the battery from the equipment so that you only need to buy batteries when you really need more. That way you end up having less of these batteries just waiting for their expiration in the garden shed.
aequitas 8y ago
4 stroke engines are doing well in this area nowadays. We have a few machanised garden tools with 4 stroke and they are not that expensive. They are not dirty cheap like the electric ones but that depends on the quality range you buy as well I guess. Added benefit of the 4 stroke is they run a lot quieter.
chrisseaton 8y ago
What is a ‘current-powered engine’? Do you mean an electric motor? Is there some significance to the unusual term you’re using?
- stan_rogers 8y ago
  The use of the word "accu" (short for some variation on "accumulator") rather than "battery" suggests that English is not the poster's native language. Here on HN, that should not be a surprising state of affairs.

ncmncm 8y ago

So, what happened? And why are we seeing this again now? Especially, when internal combustion is about obsolete?

owenversteeg 8y ago
Because there are a lot of applications where you've just got to have an internal combustion engine, and that will remain the case for many years. Everything from aerospace to long-distance to simply low-cost applications usually require ICEs and the high fuel density that comes along with them.
- zrobotics 8y ago
  Another point is easily refuelable. Chainsaws are by and large 2 stroke due to weight, and while electric saws do exist they have a short runtime. Hauling enough batteries into the woods for a day of firewood cutting isn't an option when 1.5gal of fuel will more than suffice.
  - dsfyu404ed 8y ago
    >while electric saws do exist they have a short runtime. It doesn't help that they're all flimsy consumer models that break if you even think about doing real work with them.
AmVess 8y ago
This article is almost 30 years old. No one pursued it because there's not a cheap and simple way of getting 2-stroke engine emissions down to an acceptable level. ICE are far from obsolete, and will be in demand until the day we wring the last drop of petrol from this Earth.
- joecool1029 8y ago
  Pretty much sums it up. Anyways there's better directions for research now like HCCI that should bring petrol engines efficiencies up: https://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition https://en.wikipedia.org/wiki/Homogeneous_charge_compression...

blutack 8y ago

KTM (large Austrian motorcycle manufacturer) have a EURO-4 emissions compliant 2 stroke by using fuel injection and metering the lubrication oil. https://enduro21.com/index.php/40-general/2184-first-look-2018-ktm-250-300-exc-tpi-2-stroke-enduro https://enduro21.com/index.php/40-general/2184-first-look-20...

cromulent 8y ago

The article talks about the innovative injection technology from the Orbital Engine Company. Here's an article about that companies history and why it never caught on apart from existing 2 stroke markets (outboard motors etc). https://www.carmrades-blog.com/all-articles/2017/11/24/failure-to-launch-the-orbital-engine-company https://www.carmrades-blog.com/all-articles/2017/11/24/failu...