
Rehabilitating the image of the two-stroke engine (1990) - camtarn
https://www.nytimes.com/1990/07/08/business/technology-rehabilitating-the-image-of-the-two-stroke-engine.html
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slededit
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
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.

~~~
cup-of-tea
I believe that's how diesel two-strokes work. Can it work with petrol? Burning
diesel is still undesirable.

~~~
kazinator
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.

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blutack
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-20...](https://enduro21.com/index.php/40-general/2184-first-
look-2018-ktm-250-300-exc-tpi-2-stroke-enduro)

------
jhoechtl
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.

~~~
chrisseaton
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
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.

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cromulent
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/failu...](https://www.carmrades-blog.com/all-
articles/2017/11/24/failure-to-launch-the-orbital-engine-company)

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

~~~
zaarn
The simple reason ICE's will remain in use is energy density, no matter how
much you wish it wasn't true.

Diesel packs 48 Megajoules per Kilogram of Mass, Jet Fuel 43 and plain old
wood does 16.

Accumulators/Batteries manage betweed 0.25 and 0.9 MJ per Kilogram, exception
being LiPo which can do 1.8 MJ per KG.

ICE's usually can do a 30% efficiency, even in crude designs, so even
accounting for that you get like 16 MJ per KG of fuel out of a diesel engine
while LiPo even at 90% efficienty manages a 1/10th of that.

If you're weight constrained like when you want to fly an aircraft, there
isn't much choice but to have a combustion engine of sorts.

If you wanted to replace an aircraft gas turbine (usually a turbojet or
turbofan) with an electric one, you'd have to make the engine and battery
combo that weighs no more than a jet fuel engine while having the same power
output.

For raw numbers

A Boeing 737 MAX has an engine that weighs 2'780 kg. Two of them. It has a
TSFC of 0.012kg/kN*s which works out to 70 MW on continous thrust. The fuel
weighs 19 tons at full load.

So the electric replacement for this engine now needs to output twice 70MW of
power for up to 7'000 kilometers of range. At normal cruising speed that's 10
hours.

140MW over 10 Hours is 1400MWh / 2.5 Gigajoules. The best battery tech we have
will result in a 2777.8 ton battery. If the electric motor can do 100%
efficiency.

2777.8 tons vs 19 tons. (If my numbers are correct, which should be the case)

~~~
Theodores
But what bit of the battery are you weighing?

If you look at how Tesla do their batteries there is the actual chemistry bit
on some thin foil that is separated with some thin plastic. This is then put
into a metal cylinder. This is then wired up in a module that holds the cells.
This is then put in a tray that holds all of the modules. Then these trays are
placed into a semi-structural floor unit which then has a titanium protection
shield under the car.

So now the chemical bits that could probably fit in a beer bottle now weigh a
metric tonne and are too big for all but American roads (Tesla cars are boat
sized in Europe, too wide for garages and country lanes or city streets).

Meanwhile ICE juice is measured without the matryoshka dolls of containers
within containers. Nobody takes the weight of the container into
consideration.

Hopefully someone will one day invent structural batteries where the whole
thing is a battery that neither zaps you or boils you to death. Then adding a
few seats will add to the range. If you have to have a cabin anyway then, if
it had dual use as energy storage, the actual energy density would not have to
be in the same league as highly explosive hydrocarbons.

There should be easy wins in this, e.g. a bicycle. The current generation of
electric bikes go for the bracket + holder + container of containers mounted
as high as possible for poor centre of gravity. I am sure there are exceptions
but ultimately the battery will end up in the frame tubes and you could double
energy density plus power to weight just by taking the integrated approach.

I know nothing about engineering and why batteries have to be ultra bulky but
I hope that we don't just stick with ICE because petrol is more energy dense.

~~~
olyjohn
In case you were wondering, here's a light-weight fuel cell made from
aluminum. It holds 20 gallons of fuel and weighs about 22lbs according to the
description.

[https://www.amazon.com/20-Gallon-Lightweight-Polished-
Alumin...](https://www.amazon.com/20-Gallon-Lightweight-Polished-Aluminum-
Street/dp/B072JBGCGM/)

This is just some random fuel cell I found on Amazon. There are probably even
lighter options out there. Racers are always looking to shed weight.

There are also lots of examples where the frame of a vehicle can perform
double-duty and hold fuel as well. I don't think that any regular production
car will ever do this as it's probably not safe, but the idea isn't a new
concept. Here's just an example:

[https://bicyclemotorworks.com/product/built-in-fuel-tank-
bik...](https://bicyclemotorworks.com/product/built-in-fuel-tank-bike-frame/)

~~~
Theodores
I think you read my comment backwards, petrol always has a simple tank, even
in F1 where a lot of baffles and what not go into the design for safety and
performance reasons.

However, on electrified transport from the humble bicycle upwards there is a
lot of extra brackets and boxes getting added.

It is like cars from before the monocoque era, a chassis where none is needed.
With the bicycle example you could put the batteries inside the frame instead
of in a box mounted on the rear rack. These 'chassis style' products are not
fine engineering and set a bad example.

~~~
olyjohn
Oh yeah I see what you're saying. It's an afterthought on so many electrified
vehicles. Makes sense and I agree. We have a lot of the Limebikes in our area,
and the battery is just bolted to your standard bike rack. Always seemed like
an afterthought to me too. Like you're saying, even in a simplistic design, it
seems like you could fit a lot 18650 cells inside a tubular frame.

