[Speedygonzales]

some videos I took.

atkinson engine
[ame="http://www.youtube.com/watch?v=bJER1Q-Dzuo"]YouTube - model IC engines (Atkinson)[/ame]

atkinson engine cycle
[ame="http://www.youtube.com/watch?v=yLIfoZ8stjk"]YouTube - Atkinson 4 stroke engine cycle[/ame]

THIS ONE IS KOOOL
sleeve valved engine
[ame="http://www.youtube.com/watch?v=Bp93qDyvBak"]YouTube - model sleeve valved engine[/ame]

[BillTodd]

Nice videos (although the schnitzel hous joke is only funny once)

Always been fascinated by the Atkinson cycle; attached is a animation based of his 1866 patent

[dynosor]

some videos I took.

Hi Speedy

Thanks for the cool videos of impressive engines.

The Atkinson engine cycle is interesting, but a little confusing: The inlet and compression "strokes" represent shorter distances the crank travels compared to the power and exhaust "stroke". This is supposed to be the key to the Atkinson cycle's efficiency, but there is no mention of the torque loads during these phases of crank travel.

If the links that drive the piston during the intake and compression stroke can make do with shorter crank travel, then surely this is combined with greater force or torque loadings to accomplish the same work?

The Toyota Prius uses a version of the Atkinson cycle. Here, intake valve closing is delayed so that some of the intake charge is blown back into the inlet manifold during compression, thereby increasing the effective length of the power stroke relative to the intake stroke (why not just delay exhaust valve opening for a longer power stroke).

Now, delaying intake valve closing to this extent would also reduce the effective compression of the engine. This reduces not only torque, but thermal efficiency - the very antithesis of diesel engine efficiency.

Toyota would not use something that doesn’t work, but it seems to be giving away something it claims to optimize. What gives? Buhler? Anyone?

[BillTodd]

Here, intake valve closing is delayed so that some of the intake charge is blown back into the inlet manifold during compression, thereby increasing the effective length of the power stroke relative to the intake stroke (why not just delay exhaust valve opening for a longer power stroke).

I thought (and I could be wrong) that the Pious engine has a short intake period (i.e. inlet the valve closes early to reduce the amount of gas in the cylinder), which allows them to use a smaller combustion volume (giving a better burn) without excessive compression ratio. Thus making the power and exhaust strokes effectively greater volume, like the Atkinson cycle.

[dynosor]

I thought (and I could be wrong) that the Pious engine has a short intake period (i.e. inlet the valve closes early to reduce the amount of gas in the cylinder), which allows them to use a smaller combustion volume (giving a better burn) without excessive compression ratio. Thus making the power and exhaust strokes effectively greater volume, like the Atkinson cycle.

From: http://www.greencar.com/articles/toy...-emissions.php

"The Prius uses a four-cylinder, 1.5-liter Atkinson cycle engine. The four-stroke Atkinson cycle, invented by James Atkinson in 1882, is different than the Otto cycle engine we’re used to driving in very distinct ways. Compared to the Otto cycle, where the intake valve is closed near bottom-dead-center, the Atkinson cycle does not close the intake valve at BDC, but leaves it open as the piston rises on the compression stroke. What this means is that some of the air/fuel charge is pushed back out and into the intake manifold and is used in other cylinders. This reduces the volume of the air/fuel mixture that’s compressed and combusted without severely restricting the throttle opening. Restricting throttle opening results in large pumping losses and greatly reduced efficiency. This method of reducing power output without incurring large pumping losses makes the Prius engine much more efficient than a conventional Otto cycle engine under most operating conditions."

[BillTodd]

Compared to the Otto cycle, where the intake valve is closed near bottom-dead-center, the Atkinson cycle does not close the intake valve at BDC, but leaves it open as the piston rises on the compression stroke. What this means is that some of the air/fuel

Hmm.

As you pointed out:

"delaying intake valve closing to this extent would also reduce the effective compression of the engine. This reduces not only torque, but thermal efficiency - the very antithesis of diesel engine efficiency."

As would allowing the piston to force heated gas back into the inlet and disrupting the momentum of the gas in the whole of the intake manifold !

I can't argue, 'cos I haven't seen a valve timing diagram for the pious, but that sounds like a bit of 'marketing-speak' to me. It seems to me, that late opening or early closing of the inlet would be better way to achieve a Miller/Atkinson cycle than that late closing.

[edit2] OK I take it all back, I'm wrong

the timing for closing the intake valve is
delayed, and in the initial stage of the compression stroke
(when the piston begins to ascend), part of the air that has
entered the cylinder is returned to the intake manifold

[edit]
There's a timing diagram of sorts in this pdf. but it's not really clear what the inlet timing actually is :shrug:

http://www.toyota.co.jp/en/tech/envi...Reports_12.pdf

[dynosor]

It seems to me, that late opening or early closing of the inlet would be better way to achieve a Miller/Atkinson cycle than that late closing.

I would think you are correct; that this would reduce pumping losses.

[BillTodd]

I would think you are correct; that this would reduce pumping losses.

I've been trying to figure out why Toyota don't do it this way; The only reason I can see is that by closing late they can absolutely ensure that it'll never try to squeeze a cylinder full into the reduced combustion volume. ???

[Speedygonzales]

Nice videos (although the schnitzel hous joke is only funny once)

Always been fascinated by the Atkinson cycle; attached is a animation based of his 1866 patent

hey common now, its no joke thats my production name!
its like watching your favorite show, the starts always the same then they have the title of the episode. no different here.

I cant help with the atkinson discussion, they are very new to me (that is the first one I saw in person.
but I am following the discussion closely

[Speedygonzales]

anyone have anymore to say about the atkinson engines?

another modeler that shares similar interests in Atkinson engines has asked me some questions that I am not sure how to answer.

he needs to find 3 improvements toward the atkinson engine (cycle).
can anyone chime in? or provide some further reading.

it sure is a head turner!.

[harryn]

I am not an expert at all on the Atkinson cycle, but I am aware of the torque loss, especially at low rpm.

What is misunderstood by many people is just how poorly the engine would perform if not for the electric assist at low speeds - the real driver for it being a hybrid. The electric brake regen feature makes up for the low speed electric motor add. Its all about the Atkinson cycle for these lower power engines.

Of course, if you want really high efficiency, use a really big, low speed diesel, but that is not practical for a car.

[mcphill]

Seems it has many similar traits to the Miller Cycle as well, right?

http://en.wikipedia.org/wiki/Miller_cycle