Atkinson Cycle Engine

[CrimsonEclipse]

The Atkinson Cycle is another bastardized term in the automotive community.

In reality, it is a standard Otto cycle engine AKA 4 stroke, with an additional pivot point allowing the piston to travel farther and/or at different speeds on each stroke depending on the geometry. This requires additional rods, bearings and support parts thus increasing complexity.

http://www.animatedengines.com/atkinson.html

The Toyota Prius claims to have an Atkinson Cycle engine. THIS IS NOT TRUE!!!

It is a MODIFIED Otto cycle engine with configurable valves, meaning, the intake valve can open during the compression stroke adjust the fuel/air charge to simulate the effects of an Atkinson cycle.

There are no additional pivot points, there is no change in piston speed or displacement. It's just variable valve timing.

A problem with most of the previously mentioned engines is the added complexity and development time of it AND their accessories.
Since they are relatively new concepts, the engines have to compete with Otto cycle engine that have been in developement for 50-70 years. Harmonics of the long connecting rods, unexpected cracking and specific metalurgical processes for each unique part will take time for the "lessons learned" phase.

The power curves might also be vastly different requiring transmission ratio changes, vibration and ware patterns that require additional material for strengthing which will require more weight which eats into the weight savings abd efficiency category.

All of these technologies need to be tested in an industrial sector first (connected to a power generator or water pump etc) to prove their worth.

 

[Cjr]

The Atkinson Cycle ( named for Mr. James Atkinson) is a thermodynamic cycle describing a set of thermodynamic conditions under which combustion occurs and energy is converted from thermal to mechanical energy. The Otto Cycle (named for Mr. Nikolaus Otto) is a different set of Thermodynamic conditions (pressure, temperature and energy flux i.e. Power) under which thermal energy is converted to mechanical energy. The Diesel Cycle ( named for Mr. Rudolf Diesel) is a third different set of Thermodynamic Conditions for turning thermal energy into mechanical energy. All three cycles have various advantages and disadvantages when they are implemented as machines.

To say that the Atkinson Cycle and the Otto Cycle are the same because they can both be implemented using pistons, valves, cylinders and crankshafts is incorrect. Atkinson's original complex machine to demonstrate his Atkinson Cycle should not be confused with the Atkinson Cycle itself. Although the modern machine to implement the Atkinson Cycle looks very similar to both Otto Cycle and Diesel Cycle machines, the modern Atkinson Cycle machine using electrically actuated valves is different because it implements very different thermodynamics. You can find information on the three different cycles and their inventors in Wikpedia (and other sources) by searching on the respective names of their 19th century inventors.

 

[Coss]

The Atkinson Cycle is another bastardized term in the automotive community.

In reality, it is a standard Otto cycle engine AKA 4 stroke, with an additional pivot point allowing the piston to travel farther and/or at different speeds on each stroke depending on the geometry. This requires additional rods, bearings and support parts thus increasing complexity.

http://www.animatedengines.com/atkinson.html

The Toyota Prius claims to have an Atkinson Cycle engine. THIS IS NOT TRUE!!!

It is a MODIFIED Otto cycle engine with configurable valves, meaning, the intake valve can open during the compression stroke adjust the fuel/air charge to simulate the effects of an Atkinson cycle.

There are no additional pivot points, there is no change in piston speed or displacement. It's just variable valve timing.

A problem with most of the previously mentioned engines is the added complexity and development time of it AND their accessories.
Since they are relatively new concepts, the engines have to compete with Otto cycle engine that have been in developement for 50-70 years. Harmonics of the long connecting rods, unexpected cracking and specific metalurgical processes for each unique part will take time for the "lessons learned" phase.

The power curves might also be vastly different requiring transmission ratio changes, vibration and ware patterns that require additional material for strengthing which will require more weight which eats into the weight savings abd efficiency category.

All of these technologies need to be tested in an industrial sector first (connected to a power generator or water pump etc) to prove their worth.

The more moving parts, the more things to go wrong.
I can see where it could come apart and turn into a large grenade of metal if anything is short cut in the quality of parts used.

 

[CrimsonEclipse]

The long connecting rods in the Eco Engine concerns me. I've seen enough conventional connecting rods blast through engine blocks and would hate to see what that would do.

 

[Cjr]

The long connecting rods in the Eco Engine concerns me. I've seen enough conventional connecting rods blast through engine blocks and would hate to see what that would do.

Again, do not confuse the "Cycle" with the machine used to implement the cycle. All the Cycles ( Atkinson, Otto and Diesel) have implementatIons that are almost identical in their parts. The 1882 version of the Atkinson engine shown by CrimsonEclipse has mechanical parts as different from today's Atkinson cycle engines as 1880 "Make and Break Ignition" engines are from today's Otto cycle engines. The Variable Valve Timing (VVT) Atkinson engines used in today's Atkinson cycle engines are identical in mechanical design to modern Otto cycle engines - only their operation "programming" changes. Most modern Atkinson cycle engines operate in both Atkinson and Otto cycles depending on the power required from them. That is creative use of modern VVT engines.

If you look at the simulation CrimsonElipse provides (it's a great one) and watch the piston, you can see that it has two distinctly different piston strokes during its four stroke cycle. Atkinson's 1882 patent was centered around having a different "compression" and "power" stroke which allowed more of the energy to be extracted from each compression and ignition than was possible when the two strokes are identical. The Atkinson engine is small displacement during intake and compression to reduce losses during those strokes at low engine power while having longer strokes during power and exhaust strokes to increase energy extraction after ignition. In 1882, Mr. Atkinson did not have today's engines to demonstrate his engine cycle so he invented the novel but complicated linkage system shown in CrimsonEclipse's animation.

Today's Atkinson cycle implementation using VVT during low engine power requirements decreases the length of the compression stroke simply by holding the intake valve open through the intake stroke and into the compression stroke. The point at which the intake valve closes determines the effective start of the Atkinson compression stroke. The mixture is compressed at a lower compression ratio, ignited, then the high temperature/pressure gasses expanded through a longer, full, power stroke. The result (at low engine power requirements like "cruise") is significantly better fuel use efficiency. Whenever high power is needed, the VVT simply reverts back to the normal equal stroke Otto cycle.

These modern Atkinson cycle engines are now in many vehicles from Toyota, Ford, Mazda, and others. They are used in hybrid applications (Prius) for over a decade and non-hybrid applications are emerging as VVT becomes more common. It is entirely possible that many of you are driving one without knowing simply because what is required is only VVT. They are most common in four cylinder applications because flow out of the cylinder during the extended intake Is drawn into an adjacent cylinder just starting its intake stroke. This further increases fuel efficiency.

 

[TheAsterisk!]

Just in case some sketches and comparative illustrations (even if they are simple) helps others as much as it usually helps me.

 

[CrimsonEclipse]

Again, do not confuse the "Cycle" with the machine used to implement the cycle. *lots of words* This further increases fuel efficiency.

CJR is probably (99.9999%) right.

CJR, I'll read this later.... It's late (early) and i can't brain right now.

 

[CrimsonEclipse]

CJR is probably (99.9999%) right.

CJR, I'll read this later.... It's late (early) and i can't brain right now.

Ok, I can't seem to find any separation of the cycles and the respective engines.
The only reference that I can find is that the Atkinsin cycles favors efficiency to power density.
The Otto engine describes the 4 stroke engine.

CJR, if you have better resources than I do, please throw them at me.

 

[Cjr]

With regards to the thermodynamics, here is a reference for Otto Cycle that discusses only the Cycle and not the engine designs using it.
https://en.m.wikipedia.org/wiki/Otto_cycle

Here is a reference for the Atkinson Cycle and various machines (engines) used to implement it. The cycle diagram is about three-quarters down the page and it shows three different (old) engine designs to implement the Atkinson cycle. There are no pictures of the current design because it is the same mechanically as a Otto cycle engine with VVT. https://en.m.wikipedia.org/wiki/Atkinson_cycle

Both the Otto cycle and Atkinson cycle engines are four (piston) cycle engines and modern VVT engines can be programmed to use either the Otto cycle for max power or the Atkinson cycle for max fuel economy. You can't tell which cycle they are running by looking at the engine and watching it run. VVT engines switching between Otto and Atkinson cycles. The above reference includes a long list of vehicles Toyota, Ford and others with Atkinson cycle capable engines. I recently saw an article that said Toyota was using an Atkinson cycle engine in a non-hybrid pickup application.
http://news.pickuptrucks.com/2015/01/how-it-works-2016-toyota-tacomas-atkinson-cycle.html

Because the Atkinson cycle engine has a ratio of expansion (power) stroke length to compression stroke length (expansion ratio) greater than one, it better expands the ignited fuel for better economy, however, the smaller compression stroke lowers the maximum power available for expansion ratios greater than one. The Otto cycle always has expansion ratio equal to one so is able to compress more air and hence burn more fuel during one cycle generating has more maximum power every cycle but sacrificing efficiency.

The genius is using VVT (Variable Valve Timing) to continuously vary expansion ratio and combine the two cycles in one machine(engine) that adapts to provide more efficiency at low power demand (Atkinson) and more power at high demand (Otto) as appropriate to the driver's throttle pedal setting.

 

[floydv]

Looks like Infiniti has finally finished twenty years of work on its variable compression engine.

Car and Driver blog.