Potential engine mod? Otto to Atkinson conversion
 

So this one hit me as I was looking around wikipedia last night. I seem to recall reading somewhere a long time ago that the CRX HF engine ran on a different "cycle" than a normal engine, partially accounting for it's increased fuel efficiency.

A few minutes of searching turned up the Otto cycle (the "normal" cycle) and the Atkinson cycle (the high FE cycle).

It looks to me as if the only appreciable difference is in the lift duration of the intake cam. If it was possible to have a new cam ground to provide this increased intake duration, you could effectively convert your engine to the Atkinson cycle, thereby raising your FE.

So the question I'm posing for all of you engine gurus out there is this:
Would this be a feasible mod for all us folks out here with Otto cycle engines?

Good idea -- I wonder what driveability is like: is there reduced power (especially torque)? I wonder if a learning curve exists in driving with this type of engine. Since it's found in some hybrid applications, the electric motor makes-up for the "getting started" part.

I'm curious if a custom cam would achieve the result...

But, I see that the original Atkinson engine had a different stroke on the intake and exhaust cycles...

RH77

I've been pondering the same thing for awhile now....

If I had the money - I'd have a custom ground camshaft machined.... As I recall, that's the key difference between an Otto and the Atkinson in several hybrid vehicles on the road at th moment...

The concern I have is backfiring... So stock setup is to spray fuel on the intake. But with a cam that leaves the cylinder open - some of that fuel fortified intake will be pushed back. Of course, under normal conditions - some fuel is left in the intake track - so I imagine it's up to the valve seals to ensure there's no backfiring...

I'm also curious as to how the manifold vacuum will change :)

I honestly think it's possible.... Just someone needs to fork up the funds for the cam (unless we can find someone that'll do it for free or does it for a living :p). If no one does before I'm out of college (and earning some dollars), I'm probably going to give it a shot :p

Yeah, about the intake charge being pushed back into the intake manifold...
I can't imagine that being a huge issue. I mean, cars with using the Atkinson cycle don't (usually) have direct injection, so they are using the same limits we are. For example, only spraying fuel when the valves are open.

Still, I'm having a hard time convincing myself that the air sensor(s) are only going to count the air that's passing through one way (into the engine). I can't help but think it'll end up enriching the mix by "re-counting" the air that has been ejected back from the engine, and re-injecting the fuel for said amount of air.

Or, that air could just be all compressed and stored in the manifold somehow (TB closed), the MAF could be too slow, etc.

I know this is a long-shot (but we're brainstorming here)...

Is any of this worthy of Grant Writing? Call me crazy, but someone might pony up a few bucks for the sake of engine research.

Any word on the emissions profile as well?

RH77 :turtle:

So I've done a bit of thought on that... Actually, that's what most of my thoughts focused on as that's arguably one of the key sensors for fuel trim that will be affected.... The conclusion I came to, for a MAF sensor, is that it will not be a problem.

So MAF sensors operate VIA the use of a heater wire (typically). Bulk flow over the wire cools it in a predictable manner. As long as the manifold vacuum is negative - there will always be positive (into engine) bulk flow. The degree of which depends on engine speed and pressure.

In my thought experiment - pressure is what will change. Rather than the typical 22" Hg (or so) - I think there will be slightly higher pressure which in turn results in less bulk flow. WHICH makes sense as we're rejecting a portion of flow per intake stroke.

That doesn't sound like a bad idea actually.... I'll stay by what I had said before about my timetable (school for me, right now, takes up all my time - despite that it also takes all my money too :p). But someone else should totally go for it if they have the means :)

No clue - that's one thing I don't even know where to begin on how to think about it :p Intuitively, I imagine that the engine management will compensate for the lower airflow (MAF) in addition to normal a/f metering (O2 sensor). I would think that exhaust temperature change would stay nominal BUT I'm not sure. Given the lower compression and longer power stroke (compared to compression stroke) - the rejection cycle might have lower temperatures (better for NOx?). Exhaust content has been a voodoo type subject for me... I personally would build it, then measure :thumbup:

Turtle
http://gallery.photo.net/photo/6065333-md.jpg

So, there may be problems....
Can't seem to find any difinitive word on the HF's particular cycle (Atkinson/Otto)

I too have been thinking about this off and on, but haven't done a ton of research on it yet. From what I've read though, the Atkinson engine is simply less power dense. I believe (although I'm far from an expert on this) that the main difference between the two engines is cam timing (probably added duration too). The intake valve closes late to allow reversion of the air/fuel back into the intake manifold. This reduces the amount of air/fuel in the chamber, but also allows higher compression ratios and that helps compensate for the power loss. The higher compression is where you get the boost in effeciency. So, it has less power, but is more effecient. If you can live with less power, your good. How much less power? I guess it all depends on how you design the system. The Prius uses a modified 1NZ-FE (11:1 CR) engine that normally puts out about 106 hp. Once the Prius engine is done being modified into the 1NZ-FXE (13:1 CR) it has 76 hp. So, you loose roughly 25%. I'm sure having an engine with VVT and some way to control this would make things infinitely easier to play with. However, adjustable cam timing pulleys would be a cheaper alternative.

Cvt
 

With detonation and torque issues, I'm wondering if a CVT transmission would be the best option. I know, cart before the horse...

Reason-being -- from driving the Prius and noting the engine speed, it seems to turn faster, and in bursts. It begs the question of the Atkins' ability to have enough power in the standing-start RPM range in either a manual or TC auto.

Variable timing may be the key, as mentioned.

BTW, Does the HF have VTEC? That might achieve the Atkinson-like operation...

RH77

Nope, HF was pre-vtec. It was a SOHC 8-valve job too.

When I bought my HF it had a cracked valve at 75k (about 1/4 of the valve face was gone:eek:) makes me wonder about the detonation thing...

And I can't help but wonder if a little low rpm detonation would be too much for an engine to cope with. They've all got knock sensors now, so the ECU just dials back the timing, and you've got a little less power to take off with.

I think the Honda D-series (B's to a lesser extent) may be good candidates, they're all undersquare, so good for torque. They have cheap parts, so easy to get the custom grind and bump up compression. And they have all of the electronics that you'd need. Plus, they're cheap and plentiful, so you could easily replace it if you broke anything :D

Oh, and the way I understood it, the Atkinson gets its efficency from retaining more of its kinetic energy from the compression stroke since it is compressing less volume than an Otto cycle engine. Sure the nomenclature remains (compression ratios) but the meaning is changes when you're not actually compressing 30% of that volume.

So I was aware of the loss of low end torque and high end power... But I wasn't aware that it caused detonation issues - I'll have to do more research as to why that happens (doesn't seem right as we'd be dealing with lower overall compression).

Keep in mind it's going to have less useful energy in the first place (controlling the rpm variable).... The major pitfall of the otto engine is that it doesn't use all of the available work in the compressed volume of ignited fuel. The expansion ratio for useful work is something like 25:1 (and it diminishes exponentially) for gasoline. Diminishing returns occur around 17:1 - 18:1 expansion ratios.... Obviously, compressing 18:1 on gasoline would cause detonation without some crazy high octane ratings.

Atkinson resolves that issue by having a disproportionate compression and power stroke to take advantage of energy that would otherwise be ejected out of the tailpipe (literally). Hrmm - thinking of it that way... I'm thinking there will be a EGT value....

cat lighting troubles, eh?

the HF, VX? and CX have the cat directly under the manifold, on the front side of the block, so that may help on that front.

2 Points
 

I'm thinking that the CAT lighting issues aren't that big of a deal: burned fuel is hot. Start any car -- even a Diesel, and let it idle for less than a minute. The A-pipe will be way too hot to the touch. Even a Prius makes heat within a minute of starting -- Atkinson style, with low emissions. It can be done.

RH77

This doesn't make sense to me. Why would you have detonation problems at low rpm without a supercharger, but with a supercharger you wouldn't? When you apply higher cylinder pressures is usually when you see more problems with detonation.

I can definitly see why the electric motor works, but why supercharger?

My bro in-law and I have talked lots about Atkinsonizing via cam grinding. This guy does grinds for the Suzukiclones, and would be someone to talk to if a clone driver wanted to try it. (He makes & sells XFi cam copies for the efficiency crowd & hot cams for the speed freaks.)

Not me, though! It would be interesting to try, but so many other things to doooo...

Note: I split off the cylinder deactivation discussion in to a new thread.

a muller cycle motor is a motor starved on the intake. this leaves more room for the hot gas to work. it dates from the 20's was used in big ship motors. and , i think in industrial motors. it cut high revs and power but keeps much of the torke. crane cams sold a cam that let some of the charge blow back. it was made for the old motors that needed hi-test gas. its not legal for cars now. but was sold for trucks. it was used on big motors. cane sold out and i don't know if its still sold.

oh' mazda used the muller cycle on its high line car. they used high boost superchargers on a small, for us, motor. the car mags said it worked great with power and less fuel

First, what is currently being recognized as an Atkinson Cycle engine is not. Only a close approximation.

The current "Atkinson" implementation, delaying the intake valve closing so that a portion of the cylinder A/F mixture, CHARGE, can be pushed back into the intake manifold, only works satisfactorily with 4 cylinder engines or multiples thereof wherein an "opposite" cylinder is in an "intake" cycle and will threfore "absorb" the A/F charge being "pushed" back into the intake manifold.

Another approach might be to use a "reed" valve, one-way shuttle valve, like that used in 2-cycle engines, to prevent reverse flow out of the intake system.

A more common approach is that developed in teh late forties, called the Miller Cycle, using a positive displacement supercharger to prevent the reverse flow and at the same time provide "make-up" for the lost efficiency HP/torque wise of the Atkinson cycle engine.

And just changing the cam profile isn't enough. The modern implementation of the Atkinson cycle typically uses a "native" cylinder compression ratio of about 13:1. So once you "push" 20-30% of the mixture back out of the cylinder you end up with a "net", effective, compression ratio of 10:1, pretty standard.

So we could take a 4 cylinder engine and have the head milled for super high compression then have a reduced duration intake lobe ground in the valve cam. That would be a miller cycle engine?

Please somebody grind a cam for my dodge daytona 2.2 before I take a grinder to my cam! Just kidding.

NO - a Miller cycle engine involves forced induction. What you just described is Atkinson cycle.

Atkinson engines work by use of an ellipsus, which allows the connecting rod's crank end to slip from a smaller stroke journal to a larger stroke journal.

The idea is that the intake stroke should be smaller, and the power stroke should be longer, which gives the best of a long stroke engine (torque) and a small displacement engine (efficiency).

Adding boost came about when it was determined at an Atkinsonized Otto-cycle engine didn't create good power, and may cause other issues with late closing of the intake valve allowing bleeding back into the intake manifold. Adding boost helps to control the intake bleed off, and adds more low-end torque to the engine.

Interesting stuff... so could we also close the intake way early instead of late? This would do away with the blow-back, create a vaccuum in the cylinder for a partial (in) stroke and partial (comp) stroke, and effectively reduce the comp ratio without affecting the other strokes.

??

Inducing vacuum in the cylinder before the valve opening event does two things - both of which are undesirable -

1. It makes for more pumping losses (try pulling two cups apart that fit perfectly in each other.)

2. It changes airflow profiles for an otherwise nicely tuned intake system, due to the vacuum caused by the cylinder being part way down with no air movement.. it would cause vacuum pulses in the intake that would ruin both harmonics (check the TB spacer thread) and the overall fluid dynamic profile of the intake itself by increasing the vacuum per intake stroke, in a pulse like fashion.

(#2 is partially speculative, and can't be held as gospel. Please research it before assuming it is correct.)

amcpacer: The modern implementation of the Atkinson cycle is an *extended* duration intake. A much later intake valve closing than typical to reduce dynamic compression while achieving benefit of high expansion ratio. Like Christ explained the original utilized "dual cranks" for small to typical compression ratio with much higher expansion ratio. The cam solution achieves the same ends without the mechanical complexity of shifting crankshaft throw lengths.

The Miller cycle used forced induction with the extended IVC timing to achieve complete cylinder fill and cut down on pumping losses but was unable to dramatically increase the mechanical compression ratio as there was no decrease of dynamic compression. Slight improvement in thermal efficiency with displacement-specific power on parity or higher than the Otto cycle (Atkinson cycle is much lower)

MazdaMatt: wouldn't do that if I were you. Creating the vacuum on the downstroke from an incomplete fill would result in much higher pumping losses on the intake side. It's a lot easier to pull mixture into the cylinder and bleed a bit of it off than it is to pull the cylinder down against a pair of closed valves. You'd wind up with MUCH less power.

uhm... although my idea struck me as stupid at first for the reasons you explained, the beginning of the comp stroke would be just as "pulled up" as the end of the suck stroke (that sounds dirty)... i would expect that it would be equalized.

...in fact, that vacuum may help with atomization :)

(and by "in fact" i mean "in pure speculation")

Lexus says the upcoming 2010 RXh uses an Atkinson cycle V6 engine. Anyone know how that was done..?

I would have thought it would have to be a Miller cycle for a V6....

V engines are more likely to utilize the technology correctly than inline engines are. In a V engine, the air that gets pushed out can simply cross over the plenum to the next cylinder in the firing order, whereas in an inline engine, the airflow has to change directions 3 times.

Once in the reversion cycle that puts it out of the cylinder, then sideways in the plenum to the next cylinder's opening (which could be against airflow, going from 1-3 and 2-4, at least in Honda engines), then down the next cylinder's runner along with fresh air.

Look at it this way...

Using the current implementation of the Atkinson cycle, delayed intake valve closing and 13:1 "native" compression ratio, look at what would happen with just a single cyclinder engine. You would have reverse airflow OUT the intake path/duct for each compression stroke, not exactly viable for a MAF/IAT equipped engine.

It appears to me that you need to go to 4 cylinders, inline or whatever, before you arrive at a solution for the reverse flow problem. With 4 cylinders you have an "opposite" cylinder beginning an intake stroke at the same time you need a place to "put" the charge being "exhausted" due to the delayed intake valve closing of the cylinder just begining a compression stroke.

The only alternative to 4 cylinders that I can see is having a one way "reed" valve to block the reverse flow. Or, of course, the Miller cycle as chosen by Mazda in the Millenia S's V6.

I think you're looking a little too far into it...

Regardless of engine size (except single cylinder low speed engines) the manifold is constantly under vacuum. When the piston pushes part of the mixture back into the manifold, it's still under vacuum, it's just under slightly less vacuum.

There is still more pressure on the other side of the throttle plate, which keeps positive airflow in the correct direction (into the cylinder, out the exhaust side.)

Even with a 6 cylinder engine, the Atkinson cycle is still effective, as a result of this fact. The only reason for introducing boost is to keep more air/fuel in the cylinder, even though some of it gets pushed back out still. Since boosting engines increases the VE of the engine by adding more air than it could normally induct at the same RPM under vacuum, it also lessens the power loss associated with not having a full cylinder when not under boost.

In other words, the only reason to add boost is to compensate for the Atkinson effect's power loss.

If you add boost, you're increasing the VE of the engine without sacrificing power. If you use Atkinson and Boost (Miller) then you're still getting the FE increase of the Atkinson cycle, while increasing the VE of the engine (less pumping loss).

It's a best of both worlds scenario.

I don't believe the actual Atkinson engine ever intended for the cam to be designed to allow reversion in the intake tract, as this is counter-intuitive for power to be made. As I noted earlier, the real Atkinson design changed only the crankshaft, by adding an ellipsus that would allow the piston to have two effective stroke lengths. A much shorter stroke would be used for intake and compression, then a longer stroke used for combustion and exhaust.

This would yield a result that had less pumping loss than a stroker, but similar torque, with the same fuel use as a smaller displacement engine. VE would also be increased. kinetic energy created per BTU of fuel also increases (energy cannot be created nor destroyed blablabla) due to the longer stroke creating more leverage on the crank during the combustion event.

The idea of the "Atkinson cam" is bunk, essentially. It may increase FE, but it sacrifices power to do it, which is exactly the opposite of the true Atkinson design.

"Atkinson cam is bunk.."

Well, since the actual Atkinson cycle engine does not make full use of the cylinder's intake "charge" capability it also sacrifices power in favor of efficiency. And remember that during the period the intake valve is left open is exactly in time with the least force capability (just leaving BDC) of the crankshaft acting to force the piston upward.

Also take note that the Atkinson cycle doesn't come up "on the step" except at something like 70% or more cylinder charge. An elongated power stroke does no good unless there is enough charge to be still producing power at or near the bottom of the power stroke.

An ideal system would leave the compression ratio at 13:1 for light cylinder charging, partial throttle, and only go into Atkinson cycle mode at 70% or more of charge.

And by the by, the Atkinson cycle is at its MOST efficient at or near WOT when there is little of NO vacuum in the intake manifold.

No, it doesn't. This is the part that makes most people walk away from any discussion about Atkinson engines. It has the same VE during intake stroke as any Otto engine with the same attributes. Nothing has changed about the intake cycle of the Atkinson ENGINE. It fills the same amount of space with the same amount of air. The part where Atkinson is supposedly better is the second "crank". It effectively makes for a longer power-stroke. That's all it does. Each piston is making power for more time. Each rod has more leverage on the crank, but only when the rods are actually pushing on the crank. When the crank is pushing the rod back up, or pulling it back down, there is less leverage, so the crank isn't working as much, and less work is wasted doing the intake/compression strokes. You can't logically compare this to an Otto engine with an Atkinson cam.
Source? I believe you're still mixing terms here. The Atkinson cycle engine is mechanically driven so that each power (combustion) stroke takes place on the longer stroke on the other side of an ellipsus on the crank shaft. Therefore, there is never a time when it's not in "Atkinson mode".See above.
Moot. Any engine is most efficient at lowest vacuum. It's called Volumetric Efficiency. This is the point of boost, initially. It increased the VE of airplane engines, so they could run better in higher atmosphere. It allowed thinner air to be compressed so that it would resemble air at or closer to sea level, and didnt' involve parasitic drag on the engine.

Using an Atkinson-style cam is no different. The point of what I said was simply to give light to the fact that the limited reversion from the cylinder isn't enough to defeat the inherent vacuum in the manifold. The fact is, even if there is LITTLE vacuum in the manifold, there is still SOME vacuum in the manifold. Since there is SOME vacuum in the manifold, there is still a high pressure spot outside the TB that keeps positive flow. This means that the atkinson cycle can work. The limit to this is when cylinder reversion causes an influx of pressure into the manifold. This prevents the pressure differential on either side of the TB plate, and allows airflow reversion from the TB. Boost solves this, hence the Miller Cycle.[/QUOTE]

I meant to address this in my reply yesterday since IIRC it came up earlier in the thread...but I think christ answers correctly.

This WOULD cause a problem with either an incorrectly designed intake or if you had a single throttle plate per cylinder with no "manifold" per se. In the first situation a proper chamber volume or resonator would buffer the pressure pulses and allow a continuous inflow through the throttle (and therefore the MAF sensor) the way that normal intakes already do this to a lesser degree. In the second situation (one butterfly/cylinder with no resonator) you don't even need a MAF sensor and can map fuel/spark from TPS and RPM.

That's one way to look at it, but I think there's another perspective that would question whether it is indeed opposite of a "true" Atkinson.

The Atkinson-style cam is intended to simulate the operating parameters of the Atkinson cycle. The Atkinson cycle is fundamentally a "normal" compression ratio with an "enhanced" expansion ratio built into an otherwise Otto cycle engine.

In the "true Atkinson" engine this is done with a really trick crankshaft and/or connecting rod journals that lets the engine have a mechanical compression ratio of say 10:1 and a mechanical expansion ratio (i.e. "power stroke") of say 13:1. Since the swept volume will be less on the 10:1 intake stroke you have a smaller displacement engine than if you were to look at the swept volume of the power stroke. Personally I would rate the engine as the displacement indicated by intake stroke swept volume. In the "Atkinson-cam" engine of the same mechanical size with a 13:1 compression/expansion ratio the swept volume is larger than of the "true Atkinson" engine. Since intake charge is bled off during compression in the "cammer" then its specific power output is less than a "true Atkinson" but it is very likely to produce equal power to the "smaller true Atkinson" that has a lower volume.

So one may say that the "true Atkinson" doesn't sacrifice power the way the "atkinson cam" does, but the end result is essentially the same because the "true" engine is a smaller displacement not capable of producing as much power while the "cam" engine produces the same power because it's slightly less displacement-efficient. All in all, the two lumps o' iron (or Aluminum) are the same package size and weight, produce essentially the same usable power, and the cam engine is easier to build and control.

What's bunk about that?

Where to start...

Okay, take a 2L displacement Otto engine and convert it to the TRUE Atkinson cycle engine and its EFFECTIVE displacement now becomes something less, as a ratio between the shortened intake/compression stroke and the power/exhaust stroke, than 2L. Giving up the POWER of a 2L OTTO engine infavor of the efficiency, longer "burn" cycle of the Atkinson engine.

The current implementation does exactly the same thing, sacrificing POWER for FE.

Pumping losses.

When the piston is at BDC the travel direction of the crank is at 90 degrees to the angle required to move the piston upward in a compression cycle. Delaying the closing of the intake valve during this early period in the compression stroke results in lowering the pumping losses since the travel angle of the crank will be closer to linear for piston travel once compression actual begins.

An ideal engine would be able to vary the compression ratio as a function of cylinder A/F mixture charge level. An engine with a fixed compression ratio, say 10:1, is not very effective at/with low charge levels. SAAB is currently testing an engine that can vary the compression ratio as a function of charge level.

My point with the Atkinson cycle is: what is the use of an elongated burn cycle if the charge level was so low that the "burn" was complete at 2/3 piston travel..?? So it would be better to not delay the closing of the intake valve for partial throttle and thereby make more efficient use of the native compression ratio of 13:1.

What drives the tubine in a turbocharged engine...??

Partial or moderate throttle = No excess energy left over to be exhausted into the turbine, NO turbine power.

Think you're ever see a turbocharged Atkinson cycle engine..??

"..buffer the pressure pulses...."

At WOT how do you "buffer" the pressure pulses in a way that prevents a pressure wave from travelling back up the intake path...??

With a 4 cylinder engine you will have ACTIVE SUCKING of the "opposite" cylinder to neutralize the pressure wave....

You have the same thing with a 6 or 8 cylinder engine. Even 5 cylinder engines, and 10 cylinder engines will always have a cylinder on intake at the same time that one or more cylinders is on power/exhaust/compression. The only exception to the rule is the single cylinder engine, and any variant of rotary engine.

The only difference is the speed and timing at which the next piston draws back the unused (expelled) intake mixture.

2 cylinder engine, pistons are working 180 from each other (normally)
3 cylinder engine, pistons are working 120 from each other (normally)
4 cylinder engine, pistons are working 90 from each other (normally)
5 cylinder engine, pistons are working 72 from each other (normally)
6 cylinder engine, pistons are working 60 from each other (normally)
8 cylinder engine, pistons are working 45 from each other (normally)
10 cylinder engine, pistons are working 36 from each other (normally)
12 cylinder engine, pistons are working 30 from each other (normally)

In every iteration of a standard balance multi piston engine, each cylinder is working opposite another one such a way that the expelled intake mixture would be recovered by another cylinder.

MechEngVT - What I meant by bunk was more like "Wasteful". I mean this because the cam causes outflow of intake mixture back into the exhaust manifold. This causes issues with intake harmonics, etc, and screws up ideal mixtures in just about any gasoline engine. What's to say that the mixture pushed out wasn't the richest part of a layered homogenous mixture? Now the mixture in the cylinder is lean! Subsequently, the engine has had another pulse of air through the induction system, which in carb'd apps already has gas in it, or in FI apps has fuel added as it flows into the cylinder, but either way - the new cylinder's mixture is ideal, but it's sucking in the richest part of the last cylinder, so now it's rich! Now you have a lean cylinder, and a rich cylinder. Who knows what part of the rich cylinder will end up in the outflow from the second piston's compression event, and so on/so forth. See what I mean? In the Atkinson Cycle engine, this isn't a concern, as there is no outflow.

Ideally, to use the Atkinson cam in place of the Atkinson engine, the outflow would either have to be precisely controlled, or fuel precisely metered AFTER the ouflow event. This is where GDI comes into play. Gasoline Direct Injection engines are similar to diesel engines in that they can directly inject the fuel into the compressed air already in the cylinder. Therefore, the Atkinson cam's outflow event would only expel unnecessary air, and the mixture could be leaned by the GDI computer (ECU) to account for the outflow from the Atkinson cam, so that each cylinder could be individually fed it's own fuel supply without an outflow of fuel from the previous cylinder to suck in.

In that sense, the Atkinson cam is less complex, and easier to create/manufacture, and wins. In any other type of engine, I don't see it being a very reliable system. (Apparently, neither do many auto mfgrs.)

wwest40 - Turbocharger exhaust turbines don't require exhaust gasses to expand to reach full spool. They only require the flow of exhaust gasses. Regardless of the expansion ratio being too large or too small for the engine, the expansion of the exhaust gasses being complete, etc... there will still be exhaust flow and heat energy (not expansion, heat... the exhaust flow will still be hot.), so the turbo will still spool and create the feedback loop that turbochargers create in order to reach maximum speed.

Guess what happens if you have a turbo running off an engine's exhaust, but feeding it's compressed air to something other than the engine that it's leeching exhaust gas pressure from? The turbine will never reach full speed, and the compressor will never reach max potential boost. Turbochargers require a feedback loop to reach their full potential, except in extreme circumstances. (Obviously, if you put a T3/T4 hybrid on a submarine engine, it's going to hit 100,000+ RPMs without the feedback loop.) So I guess I should restate to include the obvious - a turbocharger sized properly for the engine will not fully spool without the feedback loop it creates.

That essentially means that your theory on why you don't see Atkinson Cycle or Atkinson Cammed engines with turbos is a myth, and holds no water in logical thinking or applied science.

If you don't believe that turbos don't require expansion of gasses (as opposed to flow) to operate, put a vacuum cleaner nozzle on one some day. I bet you a dollar it starts to spool up.

And you think an the high volume exhaust flow, enough to drive a turbocharger into overboost, isn't energy that could be better/different used...???

The volume of exhaust flow isn't any different than the Otto engine w/ the same initial displacement as the intake cycle of the Atkinson engine. The volume of gasses is the same.

To answer your question: No, the energy from pulsing exhaust gasses isn't better used than to create more power with less spent energy. The idea of turbocharging has been openly displayed in earlier posts. Given that the actual volume of gas exiting both engines is the same (for comparative purposes), the only difference is that the Atkinson engine has already spent more heat from the expansion of gasses than the Otto engine has. That said, the Atkinson engine already has both a performance and an efficiency advantage over the Otto engine. Being that turbochargers generally exaggerate common efficiency of engines, the Atkinson only stands to benefit from the turbo by a ratio linear with it's advantage over the Otto engine, based on the second "stroke" length of the Atkinson engine in reference as a percentage to the first, i.e. 115% stroke means the Atkinson has a displayed advantage of 15% over the Otto.

What this means for practical application - While an Otto cycle engine has a marginal advantage in complexity and cost of manufacture, the Atkinson engine still proves to be numerically more efficient in an exponential fashion when compared to the Otto. Turbochargers, as suspected, compound the VE advantage that would normally be seen in the Atkinson engine, as do they compound the VE of either engine upon installation.

Unless you can come up with something that hasn't already been discussed, this thread will have reached the end of it's useful life, and I will no longer entertain the same argument without basis for it's existence.

wwest40:

I don't think any engine's combustion event has fizzled out before BDC on the power stroke, by which time the exhaust valve has already opened. Even at partial throttle there is enough air/fuel mixture in a cylinder for very substantial expansion as the fuel vapor is combusted. Expanding the combustion cycle in the Atkinson engine doesn't "waste" movement/momentum on the elongated power stroke, it merely extracts more energy from the expanding gases.

And you don't just compress it to a "native" 13:1 because of detonation. ESPECIALLY at partial throttle. While it is full-load spark knock that will kill an engine in a heartbeat, it is part-throttle pinging that will kill an engine with 10,000 paper cuts. Until we get to high anti-knock index fuels (methanol) you'll be stuck at 11-12:1 max with naturally aspirated Otto cycles.

Christ is right re: turbos' operation, only the reason that you'll never see a turbocharged Atkinson engine is that a "turbocharged Atkinson" is called a Miller engine.

Buffering pressure pulses: ever heard of the analogy between intake air flow and acoustics? The intake "manifold" is somewhat of a muffler on the intake side of the engine. On ALL engines, not just Atkinson, there is unsteady intermittent flow going into each cylinder and when the air mass in the intake ports flows it gains momentum. When the intake valve closes the momentum of the port flow stops and sends a pressure wave reverting up the port opposite the "flow" direction. These pressure pulses leave the intake port into the plenum, which is essentially an open volume common to all (or a good number of) the intake ports and is fed by the throttle body or carb. Since not all reversion pressure waves occur at the same time and each of them is small in magnitude relative to the volume or mass of air in the plenum the plenum pressure is more consistent than the port pressure. Therefore, the plenum acts as a resonant chamber or "buffer volume" to help equalize the effects of the unsteady flow between the cylinders. In the Atkinson engine there is actually a small amount of reversion mass flow instead of just inertial pressure. This reversion flow is small relative to the inlet charge and therefore small relative to the port volume. Port volume is typically small relative to plenum volume, so in this respect both the intake port and plenum act as "buffers."

Christ:

I think you're reading too much into the intake reversion flow. Contrary to popular opinion port fuel injection systems typically inject fuel into the intake port onto a CLOSED intake valve (to give more time to inject fuel and to ensure full vaporization). The head of combustion/exhaust of the preceding cycle starts to vaporize the liquid fuel droplets and the turbulence of the intake event homogenizes the mixture. In a homogeneous mixture there is no "rich" or "lean" part as that would indicate it is non-homogeneous. Since fuel is injected toward the valve the "rich" part of the inlet charge would be drawn in first and turbulence would mix it well or if not the rich portion would swirl near the piston during the intake stroke. With the Atkinson-cam it is the last portion of inlet charge that is expelled. This would either be fully mixed near stoichiometric or worst-case be the "lean" portion of the charge. Since the expelled volume is small relative to the intake port most of this air should remain near the valve of the same cylinder to be re-used during the next intake event in that cylinder. Over multiple cycles the closed-loop ECU control system would learn from the O2 sensor how much fuel needs to be injected PER CYCLE which would already account for the expelled mixture from the previous cycle. Engines and electronic control systems are pretty robust in this regard; they can run sub-optimally pretty well and can be adjusted incrementally.