Atkins cycle/PRIUS/Waste heat - Lithium wheelchairs
Discussion
I see that Prius runs on the Atkins Cycle which over-expands the combustion gases during the power stroke to extract more power ... rather than dump it down the exhaust.
A neat trick - increasing economy and a breath of fresh air for the old IC engine as oil prices and pollution close in on it.
Before we are all forced into the innevitable Lithium powered wheelchairs - are we missing something important in this extended power stroke technology ?
A neat trick - increasing economy and a breath of fresh air for the old IC engine as oil prices and pollution close in on it.
Before we are all forced into the innevitable Lithium powered wheelchairs - are we missing something important in this extended power stroke technology ?
Atkins cycle et al:
It may be worth taking a look at the MECXIC engine ?
It may be worth taking a look at the MECXIC engine ?
cptsideways said:
It's only really suitable for applications with additional load motors, its not ideal for high output applications due to emissions I beleive. Ideal if the engine only ever runs in Lambda I believe.
I might be wrong though!
I might be wrong though!
David Mason said:
I see that Prius runs on the Atkins Cycle which over-expands the combustion gases during the power stroke to extract more power ...
Essentially an Atkins cycle engine has a greater effective power stroke than inlet stroke. The new Fiat Multi-air engine uses the same technique as the Prius; by keeping the inlet valve open somewhere past BDC you reduce the effective inlet stroke. This also allows you to "throttle" the engine without the associated pumping losses of an actual throttle.Don't think the purpose of Prius cycle is improved throttling - the whole idea is to over-expand the intake charge and extract more work from the heat which we currently are all guilty of dumping down the exhaust pipe !
What we need to think about is how to achieve this type of engine cycle:
Suck in eg 100c3 air: add just enough fuel for 100c3: BUT now EXPAND it through (eg) 150c3 to extract more work from the heat we have just added.
Normal IC engine suck in and expand by the same volume due to their crank/piston geometry - we need to stop dumping these red hot unexpanded gases down the exhaust pipe and expand the power stroke further - if we can do this properly it will give the old (and soon to die I fear) IC engine a shot in the arm and a quantum leap in it's efficiency/consumption/exhaust gas pollution.
MECXIC takes it several steps further if you see the animation.
What we need to think about is how to achieve this type of engine cycle:
Suck in eg 100c3 air: add just enough fuel for 100c3: BUT now EXPAND it through (eg) 150c3 to extract more work from the heat we have just added.
Normal IC engine suck in and expand by the same volume due to their crank/piston geometry - we need to stop dumping these red hot unexpanded gases down the exhaust pipe and expand the power stroke further - if we can do this properly it will give the old (and soon to die I fear) IC engine a shot in the arm and a quantum leap in it's efficiency/consumption/exhaust gas pollution.
MECXIC takes it several steps further if you see the animation.
Edited by David Mason on Friday 20th November 12:56
Edited by David Mason on Friday 20th November 13:06
Thoroughly agree Guy - it's a super little car and probably the inevitable future (and so quiet too - my dog approves, but I remember Twin-cam Escorts and Quattroes crackling though forests at dawn).
We need to extract every last unit of power out of our IC engines and drop it's pollutants as low as practical before it is universally scrapped soon.
MECXIC goes a long way to achieving this with it's over-expansion approach.
We need to extract every last unit of power out of our IC engines and drop it's pollutants as low as practical before it is universally scrapped soon.
MECXIC goes a long way to achieving this with it's over-expansion approach.
Edited by David Mason on Friday 20th November 13:06
the atkins cycle works by holding the inlet valve open for longer past btc reducing the compression, the engine itself revs only to around 3000rpm this creates less loads on the engine as its main function is to recharge the batery through the motor in the gear box, the battery then powers the 2nd motor in the gearbox to the wheels.
with the lower compression less fuel is used and prevents strain on the engine its self as its rarely abussed, it also always burns the right amount of fuel as only a small amount of it gets fully compressed and burt.
with the lower compression less fuel is used and prevents strain on the engine its self as its rarely abussed, it also always burns the right amount of fuel as only a small amount of it gets fully compressed and burt.
Yes, that's how I understand the workings of the Prius Atkins cycle too Skid-Mark .... but the whole purpose is to over-expand the reduced intake charge and suck more heat out of it as useable work.
I bet the thermal efficiency of the Prius engine is much better that 'normal' ICs and therefore the economy is better too.
I'm sure more & more engines will run on the Atkins cycle soon ?
I bet the thermal efficiency of the Prius engine is much better that 'normal' ICs and therefore the economy is better too.
I'm sure more & more engines will run on the Atkins cycle soon ?
i'm sure more engines will use the atkins cycle but only if they have another power soure to back it up ie batterys as on its own its not powerfull enough, the newest valve tec is the vavle matic developed by toyota again, this time the inlet vavles are controled by an electric motor, the vavles move up and down adjusting the length they are opened works a bit like vvt but the valves are belive it or not controlling the engines speed, this does away with all the throttle buterfly control, the elec motor is sat on the side of the cylinder head as it recives the signal to rev higher the motor turns a shaft which has a set of gears on it, the gears act like a corkscrew the more it turns the more the vavle opens in lengh allowing the engine to rev higher,
this also befits in the same way with precise fueling/vavle clearance to achive a powerful engine with low emissions.
this also befits in the same way with precise fueling/vavle clearance to achive a powerful engine with low emissions.
skid-mark said:
i'm sure more engines will use the atkins cycle but only if they have another power soure to back it up ie batterys as on its own its not powerfull enough, the newest valve tec is the vavle matic developed by toyota again, this time the inlet vavles are controled by an electric motor, the vavles move up and down adjusting the length they are opened works a bit like vvt but the valves are belive it or not controlling the engines speed, this does away with all the throttle buterfly control, the elec motor is sat on the side of the cylinder head as it recives the signal to rev higher the motor turns a shaft which has a set of gears on it, the gears act like a corkscrew the more it turns the more the vavle opens in lengh allowing the engine to rev higher,
this also befits in the same way with precise fueling/vavle clearance to achive a powerful engine with low emissions.
BMW have been fitting their version of this variable inlet valve lift throttle elimination system to their engines for years now.this also befits in the same way with precise fueling/vavle clearance to achive a powerful engine with low emissions.
I don't consider that the Atkins cycle is a secondary solution Gavin - it sets out to extract more heat (power) from the same charge than a traditional reciprocating engine could.
I'm sure we are about to see a huge surge of interest in over-expanding during the power stroke of all IC engines..... as I said - look at MECXIC: more power and whacking torque due to eccentric offset of the crank during the power stroke from a given intake charge!
Big gains in power and economy are out there just waiting for us to find a neat and effective mechanical arrangement to release them and give the IC engine a new lease of life.
We have to find a way of extracting more heat from each bang - rather than dumping it down the exhaust pipe as we currently do.......
Think of double or triple expansion in the highly efficient (and powerfull)steam engines - but applied to IC engines, and we are on the right track I think.
I'm sure we are about to see a huge surge of interest in over-expanding during the power stroke of all IC engines..... as I said - look at MECXIC: more power and whacking torque due to eccentric offset of the crank during the power stroke from a given intake charge!
Big gains in power and economy are out there just waiting for us to find a neat and effective mechanical arrangement to release them and give the IC engine a new lease of life.
We have to find a way of extracting more heat from each bang - rather than dumping it down the exhaust pipe as we currently do.......
Think of double or triple expansion in the highly efficient (and powerfull)steam engines - but applied to IC engines, and we are on the right track I think.
the best way to use the atkins cycle is in a rotary engine this i can see to be a big winner as it can run on diesel,petrol or hydrogen with out to much modification and achive big power,
however you will always have problems of achiving big power using the atkins cycle vs the otto cycle because part of the atkins cycle is compressing the inlet fuel/air mixture back to atmosphere yes it is very good at not producing much heat waste but in doing so its not compressing as much air as a otto cycle thus making it under powered but very fuel efficient.
however you will always have problems of achiving big power using the atkins cycle vs the otto cycle because part of the atkins cycle is compressing the inlet fuel/air mixture back to atmosphere yes it is very good at not producing much heat waste but in doing so its not compressing as much air as a otto cycle thus making it under powered but very fuel efficient.
David Mason said:
Did you mean EXPANDING back to atmospheric skid-mark ?
I can forsee a huge benefit in turbo IC engines in over-expanding the power stroke as there is so much heat dumped (even allowing for the expansion through the turbo) ......
Thats how the Mazda Millenia engine works I can forsee a huge benefit in turbo IC engines in over-expanding the power stroke as there is so much heat dumped (even allowing for the expansion through the turbo) ......
from 10 years agoDavid Mason said:
Mazda Millenia: Now that's really interesting - any idea how the engine achieved this cptsideways ??
From wiki Edited by David Mason on Tuesday 1st December 10:04
This type of engine was first used in ships and stationary power-generating plants, but was adapted by Mazda for their KJ-ZEM V6, used in the Millenia sedan, and in their Eunos 800 sedan (Australia) luxury cars. More recently, Subaru has combined a Miller cycle flat-4 with a hybrid driveline for their "Turbo Parallel Hybrid" car, known as the Subaru B5-TPH.
A traditional Otto cycle engine uses four "strokes", of which two can be considered "high power" – the compression stroke (high power consumption) and power stroke (high power production). Much of the internal power loss of an engine is due to the energy needed to compress the charge during the compression stroke, so systems that reduce this power consumption can lead to greater efficiency.
In the Miller cycle, the intake valve is left open longer than it would be in an Otto cycle engine. In effect, the compression stroke is two discrete cycles: the initial portion when the intake valve is open and final portion when the intake valve is closed. This two-stage intake stroke creates the so called "fifth" stroke that the Miller cycle introduces. As the piston initially moves upwards in what is traditionally the compression stroke, the charge is partially expelled back out the still-open intake valve. Typically this loss of charge air would result in a loss of power. However, in the Miller cycle, this is compensated for by the use of a supercharger. The supercharger typically will need to be of the positive displacement (Roots or Screw type) type due to its ability to produce boost at relatively low engine speeds. Otherwise, low-rpm torque will suffer.
A key aspect of the Miller cycle is that the compression stroke actually starts only after the piston has pushed out this "extra" charge and the intake valve closes. This happens at around 20% to 30% into the compression stroke. In other words, the actual compression occurs in the latter 70% to 80% of the compression stroke.
In a typical spark ignition engine, the Miller cycle yields an additional benefit. The intake air is first compressed by the supercharger and then cooled by an intercooler. This lower intake charge temperature, combined with the lower compression of the intake stroke, yields a lower final charge temperature than would be obtained by simply increasing the compression of the piston. This allows ignition timing to be advanced beyond what is normally allowed before the onset of detonation, thus increasing the overall efficiency still further.
An additional advantage of the lower final charge temperature is that the emission of NOx in diesel engines is decreased, which is an important design parameter in large diesel engines on board ships and power plants.
Efficiency is increased by raising the compression ratio. In a typical gasoline engine, the compression ratio is limited due to self-ignition (detonation) of the compressed, and therefore hot, air/fuel mixture. Due to the reduced compression stroke of a Miller cycle engine, a higher overall cylinder pressure (supercharger pressure plus mechanical compression) is possible, and therefore a Miller cycle engine has better efficiency.
The benefits of utilizing positive displacement superchargers come with a cost. 15% to 20% of the power generated by a supercharged engine is usually required to do the work of driving the supercharger, which compresses the intake charge (also known as boost).
A similar delayed-valve closing method is used in some modern versions of Atkinson cycle engines, but without the supercharging. These engines are generally found on hybrid electric vehicles, where efficiency is the goal, and the power lost compared to the Miller cycle is made up through the use of electric motors.
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