Scuderi puts another twist on the Otto cycle
I'll admit to having a soft spot in my heart for those that make an honest effort at refining 140-year-old technology, and so I'm eagerly awaiting to see the outcome of Scuderi's recent win of a $1.2M Department of Defense contract to develop its split-cycle engine.
So what exactly does Scuderi's concept involve? I think it's best shown via an animation or a walk though the company's full theory of operation, but if forced to put it into a few words, I'd describe this as a Miller-cycle engine that uses half of the engine's cylinders to provide mechanical supercharging.
So, what are the advantages of
this combustion cycle? Well essentially, it aims to do what any refinement of the Otto cycle wishes to achieve - higher peak
pressure, and lower post-combustion pressures. If we look at this graph of the cycle to the left, it's advantageous to
increase the height of points 3 and 4 while decreasing the height of point 5 and 6 (and the closer we can gets points 5
and 6 to each other, the more energy we extract from the fuel). Specifically, Scuderi's cycle is much like the Miller cycle in that it attempts to delay the opening of the exhaust valve as much as possible to take full advantage of the expanding combustion gases. Traditionally, the Miller cycle -completely unrelated to Miller Time, by the way - uses a mechanical supercharger to prevent reversion of the exhaust gases into the intake tract. Scuderi uses the compression cylinder and a poppet valve and check valve arrangement in the crossover passage to the same effect.
Additionally, Scuderi claims that the mixture has a much faster burn rate, and can be ignited at or just after top dead center (TDC). Typical Otto cycle engines touch off the mixture 30-40 degrees before TDC, and thus there is some counterproductive use of the mixture as it starts to expand while the piston is still attempting to compress it. Because of this, there's also said to be a decrease in the oxides of nitrogen (NOx) emissions. Since preignition is less of a concern, the compression ratio can be increased as well.
Scuderi claims that, despite the use of half the cylinders for compression, the engine is more efficient and powerful than a traditional Otto cycle engine of the same displacement and cylinder count. I have no way of personally verifying these claims, so we'll just have to wait and see what the outcome is of the company's DoD contract win.
Reader Comments (Page 1 of 2)
paul 11:23AM (2/14/2006)
Sal my good man, I think you scared everyone off! I'll try to stir up some much-needed discussion here.
Will you be able to effectively cool the block without using an expensive, exotic metal in its construction? Have additional water passages around the cylinder been considered in the design at Southwest Research Institute?
-How about the long term stresses on a block where the side containing the power cylinders reaches a much higher temperature than the compression cylinders? Warping of the block would be catastrophic to all of the internal components. Minor warping would at least tear up the piston rings. Perhaps staggering (flipping around) the placement of power/compression cylinders could help alleviate this.
The air tank seems to help with the volumetric losses that might be associated with the previous design's short crossover valve. Valve timing is still essential such that the air is let into the power cylinder at just the right time and without any of the flame making its way back into the air tank. Will mechanical means (ie a cam) control these valves or do you anticipate the ability to control these valves pneumatically with the air tank? Will there only be two valves (in/out) on the air tank between the compression and combustion chambers?
Imagine a military application where the air tank of one vehicle is being utilized by many external accessories at once. How will this air pressure be regulated? It seems possible to overuse the compressed air in the tank and rob the engine of getting enough compressed air into the power cylinders.
Looking forward to your answers!
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terry miller 10:44PM (3/20/2006)
Paul posted some very good questions on Feb 14th in response to Sal Scuderi's informative letter on Jan 24th that I hoped would be answered. Three real concerns- engine block heat, valve timing in the combustion chamber,and valve speed and timing on the compression side.
Please respond
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Ed Pineville 8:14PM (3/25/2006)
US 6,340,004 (issued Jan. 22, 2002) by Richard Patton disclosed a split cycle engine which has what I consider all the elements of the Scuderi cycle. In addition, it has a regenerator which recovers the heat from the exhaust gas, which allows the air, after being compressed, to be preheated by the heat of the exhaust recovered by the regenerator. I would expect such an engine to be made even more efficient. I would like to hear what others have to say about the Patton cycle and its comparison with the Scuderi cycle.
Patton has also two followup patents: us 6,606,970 and 7,004,115.
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paul 4:51PM (4/04/2006)
I spoke to Sal about the heat issue during a recent meeting. In the computer simulations, there is not a significant enough difference in temperature on the compression vs power side to warrant concerns about block warpage.
The valve timing issues are really all about careful timing. A new valve for the exhaust fumes has been developed which will help expel a higher percentage of spent gasses. The valve from the crossover side must be closed before the 'flame front' reaches it. This means that it remains open after the spark plug fires. The flame spreads downwards towards the piston, then comes back up towards the top of the combustion chamber at which point it should be closed.
Regarding the preheating on the Patton cycle, heating intake air (whether charged or not) is counterproductive as it makes the air less dense. Cars with turbo- or superchargers have intercoolers for the purpose of cooling charge air and making it more dense and thus increasing the engine's output.
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Roger Pham 7:17PM (4/17/2006)
Sal Scuderi and Paul did not give satisfactory answer to the question regarding the potentially severe heating of the power cylinder. To understand the magnitude of the severity of this problem in the Scuderi engine in which the power cylinder is constantly underfire and never has a chance to be cooled off by a fresh, cool, low pressure intake charge, we must look at the heat problem in a two-stroke cycle engine. Two stroke engine promises twice the power density as the ubiquitous four-stroke engine, but never, for the past 100 years, get any foothold into significance engine application. Direct injection 2-stroke Orbital engine never made it. Even most lawnmowers and 50cc motorbike uses four-stroke engine. The reason is that excessive heat built-up in the two-cycle engine affecting its reliability, causing frequent engine seizure due to lubricant failure, as can be seen in the high failure rates of two-stroke engine of ultra-light aircraft. And yet, even the failure-prone two-stroker has much more cooling opportunity than the Scuderi engine. After the exhaust stroke, cool intake charge enters the intake ports of a two-stroke engine, and loop-scavengine mechanism carries this cooling charge all the way to the cylinder's head. None of this is happening in the Scuderi engine, making it running even hotter. Analogous to the Scuderi engine is the gas turbine, which has the compressor separate from the combuster-expander (turbine) section, and the turbine blades in these engine encounter heat from 2500-3000 degrees F, forcing very expensive metallurgy in the turbine blades. Aluminum piston melts at ~1200 degrees F or less.
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Craig Beshore 9:00PM (4/30/2006)
For a much simpler way to do this - only one cylinder and piston, see supertwostroke.com
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Gary Allan 1:27PM (5/04/2006)
I'll believe it when I see it. Even with DOD footing a major R&D bill (recouping many $$$) ..this will be too expensive to result in any substantial gain over conventional engines. It always works out that way.
I predict that you will just take what you can get from whomever is willing to pay the premium ..even though it won't pay ..instead of working on lower margins (gotta get that rate of return) and seeing your dream come true.
Good luck!
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Gary Allan 5:50PM (5/04/2006)
Read the concensus of opinion:
http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=8;t=008007;p=1#000008
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Tom 9:57AM (5/16/2006)
Regarding Paul's comments (copied below):
[begin quote]
Regarding the preheating on the Patton cycle, heating intake air (whether charged or not) is counterproductive as it makes the air less dense. Cars with turbo- or superchargers have intercoolers for the purpose of cooling charge air and making it more dense and thus increasing the engine's output.
[end quote]
This is incorrect. Heating the intake air in an open system (as per the intake manifold) does result in lower density and therefore reduced volumetric efficiency and power and so on. Heating the charge in a closed volume (such as in-cylinder or in the crossover passage of this engine) increases the *pressure* and temperature and does not reduce the density, it just adds energy to the charge. The effect of burning fuel in the cylinder is to add heat to the charge, and that definitely does not reduce efficiency, right?
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Phil 3:08PM (5/21/2006)
Regarding the potential heat problems, I think that we need to remember that the Scuderi design fires after top dead center. Since the flame needs to catch up to the power piston the peak temperature on the power piston should be significantly LESS. Therefore, this may not be as big a problem as I initially thought when I first saw the design.
However, the power piston still needs to fire once per revolution, which obviously significantly INCREASES the heat on the power piston.
Therefore, a question remains. Is the decrease in peak temperature enough to overcome the additional heat caused by firing once per revolution? I do not think that this is a question that anyone could reasonably answer without a very through analysis or a prototype.
I would speculate that even if the decrease in peak temperature is not QUITE enough to overcome the additional heat caused by firing once per revolution, it is likely to be relatively close. Perhaps this is a problem that could simply be solved by the use of cooling coils. We will see.
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THOMAS ALLEN GRAVES 3:51PM (11/17/2008)
...Captive Pulse engines include smoothbore two-strokes, they've been in development for many years...You can learn more at www.gravesmagnadyne .com....Get real!
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Shane 5:48PM (6/05/2006)
From what I've seen, Scuderi has something good here. Another company working on a variation of the air injection engine, with some very unique differences, and perhaps advantages, is D-J Engineering. They have also patented their process. I've heard they have a 4-cyl. engine using their technology already installed in a vehicle and they are working to finalize the prototype.
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Butch 7:17PM (7/28/2006)
What is the point of commenting on something that does not exist to date!
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Cactus 5:11PM (9/01/2006)
How about turning this into a two-stroke?
Most of the ingredients are already there.
I'll explain strictly from the perspective of the "power" cylinder, since compression cylinder is independent:
Step 1: Ignition takes place in the "power" cylinder.
Step 2: As the piston nears the bottom of its cycle, it passes by the exhaust port. As exhaust gas begins to rush out, compressed air from the passage is let into the cylinder. This would both scavange the exhaust and help cool the cylinder.
Step 3: On its way back to the top of the stroke, the cylinder passes past the exhaust port, effectively sealing itself.
To me, this seems like a far better approach, especially since this would make it possible to have a huge single valve on the very top of the cylider for optimal air flow.
However, it also makes the whole point of having a compression cylinder redundant. Since mechanical superchargers are far more efficient in compressing air, without having to worry about block warping.
In addition, having an "air-hybrid" option would be far easier to achieve: a simple clutch on the supercharger would do the trick.
Can anyone point to problems with my approach?
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Mark Eckerberg 3:35PM (9/04/2006)
Possible problem:
The crossover valve will need to be able to withstand a pressure differential from either direction. They say it is a common poppet-style valve which will be self-sealing against its seat during the power cycle, but will crack open against its valve spring during the exhaust cycle. This is based on the statement that combustion pressure is maintained in the crossover passage. The crossover valve would have to be some sort of rotary valve.
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hyperbaric_lenior 9:08PM (7/26/2009)
It seems to me to be that this is less of a twist on the Otto cycle than a Lenoir cycle that has been supercharged. A lot of fuss has been made made about firing a few degrees after TDC. Eh hem, The Lenoir cycle engine in it's usable form fired about 90 degrees after TDC. That is not a very good practice for a couple of reasons such as for the sudden reversal of mechanical stresses that are set up and the flame having to chase the piston but it worked well enough to put on the market at the time. As I recall in a video, A mention of high speed gases and turbulence was made as the methods used to allow for firing after TDC. It seems as more compensation for firing after TDC might actually be needed. See their patent concerning piston dwell. It's a bit of sophistication to allow a relative slowing of the piston's movement while the flame is burning. I would think that once a designer would deviate from a simple sinusoidal reciprocation then a cam of some sort would be in order and crankshafts of any sort put aside. Because there is intake pressure already existing to coax the piston "downward", the issue of pulling on the piston as does a crankshaft and con-rod arrangement might be a mute or easily resolved issue. For instance: In a flat engine design the opposing pistons could be linked together with an extension spring between them. The compression cylinder and the intake system that they have seems way too complicated. I go back to the fact that this is really more like a Lenoir cycle engine with a supercharger. To simply have a few bar of air pressure on tap at the intake that is generated by one of the more efficient means of doing so than by a piston compressor seems like a better way to go. Throttling....Ah, I love this one..shut the intake valve early and light the charge early for lower power. The bonus of this would be more "Miller effect". Perhaps even to an extreme that would provide cool and quiet exhaust. (Stealthy) Now, Back to the cam to be used instead of a crankshaft. It would likely be much like a common cardio cam but it would allow for a pause or dwell after the piston travels downward for a portion of its stroke. During this pause the flame could be given a bit of time to travel. The pause wouldn't have to be a total stopping of the piston but if compression ignition were to be desired then a total pause might be needed and then followed by a short "upward" movement of the piston followed by the "downward" stroke to harvest the power.The cam could be biased to allow for more time (past 180 degrees of rotation) for the power portion of the piston's movement at the expense of the time given to the exhaust portion of the piston's movement. Common poppet valves would be suitable however some procedure to counter the tendency for intake pressure to open the the intake valves might become an issue. Basically this could be just as simple as using some heavier than usual springs or by employing some pneumatic compensating device. Some heads have been designed already that use only air or gases such as nitrogen to replace the more common helical springs. The heads would have no need for a combustion chamber so we would have to create a new head design, right? I don't think so. Some engines have already been made sans combustion chambers in the heads. Some old Lincoln heads and some diesel engine heads were made that way but the most promising to me right now seems to be some heads put out by the Edelbrock company now to fit onto Chevrolet's old "W" engine. You know, the 409 etc. Well, that's all for the moment. Any questions? Feel, free to comment. Walter :)
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Miroslav Kostadinov 6:21AM (9/08/2006)
OK, there are some obvious problems with this design, however there is funding so some people believe these problems could be solved unless they are only interested in easy money ;-)
Several years ago I suggested similar idea to BMW innovation agency. It took them few months to consider it and at the end their conclusion was “thank you, we are not interested”... I understand the BMW decision very well and I agree with them.
In general it does not matter how many advantages you have in your idea if you have a single unsolvable problem that makes the whole design unfeasible. In my case I have the same overheating problem, but let’s assume Scuderi can solve this problem. Then I can give them several ideas how to get even more advantages.
Idea #1.
In the Scuderi design we have separate compression. So why not use some really nice compressor instead of this single acting cylinder–piston type ??
You can use any radial or axial piston type, you can use vane, you can scroll… There are so many compressor types which are more efficient, lighter, simpler, less noise, less vibration, no mass reversion etc.
I use to explain my idea using sliding vane compressor, but you can really use any other type connected to the same shaft.
For a diesel cycle you can use double staged compressor increasing even further the efficiency.
Idea #2
Imagine you choose vane compressor, but why not one with a variable displacement?
Usually you can adjust the displacement in a narrow range, but few % change in the displacement/flow will give you a feasible pressure change in the output. This will give you the ability to dynamically adjust the pressure versus other parameters like engine temperature, air temperature, elevation or even driver’s mood if you want.
Idea #3
Variable displacement compressors can have interesting feature – when you set eccentricity to near zero they can rotate without doing work. This could be very useful in a pneumatic hybrid where the engine can do no compression and run only from a small air tank. Turning off the compression for a short period like acceleration will give you instant boost in the power.
Idea #4
The so called “power cylinder” is nothing but a pneumatic motor. And again the cylinder piston type is not the best type. As I said the heating here is a big problem, so cylinder type can have some advantage in this respect, but the heat is heat for any type and if you could do cylinder-piston, probably you could let’s say vane as well?
I hope there is no need to list again the advantages and variable displacement and so on…
Idea #5
Assuming you have vane compressor and vane motor (or any other rotating type) you can easily implement a diesel cycle, without *any* valve. You can directly connect the compressor and the motor and only have to inject the fuel near by the motor inlet. The design will look very close to a turbine or jet engine…
Idea #6
If you have variable displacement in both compressor/motor you could improve the throttling… Once again in a normal compressor or motor application you do not change the displacement much because change above 5-7% disturbs the volumetric efficiency.
This is like leaving the inlet valve open during the beginning of the compression stroke, but just much simpler to implement.
Idea #7
The motor or as you call it “power cylinder” works between P4 and P5 in your PV diagram, where P5 is usually above the atmospheric pressure…. Why not let the working gas to expand to P7 where P7 to be much lower than the atmospheric level?
In this way the motor will work on a higher pressure difference and will produce more power of course. But also due to the “increased” expansion, the gas temperature will drop as well, reducing the mean temperature.
Of course if P7 is bellow atmospheric pressure level, where the exhaust goes? You need something like a vacuum pump to keep P7 low, right? The vacuum pump is actually another compressor that will “compress” from P7 to P1.
You think that this is a stupid idea?
YES, it will be very stupid if you do not change the gas temperature. However, if the exhaust leaves the motor section with high temperature and traveling down the exhaust pipe it gets cooler and then when it gets cold enough it enters the vacuum pump (compressor) you have yet another thermo dynamical cycle…
Take a pencil and paper and draw the PV diagram!
There are some problems of course; first you need to increase the motor volume. Second, due to the decreased pressure in the exhaust pipes, the gas will not loose as much as of its temperature as it does in a regular engine. So heat rejection must be improved.
What you gain? You can consider this as extra cycle. The efficiency of this cycle will be no better than 10%. So in fact it is questionable – do you want to double the engine size to get 5-10% more efficiency? But don’t forger that this also lowers the average temperature which could be more important in the case…
Idea #8
It is hard to prove that design like the one I describe has any significant advantage over the existing engines. In terms of thermodynamical efficiency or peak efficiency it is very difficult to claim any significant improvement. However, the problem of the existing engines is not the peak efficiency. They do have reasonable efficiency which can hardly be improved, but they can also have extremely BAD efficiency when running idle or out of optimal power level. This is where the hybrids get significant advantages.
I don’t want to discuss all the hybrid-like options which you can get with this design, because too many. For example at any given speed (rpm) using variable displacement you may have completely different mode of operation. The engine could work as compressor only (motor eccentricity near zero), or the opposite – it can work in pure motor mode without wasting power for compression.
You may have more than one compressor, one motor etc, but several units on single shaft or differential (planetary gears). Thus, by turning one unit on or off you can greatly affect the power and efficiency.
Note that once you have small air tank you can easily “start” one unit or the whole engine. The passengers will not feel when the computer is switching one or all units on or off. Just like with the electric motors…
In theory you can reverse the functions. For example if you make the motor eccentricity negative – it will reverse the gas flow and it will start working as a compressor without changing it’s direction of rotation. Imagine what will be the difference in a regular engine if you can have all cylinders doing compression only or all cylinders doing power strokes only. Of course this may not be practical due to the temperature stress…
There are endless combinations, but the most important thing is that such engine can have real idle mode and consume fuel only when producing power. While the existing engines always consume fuel, but not always producing power. They consume fuel even when you hit the brakes…
Isn’t it better if your engine is compressing air when you hit the brakes without burning any fuel, and in the following acceleration it uses this air without doing any compression??
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ke Olofsson 8:22AM (10/05/2006)
I have been in the same thoughts as Scuderi and can see many advantages with his engine. Why not go further to a rotary engine with a similar principle as in the Aucon engine? See www.aucon.se
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Jyoti 12:14PM (11/05/2006)
The expansion piston of Scuderi enine having about 50 degrees phase advance to compression piston. Therefore- according to Scuderi patent (US Pat. No. 7,017,536)- as crossover delivery starts after TDC position of expansion piston, the compression piston gets only 20-25 deg. crank angle (considering the crankshaft offset) to deliver compressed air to the crossover passage before the compression cylinder reaches its TDC. Thereby builds up a massive compression pressure (higher than 750 psi) before the opening of crossover valve and the compression force substantially derived from the drive-shaft. Unfortunately, only 8:1 compression ratio of charge is used for combustion. I think, only this single fact is enough to spoil the claimed benefit of Scuderi engine.
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Mike in SD 1:59AM (10/25/2006)
Forgive a non-engineer's naivete, but the one basic problem that remains unresolved, even with an innovative, imaginative and hopefully successful design like this one, is the loss of efficiency inherent in any resiprocating engine. Might not some of Scuderi's ideas be applied to rotary engines such as the Wankel - or form the basis for an even better new design other than the reciprocating one?
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