• Jan 19, 2006
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. 


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  • 22 Comments
      • 8 Years Ago
      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.
      • 8 Years Ago
      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.
      • 9 Years Ago
      mc culloch chain saw company developed a 2 stroke engine using the same system,a extra piston to compress the fuel mixture back in 1971. we tested them on go karts but the never made it to market
      • 9 Years Ago
      Can you imagine how much hotter the combustion cylinder would be compared to the compression cylinder? That seems to me like a lot of stress on an engine block.
      I guess when you only run computer simulations you don't have worry about these sorts of issues.
      • 8 Years Ago
      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
      • 8 Years Ago
      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.
      • 9 Years Ago
      There has been a significant amount of questions recently regarding the Scuderi Engine, especially in light of the funding approved by the federal government for its development. As president of the Scuderi Group and one of the inventors of the engine, I thought it might be helpful to try to clear-up some of the basic misconceptions about the engine.

      The Scuderi Engine does take advantage of the Miller Effect but not in the method used by conventional engines. The Miller Effect in the Scuderi Engine is achieved by having a longer stroke on the power cylinder verses the compression cylinder - not by leaving the intake valve open and supercharging the intake. However, this is only one feature of the Scuderi Engine that helps to improve efficiency. From a thermodynamic prospective the objective for increasing engine efficiency is to somehow increase the area under the pressure volume (PV) curve of the Otto Cycle. In the Scuderi Engine, the PV diagram is really two separate curves - one for compression and one for combustion. It is the difference in the areas under the curves that determines the efficiency of the engine.

      There have been split-cycle engines in the past. However, they have never functioned as well as conventional Otto cycle engines for two main reasons. First, their volumetric efficiency (how well air is pumped through the engine) was never as good as a conventional design. This caused the split-cycle engines to be larger resulting in a lower power density and greater frictional losses especially on part load. Second, compressing the gas in the compression cylinder and again in the power cylinder (because they fired before top dead center) was doing work on the gas twice. Consequently, they were never as efficient as a conventional engine. However, if you could solve these problems, the advantage of the split configuration is that it really is two systems in one - a compressor and an engine. This gives you a great deal of design flexibility.

      The Scuderi Engine solves both problems by using some unique valve designs and by firing after top dead center (ATC). It was the firing ATC that was really the major hurtle that had to be overcome. Normally firing ATC is considered bad practice in engine design; it causes reductions in both power and efficiency. In the Scuderi Engine, the combustion process begins with high pressure air entering the power cylinder from the crossover passage. Massive turbulence is generated in the cylinder causing very rapid atomization of the fuel-air mixture. The result is a flame speed, or rate of combustion, that is twice as fast as anything previously obtainable. Because of the rapid rate of combustion, high pressures on the power piston are achieved even though the piston is pulling away from the firing point. The effect is a split configuration with actually higher efficiency and more power density than a conventional engine. (The firing point for the Scuderi Engine is between 10 and 15 degrees ATC.)

      An interesting phenomenon that resulted from firing after top dead center was reduced peak temperatures. Our power cylinder does have higher average temperatures than a conventional system; however, its peak temperatures are considerably lower. It is the peak temperatures of combustion that generate the NOx emissions. Because Scuderi Engines peak temperatures are significantly lower, the amount of NOx produced is up to 80% less than a conventional engine.

      Because of its design flexibility, the Scuderi Engine makes it possible to enhance efficiency and performance in ways that are difficult, if not impossible, in a conventional design. The Miller Effect, for example, can easily be achieved by increasing the length of the power cylinder. Simply increasing the diameter of the compression cylinder can supercharge the engine without any added equipment or complexity. (A four-cylinder engine could give you the power of a six-cylinder engine but have approximately the size, weight and cost of a four cylinder.)

      However, one of the most amazing features of the Scuderi Engine is that it really is two systems in one - an air compressor on one side and a combustion engine on the other. By having fuel only enter the engine at the power cylinder through direct cylinder injection, the compression cylinder is pumping only air. This makes the Scuderi Engine the ideal engine for an air-hybrid system. This feature of the engine has only recently been patented and is expected to have a huge impact on the market.

      By simply adding a storage tank and some controls, the engine would have the ability to store energy normally lost during braking. (Similar to the current electric hybrids) The big difference is that the Scuderi Air-Hybrid only requires one system, not two. Since the Scuderi Engine already uses compressed air in its combustion process, it can utilize the energy stored in the tank without modifying how it op
      • 8 Years Ago
      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?
      • 8 Years Ago
      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?
      • 8 Years Ago
      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.
      Butch
      • 8 Years Ago
      What is the point of commenting on something that does not exist to date!
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