SPLIT-CYCLE ENGINES

Contents

Sr. No Title Pg. No1 Introduction 22 What is Split Cycle 33 Problems with previous Split Cycle 4

3:1 Breathing (volumetric efficiency) 43:2 Low Thermal Efficiency 4

4 Scudri Split Cycle 55 How Scudri Split Cycle Works 66 How does the air get from one cylinder to the other 87 When and where is the fuel injected 98 P-V curves 99 Why is the Scuderi Spit Cycle Engine Exceptional 11

9:1 Solving Problems 1110 High pressure and massive Turbulence 1111 Advantages of Scuderi Spit Cycle 1212 Conclusion 1313 References 14

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SPLIT-CYCLE ENGINES

1. Introduction

The split-cycle engine is a type of internal combustion engine.

The first four-stroke piston was developed in 1876. This four-stroke piston arrangement is still the primary design of engines built today.

In a conventional otto cycle engine, each cylinder performs four strokes per cycle: intake, compression, power, and exhaust. This means that two revolutions of the crankshaft are required for each power stroke.

The split-cycle engine divides these four strokes between two paired cylinders: one for intake/compression and another for power/exhaust. Compressed air is transferred from the compression cylinder to the power cylinder through a crossover passage. Fuel is then injected and fired to produce the power stroke.

Today’s engines operate at only 33% efficiency. This means that only 1/3 of the energy in each gallon of fuel is used-the rest is lost through friction and heat .With over a billion engines currently in worldwide, even small gains in efficiency will have impacts on the economy, dependency on foreign oil, and the environment.

Split engines appeared as early as 1914.Split cycle engines separate the four strokes of intake, compression power, and exhaust into two separate but paired cylinders. The first cylinder is used for the intake and compression. The compressed air is transferred through a connecting passage or tube from the compression cylinder into the second cylinder where combustion and exhaust occur.

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SPLIT-CYCLE ENGINES

2. What Is Split Cycle?

Split cycle engines are the ones which separate the four strokes intake, compression, power and exhaust of conventional engine in to two separate paired strokes to occur in two separate cylinders namely compression and power cylinders. In the compression cylinder the Intake and compression of air takes place.

The compressed air is then transferred through a crossover passage from the compression cylinder in to the power cylinder. In the power cylinder the fuel is injected and burned to undergo combustion and exhausted stroke. A split cycle is an air compressor on one side and the combustion chamber on another side.

When compared to the convention spark ignition engine, the split cycle engine will be having two cylinders namely compression and power cylinders, two pistons which are connected to the crank shaft with some phase difference. The split cycle engine will produce one power stroke for every one revolution of the crank shaft when compared to the conventional engine producing one power stroke for every two revolutions of the crank shaft.

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SPLIT-CYCLE ENGINES

3. Problems with previous Split Cycle Engines

The two main drawbacks of split cycle engine are poor breathing and low thermal efficiency.

3.1 Breathing (Volumetric Efficiency)

The breathing problem was caused by high-pressure gas trapped in the compression cylinder. This trapped high-pressure gas needed to re-expand before another charge of air could be drawn into the compression cylinder, effectively reducing the engine's capacity to pump air and resulting in poor volumetric efficiency.

3.2 Low Thermal Efficiency

The thermal efficiency of split-cycle engines has always been significantly worse than a conventional Otto cycle engine. The primary reason: They all tried to fire like a conventional engine - before top dead center (BTDC).

In order to fire BTDC in a split-cycle engine, the compressed air, trapped in the crossover passage, is allowed to expand into the power cylinder as the power piston is in its upward stroke. By releasing the pressure of the compressed air, the work done on the air in the compression cylinder is lost. The power piston then recompresses the air in order to fire BTDC.

By allowing the compressed gas in the transfer passage to expand into the power cylinder, the engine needs to perform the work of compression twice. In a conventional engine, the work of compression is done only once; consequently, it achieves much better thermal efficiency.

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SPLIT-CYCLE ENGINES

4. Scuderi Split Cycle Engine

This engine is proposed by late Carmelo scuderi (1925 -2002) who spent over 40 years inventing, developing and commercializing new technology.

The Scuderi split cycle engine technology changes the heart of the I.C engine. By using fluid and thermodynamic techniques, the scuderi technology improves how an engine converts chemical energy to mechanical energy.

In Scuderi engine as shown in the Fig , the two pistons are connected to the crank shaft with two different crank throws and are in phase with each other.

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SPLIT-CYCLE ENGINES

5. How It Works

The base Scuderi Engine is a split-cycle design that divides the four strokes of a conventional combustion cycle over two paired cylinders. one intake/compression cylinder and one power/exhaust cylinder. The power piston will be leading the compression piston by 25o of crank angle. i.e., when the power piston is at the TDC the compression piston is approaching the TDC and when the compression piston reaches TDC, power piston is moving away from the TDC. Another modification proposed by Scuderi is firing after top dead centre. All the split cycle are fired before top dead centre which leads them to low thermal efficiency. The method of firing ATDC will reduce the work of recompressing the gas, which generally takes place in ordinary split cycle engines.

Due to high compression ratio the high pressurized gas will be entering into the power cylinder with high turbulence, this result in very rapid atomization of the fuel and creates a fast flame speed or combustion rate faster than any previous methods. This will enhance the thermal efficiency of the split cyclIn the Scuderi Engine, firing ATDC is accomplished by using a combination of high-pressure air in the transfer passage and high turbulence in the power cylinder.

Because the cylinders in a Scuderi Split-Cycle Engine are independent from each other, the compression ratio in the compression cylinder is not limited by the combustion process. A compression ratio in the order of 75:1 is obtained, with pressure in the compression cylinder equal to that of a conventional engine during combustion. The pressure in the compression cylinder and the crossover passage reach more than 50 bar (725 psi) on our naturally aspirated (NA) engine and more than 130 bar (1885 psi) on our turbocharged (TC) engine.

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SPLIT-CYCLE ENGINES

This high-pressure air entering the power cylinder creates massive turbulence. The turbulence is further enhanced by keeping the valves open as long as possible during combustion.

The result is very rapid atomization of the air/fuel mixture, creating a fast flame speed or combustion rate faster than any previously obtained.

The combination of high starting pressure and fast flame speed enables combustion to start between 11 and 15 degrees ATDC and end 23 degrees after ignition.

The result is a split-cycle engine with better efficiency and greater performance than a conventional engine. e engines.

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SPLIT-CYCLE ENGINES

6. How Does The Air Get From One Cylinder To The Other

There is a short passageway connecting the cylinders.

A conventional cam-actuated valve admits air to the combustion chamber, but a pressure activated disk type valve admits air into the passageway from the compression chamber and prevents it from leaking back onto the intake cylinder.

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SPLIT-CYCLE ENGINES

7. When and where is the fuel injected

Fuel is injected directly into the cylinder just as the valve opens.

The highly compressed air whooshes in so quickly and atomizes the injected fuel so thoroughly that the spark is fired to ignite it 11 to 15 degrees after TDC, even when running lean mixtures for increased efficiency.

The combination of high starting pressure and fast flame speed enables combustion to start between 11 and 15 degrees ATDC and end 23 degrees after ignition. The result is a split-cycle engine with better efficiency and greater performance than a conventional engine.

8. P-V Curves

In an internal combustion engine, the two high-pressure strokes of compression and power consume and produce energy. The compression stroke is negative work, or energy that the engine expends to do work on the gas. T

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SPLIT-CYCLE ENGINES

he power stroke is positive work, or energy that the expanding gases of combustion perform on the engine to create mechanical work.

The net energy produced by the engine (its efficiency) is the energy generated during the power stroke less the amount of energy consumed by the compression stroke. The areas inside the curves reflect the amount of energy used or generated during each cycle.

Whenever the engine is operating on compressed air stored in its air storage tank, the losses due to compression are reduced to nearly zero. The resulting efficiency of the engine under this mode of operation is essentially the total area of the power curve

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SPLIT-CYCLE ENGINES

9. Why Is The Scuderi Split-Cycle Engine Exceptional?

The Scuderi Split-Cycle Engine solves both the breathing and thermal efficiency problems with two unique and patented concepts.

9.1 Solving the Thermal Efficiency Problem - Firing After Top Dead Center (ATDC)

Although considered bad practice in conventional engine design, firing ATDC in a split-cycle arrangement eliminates the losses created by recompressing the gas.

The big issue was not how to solve the thermal efficiency problem of the split-cycle engine, but rather how to fire ATDC. In fact, determining how to fire ATDC is possibly the single most important breakthrough of the Scuderi Engine design.

10.High Pressure and Massive Turbulence

In the Scuderi Engine, firing ATDC is accomplished by using a combination of high-pressure air in the transfer passage and high turbulence in the power cylinder.

Because the cylinders in a Scuderi Split-Cycle Engine are independent from each other, the compression ratio in the compression cylinder is not limited by the combustion process.

A compression ratio in the order of 75:1 is obtained, with pressure in the compression cylinder equal to that of a conventional engine during combustion. The pressure in the compression cylinder and the crossover passage reach more than 50 bar (725 psi) on our naturally aspirated (NA) engine and more than 130 bar (1885 psi) on our turbocharged (TC) engine.

This high-pressure air entering the power cylinder creates massive turbulence. The turbulence is further enhanced by keeping the valves open as long as possible during combustion. The result is very rapid atomization of the air/fuel mixture, creating a fast flame speed or combustion rate faster than any previously obtained. The combination of high starting pressure and fast flame speed enables combustion to start between 11 and 15 degrees ATDC and end 23 degrees after ignition. The result is a split-cycle engine with better efficiency and greater performance than a conventional engine.

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SPLIT-CYCLE ENGINES

11. Advantages of the Scuderi Split-Cycle

One of the biggest advantages of the Scuderi Split-Cycle Technology is design flexibility.

Many features that require additional equipment or are just too difficult to implement in a conventional engine design are easily accomplished with a Scuderi Split-Cycle configuration.

For example, supercharging can be added simply by increasing the diameter of the compression cylinder. Piston friction can be reduced by offsetting the compression and power cylinders.  

The split-cycle design proves not only to be more efficient but also less polluting:

Up to 50% decrease in CO2 emission.

Potential for a substantial decrease in NOx emission

Reduction in CH and CO emission

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SPLIT-CYCLE ENGINES

12.Conclusion

From the functional point of view the Scuderi split cycle engine is having an inbuilt turbo charger. The peak pressure obtained in the Scuderi engine is 11 bar more than the conventional engine at 3000 rpm. The combustion in the Scuderi engine is rapid when compared to the conventional SI engine due to high initial pressure, temperature and turbulence. The turbulence in the Scuderi engine is high compared to the conventional engine which aids in rapid propagation of flame and rapid combustion.

There will be difference between the peak pressure developed in the fuel air cycle and the analysis result, because the fuel air cycle cannot take the losses into consideration. In p-V plots the area under the curve of Scuderi engine is more. Hence the work done on the piston is more in this case when compared to the conventional SI engine. The torque of the Scuderi is more at low speed and gradually decrease as it reaches high speed, which is the characteristic nature of diesel engines. The thermal efficiency of the Scuderi engine is 5-10% more than the conventional SI engine. Finally, from the power and torque curves, we can see that the performance of Scuderi engine is 15- 20% more compared to conventional engine.

The scuderi split cycle engine is having thermal efficiency about 42.6%,which is far more better then conventional engine.

It greatly reduces the wastage of fuel, which is most important thing to countries like India ,which is dependent on foreign countries for petroleum fuels. It reduces the burden on the imports customs.

By using ATDC technique we can greatly reduce the losses created by re-compressing the gas. So , by using this scuderi split cycle engine, we can change the world of IC engines.

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SPLIT-CYCLE ENGINES

13. References

[1] Scuderi Group LLC (2009), Split Cycle Four Stroke Engine, available at www.freepatentsonline.com.

[2] Scuderi Group LLC, “Split Cycle Engine With helical Crossover Passage”, at www.ScuderiGroup.com.

[3] Scuderi Group LLC, “Part Load Control in Split Cycle Engine”, at www.scuderigroup.com

[4] Ganeshan,V.(2007) “Internal Combustion Engines, Third edition”, Tata McGraw-Hill, New-Delhi,.

[5] John Heywood, (1988) “Internal Combustion Engine Fundamentals”, Tata McGraw-Hill. New-Delhi.

[6] Scuderi Group LLC, “Scuderi- Engine Brochure”, at www.ScuderiEngine.com

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