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The heart of the internal combustion engine is a piston connected to a crankshaft, moving up and down in a cylinder through the four strokes of the Otto Cycle, the intake, compression, power and exhaust strokes. In a typical four-stroke cycle engine, power is recovered from the combustion process in these four separate piston strokes within each single cylinder. This basic design has not changed for more than 100 years. The Split-Cycle Engine changes the heart of the conventional engine by dividing (or splitting) the four strokes of the Otto cycle over a paired combination of one compression cylinder and one power cylinder. By splitting the strokes of the Otto cycle over a pair of dedicated compression and power cylinders, the design of each cylinder can be independently optimized to perform the separate and distinct tasks of compression and power.

Gas is compressed in the compression cylinder and transferred to the power cylinder through a gas passage. The gas passage includes a set of uniquely timed valves, which maintain a pre-charged pressure through all four strokes of the cycle. Shortly after the piston in the power cylinder reaches its top dead center position, the gas is quickly transferred to the power cylinder and fired (or combusted) to produce the power stroke. As a result, the split-cycle design provides more flexibility in how engines are built. Features that were understood to be beneficial but impossible to implement in a conventional design can be implemented in the split-cycle design. This paper tries to study the flexibility created by the splitting and device an engine exclusively for bio-diesel.


The first four-stroke piston engine was developed in 1876. This four-stroke piston arrangement is still the primary design of engines built today. Today’s engines operate at only 33% efficiency. This means that only 1/3 of the energy in each litre of fuel is used – the rest is lost through friction and heat. With over a billion engines currently in use worldwide, even small gains in efficiency will have huge impacts on the economy, dependency on foreign oil, and the environment.

Despite immense efforts over the past century, engine efficiency has remained the same. The heart of the internal combustion engine is a piston moving up and down in a cylinder connected to a crankshaft. Its simplicity makes improving performance almost impossible. Small improvements have proven difficult and large improvements have been considered impossible. While the industry struggles for gains in the 1% range; the design of the Split-Cycle Technology pushes engine efficiency and performance to an entirely new level. The very concept of the split cycle gives way to certain in-built advantages:

  1. The power stroke can be made longer than the compression stroke to over-expand the gas for increased thermal efficiency.
  2. The compression piston diameter can be made larger than the power piston diameter to supercharge the gas for increased power; and
  3. The compression and power cylinders can be independently offset to almost any angle for increased mechanical efficiency.

The unique combination of maintaining a pre-charged pressure in the gas passage and firing after top dead center in the power cylinder produces several additional advantages. These advantages include:

  1. An extremely fast combustion rate,
  2. A further increase in thermal efficiency, and A significant reduction in nitrogen oxide (NOx) emissions

The BasicS

The basic concept of the Split cycle Engine is to divide the four strokes of a standard engine over a paired combination of one compression cylinder and one power (or expansion) cylinder. These two cylinders perform their respective functions once per crankshaft revolution. A common misconception is that twice as many cylinders are required. This is simply not accurate. Because this engine fires every revolution instead of every other revolution, the number of power strokes produced is equal to the power strokes produced by two of the conventional piston/cylinder designs. A four cylinder engine would still have four cylinders. There would simply be two sets of paired cylinders instead of four individual cylinders.

Intake and Compression

In the configuration shown, an intake charge (Fig. 1) is drawn into the compression cylinder through typical poppet-style valves.

presentation topics - alternative fuels
presentation topics – alternative fuels

Figure 1 – Intake Stroke

The compression cylinder then pressurizes (Fig. 2) the charge and drives the charge through the crossover passage, which acts as the intake port for the power cylinder. In this illustration, a check is used to prevent reverse flow from the crossover passage to the compression cylinder, and likewise a poppet-style valve (crossover valve) prevents reverse flow from the power cylinder to the crossover passage. The check valve and crossover valve are timed to maintain pressure in the crossover passage at or above firing conditions during an entire four stroke cycle.

presentation topics - alternative fuels
presentation topics – alternative fuels

Figure 2 – Compression Stroke

Power and Exhaust

Combustion occurs (Fig. 3) soon after the intake charge enters the power cylinder from the crossover passage. This means that the start of combustion occurs after the power cylinder passes through its top dead center position (ATC).

The resulting combustion drives the power cylinder down

presentation topics - alternative fuels
presentation topics – alternative fuels

Figure 3 – Power Stroke

Exhaust gases are than pumped out of the power cylinder through a poppet valve to start the cycle over again.


The split cycle engine is a revelation engine design aimed at giving a power boost to the engine’s performance. It combines the merits of the four-stroke engine with the power of two-stroke operation as the engine gives output every two strokes of the piston. Also due to the lower peak temperature we can reduce the NOx emissions. The diesel engine can be made to run completely in bio-diesel by using the heat of the exhaust. To sum up, the split cycle engine is really the engine for tomorrow.



This is Mr.Jose John, 21 yrs old guy, currently pursuing final year mechanical engineering, now become an enthusiastic blogger and a successful entrepreneur.
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  1. Vishwa Gilitwala says:

    Though…I am from Electronics & Communication Engineering Field…But Still this website become the most helpful & make a electronic engineer capable to present the paper on mechanical engineering topic…But At the End of the Day…EC Engg. Rocksss!…So, please also suggest something new for the Electronics world…..Thank You…:)

  2. Bianca says:

    pretty nice stuff.

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