Study of split engine
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The first four-stroke piston was developed in 1876.
This four-stroke piston arrangement is still the primary design of engines built today.
Todays 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.
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Ever since the invention of first IC engine (Otto engine) in 1976 by NIKOLAUS OTTO, the efficiency of these engines has stagnated at nearly 30%. In spite of rapid advancement in manufacturing and design technologies higher efficiency.
The reason behind it is that, we have been just modifying the engine accessories for better performance.
But the core of the engine is untouched. One of such innovation, which changes the heart of the engine is THE SPLIT INGINE.
The split-single (Doppelkolbenmotor to its German and Austrian manufacturers), is a variant on the two-stroke engine with two cylinders sharing a single combustion chamber.
WHAT IS A SPLIT ENGINE:
Split-cycle engines separates the four strokes of intake, compression, power, and exhaust into two separate but paired cylinders. The first cylinder is used for intake and compression.
Connecting the cylinders is a pressurized crossover passage. The compressed air is then transferred through a crossover passage from the compression cylinder into the second cylinder, where combustion and exhaust occur.
A split-cycle engine is really an air compressor on one side with a combustion chamber on the other.
HOW IT WORKS:
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 precharged 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 to produce the power stroke.
Camshaft-driven poppet valves control airflow in and out of the power cylinder and prevent the combustion process from “backtracking” into the crossover chamber.
The hybrid element of the engine begins in this crossover chamber, where a separate valve controls the flow of excess air into an external storage tank.
The tank is pressurized to a similar degree as the combustion chamber gases – about 735 psi (50 bar) and has a volume of about 1L per each of the engine’s cylinders.
COMPARED TO CONVENTIONAL ENGINES:
Fuel efficiency improvements of 15%-30% initially with further improvements possible.
Potential reduction of NOx emissions of 50% - 80%.
Lower, average operating engine speed reduces engine wear and tear
Design Flexibility—more controllable parameters available for achieving enhanced or customized performance
High torque at low RPM means higher power at lower engine speeds
Same total engine size (number of cylinders and displacement) as comparable conventional internal combustion engines
PROBLEMS ASSOCIATED WITH PREVIOUS SPLIT ENGINES:
On the compression side there was difficulty in moving all the compressed air from the compression cylinder into the crossover passage.
In order to take in the next charge of air, this high pressure air trapped in the cylinder would have to expand out to below atmospheric pressure.
The cylinder size of previous split-cycle engines needed to be larger than the cylinders of conventional engines in order to pump out the same amount of air. The result was a larger, more expensive and less efficient engine
Unique valve design:
On the compression side of the Scuderi Engine, the solved by reducing the clearance between the piston and the cylinder Problem associated with the transfer of high pressure gas is head to less than 1mm.
. This design requires the use of outwardly opening valves that enable the piston to move very close to the cylinder head without the interference of the valves.
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, which has been solved by the below technology.
HOW THE EFFICIENCY IS MORE:
Once the tank is charged, the air supply can be used in several ways.in low-load situations, the compression cylinder can be disabled, allowing the power side of the engine to be fed with stored compressed air from the tank.
Conversely, the power cylinder can be switched off during coasting and braking, thereby allowing the compression cylinder to act as a built-in engine brake.
The charged air could be used to start the engine if the battery runs low, that would have considerable value for commercial trucking and military applications.
In addition, the compressed air could be used to power a pneumatic valve system for the power cylinder, enabling a completely camless design and further improving efficiency.
The compatibility with various types of fuel, including gasoline, diesel, biofuels and natural gas, is just one of the many benefits the company touts.
The split-cycle technology can produce significantly more power than a conventional engine of equal size; nearly double a vehicle’s fuel economy; improve the efficiency of current engines by 24%..
Due to the much faster than in a conventional engine.massive turbulence created by the pressurized air entering the combustion chamber from the crossover passage, the fuel/air charge vaporizes
The power stroke can be made longer than the compression stroke to over-expand the gas for increased thermal efficiency (the Miller Effect).
The compression piston diameter can be made larger than the power piston diameter to supercharge the gas for increased power.
The compression and power cylinders can be independently offset to almost any angle for increased mechanical efficiency.
An extremely fast combustion rate.
A further increase in thermal efficiency.
As the high pressure gas is transferred from one cylinder to another, there may be chances of leakage.
As the power stroke is more turbulent and massive, engine smoothness may get affected. This in turn demands stringent flywheel design.
As the operating temperatures are high, more stable materials have to be used. This may increase its initial cost slightly.
Compression ratio, expansion ratio, TDC phasing and combustion duration are parameters which determines the performance of an IC engine.
When these parameters are applied in the proper configuration, there is a significant improvement in both brake thermal efficiency (BTE) and NOx emissions of an IC engine.
From above discussion we can conclude that there is a significant improvement in above mentioned parameters in Split cycle than the existing conventional engine.