A diesel engine is an internal combustion engine that uses the heat of compression to initiate ignition to burn the fuel, which is injected into the combustion chamber during the final stage of compression. Diesel engines have wide range of utilization for automobiles, locomotives & marines and co-generation systems. However, large problem is still related to undesirable emission.
The six-stroke engine is a type of internal combustion engine based on the four-stroke engine but with additional complexity to make it more efficient and reduce emissions. Two different types of six-stroke engine have been developed:
In the first approach, the engine captures the heat lost from the four-stroke Otto cycle or Diesel cycle and uses it to power an additional power and exhaust stroke of the piston in the same cylinder. Designs use either steam or air as the working fluid for the additional power stroke. The pistons in this type of six-stroke engine go up and down three times for each injection of fuel. There are two power strokes: one with fuel, the other with steam or air. The currently notable designs in this class are the Crower Six-stroke engine invented by Bruce Crower of the U.S. ; the Bajulaz engine by the Bajulaz S.A. company of Switzerland; and the Velozeta Six-stroke engine built by the College of Engineering, at Trivandrum in India.
The second approach to the six-stroke engine uses a second opposed piston in each cylinder that moves at half the cyclical rate of the main piston, thus giving six piston movements per cycle. Functionally, the second piston replaces the valve mechanism of a conventional engine but also increases the compression ratio. The currently notable designs in this class include two designs developed independently: the Beare Head engine, invented by Australian Malcolm Beare, and the German Charge pump, invented by Helmut Kottmann.
To improve exhaust emissions from diesel engines, a new concept of Six Stroke Engine has been proposed. This engine has a second compression and combustion processes before exhaust process. [pic]
Fig 1 Diesel engine sectional view Fig 2 Ideal Otto cycle
Fig 3 Pressure- Volume diagrams for dual cycle
As the fuel in one cycle was divided into two combustion processes and the EGR (Exhaust Gas Recirculation) effect appeared in the second combustion process, the decreased maximum cylinder temperature reduced Nitrous Oxide (NO) concentration in the exhaust gas. It was further confirmed that soot formed in the first combustion process was oxidized in the second combustion process .Therefore, a six stroke diesel engine has significant possibilities to improve combustion process because of its more controllable factors relative to a conventional four-stroke engine.
Since the cylinder temperature before the second combustion process is high because of an increased temperature in the first combustion process, ignition delay in the second combustion process should be shortened. In addition, typically less desirable low cetane number fuels might also be suitable for use in the second combustion process, because the long ignition delays of these fuels might be improved by increased cylinder temperatures from the first combustion process.
Methanol was chosen as the fuel of the second combustion. The cetane number of methanol is low and it shows low ignitability. However, since methanol will form an oxidizing radical (OH) during combustion, it has the potential to reduce the soot produced in the first combustion process.
Fig 4 Comparison of 4 stroke and 6 stroke cycle
2. BAJULAZ SIX STROKE ENGINE
The majority of the actual internal combustion engines, operating on different cycles have one common feature, combustion occurring in the cylinder after each compression, resulting in gas expansion that acts directly on the piston...
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