04-08-2012, 03:10 PM
Design and fabrication of two stroke engine powered by compressed gas
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INTRODUCTION
The project titled “Design and fabrication of two stroke engine powered by compressed gas” is an attempt to highlight the various possibilities of acquiring an environmentally friendly and efficient power source. The use of high pressure, expanding gas, to power the engine piston is the fundamental process in the function of all engines with reciprocating pistons.
In this project we have used highly pressurized gas to provide that necessary force to cause reciprocation of the piston and thereby produce power. This gas is introduced into the engine cylinder at the Top Dead Center position of the piston through a timing valve, thereby giving the gas the maximum capacity to impart its force on the piston.
The emission from this process is nil and 100% environmentally friendly. We have shown that with the smallest of changes in our existing engine design we can incorporate this technology in our present modes of transportation. The simple yet dramatic change brought by this system is according to us the most significant aspect of our project.
NEED FOR ALTERNATIVE FUELS
Automobiles are responsible for a tremendous amount of air pollution and wasted energy. These problems impact people all over the world, both motorists and non-motorists alike, by affecting their health, their economies, and their communities.
One way cars create pollution is by contributing to the amount of ground-level ozone (not to be confused with the atmospheric ozone layer).
In the atmosphere, the ozone layer shields the planet from harmful ultraviolet radiation rays. But on the ground, ozone is another matter, causing hazy smog and respiratory problems. Most ozone pollution is caused by motor vehicles, which account for 72% of nitrogen oxides and 52% of reactive hydrocarbons. The seriousness of ground-level ozone should not be underestimated.
Cars also pollute by emitting lead from leaded gasoline. Although the use of lead in gasoline is banned in the United States, leaded gasoline is common in other countries. In fact, of the countries for which data is available, 43% use nothing but leaded gasoline. Many of the rest use at least some leaded gasoline in their energy mix. This is a definite cause for concern.
FOSSIL FUEL AVAILABILITY AND CONSUMPTION
Fossil fuels are hydrocarbons, primarily coal, fuel oil or natural gas, formed from the remains of dead plants and animals. Today most of the automobiles are powered by fossil fuels especially gasoline, diesel and natural gas, which comes under the non-renewable type. According to statistics the estimated reserves of the major fossil fuels are, Oil: 1,050,691 to 1,277,702 million barrels (2003-2005), Gas: 6,040,208 - 6,805,830 billion cubic feet (2003-2005), Coal: 1,081,279 million short tons (2004).
IC ENGINE COMPONENTS
Cylinder
The cylinder of IC engine is considered as the main body of the engine in which piston reciprocates to develop power. It has to withstand very high pressure and temperature because there is direct combustion inside the cylinder. Therefore, the material used should be such that it can retain strength at high temperature, should be good conductor of heat and should resist rapid wear and tear due to reciprocating parts. Generally ordinary cast iron is used but in case of heavy duty engines alloy steels are used.
Cylinder Head
The cylinder head closes the one end of the engine. It houses the inlet and exhaust valve through which the charge is taken inside the cylinder and burnt gases are exhausted to the atmosphere from the cylinder. It is usually cast as one piece and bolted to the top of the cylinder.
Piston and Piston Rings
The function of piston is to compress the charge during compression stroke and to transmit the gas force to the connecting rod and then to the crank during power stroke. The piston of IC engine is usually made of aluminum alloy because of its high thermal conductivity and lower specific gravity.
The piston rings are housed in the circumferential grooves provided on the outer surface of the piston. It gives gas tight fittings between the piston and the cylinder and prevents the leakage of high pressure gases.
WORKING
In four-stroke engine, working cycle is completed in four stroke of the piston or two revolution of the crank. Here, intake and compression process is completed during the first revolution of the crank and correspondingly the expansion and exhaust process are completed during the other revolution of the crank and this cycle is repeated. The various processes are
Intake:
During the intake stroke, the piston moves downward, drawing a fresh charge of vaporized fuel/air mixture. The illustrated engine fuels a poppet intake valve which is drawn open by the vacuum produced by the intake stroke.
Some earlier engines worked this way, however, most modern engines incorporate an extra cam/lifter arrangement as seen on the exhaust valve. The exhaust valve is held shut by a spring.