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Bryson Jones Per. 6-7 Auto Final Paper The four-stroke cycle is a common way of an engine to go through the four steps of the combustion prosses that powers the crank shaft. The cycle will start with then intake stroke when the intake valve opens and the piston moves from TDC (Top Dead Center, where the piston is at its highest point) to BDC (Bottom Dead Center, where the piston is at its lowest point), By doing this the cylinder is filled with the air/fuel mixture (air/fuel mixture is about 14.7 parts air to 1-part fuel it’s like this because of atmospheres common pressure at sea level is 14.7 pounds). When it reaches close to BDC the intake valve closes sealing the combustion chamber. The reason that this process works is because the volume of the cylinder will increase making a low pressure, similar to pulling on a nerfs gun plunger, with this low pressure the high pressure will rush to the low pressure thus filling the cylinder with the air fuel mix. Near BDC is where the compression Stroke will begin with both valves sealed and the cylinder filled with the air/fuel mix the piston will begin to travel to TDC while doing this the volume in the combustion chamber will decrease thus compressing the air/fuel mixture (this is where compression ratio will come into play, compression ratio is the volume of the combustion chamber at BDC over volume at TDC 8:1 is a normal gas car compression ratio this mean the volume at BDC is about 8 times bigger then the volume at TDC). This will raise the temperature of the mix and will make ignition more efficient. The piston will be approaching TDC when the air/fuel mixture will be ignited, the ignition will cause the fuel gasses to expand and begin the power stroke while the gasses expand the cause high pressure in the combustion chamber and the top of the piston shoving it from TDC to BDC this is where this energy that powers the crank comes from. As the piston is about at BDC the exhaust valve will open. Once again, the piston will move from BDC to TDC and will push all the burnt gasses out of the cylinder through the exhaust valve which was opened at the end of the power stroke. Once the piston reaches TDC the exhaust valve will close and the intake valve will open and begin the cycle all over again. During this process the crankshaft will have completed two complete rotations. The cylinder head has many important components it is also where all the engines power comes from. The cylinder head holds many sealing parts, for example it holds the intake and the exhaust valves these two components are vital for engine for the engine to work they will seal the combustion chamber where compression is formed, and the gasses push off of to push down on the piston. The actuation of the valves is done by the rocker arms which when pushed down will press down on the valve spring and valve stem which will push down and unseal the valve, when this happens it allows the passage of gas in or out of the cylinder. The cam shaft will do the job of pushing down on the rocker arms in a OHC (overhead cam) assembly or pushing up on the valve lifter in a OHV (overhead valve) assembly which will in turn push up on the bottom of the rocker arm opening the valve. The combustion chamber is also formed in the head and the top of the combustion chamber is where the valves are located. The size of the combustion chamber is determined by how deep the head designers decide to make it, it can also be determined by the head gasket the size of the gasket can also contribute to combustion chamber size. The cylinder head also holds passages for intake of the mix of air/fuel to the cylinder. The engine block is the largest part of the engine and holds together the whole engine assembly. The engine block holds many key parts of the engine including the cylinder wall the cylinder wall is where the piston will be held and, where the piston will go to TDC and BDC to pull, compress, and push out gasses. The piston assembly is also held in the engine block the piston assembly is made up of the piston which is then attached to the connection rob by a wrist pin which will also allow for back and forth movement of the piston in the chamber then the connection rod will attach around the crankshaft with connection rod bearing that allow the crankshaft to spin inside of the connection rod and connection rod end cap there is also rings on the piston that allow for the piston to seal to the side of the cylinder. The crankshaft turns the up and down movement of the pistons and translates that to rotational movement that powers not only the drive train but also the cam through the timing-belt. The whole assembly is held together by the main bearing end cap that holds the crank to the bottom of the block. The lubrication system takes the job of moving oil around the entire engine, the reason this is important is because oil serves many applications including lubricating, cushioning, cleaning, cooling, and sealing. Lubricating oil come in three varieties conventional meaning it comes from crude oil and not man made, synthetic its man made this type of oil is more expensive but it does work better, and a synthetic blend that is a mix of the two. All oil has additives that will allow it to work better, additives is what make crude oil into lubricating oil. The crude oil in the lubricating oil is not what wears out over time rather the additive will slowly be burned or used up and once this happens the oil will have to be replaced. If the lubricating system did not do its job it risks the engine seizing or over-heating, the job of the lubricating system is to move the lubricating oil around the engine, it can do this in two basic ways, one way is splash lubrication when the engine relays on moving parts in the engine to splash the oil around the engine, the other way it can move the oil is in a closed system that uses a mechanical pump to pull the oil from the sump and transfer it around the engine through multiple galleries around the head and block. Oil will also help cool the engine, it can do this by running the hot oil through a radiation like device that the oil will conduct its heat on to. If the oil does not cool its life will be cut short because the additives will burn off faster. Engine oil has a specified life cycle depending on your car but you should check the oil every two gas ups.  

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