Cars do have many parts, but the main center of action is their engines. These engines are the sources of power of our cars to make them move and perform their function.
So, how do cars work?
Cars, as well as other types of vehicles, work on the basis of the laws of thermodynamics. Engines operate on a thermodynamic cycle to extract mechanical energy from the heat of combustion. They convert heat to mechanical work. This obeys the first law, which states that one form of energy can be converted into another, as well as the second law, which states that the natural tendency of the heat is to flow from the high temperature reservoir to the low temperature reservoir.
How do engines work?
The automobile engines are internal combustion engines where the combustion takes place internally.
The principle behind any reciprocating internal combustion engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas.
Most cars currently use a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867.
1stStroke - INTAKE: The piston starts at the top, the intake valve opens. When the piston reaches the bottom of the intake stroke, the intake valve closes, trapping the air-fuel mixture in the cylinder. Gasoline needs to be mixed into the air for this to work.
2nd Stroke - COMPRESSION: The piston moves back up to compress this fuel/air mixture. The mixture is compressed tightly into a small space just beneath the spark plug. The amount that the mixture is compressed is determined by the compression ratio of the engine. Most car engines can squeeze this mixture to about one eight to one tenth of its original volume. (Greater compression means greater pressure and greater temperature.)
3rd Stroke – EXPLOSION: The piston then reaches the top of its stroke, the spark plug emits a small surge of voltage to ignite the mix, cause an explosive combustion (change of chemical energy to heat energy), and produce a powerful expansion of vapor. When the fuel/air mixture in the cylinder burns, the temperature rises. The fuel is then converted to exhaust gas which expands and exerts pressure in the cylinder forcing the piston down. (Here, the heat energy is converted into mechanical energy.)
4th Stroke - EXHAUST: Once the piston hits the bottom of its stroke, the exhaust valve opens. Here the pressure is released and the burnt fuel sent off the to the exhaust system ( to where a catalytic converter can remove a lot of the pollutants). Since the cylinder contains so much pressure, when the valve opens, the gas is expelled with a violent force (that is why a vehicle without a muffler sounds so loud). This exhaustion enables the piston to rise once more to lower again in the next intake stroke, so completing the four stroke cycle.
According to Sadi Cranot, the father of thermodynamics, the efficiency of the engine (Carnot’s heat engine) is dependent just on two temperatures: the temperature of the source (hot body) from where the engine absorbs heat and the temperature of the sink (atmosphere) where the engine gives up the exhaust heat. (The higher the temperature of the source and the lower the temperature of the sink, higher is the efficiency of the engine.)
Inside the engine, some part of the heat generated is used to perform the work moving piston inside the engine cylinder. The motion of the piston is converted into the rotary motion of the crankshaft, which is converted to the rotary motion of the wheels. The remaining part of the heat generated inside the engine is released to the atmosphere through the exhaust valves. The heat generated is called as source, whereas the atmosphere where heat is released is called as sink. Therefore, if the temperature of the source is greater than the temperature of the sink, an engine is more efficient.
Engine Cooling
The continuous combustion process generates massive amount of heat, but internal combustion engines must maintain a stable operating temperature. Therefore, engines must be cooled to avoid engine’s self-destruction. The vast majority of engines are liquid cooled. The water pump circulates coolant (usually a mixture of ethylene glycol (antifreeze) and water) throughout the engine, hitting the hot areas around the cylinders and heads and then sends the hot coolant to the radiator to be cooled off. Once the fluid is cooled, it returns to the engine to absorb more heat from the pistons.
A thermostat, used to control the temperature of the coolant, is placed between the engine and the radiator to make sure that the coolant stays above a certain preset temperature. If the coolant temperature falls below this temperature, the thermostat blocks the coolant flow to the radiator, forcing the fluid instead through a bypass directly back to the engine. The coolant will continue to circulate like this until it reaches the design temperature. In order to prevent the coolant from boiling, the cooling system is designed to be pressurized. Under pressure, the boiling point of the coolant is raised considerably.
The coolant in today's vehicles is a mixture of ethylene glycol (antifreeze) and water. The recommended ratio is fifty-fifty. In other words, one part antifreeze and one part water. This is the minimum recommended for use in automobile engines. Less antifreeze and the boiling point would be too low. In certain climates where the temperatures can go well below zero, it is permissible to have as much as 75% antifreeze and 25% water, but no more than that. Pure antifreeze will not work properly and can cause a boil over.
Antifreeze is poisonous and should be kept away from people and animals, especially dogs and cats, which are attracted by the sweet taste. Ethylene Glycol, if ingested, will form calcium oxalate crystals in the kidneys which can cause acute renal failure and death.
Additional Info:
The automotive battery, also known as a lead-acid storage battery, is an electrochemical device that supplies electric energy to an automobile. It provides a nominal 12-volt potential difference by connecting six galvanic cells in series. Each cell provides 2.1 volts for a total of 12.6 volt at full charge. Lead-acid batteries are made up of plates of lead and separate plates of lead dioxide, which are submerged into an electrolyte solution of about 35% sulfuric acid and 65% water. This causes a chemical reaction that releases electrons, allowing them to flow through conductors to produce electricity. As the battery discharges, the acid of the electrolyte reacts with the materials of the plates, changing their surface to lead sulfate. When the battery is recharged, the chemical reaction is reversed: the lead sulfate reforms into lead oxide and lead. With the plates restored to their original condition, the process may now be repeated.
References:
http://www.howitworks.net/how-automobiles-work.html
http://auto.howstuffworks.com/
http://www.familycar.com/Classroom/
http://www.brighthub.com/engineering/mechanical/articles/38344.aspx
http://www.school-for-champions.com/science/thermodynamics.htm
http://www.ftexploring.com/energy/first-law.html
http://www.chemcases.com/fuels/fuels-c.htm
http://en.wikipedia.org/wiki/Car_battery
http://www.nature.com/nature/journal/v113/n2829/abs/113079a0.html
http://thermodynamicspedia.blogspot.com/2009/05/thermodynamics-principles-and.html
*I did this as a requirement of Chm022. =)
So, how do cars work?
Cars, as well as other types of vehicles, work on the basis of the laws of thermodynamics. Engines operate on a thermodynamic cycle to extract mechanical energy from the heat of combustion. They convert heat to mechanical work. This obeys the first law, which states that one form of energy can be converted into another, as well as the second law, which states that the natural tendency of the heat is to flow from the high temperature reservoir to the low temperature reservoir.
How do engines work?
The automobile engines are internal combustion engines where the combustion takes place internally.
The principle behind any reciprocating internal combustion engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas.
Most cars currently use a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867.
1stStroke - INTAKE: The piston starts at the top, the intake valve opens. When the piston reaches the bottom of the intake stroke, the intake valve closes, trapping the air-fuel mixture in the cylinder. Gasoline needs to be mixed into the air for this to work.
2nd Stroke - COMPRESSION: The piston moves back up to compress this fuel/air mixture. The mixture is compressed tightly into a small space just beneath the spark plug. The amount that the mixture is compressed is determined by the compression ratio of the engine. Most car engines can squeeze this mixture to about one eight to one tenth of its original volume. (Greater compression means greater pressure and greater temperature.)
3rd Stroke – EXPLOSION: The piston then reaches the top of its stroke, the spark plug emits a small surge of voltage to ignite the mix, cause an explosive combustion (change of chemical energy to heat energy), and produce a powerful expansion of vapor. When the fuel/air mixture in the cylinder burns, the temperature rises. The fuel is then converted to exhaust gas which expands and exerts pressure in the cylinder forcing the piston down. (Here, the heat energy is converted into mechanical energy.)
4th Stroke - EXHAUST: Once the piston hits the bottom of its stroke, the exhaust valve opens. Here the pressure is released and the burnt fuel sent off the to the exhaust system ( to where a catalytic converter can remove a lot of the pollutants). Since the cylinder contains so much pressure, when the valve opens, the gas is expelled with a violent force (that is why a vehicle without a muffler sounds so loud). This exhaustion enables the piston to rise once more to lower again in the next intake stroke, so completing the four stroke cycle.
According to Sadi Cranot, the father of thermodynamics, the efficiency of the engine (Carnot’s heat engine) is dependent just on two temperatures: the temperature of the source (hot body) from where the engine absorbs heat and the temperature of the sink (atmosphere) where the engine gives up the exhaust heat. (The higher the temperature of the source and the lower the temperature of the sink, higher is the efficiency of the engine.)
Inside the engine, some part of the heat generated is used to perform the work moving piston inside the engine cylinder. The motion of the piston is converted into the rotary motion of the crankshaft, which is converted to the rotary motion of the wheels. The remaining part of the heat generated inside the engine is released to the atmosphere through the exhaust valves. The heat generated is called as source, whereas the atmosphere where heat is released is called as sink. Therefore, if the temperature of the source is greater than the temperature of the sink, an engine is more efficient.
Engine Cooling
The continuous combustion process generates massive amount of heat, but internal combustion engines must maintain a stable operating temperature. Therefore, engines must be cooled to avoid engine’s self-destruction. The vast majority of engines are liquid cooled. The water pump circulates coolant (usually a mixture of ethylene glycol (antifreeze) and water) throughout the engine, hitting the hot areas around the cylinders and heads and then sends the hot coolant to the radiator to be cooled off. Once the fluid is cooled, it returns to the engine to absorb more heat from the pistons.
A thermostat, used to control the temperature of the coolant, is placed between the engine and the radiator to make sure that the coolant stays above a certain preset temperature. If the coolant temperature falls below this temperature, the thermostat blocks the coolant flow to the radiator, forcing the fluid instead through a bypass directly back to the engine. The coolant will continue to circulate like this until it reaches the design temperature. In order to prevent the coolant from boiling, the cooling system is designed to be pressurized. Under pressure, the boiling point of the coolant is raised considerably.
The coolant in today's vehicles is a mixture of ethylene glycol (antifreeze) and water. The recommended ratio is fifty-fifty. In other words, one part antifreeze and one part water. This is the minimum recommended for use in automobile engines. Less antifreeze and the boiling point would be too low. In certain climates where the temperatures can go well below zero, it is permissible to have as much as 75% antifreeze and 25% water, but no more than that. Pure antifreeze will not work properly and can cause a boil over.
Antifreeze is poisonous and should be kept away from people and animals, especially dogs and cats, which are attracted by the sweet taste. Ethylene Glycol, if ingested, will form calcium oxalate crystals in the kidneys which can cause acute renal failure and death.
Additional Info:
The automotive battery, also known as a lead-acid storage battery, is an electrochemical device that supplies electric energy to an automobile. It provides a nominal 12-volt potential difference by connecting six galvanic cells in series. Each cell provides 2.1 volts for a total of 12.6 volt at full charge. Lead-acid batteries are made up of plates of lead and separate plates of lead dioxide, which are submerged into an electrolyte solution of about 35% sulfuric acid and 65% water. This causes a chemical reaction that releases electrons, allowing them to flow through conductors to produce electricity. As the battery discharges, the acid of the electrolyte reacts with the materials of the plates, changing their surface to lead sulfate. When the battery is recharged, the chemical reaction is reversed: the lead sulfate reforms into lead oxide and lead. With the plates restored to their original condition, the process may now be repeated.
References:
http://www.howitworks.net/how-automobiles-work.html
http://auto.howstuffworks.com/
http://www.familycar.com/Classroom/
http://www.brighthub.com/engineering/mechanical/articles/38344.aspx
http://www.school-for-champions.com/science/thermodynamics.htm
http://www.ftexploring.com/energy/first-law.html
http://www.chemcases.com/fuels/fuels-c.htm
http://en.wikipedia.org/wiki/Car_battery
http://www.nature.com/nature/journal/v113/n2829/abs/113079a0.html
http://thermodynamicspedia.blogspot.com/2009/05/thermodynamics-principles-and.html
*I did this as a requirement of Chm022. =)
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