Because of the continuous need of improving the design of machined part, the car engine basic part responsible of delivering the power produced by the engine to move the car. One of the major problems that the engine will occur during the engine operating is the buildup heat in the engine. This search will study carefully the engine heating and the ways that are being used to lower the engine's temperature. (Happian-Smith, 2002)
Figure 1: The parts of engine cooling [1]
The figure shows the parts that the water cooled system; in this project each part will be studied in such away the benefit upon installing it in the system is illustrated. For example the radiator is the part responsible of heat exchanging between the IC engine and the surrounding. The hot water coming from the hot area of the engine will be lowered in the radiator by the fan is rotating and makes the surrounding air that touches the heat transfer area.
There are several problems related to the high engine temperature, this is one of the main topics that this research will consider. It is well known that each material in the world has it is own melting temperature, cooling is being used to ensure that the temperature of the materials in the engine will not exceed it is melting temperature. In fact, the design study the expected engine heating temperature and the designer put in his mind how to release the excessive heat. The project will illustrate the ways that the designer will consider to protect the engine and the ways that being used to improve the cooling process. (Taylor, 1993)
Heat is being transferred out of any system in three main types: conduction, convection and radiation. The conduction is the energy transfer occurred between two bodies that are connected directly together and a temperature difference between these bodies is introduced. The two bodies can be solids, liquids or gases. The conduction heat transfer depends in the Fourier's law of heat conduction as the following relation:
(1)
Q: The heat transfer by conduction
k: The thermal conductivity
A: The heat transfer area
dT: The temperature difference between two surfaces
The thermal conductivity is a material property that diverges from one material to another. The convection heat transfer is the second method of heat transfer, and it represents the energy transfer between a solid surface and adjacent liquid or gas surface. Conduction is being known as the fluid motion.
(2)
: The heat convection heat transfer coefficient
: The surface area through which convection heat transfer takes place.
: The surface temperature. : The fluid temperature.
The radiation is the third way the heat is being transferred on. Radiation represents the energy emitted by matter in the photons type. The energy is being emitted because of the electronic change of molecules or atoms. The following correlation shows how to calculate the heat transfer from radiation (Cengel, 2002)
: the body emissivity (0<<1)
: Stephan- Boltzman constant
Detailed aims and objectives:
Engine parts and the purpose of each part
The engine has some basic parts will be illustrated and the main part purpose will be given, the engine is the responsible part for producing energy for the whole car system and the following is the main part that the engine has:
Block: Body of engine, made of cast iron or Aluminium. Covered with water jacket or cooling fins
Cylinder: The part of the engine block in which pistons reciprocate. Its walls have highly polished hard surfaces, to ensure smooth movement of the pistons.
Combustion Chamber: The space in the cylinder between the head and the piston face. Its size changes continuously during operation.
Piston: Cylindrical mass transferring the pressure forces in the combustion chamber to the crankshaft. The top surface is called: the crown, which can either be flat or of a concave shape. The sides of the piston are known as the skirt.
Piston rings:
â€"Compression rings: Metal rings that seal between the piston and the cylinder walls to prevent the high pressure gases from escaping into the crankcase.
â€"Oil ring: Assisting in lubrication and scraping excess oil.
Connecting rod: Rod connecting the piston with the rotating crankshaft.
Crankcase: Part of the block surrounding the crankshaft. The oil pan can make part of it.
Camshaft: Rotating shaft used for opening valves at the proper time of the cycle. Driven off the crankshaft by a belt or chain (timing belt/chain).
Push rod: A rod linking the valves in the cylinder head with the camshaft.
Cylinder head: Made of cast iron or Aluminum. Containing the spark plug, the fuel injectors and most cases the valves.
Valves: Allow flow in and out of the cylinder. Poppet valves -which are spring loaded-are most common. Should close perfectly on the surface called valve seat.
Intake manifold: Piping system carrying fresh air to the engine cylinders. Fuel is added either through injectors or with the aid of a carburetor.
Exhaust manifold: Piping system carrying away exhaust gases.
Spark plug: For initiation of combustion in S.I. Engines.
Carburetor: Fuel metering device in old S.I. Engines.
Flywheel: Rotating mass mounted on the crankshaft to store energy and smoothen the engine operation
Radiator: Liquid/Air heat exchanger to remove heat from the engine coolant.
Fan: To increase air flow through the radiator.
Fuel pump
Oil pump
Water pump
Figure 2: Internal Combustion Chamber main parts [2]
The components of the cooling system
In cars the purpose of cooling systems is to control the temperature of metals that forms the engine, this control will put these metals into a safe limits by removing excess heat that is produced by the engine. This heat is being rejected is very high even if the speed of the car is considered as moderate. The temperature of gas combustion can exceed 2000oC, it is also important to inform that the lubricated parts (as the piston) in the engine may run in lower temperatures where these parts temperature may reach the water boiling temperature or less than that. This can show how important to use adequate cooling system, otherwise engine damage may occur.
In computers; fans are attached to the system to keep the processor cooled down to a secure temperature limit. Another secure option in computers is the shutting down of computers to keep the inside parts of the computer out of any possible damage if the temperature is raised. Due to the rapidly increase in processors technologies the attached fans are not enough to keep computers in the safe operating conditions so another cooling system is being studied as those installed in cars where water is being used as a cooling system. Water is being preferred against any other coolant system for it is large amount of heat rejected by this coolant.
In cars the cooling system consists of water that rotates in a closed circle that moving against the parts that is heated up, because of this the hot parts will cooled down. The closed circle of the cooling system consists of connected pipes with a radiator. The radiator is a group of nearby metal surfaces that water pipes go through it; the radiator will help water to reject water. The cooled water is then goes back to the high temperature engine parts. The purpose of the fan in the cooling system is to make air turbulences to the radiator. Engine heat up is a normal process that comes from fuel burning in the engine. Car cooling engine has the following parts:
Water pump: The purpose of this part is to circulate water in the closed pipes.
Radiator: to help water to reject the unnecessary heat.
Fan: It is attached to the radiator to increase the heat transfer rate from water.
Water tank: to collect the needed amount of water.
Pipes: Those are separated in such away the heated parts are attached on.
Coating importance
Coating system in car engine is being attached to the design in order to decrease the wear levels and to help the system to overcome the overheat coming from the combustion chamber. In car vehicle the main parts are oil pump, piston, valves, camshaft, valve springs, piston rings, coolant, journal bearing and rocket.
Coating is being used in car engine when these parts forces high loads, high speeds and temperature. The design improvements can enhance:
Saving the quality of oil (Lubrication system).
Reduction in cost maintenance.
Reduce the harmful gases.
Output power will be increased.
Increase in the engine parts life.
Coating can improve the hardness of the metal; the corrosion resistance also can be improved by using the most convenient coating material. In this project some of the coatings will be studied and a comparison between these materials will be overtaken and the suitable one will be selected.
Types of cooling systems
The main cooling systems are either air cooled system and water cooled system, the air cooled system is the system that depends on air as the main heat transporter. This cooling system is being found in small engines and some medium sized engines. Air cooled engines rely on a flow of air across external surfaces to remove the necessary heat to keep them from overheating. The outer surface of engine is made of a good heat conducting metals to have a maximum heat transfer rate from the engine. To increase the air flow rate fans are attached and directed to the desired directions.
Air cooled engines forces some difficulties than water cooled by obtaining a uniform cooling cylinders, this is why water cooled systems are found; also the thermal properties for liquids are better than air (as convection coefficients, specific heats, and other). The difficulties in water cooled or other liquid cooled systems are less than the air cooled in which higher control can be obtained. Air cooled has less cost than liquid cooled because of the lighter weight.
Water cooled engines are those engines surrounded with a water jacket and the coolant liquid flows. This is why higher control of heat removal is the case in such engines.
Enhancements of the cooling system
The increase of the mechanical equipment design importance was the milestone of the need in new coating techniques and improvement. Tribological coating is one of the improvements in the coating techniques.
Tribology is the an engineering branch in which it is components encounter phenomena’s related to friction and wear, also tribological coating can result in cost reduction, maintenance cost reduction, material cost reduction, material and energy conservation.
In industries wear and friction need to be controlled for several reasons, such as increasing the devices efficiency, extending the machinery cyclic time and to conserve scarce material resources. Tribological coating get is a good control strategy to wear and friction.
It is important to say that this type of coating can be one of the improvements that any cooling system need in order to help this system to reject heat, the importance of this coating type can be concluded as an enhancement system to the lubrication and this can help to increase the amount of heat rejected from the total system. Also this coating can reduce the amount of friction and therefore, make the piston moves smoothly and increase the efficiency of the system.
In some cases and in high speed applications, the generated heat gets higher so our target is to increase the rejected heat. In these applications sometimes increasing the area of the radiator can increase the rejected heat area and therefore, increase the heat going out of the system.
In water cooled system, very few of these engines uses just water as the coolant fluid in the water jacket. Physical properties of water are very good but with some drawbacks. Pure water freezing is one of the properties that are considered as a block in freezing conditions. Water freezing point is (0O C). A mixture of water and antifreeze liquid as Ethylene Glycol (C2H6O2) can pass the water freezing problem. Ethylene Glycol acts as inhibitor and water pump lubricant.
When the antifreeze being added to water, it lowers the freezing temperature and raises the boiling temperature, both desirable consequences. The water glycol mixture can reach up to 70%. This mixture has lower freezing point because of the unique temperature-concentration-phase relationship but if the concentration of ethylene glycol is getting high then the freezing temperature will rise again. Pure ethylene glycol should not be used as an engine coolant.
Aims and Objectives:
At the final of the project the upcoming points expected to be met:
Heat transfer types will be studied to see the relation of each way with the value of heat transfer.
The problems related to engine heat up will be studied to see the relation between each one with the heat transfer value.
Engine coating will be also studied to select the most suitable coating for such application.
A car engine will be studied in which all components of the motor will be illustrated and a deep study of the components that affect the cooling system in the motor will also be carried.
Improvements of cooling system will also be studied to see how this will affect in the motor.
Chapter Tow: Literature review
The continuous studies on the IC engine concentrate on reducing the heat transfer to the water cooling jackets. The experiments results to that most of the heat not transferred through the insulation walls will be found in the exhaust gas. Georges Descombes, et al, gave a contribution to understand the energy transfer phenomena between the exhaust and cooling systems for a reciprocating engine. The results that they obtain is that a local unsteady approach between the thermodynamics expansion velocity and the heat propagation velocity on the expansion stroke. (Georges Descombes, et al, 2003)
Oil is one of the important issues that depend on the cooling system will temperature change for the oil will change the oil characteristics. Hosny Abou-Ziyan does experimental work to study the heat transfer from a cast iron specimen to oils that being in engines. The main purpose of this work was to evaluate the thermal characteristics of some used oils when being on contact with high temperature parts of internal combustion engine. (Hosny Abou-Ziyan. 2003)
Chapter three: Methodology and Analysis
The selection of the cooling system is important since it is well known that some car engines being cooled using air while the most widely used engine cooling type is the water cooling. Water is preferred than the air since this the specific heat (the heat needed to raise the water temperature one degree Celsius) is greater than it for the air and hence the heat being transferred by water is much higher than it for air.
The project will use one of the most widely used engineering programs (Pro-Engineer) to do the analysis for a selected system. The main purpose of this analysis is to make sure that the design selected will improve the efficiency of the cooling system.
The most important of this project is to design a reliable and effective cooling system that being installed in a car to ensure no failure due to temperature raise the motor will face.
Chapter Four: Conclusions
A comparison between the two mainly cooling types (air cooled and water cooled) is one of the most important issues that the project will study where it will show why most of car manufacturer prefer water cooled IC engines. Also the relation between the oil type and performance with temperature raise is another important thing likely to be studied.
The use of computer aided design programs can reduce the cost and time for both the designer and the manufacturer to predict the performance of the designed system.
Chapter Five: References
Yunus Cengel, Heat and mass Transfer a practical Approach, 2002, McGrow Hill
Julian Happian-Smith, Introduction to Modern Vechile Design, 2002, Butterworth-Hienemann.
C.M. Taylor, Engine Tribology, 1993, Elsevier, Netherlands
Georges Descombes, et al, Fadila Maroteaux, and Michel Feidt, Study of the interaction between mechanical energy and heat exchanges applied to IC engines, 2003, Elsevier
Hosny Abou-Ziyan, Heat transfer characteristics of some oils used for engine cooling, 2003, Elsevier
Willard W. Pulkrabek, Engineering Fundemental of the Internal Combustion Engine, 2002, Prentice Hall, New Jersey
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