Water-cooled System vs.
Cooled System Air-cooled System
Thermal energy from fuel combustion is converted about a third of it into usable efficient work, and the rest is lost almost equally in the cooling and exhaust system.
Function of the cooling system:
– Rapid access to operating temperature
– Elimination of excess heat
– Maintaining operating temperature
– Reducing the temperature difference between engine parts (temperature equalization)
|Water Cooling System|
|Air Cooling System|
|Parts difference:||– Water shirts surrounding the cylinders in the engine body, and around the valves in the cylinder head|
– Radiator – Heat exchanger (radiator) with a capacity of 5-20 liters
– Water pump
– Thermal switch (thermostat)
– Temperature sensor (1 or 2)
– Overflow tank
– Anti-freeze fluid – Anti-freeze
protection pads inside the engine
|– Large fan|
– Air guide
– Oil cooler
– Separate cylinders with fins.
|water cooling system||air cooling system|
|Advantages||Water has a high heat capacity for rapid disposal of high amounts of heat (we need 4 times the same weight of air for water or 4000 equal volumes of air for water to get rid of the same amount of heat), but the air can be collected and disposed of, but the water must remain and be carried in the car ( Closed circle).|
Water has a high heat capacity; A certain amount of water, heated to a certain temperature, needs a higher amount of heat than any other substance.
Water is available in most parts of the world and its cost is cheap.
The operational life of water-cooled engines is 50% longer than that of similar air-cooled engines, due to the constant, correct operating temperature that water-cooled engines provide during operation. The breakdown of the lubricating oil does not occur quickly.
Water-cooled engines save fuel consumption due to the constant operating temperature compared to air-cooled engines.
The cylinders can be placed more closely together, making the engine smaller
. The fan in the water cooling system is smaller, less noisy, and consumes a fraction of the engine’s power.
There is nothing to impede access to the engine parts because there is no air guide over and around these parts.
Water shirts dampen noise from inside the engine (a less noisy engine).
– The engine works in harsh weather conditions of heat without experiencing the problem of overheating.
High operating temperature with closed system increases operating efficiency. Therefore, it allows the use of a smaller radiator for engines operating at a lower temperature (cold).
|Air is cheaper, lighter, and more accessible than water.|
The main advantage of air-cooled engines is the simplicity of the design, as they contain fewer parts involved in the system, and because of this, they are less expensive and less expensive, as well as lower maintenance expenses.– Simplicity, and there is no problem related to water leakage, radiator, or water pump … There are no dangers from puncturing the radiator or connections..etc.
Maintenance required for the system is very low.
There is no possibility of damage from freezing in cold weather. Therefore, no antifreeze or antirust additives are required.
– Aluminum alloy is usually used to manufacture the engine and its parts, as it is better in conductivity than cast iron or steel; This ensures that the air-cooled engine is lighter than a similar water-cooled engine. Plus the weight of the water shirt.
Air-cooled engines can quickly reach operating temperature in a shorter time than water-cooled engines.
The engine can operate at higher temperatures than similar water-cooled engines, which increases operating efficiency.
– If the cylinder head interlock is damaged. In air-cooled engines, the equipment or vehicle can be driven to a repair shop with this defect. In some cases, the operator of the equipment or the car may not feel any problem as a result of this malfunction. As for water cooling units, damage to the cylinder head interlock will cause cylinder pressure to leak into the cooling system. This will result in high pressure draining off the cooling water, causing the engine to overheat and not start. Also, the cooling water leaving the system is not borne by the overflow tank, which leads to its leakage outside, which negatively affects the environment, as the coolant is considered harmful to the environment.
Putting a large amount of cooling water is to increase the safety limit of the engine overheating risk when the engine is exposed to harsh operating conditions, so that the water can accept excessive heat for an extended period of time.
As for air-cooled engines, they are not equipped with this kind of increase in the safety limit, and therefore the temperature of the lubricating oil increases (as it is the medium available to get rid of the heat of the piston, piston rings and bearings), and for this reason, air-cooled engines need a heat exchanger (oil cooler) for the cooling oil – this Although it is smaller and lighter than a water radiator, it is not the cheapest.
– In both cases of cooling, the heat transfer is more efficient when the temperature of the surface that gives heat to the air is much higher than the air – in other words, when the tendency of the temperature difference is higher,
therefore, at high air temperatures, air-cooled engines are better than water-cooled engines.
Easier and less expensive when doing packing, Umrah.
|Defects||Water leakage is one of the biggest problems facing water cooling engines, as high temperature leads to engine damage. In military vehicles, hitting the radiator with a bullet or shrapnel leads to the vehicle stopping as a result of the engine blocking (hardening).|
Improper disposal of coolant is harmful to the environment.– Damage to the thermal switch (thermostat) (continuous shutdown), fan failure, which leads to engine overheating, and parts damage.
Opening the thermostat, leads to excessive cooling, reduced engine efficiency and increased fuel consumption.
– The problem of the breakdown of the interlocking head of the cylinders. lead to water leakage.
Water boils at a temperature lower than what is required for the optimal performance of the engine, especially in areas higher than sea level (the boiling point of water decreases with increasing altitude because the pressure decreases with altitude).
This problem can be overcome by operating the system under pressure. The boiling temperature can be increased by 1°C for each increase of 4 kN/mm2.
It freezes at a temperature often encountered during the winter in many parts of the earth. Since the snow expands with decreasing temperature, there is a high risk of a crack in the engine block if freezing occurs.
The freezing temperature of the coolant can be reduced by adding antifreeze. The most used antifreeze is ethylene glycol, and a solution of it containing 20% of that with water is sufficient to give adequate protection from the dangers of cold areas. Which represents an additional cost for the water cooling system. Refrigerant such as propylene glycol remains liquid up to -55°C and has a working life of 10,000 hours.
Water may cause rusting of some metal parts that come into contact with it. (The risk of rust can be avoided by adding some chemicals. This is mostly done by adding antifreeze with it) which increases the operating cost of the system.
The water leaves lime and salt deposits inside the system, which depends on the water quality.
maintenance problems; The water cooling system poses a risk of burns due to exposure to hot radiator water (radiator cap open while engine is hot).
maintenance problems; Care must be taken when working near the cooling fan (risk of injury to the hand as a result of the fan blades), especially the electric fan, which may operate suddenly without warning. (When working near the electric fan, it is recommended to disconnect the negative electrode).
The engine is heavier not only in relation to the parts but also because of the water and in general the engine is heavier relative to a similar air-cooled engine.
– The engine takes longer time to reach the operating temperature (the time needed to heat the water)
– In the case of using water, the temperature should not exceed 85 to 90 degrees Celsius to avoid boiling water
– The engine is exposed to damage as a result of freezing water in cold weather
– Needs many From maintenance operations such as checking the water level, adding anti-freeze, cleaning the sediments.
Cooling water boils at the same temperature required to cool the engine. This gives it a great advantage in terms of absorbing a large amount of energy accompanied by a slight rise in the temperature of the water (called the heat of vaporization), which is good for keeping things cool, especially when a stream of coolant passes over several hot parts to reach an equal temperature. On the contrary, when the air passes over several hot parts in a row, which leads to the heating of the air (its temperature) during the process of passing over the parts, and the first part may be over-cooled and the last part slightly cooled.
But in the case of boiling water, the medium becomes insulating, and leads to a sudden loss of cooling as there are air bubbles. Unfortunately, the vapor may return to the liquid state when mixed with the other coolant, and this may deceive the temperature sensor, as the sensor may indicate an acceptable temperature, although there are local points where the temperature has reached a high degree and the parts may be damaged.
The engine is more expensive than its air-cooled counterpart.
More parts and more maintenance
|– Needs a large fan and an air duct (sheet metal case). A fan of this type consumes a portion of the engine’s power when it is driven by the engine and thus reduces the engine’s used power. Also, a fan of this size emits the sound of pushing air, which increases the noise.The air guide around the engine makes it difficult to access engine parts for maintenance and adjustment. And it works as an amplifier, and if it is not connected well, it leads to noise.|
– In the absence of the water shirt damping the noise from the engine, it will lead to a loud operation which will often be amplified by the parts of the air guide system.
The mechanical noise of the engine increases due to the fins.
It is difficult to control the change in operating temperature in air cooling systems and this leads to a change in the temperatures of different parts of the engine, which may lead to deformation in the main parts.
Difficulty accessing sensitive areas inside the engine to cool it (exhaust valves base, spark plug hole), so water or oil is used as a medium.
The engine is subject to overheating under the influence of difficult weather factors, unlike a water-cooled engine.
In most cases it is necessary to make the cylinders separate to ensure that the fins are properly formed; The cylinders must be spaced at relatively large distances to ensure the formation of the fins, which causes the length of the straight-shaped engine, the length of the crankshaft and the crankcase and therefore heavier weight. Therefore, most air-cooled engines are V-shaped or horizontal, which is less long and more expensive than a simple straight-line engine system.
The cylinders are made separately to position the fins, which makes them more expensive.
It is difficult to make a heating system for the car space from the inside.
Air engines operate at higher temperatures than other types of engines, and therefore must be designed with greater clearances between moving parts to allow expansion.
As for the high operating temperature, it needs a more advanced type of lubricating oil, more expensive.
The air-cooled engine is more exposed to the possibility of fire, as the air wave surrounding the engine is prone to absorb oil and fuel, in addition to other plankton, which makes them a source of the possibility of fire.
In some (old) applications, air-cooled engines were run on rich fuels until they were cooled by the fuel. This increases fuel consumption.
Some air-cooled car engines suffer from rapid wear in normal use, and sometimes they have a sudden failure when working in hot weather.
It is difficult to get low pollution or low noise from the air-cooled engine. These are two other reasons why most cars use water-cooled.
There is a problem with the manufacture of large air-cooled engines, most air-cooled engines are less than 500 kilowatts, as water-cooled engines may reach 80 megawatts.
|the use||Most cars use water-cooled engines.||Many motorcycles use air cooling to reduce weight and reduce system complexity.|
Most piston aircraft engines use air cooling.Hand-held, motor-driven equipment is air-cooled. Like a tree cutter. and lawn mowing machines.
Military vehicles are mostly air-cooled.
* The energy in the fuel is utilized through combustion. This energy is converted into thermal energy, which heats the air inside the cylinder (closed space) and increases the pressure inside the cylinder. The pressure affects the inner surfaces of the cylinder, including the piston area, where the pressure on the piston surface is converted into a force that pushes the piston down during the power stroke (force = pressure in the piston surface area). And through the crankshaft, that force is converted into torque that turns the wheels, through the gearbox and wheel axle, and pushes the car. Some of this thermal energy reaches the cylinder wall (25% to 30% of the thermal energy) and raises the temperature of the cylinder wall, piston, etc.
For an increase in the temperature of about 150 degrees Celsius, as by increasing the temperature from this value, the lubricating oil on the cylinder wall is evaporated, which leads to dry friction between the piston and the cylinder wall, and this increases the temperature at a high degree that leads to adhesion of the friction surfaces and damage The machine (the expansion of the parts also leads to the wear of the parts, but some say that the main cause of machine damage (stuffing / hardening) is due to the first reason), and the increase in temperature leads to the expansion of the metal parts, stresses as a result of the temperature difference of the parts, reducing the strength of resistance The metal stresses (strength).
The engine temperature increases above the designed rate as a result of a malfunction in the cooling circuit, (such as water leakage, damage to the thermostat so that it remains closed, the cooling fan not working, an obstacle on the radiator surface, ….), overloading the car (brake loading, weight gain, climbing Mountain road, tire wear pomegranate, tire inflation not controlled,….), engine failure (spark delay, poor fuel mixture,……).
Excess cooling also has its negative effects, not installing the thermal valve (thermostat), walking a few distances and then stopping (small range trips), a large volume of the radiator in relation to the air temperature… This leads to problems of condensation of water and fuel vapor on the cylinder wall and piston, which works to wash The oil from the surfaces, and the condensation of the steam creates sulfuric acid (combustion products) and the two main causes to erode the surface of the cylinders, valves, and valves. It also deteriorates the condition of the oil in the oil pan. It also reduces the viscosity of the oil, which increases friction, which reduces mechanical efficiency and increases fuel consumption.
There are two ways to transfer that heat from hot engine parts to the atmosphere either directly through the air or indirectly using water as a medium to transfer heat from the engine parts to the air. Water cooling is actually air cooling, by putting a shirt of water around the cylinders, the water transfers heat from the engine parts, then through the radiator it is lost to the air (the engine is cooled by water and then the water is cooled by air) and then the water returns to The motor to absorb some of the heat again. This means that the engine is finally cooled by air, with water as the heat transfer medium (indirect air cooling).
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