1. Normal engine temperature
Due to combustion of fuel and friction between parts, a large amount of heat is generated, so that temperature in cylinder can reach 1800 ℃ ~ 2000 ℃, part of heat is removed with exhaust, and other part is directly transferred to piston, valve, cylinder head , cylinder, etc. If it is not cooled in time, it will lead to overheating and expansion of moving parts, damage to matching gap, increased friction resistance and serious jamming, deflagration, so hot parts inside engine must be cooled.
The cooling of engine should be moderate, if cooling is excessive, heat loss will be too great, combustible mixture entering cylinder will be difficult to ignite or combustion will be slow due to low temperature, power output will decrease and fuel consumption will increase. The viscosity of oil increases, lubrication deteriorates, friction resistance increases, wear of rod wall accelerates, oil in oil pan is diluted, which affects lubrication effect.
Secondly, composition of cooling system
At present, most of water cooling systems used in automotive engines are forced circulation water cooling systems that use water pumps to force water circulation in cooling system. It consists of a radiator, a water pump, a fan, a cooling water jacket and a temperature control device.
3. Cooling System Components
Function: increase heat dissipation area, accelerate cooling of water and reduce temperature of water passing through it by 10℃~15℃.
Composition: A radiator is also called a water tank, which is composed of an upper water chamber, a radiator core and a lower water chamber.
The cross section of cooling pipe is mostly flattened, connecting upper and lower water chambers
Advantages and disadvantages: large heat dissipation area, increased rigidity and strength of heatsink, high pressure resistance, but complex manufacturing process and high cost.
Use cooling pipes and heat dissipation plates arranged vertically at intervals
Advantages and disadvantages: improved heat dissipation, simple manufacturing process and low cost, but rigidity and strength are not as good as tubular fin type. It is commonly used in automotive engines and is also used in mid-range premium cars.
Classification of radiators
(2) water tank cover
Function: pressurizing cooling system, reducing cavitation, protecting refrigerant gas hose, preventing or reducing pressure surges, etc. Currently, a closed water cooling system is used.
Water tank cover
Function: increase pressure of coolant, accelerate circulation of coolant, and ensure reliable cooling. Centrifugal water pumps are mainly used in automobile engines
The characteristics of centrifugal water pump: its advantages are simple structure, small size, large displacement and easy maintenance.
Composition: centrifugal water pump is mainly composed of pump body, impeller and pump shaft
Composition. Impellers are usually radial or backward curved, and their number is usually 6 or 9.
Performance: low viscosity, good fluidity, low freezing point, dry boiling point, good corrosion resistance, difficult scaling conditions, good anti-foam properties.
Selection and application: The coolant is divided into 6 levels of freezing point -25, -30, -35, -40, -45 and -50.
(1)-25 can be used in areas north of Yangtze River in my country and areas where lowest ambient temperature in North China exceeds 15°C
(2) -35 is cold in northeast, most of northwest and north of China with lowest ambient temperature above -25°C
(3) No. 5 is used in cold regions such as northeast, northwest and north of China where lowest ambient temperature is above -35°C
Coolants from different manufacturers have same concentration, but different freezing points. For Santana, Audi, Hongqi, Jetta, Crown 3.0, Lexus L.S400, Mercedes-Benz .5t0 and Cadillac engine coolant, a mixture of G1I antifreeze and water is recommended.
Proper use: Distilled water or deionized water should be used to dilute concentrated solution. When replacing water with a glycol-based engine coolant, engine cooling system must be thoroughly cleaned, coolant level checked frequently and topped up as needed.