Engine Cooling and Systems

Engine Cooling

• Engine cooling is crucial to prevent overheating of engine components.
• Excessive heat can lead to pre-ignition, reduced material strength, and piston seizure.
• Lubricating oil deteriorates at high temperatures, causing further damage.
• High temperatures cause uneven expansion, potentially resulting in cracking.
• High temperatures reduce the density of the fresh air charge, impacting power output.

Disadvantages of Cooling

• Low engine temperatures make starting difficult.
• Corrosion increases at low temperatures, shortening engine lifespan.
• Low temperatures lead to the formation of corrosive acids from fuel combustion, damaging the cylinder barrel.
• Optimal engine operation requires a suitable operating temperature.

Cooling Systems

• Air Cooling: Air alone directly cools the engine

• Air cooling is used for smaller engines needing less weight.

• Examples include aircraft, agricultural, and industrial engines.

• Cylinder and cylinder heads are finned to increase surface area, promoting heat transfer.

• Fin height (15-25 mm) impacts engine size and thermally-stressed parts need adequate fins.

• Water Cooling: Water cools the engine

• Water is used in car engines.

• Coolant flows through a water jacket surrounding the cylinder and head.

• Water velocity and flow are important for effective cooling.

• Anti-freezing agents (kerosene, alcohol, etc.) are used in cold temperatures.

• Cooling methods include thermo-syphon, thermostat, pressurized water, and evaporative cooling.

Cooling System Operation

• Engine Cold (Thermostat Closed): Coolant circulates through a bypass to the pump, and back to the engine, not going through the radiator.
• Engine Warm (Thermostat Open): Coolant circulates through the radiator, cooled by passing through it.

Advantages and Disadvantages of Air Cooling

• Advantages: Lightweight engine, simpler design, less sensitive to climate, better warm-up, reduced carbon deposits, easier control.
• Disadvantages: Higher combustion noise, lower volumetric efficiency, and higher cylinder head temperature.

Advantages and Disadvantages of Water Cooling

• Advantages: Higher latent heat of water enables more heat removal from hot spots, higher volumetric efficiency, easier to place anywhere in the vehicle, higher output
• Disadvantages: Increased weight and size of the engine, needs more maintenance.

Radiator

• The radiator's function is to transfer coolant heat to the atmosphere.
• Heat transfer occurs via conduction and forced convection, not radiation.
• The cooling effect is achieved by dividing the hot coolant into fine streams that then heat the large metal surfaces of the radiator.

Fan

• Fans maintain adequate air flow across the radiator, especially at low speeds and during idling.
• Disadvantages: Increased noise level, higher power consumption, and possibility of overcooling.

Quantity of Cooling Water

• Quantity of required cooling water is calculated using the formula: Mf = QBP /(K * ΔΤ).
• QBP is the heat transferred to coolant, ΔT is permissible temperature increase, and K is a constant dependent on compression ratio and water consumption.

Solved Example

• Calculation of cooling water required for a 100 kW petrol and diesel engine with water temperature increase of 30°C.
• Thermal efficiencies and percentages of heat loss to coolant are used in the calculations.