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Volvo Diesel Engine Cooling System

Jun. 07, 2018

Volvo Diesel Engine Cooling System

 

Charge air cooler, coolant-to-air type

 

Engine coolant is used to cool charge air in TWD engines. Coolant is pumped through the circuit via a pipe from the radiator to the charge air cooler. After coolant has passed through the charge air cooler tubes it is fed to the pump.

The illustration shows twin charge air coolers on a TWD1643GE engine.

1 Coolant to charge air coolers

2 Coolant from charge air coolers

3 Charge air cooler

4 Inlet cover

5 Turbocharger



P0011516.jpg

 

Expansion tank and venting circuit

This circuit comprises:

- Expansion tank

- Pressure cap

- Venting nipples and hoses

- Coolant level indicator (optional)


P0004181.jpg



Expansion tank

The expansion tank is installed separately.

The expansion tank has four different functions:

- To provide space for coolant heat expansion in the liquid cooling system.

- To separate air from the coolant.

- To maintain a static pressure on the coolant pump suction side to prevent cavitation.

- To provide a given system pressure by building up pressure in the air above the coolant surface.

 


Installing a separate expansion tank

1 Venting hose from the radiator to the expansion tank. The hose must slope upwards all the way. If it does not slope a venting tap must be used.

2 Expansion tank.

3 Pressure cap.

4 Connector for coolant level indicator (option).

5 Hose from expansion tank to coolant pump inlet.

6 Charge air cooler venting

7 Venting hose from thermostat housing to expansion tank. The hose must slope upwards

8 Charge air cooler.



P0004164.jpg

 

Type of pressure cap and opening pressures depending on height

 

Height (H)

Type of pressure cap

-2.0 m (-6.5 ft.)

2.0-5.0 m (6.5-16.5 ft.)

5.0–7.0 m (16.5–23.0 ft.)

75 kPa (10.9 psi)

50 kPa (7.3 psi)

30 kPa (4.4 psi)

 

 

Pressure cap

The aim of a pressurized system is to raise coolant boiling point and prevent cavitation in the coolant pump. This is especially important at high ambient temperatures and altitudes. The pressure cap also prevents boiling and coolant loss when a hot engine is shut down. When coolant temperature drops a negative pressure is created in the system. There is a vacuum valve in the cap to prevent this negative pressure from becoming too low. The lowest permissible negative pressure 10 kPa (1.5 psi).

 

 

Altitude AMSL

(m)

Atmospheric pressure

(kPa)

Boiling point at at.

pressure

(°C)

Boiling point with

50 kPa cap

(°C)

Boiling point with

70 kPa cap

(°C)

0

500

1000

1500

2000

2500

3000

3500

4000

101

95

89

84

79

74

69

65

61

100

98

96

95

93

92

90

88

86

112

110

109

108

107

106

105

104

103

115

114

113

112

111

110

109

108

107

 

 

Venting nipples and hoses

It is crucial that the coolant is free from air and that the system can be completely filled for the system to function correctly. Venting nipples must be installed so that air cannot become trapped anywhere in the coolant cooling system. If air is mixed with the coolant, or if air is trapped it may have the following consequences:

- Cooling system cooling capacity is impaired.

- Heat absorption and transfer characteristics are impaired.

- The coolant may boil locally, which will cause high metal temperatures.

- Coolant loss due to air expansion.

- Cavitation in the coolant pump and lines.

- Seized cylinders.

All engines are fitted with a venting nipple connected to the thermostat housing. Venting hoses must slope upwards all the way to the expansion tank. U-bends in hoses may cause fluid locks and must be avoided.

 

Coolant level indicator

A coolant level indicator is available as standard.

 

Cooling Performance

 

Cooling Capacity

The cooling capacity of an installation depends on engine heat transfer and all the cooling system components:

• Radiator

• Fan type and diameter

• Fan speed ratio

• Type of fan ring and fan location

• Accessory components in the cooling air system

• Engine compartment and cooler heating

• Accessory components in the cooling water system

• Air ducts and pressure drops across the installation

 

 

ATB and AOT

Cooling capacity is expressed by the terms ATB (Air To Boil) and AOT (Air On Temp). ATB temperature is defined as the ambient temperature that provides maximum permissible coolant temperature. AOT temperature is defined as the cooling air temperature at the charge air cooler that provides maximum permissible coolant temperature. The difference between AOT and ATB is that AOT uses cooling air temperature at the charge air cooler as a reference instead of ambient temperature. Thus AOT is independent of cooling air heating by the installation. The max permissible temperatures for each engine type are specified in Sales Support Tool, Partner Network.

 

 

AOT temperature is the same as ATB temperature on engines using puller fans. If a pusher fan is used, cooling air is first heated by the engine before passing through the radiator (or charge air cooler on TAD engines). On generator sets, the air is also heated by the generator and ATB temperature is equivalent to AOT temperature minus the temperature increase across the generator and engine. Refer to the illustration below.


P0011819.jpg

 

The AOT temperature for each engine using the standard Volvo Penta cooling system is specified in Sales Support Tool, Partner Network. Recommendation: ATB temperature must be at least as high as the highest anticipated ambient temperature. In tropical conditions ATB must be approx. 50 °C (122 °F). AOT temperature for generator sets is calculated by adding the temperature increase across the generator and engine.

 

 

ATB and AOT are calculated as follows

ATB definition = tmax permissible coolant temp. – tcoolant temp. after the engine + tambient temp.

AOT definition = tmax permissible coolant temp. – tcoolant temp. after the engine + taverage cooling air temp. at the charge air cooler

Cooling air heating = tcooling air temp. – tambient temp.

 

 

External flow restriction

Pressure drop on the cooling air side comprises the pressure drop across all of the components in the system. When cooling air has passed the engine and radiator there must be a pressure reserve to overcome installation flow restrictions.

 

This value is specified in the Sales Support Tool, Partner Network as the external flow limitation. This means that the pressure drop across air ducts, engine compartment, A/C condenser, radiator grille and sound insulation may not exceed the external flow limitation, otherwise cooling capacity is reduced.

 

Example:

If net power output from an engine is 262 kW at 1500 rpm. The following values have been extracted from the Sales Support Tool, Partner Network: 

AOT temperature: 50 °C (122 °F)

Airflow: 5.85 m3/s (206.6 cu. ft.) 

External flow limitation: 685 Pa (0.099 PSI) 

 

Temperature increase across the generator and engine is calculated according to the formula:

 

     QHeat

ΔT: –.–.–.–.–.

     ρ x qA x CP

ΔT: Temperature increase (°C)

QHeat: Heat effect from generator and heat radiation

from engine (kW)

ρ: Air density (kg/m3)

qA: Cooling air flow (m3/s)

CP: Specific heat of air (kJ/kg °C)

 

Anticipated generator efficiency: 0,93.

93 % of engine power is converted to electrical power,

-7 % is heat loss.

Heat loss from generator: 0.07 x 387 = 27 kW

Heat radiation from the engine is 19 kW at 1500 rpm.

QHeat = 20 + 27 = 47 kW

Air density and specific heat are provided in a table:

At 50 °C (122 °F)

ρ = 1.09 kg/m3 (0.068 lb/ft3)

CP = 1.009 kJ/kg (0.434 BTU/lb)

Cooling air temperature increase can be calculated

according to the formula:

 

 

QHeat 47

ΔT: ––––––––– = – ≈ 7 °C (44.6 °F)

ρ x qA x CP 1.09 x 5.85 x 1.009

ATB temperature is now AOT temperature minus the

temperature increase:

ATB = 50 - 7 = 43 °C (77.4 °F)

Max ambient temperature in which the engine may be run is approx. 43 °C (77.4 °F).

NOTICE! The example above does not take into account heat from e.g. uninsulated piping or an

exhaust silencer located inside a generator set cover. In this case cooling air temperature would increase further and lead to a lower ATB temperature. Furthermore, it is probable that the actual installation pressure drop will differ from the theoretical pressure drop and affect the cooling airflow used in the example. Volvo Penta recommends carrying out practical cooling capacity tests in order to determine a correct ATB temperature. Refer to the chapter “Evaluation and

testing”.

 

For More Volvo Engine workshop information, please visit


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