Cooling System of Volvo Generator TWD1643GE Engine
by Starlight Generator dieselgeneratortechVolvo Penta 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
Expansion tank and venting
circuit
This circuit comprises:
- Expansion tank
- Pressure cap
- Venting nipples and hoses
- Coolant level indicator
(optional)
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.
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.
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”.
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Created on Aug 1st 2018 05:13. Viewed 613 times.