| Summary: | This work focuses on the cooling of diesel engines. Facing heavy constraints such
as emissions control or fossil energy management, political leaders are forcing car
manufacturers to drastically reduce the fuel consumption of passenger vehicles. For
instance, in Europe, this fuel consumption has to reach 120 g CO2 km by 2012, namely 25 % reduction from today's level.
Such objectives can only be reached with an optimization of all engines components
from injection strategies to power steering. A classical energy balance of an internal
combustion engine shows four main losses: enthalpy losses at the exhaust, heat
transfer to the cylinder walls, friction losses and external devices driving. An
optimized cooling will improve three of them: the heat transfer losses by increasing
the cylinder walls temperature, the friction losses by reducing the oil viscosity and
the coolant pump power consumption.
A model is rst built to simulate the engine thermal behavior from the combustion
itself to the temperatures of thedierent engine components. It is composed by two
models with different time scales. First, a thermodynamic model computes the in cylinder
pressure and temperature as well as the heat flows for each crank angle.
These heat flows are the main input parameters for the second model: the nodal
one. This last model computes all the engine components temperatures according
to the nodal model theory. The cylinder walls temperature is then given back to
the thermodynamic model to compute the heat flows.
The models are then validated through test bench measurements giving excellent
results for both Mean Effective Pressure and fluids (coolant and oil) temperatures.
The used engine is a 1.9l displacement turbocharged piston engine equipped with
an in-cylinder pressure sensor for the thermodynamic model validation and thermocouples
for the nodal model validation.
The model is then used to optimize the coolant mass flow rate as a function of
the engine temperature level. Simulations have been done for both stationary
conditions with effciency improvement up to 7% for specific points (low load, high
engine speed) and transient ones with a heating time improvement of about 2000s.
This gains are then validated on the test bench showing again good agreement.
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