Diesel thermal management optimization for effective efficiency improvement

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 first built to simulate the engine thermal behavior from the combustion

itself to the temperatures of the different 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.