A new mean value engine model was developed in order to investigate the dynamic performance of vehicles equipped with turbocharged diesel engines, especially as far as the acceleration transients are concerned, where the turbolag phenomenon plays a major role.
The turbocharger was modeled through the mass flow and efficiency maps which are usually provided by the manufacturer, with additional extrapolation routines for the map area in the low compression/expansion ratio region, which is particularly important for tip-in manoeuvres simulation. For the internal combustion engine modeling, experimentally derived maps of indicated efficiency, volumetric efficiency and exhaust gas temperature as a function of engine speed and load were used. Finally, a mass balance in the intake and exhaust manifolds was carried out with a filling and emptying technique.
In this way, the model developed removes some disadvantages of detailed one-dimensional engine models, such as the need of extensive input data sets and long computational time.
The proposed mean value model allows an easy and quick investigation on the impact on vehicle's performance of several parameters, such as, for instance, turbocharger inertia, driveline gear ratios and vehicle mass. Moreover, the model is also suitable to evaluate the impact of different control strategies, concerning the smoke-related fuel injection limitation, the boost control through the VGT position and the EGR control.
Simulations were carried out for several vehicles and turbocharged diesel engines ranging from 1.3 to 1.9 liter total displacement, and comparisons with experimental data recorded during a number of acceleration tests showed a good agreement with simulation results.