The downsizing of spark ignition engines should be an issue to decrease the consumption and to fulfil the ACEA commitment, i.e. 140 g CO2/km in 2008 and maybe 120 g/km in 2012. To achieve very low specific fuel consumption, the use of very downsized engines should be a solution. However, it is well known that one problem with such engines, that means very small turbocharged engines with high specific power (up to 100 kW/l), will be the turbo lag [5-6].
Different ways are possible to avoid it: some changes in intake layout, exhaust manifolds, turbo inertia, valve timings can be considered, or more sophisticated systems (such as electrically assisted compressor [3], volumetric compressor …) can be envisaged.
To classify the interest of such solutions, it is very useful to compute their transient behaviour and, thus, to have accurate models to predict their impact under transient conditions like tip-in at constant speed but also tip-in on a vehicle (varying speed conditions).
In this paper, we will describe first a methodology for the evaluation of such technologies on test benches under transient conditions at low-end speed. Then we will propose to describe how can be reproduced those transients by 1D software.
We will show that:
transients tests have to be performed with many care especially for initial thermal conditions and tuning effects;
transient models, with parameters has been set from steady state full load conditions, are not sufficient to predict accurately the transient behaviour;
some parameters (variation of combustion laws with load, transient of thermal models, …) have to be introduced in order to match more accurately the test bench results;
This calculation methodology has been developed with the GT Power 1D code. However it can be adapted to other codes.