In the last two decades, piston engine specifications have
deeply evolved. Indeed, new challenges nowadays concern the
reduction of pollutant emissions (EURO regulations) and CO2
emissions. To satisfy these new requirements, powertrains have
become very complex systems including a large number of high
technology components (high pressure injectors, turbocharger,
Exhaust Gas Recirculation (EGR) loop, after-treatment devices...).
In this context, the engine control plays a major role in the
development and the optimization of powertrains.
Few years ago, engine control strategies were mainly defined by
experiments on engine test benches. This approach is not adapted to
the complexity of future engines: on the one hand, tests are too
expensive and on the other hand, they do not give much information
to understand interactions between components. Today, a promising
alternative to tests may be the use of 0D/1D simulation tools.
These methods have been widely used in the past ten years and allow
building engine control algorithms. However, they are generally
based on empirical models and often suffer from a lack of
predictivity. A solution for extending the range of application of
the system simulation consists in developing more physical models
based on the 3D calculations experience. This way has been recently
followed at IFP Energies nouvelles, leading to the development and
implementation of several libraries dedicated to powertrains
(IFP-Engine, IFP-Exhaust) and drivetrains (IFP-Drive) in the AMESim
simulation software.
The work we propose here is coherent with the approach chosen at
IFP Energies nouvelles and aims at developing a phenomenological
model for the pollutants emissions in a combustion chamber of a
piston engine.
For this purpose, a model able to take into account multiple
injections, conventional diesel mode and Homogeneous Charge
Compression Ignition (HCCI) mode have been developed modeling
physical phenomena like: - spray atomization and the liquid phase
penetration, - vaporization deduced from a characteristic time, -
presumed mixing distribution computed with a β-function where the
mixture fraction variance equation is obtained from the integration
of turbulence, inlet/outlet spray zone mass and evaporation, and -
the auto-ignition and diffusive combustion regimes determined by
Flame Propagation of ILDM (FPI/Intrinsic Low-Dimensional Manifolds)
tabulation combined with turbulence regime by a Presumed
Conditional Moments (PCM) method.
In this paper, we propose a modeling of NOx based on tabulations
of a characteristic time and NO mass fraction equilibria. After a
brief introduction of the combustion model, the NOx model is
theoretically described and results on a diesel conventional engine
are presented, compared to experimental data.