**8. References**

Küsell, M.; Moser, W.; Philipp, M. (1999). Motronic MED7 for gasoline direct injection engines: engine management system and calibration procedures, SAE Paper 1999- 01-1284

Three injectors are preliminary experimentally investigated with the aim of building a comprehensive database for the assessment of a proper spray model. The injectors are all characterised, under various injection strategies, in terms of both measurement of the instantaneous mass flow rate and visualization of the fuel dispersion in an optically accessible vessel. The developed spray model exploits a log-normal distribution of the initial droplets size of given expected value and variance. The expected value is theoretically determined as a function of the experimental injection velocity and backpressure, whereas the variance is properly tuned, together with a constant regulating the adopted droplets break-up model. Tuning of the constants is realised by assessing an automatic novel procedure within an optimisation software. The model portability with respect to the

A 3D CFD model able to define the main guidelines for the management of the mixture formation process in a high performance GDI engine is then assessed. Simulation of the whole four-stroke engine cycle is effected by considering gasoline adduction during intake through one of the tested injectors. Boundary and initial conditions for the 3D model are defined, as a function of time, on the ground of a 1D simulation of the whole propulsion

The mixture formation process under high-speed high-load working conditions is shown to be strongly affected by the choice of the angle of inclination of the injector axis w.r.t. the cylinder axis. For lower angles, the gasoline droplets remains confined in the vicinity of the walls or quickly reach the surface of the piston, where they remain for a long time, especially during compression due to the motion of the piston itself. The choice of the SOI is made in order to fully exploit the turbulent motion of the entering air. The injection pressure

A moderate speed, moderate load condition is also studied into detail, where the air-to-fuel ratio is maintained lean. Both single and double injection events are considered. Optimal choice of both the start of the single injection strategy and the time of spark advance is realized by means of the Simplex algorithm, in order to minimize the fuel consumption. The same criterion is adopted in the numerical study of mixture formation and combustion consequent a double injection. The start of the first pulse and the dwell time between two successive pulses, both characterized by the same gasoline mass, are searched, together with the best time of SI. The optimal solution is shown to reduce the fuel consumption with respect to the case injection is realized in one shot, thus confirming the possibility to resort to split injections to improve the quality of the charge stratification under lean operation. The assessed procedure, where a properly developed 3D engine model is coupled with an

Authors wish to thank Mr. Alessandro Montanaro, Mr. Ugo Sorge and Mr. Salvatore Alfuso for the long day assistance in the development of the work here presented. A special thank goes to Prof. Fabio Bozza for the important support given in the 1D engine modelling.

Küsell, M.; Moser, W.; Philipp, M. (1999). Motronic MED7 for gasoline direct injection

engines: engine management system and calibration procedures, SAE Paper 1999-

injection pressure and the kind of injector is demonstrated.

must not be increased so much in order to limit the NO formation.

optimization tool, is proven to be a valuable tool in the phase of engine design.

system.

**7. Acknowledgment** 

01-1284

**8. References** 


**10**

Fang Wang *Beihang University* 

*China* 

**Turbulent Combustion Simulation**

Combustion is a natural phenomenon. It happens in forest, automotive engine and gas cooker. In Computational Fluid Dynamics (CFD), the combustion phenomenon complies with a set of partial differential equations. According to the resolution scale, from big to small, the simulation methods in combustion are Reynolds Averaged Navior Stokes method (RANS), Large Eddy Simulation (LES), and Direct Numerical Simulation (DNS).

In this chapter, an Algebraic Sub-grid Scale turbulent Combustion Model (ASSCM) for LES is brought forward. Then this model is applied to a partly diffusion jet flame and a premixed flame, after that, the database of the LES simulation results is used to test a RANS turbulent combustion model closure idea. Finally, a DNS by spectral method (Xu et al, 1996) in channel flow is carried on with consideration of buoyancy effects, and the database of the DNS simulation results is used to study RANS and LES turbulent combustion models.

The Sub-Grid Scale (SGS) turbulent combustion model is a key point in LES study. There are two methods in modelling: one is to build the turbulent combustion model for all turbulence scale, the other is to build the models for big scale and small scale separately. Generally, there are probability density function models, laminar flame-let models, eddy break up

As for probability density function models, there are filtered density function method (FDF), probability density function method (PDF), and filtered mass density function method (FMDF), which are similar methods and all rooted in the probability function. They solve the PDF transport equation by the Lagrangian Monte Carlo scheme without using the assumed PDF functions. Also the detail chemical reaction kinetics can be applied directly without models, while the mixing term and the convection term need to be closed. The value of the filtered scaler, such as the averaged temperature, can be calculated by the integration over the composition space. When the FMDF or FDF method extended into turbulent combustion SGS model, the joint probability density function of the sub-grid-scale (SGS) scalar quantities are obtained by solution of its modelled transport equation. In the work of Colucci et al 1998 and James et al 2000, the FMDF combined with detail reaction gave good prediction in temperature

Combustion model research in RANS and LES was, is and will still be a hot topic.

**2. Turbulent combustion models in LES** 

model, and ASSCM sub-grid scale model, etc.

**1. Introduction** 

**and Direct Numerical Simulation** 

**by Large Eddy Simulation**

Li, T.; Nishida, K.; Zhang, Y.; Hiroyasu, H. (2007). Effect of split injection on stratified charge formation of direct injection spark ignition engines, *International Journal of Engine Research*, Vol. 8, pp. 205-218
