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As a contribution to the research into HCCI engines which have a potential of achieving low fuel consumption with low particulate and low NOx emissions, a six zone simulation model coupled with the cycle simulation code AVL Boost was previously developed. The model uses comprehensive chemical kinetics and shows good agreement with experimental results. At the point of transition from the gas exchange process to the high pressure cycle, which is multi-zonal, the model assumes equal gas mixtures in all zones. Therefore, the model is suitable for perfectly homogeneous mixtures, and since it has no ability to receive fuel during compression, the mixture has to be prepared outside the cylinder. Further development of this model, which will be shown in this paper, includes the introduction of initial conditions with non-uniform mixtures and the possibility of receiving fuel during compression.

Today, the potential of HCCI engines, i.e., their high efficiency with low NO and particulate emissions, is very well known. Besides this potential, the problems that are related to HCCI engines, particularly the control, are also known issues. In order to be able to develop and assess the control strategies for HCCI engines, one needs models for the control development. In addition to mean value models crank-angle resolved control-oriented computer codes have also been developed lately (e.g., Boost RT). In these codes, complex 1D gas dynamics and complex combustion models are omitted, while the in-cylinder calculation is crank-angle resolved. Simple combustion models are variations of Vibe and the combustion defined by a table. Since the HCCI combustion is controlled by the state of the gas in the cylinder, parameters of Vibe functions depend on the factors that define this state.

Research into internal combustion engines requires the development of engine simulation models which should ensure acceptable results of engine performances over a wide range of engine speeds and loads. Due to high costs of experiments and a rapid increase in the computer power, researches all over the world devote great effort to the development and improvement of simulation models. Well-known multi-dimensional simulation models (CFD models) of the engine cycle are the most demanding models in terms of computational resources. On the other hand, there are multi-zone models that are very robust and that are able to capture a certain in-cylinder property during the engine operating cycle. It is known that turbulence effects inside engine cylinder play an important role in the combustion process. In order to properly predict combustion process, characteristics of the turbulent flow field should also be accurately defined.

The paper presents the experimental study of an active pre-chamber volume variations on engine performance and emissions. The experiments were performed on a test setup equipped with a single cylinder engine. The modular and custom-made pre-chamber design was used, enabling the variation of pre-chamber volume in the range of 3-5% of clearance volume. During the variation of pre-chamber’s geometrical parameters, the ratio of total nozzle area to the pre-chamber volume was fixed at a value of approximately 0.033 cm-1. At a given pre-chamber volume the variation of engine load was achieved by the change of excess air ratio in the main chamber from stochiometric mixture to lean limit, while the engine speed was fixed to 1600 rpm. For each pre-chamber variation and on each of the investigated operating points, a spark sweep was performed to obtain the highest indicated efficiency while satisfying the imposed restrictions regarding combustion stability and knock occurrence.

Nowadays, the main potential of the HCCI engine, i.e. high efficiency with low NOx and soot emissions, is a well-known fact. Main limitations that prevent the commercial application of the HCCI engine are the control of combustion timing and low power density. Higher power density could be achieved by boosting the engine, but low exhaust temperatures associated with the HCCI combustion require a different approach when trying to achieve a boosted HCCI engine. This paper presents a numerical study on two boosting configurations that will enable high boost levels and high load, as a consequence, in the Ethanol fueled HCCI engine, in the engine speed range of 1000 - 4000 rpm. For the purposes of this study, a four-cylinder HCCI engine model has been made in the cycle-simulation software. The model includes the entire engine geometry and all elements necessary for representing the entire engine flow path.

Exhaust gas recirculation (EGR) is a proven strategy for the reduction of NOX emissions in spark ignited (SI) engines and compression ignition engines, especially in lean burn conditions where the increase of thermal efficiency is obtained. The dilution level of the mixture with EGR is in a conventional SI engine limited by the increase of combustion instability (CoV IMEP). A possible method to extend the EGR dilution level and ensure stable combustion is the implementation of an active pre-chamber combustion system. The pre-chamber spark ignited (PCSI) engine enables fast and stable combustion of lean mixtures in the main chamber by utilizing high ignition energy of multiple flame jets penetrating from the pre-chamber to the main chamber. In this paper, as an initial research step, a numerical analysis is performed by employing the 0D/1D simulation model, validated with the initial experimental and 3D-CFD results.