The pre-chamber ignition concept is an attractive strategy to enable the operation of spark-ignition engines in lean or diluted conditions keeping a suitable combustion process. According to the results the benefits in lean conditions include the fastening of the combustion process, the improvement of combustion stability, the increase of combustion efficiency by lowering carbon monoxide and hydrocarbons emissions. Thus, the pre-chamber ignition concept, especially in its passive version, arises as a promising alternative for future spark-ignition engines for passenger car applications. In this framework, an experimental investigation has been carried out to evaluate the potential of passive pre-chamber ignition concept in a high compression ratio, turbocharged, port fueled spark-ignition engine, using 95 Research Octane Number gasoline. As a first step, a 1D Wave Action Model was generated to design the pre-chamber geometry taking the fuel available at the start of pre-chamber combustion and the pressure difference between the main chamber and pre-chamber as key parameters. In a second step, these pre-chamber designs were experimentally validated at high load/speed conditions (4500 rpm, 12.5 bar Indicated Mean Effective Pressure) and compared with the conventional spark-ignition concept. Experimental results show how the passive pre-chamber concept increases efficiency with good combustion stability and high combustion efficiency in stoichiometric conditions. Nevertheless, maximum lambda attainable with the passive system is similar than that of the conventional spark and much lower compared to the maximum levels reported for the active system.

ElsevierBroatch Jacobi, JA.; Margot, X.; Novella Rosa, R.; Gómez-Soriano, J. (2016). Combustion noise analysis of partially premixed combustion concept using gasoline fuel in a 2-stroke engine. Energy. 107:612-624. AbstractIn the last decade, different advanced combustion concepts based on generating totally or partially premixed conditions have been investigated in CI engines with the aim of achieving lower NOx and soot emissions. Most of the drawbacks inherent to this type of combustions, such as the combustion phasing control or combustion stability, can be mitigated by combining the PPC concept fueled by gasoline and a small 2-stroke HSDI engine. However, combustion noise issue remains unsolved while it is a critical aspect due to its strong influence in the customer purchasing decision and compliance of more stringent regulations. In this work, an analysis of the combustion noise generated by PPC combustion concept is performed in order to identify the most influential parameters and to define key paths for controlling the noise level. In addition, 3D CFD simulations have been performed to further understand the combustion noise generation mechanisms. Results evidence how the strong impact of the maximum pressure time-derivative achieved during combustion process renders all other sources of noise generation irrelevant. The trade-off between combustion noise and combustion efficiency of this PPC concept has been confirmed, while the intrinsic relation between such parameters and the engine efficiency has been also evaluated.

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In this paper, the unsteady behaviour of a compression-ignited (CI) engine combustion chamber is studied by analyzing the results of a Computational Fluid Dynamics (CFD) model through the application of different flow decomposition techniques, aiming to resolve the underlying modal structure of the process. Experimental validation for the combustion simulation is provided, and a methodology for extracting coherent pressure information is proposed in order to provide a suitable input for different analysis methods. These range from straightforward Fourier transform techniques to more sophisticated modal decomposition approaches. In particular Proper Orthogonal Decomposition (POD) is shown to provide valuable insight into the time-spatial structure of the combustion flow field, allowing the establishment of correlations between pressure modes and physical parameters of the combustion, such as the injection timing or the chamber geometry. Dynamic Mode Decomposition (DMD) on the other hand is proven to successfully highlight the link between the frequency of the unsteady energy components and their spatial distribution within the chamber. Advantage is then taken of the modal characterization of the unsteady behaviour in the chamber to showcase how physical parameters such as the spray angle can be modified to optimize the acoustic signature of the combustion process, helping CI internal combustion engines reduce their acoustic environmental impact.

In this paper, a numerical Computational Fluid Dynamics (CFD) study is carried out with the purpose of understanding how the injector design may impact on the in-cylinder processes, which cause noise emission. This study is based on a combination of the gasoline partially premixed combustion concept with a new high speed direct injection 2-stroke engine, which emerges as a promising solution able to comply with nitrous oxides and particulate matter emissions standards, while ensuring combustion control and stability. The original engine configuration is varied by modifying the included spray angle and the number of injector nozzles in order to evaluate other design solutions for mitigating combustion noise. Results show that the maximum pressure time-derivative achieved during the combustion is the most influential parameter on the acoustic response of the in-cylinder noise source. However, they also evidence that for some operation conditions the resonance phenomena can enhance their contribution, thus playing a relevant role in the engine noise level. Further analysis allowed to identify three combustion-related parameters, which characterize this phenomenon and allow identifying key paths to minimize its levels.