Abstract
Nowadays reducing green-house gas emissions and pushing the fossil fuel savings in the field of light-duty vehicles is compulsory to slow down climate change. To this aim, the use of new combustion modes and dilution strategies to increase the stability of operations rich in diluent is an effective technique to reduce combustion temperatures and heat losses in throttled operations. Since the combustion behavior in those solutions highly differs from that of typical market systems, fundamental analyses in optical engines are mandatory in order to gain a deep understanding of those and to tune new models for improving the mutual support between experiments and simulations. However, it is known that optical accessible engines suffer from significant blow-by collateral flow due to the installation of the optical measure line. Thus, a reliable custom blow-by model capable of being integrated with both mono-dimensional and three-dimensional simulations was developed and validated against experimental data. The model can work for two different configurations: (a) stand-alone, aiming at providing macroscopic data on the ignitable mixture mass loss/recover through the piston rings; (b) combined, in which it is integrated in CFD engine simulations for the local analysis of likely collateral heat release induced by blow-by. Furthermore, once the model was validated, the effect of the engine speed and charge dilution on the blow-by phenomenon in the optical engine were simulated and discussed in the stand-alone mode.
Highlights
Nowadays optical accessible engines are fundamental devices for studying and testing innovative combustion systems in order to discover and improve high efficiency solutions, such as spark-assisted compression ignition (SACI), spark-controlled compression ignition (SPCCI) or homogeneous charge compression ignition (HCCI) [1,2,3]
The blow-by model in stand-alone mode is validated against experimental data at both motored and firing conditions
The piston temperature optical engines is usually lower thatfirof commercial-like engines due to the overallin lower thermal regime imposed bythan limited commercial-like due to the overall lower thermal regime imposed by limited mode firing ing time
Summary
Nowadays optical accessible engines are fundamental devices for studying and testing innovative combustion systems in order to discover and improve high efficiency solutions, such as spark-assisted compression ignition (SACI), spark-controlled compression ignition (SPCCI) or homogeneous charge compression ignition (HCCI) [1,2,3]. One can distinguish between burnt mixture from the flame and that from auto-ignition The latter difference could be captured from the imaging during combustion from the optical window placed on the piston crown, and used to develop and validate SACI combustion models. The effects of alternative fuels and biofuels on combustion and lubricants in both automotive and heavy-duty applications are being investigated, aiming at a greener transition from traditional gasolines and diesel fuels [4,5,6] In this scenario, while numerical setups are being implemented on a larger scale for commercial engines due to their time saving potential, it is mandatory to implement ad hoc models for optical accessible engines, which are still playing a key role in the extensive characterization of in-cylinder phenomena. Blow-by needs to be accounted for in order to perform a comprehensive analysis of the phenomena occurring in the combustion chamber by evaluating the reactive gas flow through the piston rings
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