CFD CODE VALIDATION AND COMBUSTION ANALYSIS OF A SPARK-IGNITION ENGINE FUELED WITH METHANE-HYDROGEN BLENDS

The motivation of the present work is first to conduct the validation of a Computational Fluid Dynamics (CFD) code, for different methane-hydrogen fuel blends in a spark-ignition (SI) engine, focusing on the newly developed combustion model. This validation is based on both performance and emissions comparison with experimental data, in order to gain a complete view of the code capabilities. Then, a detailed combustion analysis is conducted, by further processing the results of the numerical code, providing insight of the flame front propagation and emissions production inside the engine cylinder. The available experimental data are from a two-cylinder SI engine with complete sets of measured values. For the current study it has been decided to focus on the effect of variable hydrogen content (from 0 up to 50% by vol. hydrogen). The CFD code is an in-house code and has been initially developed for simulating hydrogen-fueled SI engines. Lately, its combustion model has been extended with the introduction of methane fuel and the reaction rates are calculated with the characteristic conversion time-scale method, while the flame front is tracked using a laminar and turbulent combustion velocity. The nitric oxide (NO) emissions are calculated according to the widely-used Zeldovich mechanism. The CFD code validation includes the comparison of calculated performance values (pressure history and heat release rates) with the measured ones for variable hydrogen content. The calculated NO emissions are also compared with the measured ones for the same conditions. From this comparison it has been revealed that a good match exists for both performance and emissions, showing that the code can be applied for detailed investigation of such combustion processes. Finally, a detailed combustion analysis is implemented with the support of the measured data, in order to examine the combustion processes and flame propagation for the different fuel blends.

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