Abstract
The use of liquid or gaseous biofuels in reciprocating internal combustion engines (ICEs) is today a relevant issue as these systems are largely diffused for both steady power generation and transportation due to their flexibility and easiness of use. The improvement and perfect control of the combustion process under non-conventional fuelling is mandatory to achieve high-energy efficiency without substantial changes to the architecture or the fuel supply system. In this perspective, the detailed characterization of multiphase reacting systems achievable though computational fluid dynamics (CFD) may give a decisive contribution. However, the assessed combustion models used for fossil fuels (diesel oil, gasoline, methane), tuned on the ground of a massive amount of experimental data, often results poor in predicting the actual behaviour of renewable fuels whose composition and properties may change also according to technology for their production. Present work aims at filling some existing gaps in biofuel combustion modeling by performing investigations on two representative engine cases, for their characterization and performance enhancement. Two approaches are followed, namely through reduced chemical kinetics coupled with turbulence within a coherent flame schematization, and through a turbulent species transport approach with detailed kinetics. Simulations are first carried out on a compression ignition (CI) ICE. The formulation of a 3D CFD model is described to reproduce the performance of this engine in a dual-fuel mode with premixed syngas from biomass gasification and a biodiesel pilot injection leading to self-ignition. Pollutants formation and energy efficiency are calculated as syngas amount and the biodiesel start of injection (SOI) are varied. Attention is then focused on the implementation of renewable alcohol fuels (ethanol and butanol), as these lasts are receiving large interest due to low production costs. A validated reduced kinetic mechanism for PRF-ethanol-butanol combustion performs well in multi-component oxidation conditions, as well as in neat fuel oxidation conditions, in terms of ignition delay time, laminar flame speed and HCCI combustion conditions. The paper shows that CFD, even at different level of approximation, may describe into detail the combustion process and provide important guidelines for the design of new generation ICEs fuelled by biofuels.
Highlights
The reduction of greenhouse gas (GHG) emissions has become an important driver for the spread of the concept of bioenergy, in particular for Countries belonging to the Organization for Economic Cooperation and Development (OECD)
Biodiesel oxidation is generally described through the development of surrogate or reduced models due to the many classes of involved molecules. This approach can be obviously applied to other biofuels, such as alcohol molecules to be used in spark ignition (SI) engines. These lasts are composed by single classes of molecules, an accurate description of the reactions related to the combustion and noxious emissions formations allows a proper characterization of the effect of these oxygenated fuels in internal combustion engines (ICEs) computational fluid dynamics (CFD) applications, where generally multi-component interactions take place as they are blended with gasoline in different percentages for anti-knocking purposes
After a first section dedicated to the description of the main production technologies of each biofuel considered in present work, and their impact on ICEs performances, the first proposed method is focused on the employment of a properly developed 3D CFD model for the simulation of a compression ignition (CI) engine under dual-fuel mode
Summary
Powering of Internal Combustion Engines: Production Routes, Effect on Performance and CFD Modeling of Combustion. The improvement and perfect control of the combustion process under non-conventional fueling is mandatory to achieve high-energy efficiency without substantial changes to the architecture or the fuel supply system. In this perspective, the detailed characterization of multiphase reacting systems achievable though computational fluid dynamics (CFD) may give a decisive contribution. A validated reduced kinetic mechanism for PRF-ethanol-butanol combustion performs well in multi-component oxidation conditions, as well as in neat fuel oxidation conditions, in terms of ignition delay time, laminar flame speed and HCCI combustion conditions. The paper shows that CFD, even at different level of approximation, may describe into detail the combustion process and provide important guidelines for the design of new generation ICEs fuelled by biofuels
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