Reduced Kinetic Schemes of Complex Reaction Systems: Fossil and Biomass‐Derived Transportation Fuels

Abstract

The kinetic modeling of the pyrolysis and combustion of liquid transportation fuels is a very complex task for two different reasons: the challenging characterization of the complex mixture of several hydrocarbon isomers and the complexity of the oxidation mechanisms of large hydrocarbon and oxygenated molecules. While surrogate mixtures of reference components allow to tackle the first difficulty, the complex behavior of the oxidation mechanisms is mostly overcome by reducing the total number of involved species by adopting a lumping approach. After a first investigation of the different liquid fuels (gasoline, kerosene, and diesel fuels), a short discussion on the lumping techniques allows to highlight the advantages of this approach. The lumped POLIMI pyrolysis and oxidation mechanism of hydrocarbon and oxygenated fuels is then used for generating several skeletal mechanisms for typical surrogate mixtures, moving from pure n-heptane up to heavy diesel fuels. These skeletal models are simply reduced with a reaction flux analysis, and they involve between 100 and 200 species. While these sizes already allow detailed computational fluid dynamics (CFD) calculations in internal combustion engines, further reduction phases are necessary when the interest is toward more complex CFD computations. To maintain the standard structure of the skeletal mechanisms, successive reduction phases are not considered. Moreover, new regulations pushed toward a greater use of renewable fuels. For these reasons, the skeletal models are also extended to biogasolines including methanol, ethanol, and n-butanol. Similarly, skeletal models of diesel and biodiesel fuels, including methyl esters, are also provided. Several comparisons with experimental data and complete validations in the operating range of internal combustion engines are also reported. The whole set of comparisons with experimental data obtained in a wide range of conditions not only validate the reduced models of specific transportation fuels but also the complete kinetic scheme POLIMI 1404

A review of the combustion and emissions properties of advanced transportation biofuels and their impact on existing and future engines

“…The overall radical pool, therefore, evolves in unison, over space or time, as various species are added, by fuel breakdown reactions, or removed, by conversion of intermediates to stable combustion products, from the radical pool [146,151]. Therefore, even though the combustion chemical-kinetic mechanisms discussed above involve hundreds to thousands of different species, it is possible to reduce the mechanism size to around 50-100 species per surrogate fuel component while maintaining reasonable simulation accuracy of major combustion properties [136,138,145,[152][153][154][155]. The number of additional intermediate species that must be added to the model, to maintain consistent accuracy, per surrogate-fuel component decreases as the total number of surrogate-fuel components increases [156,157], because many of the intermediate chemical species are shared between all hydrocarbon fuels [146][147][148][149][150][151][152].…”

Progress in kinetic predictions for complex reaction of hydrocarbons: from mechanism studies to industrial applications

“…Saggese et al (2013) used a lumped approach to model cracking reactions at the free radical level. Recently, Ranzi et al (2014) described a kinetic model and corresponding reduction techniques for biomasses at the free radical level.…”

Experimental Validation of Combustion Models for Diesel Engines Based on Tabulated Kinetics in a Wide Range of Operating Conditions

“…IDEA is a mixture of 70% n-decane and 30% methylnaphthalene and the reduced chemical mechanism employed for table generation considers 127 species and more than 1000 reactions. Validation of such mechanism and details about the reduction algorithm can be found in [36,37]. Four hours are necessary to generate the chemistry table for the PCCI combustion simulation.…”