Relative Reactivity of Oxygenated Fuels: Alcohols, Aldehydes, Ketones, and Methyl Esters

Abstract

This work aims at comparing and highlighting the main reaction pathways characterizing the combustion behavior of oxygenated fuels. Ethanol and heavier alcohols are already viable biofuels, despite some concern about their aldehydes and ketones emissions. Recently, the potential of 2-butanone (methyl ethyl ketone, MEK) as anti-knocking fuel was investigated at engine-relevant conditions. Moving from methyl butanoate (MB), long-chain fatty acid methyl esters are largely considered and used as biodiesels, mainly in Europe. Starting from a consistent assessment of C-H and C-C bond dissociation energies (BDEs) in n-butane, n-butanol, n-butanal, MEK, and MB, their impact on the selectivity of the different H-abstraction reactions and their relative reactivity are analyzed. Low-temperature oxidation mechanisms of 1-butanol and 2-butanone are also presented and discussed. Based on the upgraded Politecnico di Milano (POLIMI) kinetic mechanism, the relative reactivity of n-butane and the different oxygenated fuels is discussed here in depth. Stoichiometric fuel/air mixtures at 10 and 30 atm and 600-1450 K are analyzed. At low temperatures (T < 675 K), n-butanol and 2-butanone show the lowest reactivity, whereas the other fuels tend to converge to a very similar behavior. n-Butanal is the fastest to ignite in the whole T range, because it has the weakest C-H BDEs. No negative temperature coefficient (NTC) behavior is observed for n-butanal and n-butanol under the investigated conditions. A weak NTC is predicted for MB, similar to that of propane. MB and 2-butanone are the slowest to ignite between 750 and 850 K. A limited number of fuel-specific reactions characterizing each fuel and deserving more accurate investigation are highlighted, together with the lack of experimental targets below 850 K for MB and 2-butanone

Detailed kinetic mechanism of gas-phase reactions of volatiles released from biomass pyrolysis

“…The calculated BDEs are in good agreement with the corresponding ones estimated with the MRACPF2 method by Oyeyemi et al [38]. Further details on these BDE calculations are reported by Pelucchi et al [39]. [26].…”

Combustion of n-C3–C6 Linear Alcohols: An Experimental and Kinetic Modeling Study. Part I: Reaction Classes, Rate Rules, Model Lumping, and Validation

“…The model was later extended to the pentanol isomers. 53 A lumped low-temperature mechanism to describe n -butanol oxidation was proposed by Pelucchi et al 20 and was extended, by analogy, to n -pentanol to investigate the operability maps of a HCCI engine fueled with n -butanol and n -pentanol. 17 …”

“… 19 Generally, the reactivity of oxygenated biofuels (e.g., alcohols, aldehydes, organic acids) is largely influenced by the presence of an oxygenated functional group that modifies bond dissociation energies and enhances, inhibits, and triggers different reaction pathways compared to the parent fuel molecule (e.g., alkane). 20 The recent interest in biofuels and bio-oils from the fast pyrolysis of biomass has motivated systematic experimental and modeling investigations of different chemical families such as aldehydes, 21 − 25 acids, 26 and oxygenated aromatics 27 − 29 to unravel the effects of different oxygenated functional groups on fuel kinetics. Beyond their application as surrogate fuel components, 30 such species are also important intermediates in the oxidation of alternative or conventional hydrocarbon fuels, because they are implicit in the hierarchical nature of complex combustion kinetic models.…”

Shock tube studies on ignition delay and combustion characteristics of oxygenated fuels under high temperature

“…Among them, as oxygen is contained in the fuel molecule, the oxygenated fuel is used as an alternative or as an additive to traditional petrochemical fuel, which plays an important role in improving the in-cylinder combustion process of the internal combustion engines and reducing pollutant emissions. [1][2][3][4][5] At the same time, using efficient combustion technology is an effective technical measure to meet higher emissions requirements, such as lowtemperature combustion and homogeneous charge compression ignition. Through the study of these new combustion modes, the researchers found the chemical reaction kinetics is the key factor to control the combustion process.…”