Dibutyl ether (DBE) is a promising biofuel due to its high cetane number (~ 100) and high volumetric energy density (31.6 MJ/L). It could either be used directly in compression ignition engines or blended with other conventional or renewable fuels. Oxidation and pyrolysis kinetics of DBE are not well known, particularly at high pressures. In this work, we have experimentally investigated the chemical kinetics of DBE in three domains: (a) ignition delay time measurements in a rapid compression machine over T = 550 -650 K, P = 10, 20, 40 bar, = 0.5, 1; (b) ignition delay time measurements in a shock tube over T = 900 -1300 K, P = 20, 40 bar, = 0.5, 1; (c) laser-based carbon monoxide speciation measurements in a shock tube during DBE pyrolysis and oxidation over T = 1100 -1400 K, P = 20 bar. Pressure timehistories measured in RCM experiments exhibited unique 3-stage and 4-stage ignition behavior predominantly at fuel-lean conditions. Experimental data were compared with the predictions of two recent chemical kinetic models of DBE. Sensitivity analyses were carried out to identify key reactions which may have caused the discrepancy between experiments and simulations. It was found that the rate of decomposition of DBE may need to be revisited to improve the oxidative and pyrolytic predictions of DBE kinetic model.
Soot emissions in combustion are unwanted consequences of burning hydrocarbon fuels. The presence of soot during and following combustion processes is an indication of incomplete combustion and has several negative consequences including the emission of harmful particulates and increased operational costs. Efforts have been made to reduce soot production in combustion engines through utilizing oxygenated biofuels in lieu of traditional nonoxygenated feedstocks. The ongoing Co-Optimization of Fuels and Engines (Co-Optima) initiative from the US Department of Energy (DOE) is focused on accelerating the introduction of affordable, scalable, and sustainable biofuels and high-efficiency, low-emission vehicle engines. The Co-Optima program has identified a handful of biofuel compounds from a list of thousands of potential candidates. In this study, a shock tube was used to evaluate the performance of soot reduction of five high-performance biofuels downselected by the Co-Optima program. Current experiments were performed at test conditions between 1,700 and 2,100 K and 4 and 4.7 atm using shock tube and ultrafast, time-resolve laser absorption diagnostic techniques. The combination of shock heating and nonintrusive laser detection provides a state-of-the-art test platform for high-temperature soot formation under engine conditions. Soot reduction was found in ethanol, cyclopentanone, and methyl acetate; conversely, an α-diisobutylene and methyl furan produced more soot compared to the baseline over longer test times. For each biofuel, several reaction pathways that lead towards soot production were identified. The data collected in these experiments are valuable information for the future of renewable biofuel development and their applicability in engines.
The combustion and pyrolysis behaviors of light esters
and fatty
acid methyl esters have been widely studied due to their relevance
as biofuel and fuel additives. However, a knowledge gap exists for
midsize alkyl acetates, especially ones with long alkoxyl groups.
Butyl acetate, in particular, is a promising biofuel with its economic
and robust production possibilities and ability to enhance blendstock
performance and reduce soot formation. However, it is little studied
from both experimental and modeling aspects. This work created detailed
oxidation mechanisms for the four butyl acetate isomers (normal-,
sec-, tert-, and iso-butyl acetate) at temperatures varying from 650
to 2000 K and pressures up to 100 atm using the Reaction Mechanism
Generator. About 60% of species in each model have thermochemical
parameters from published data or in-house quantum calculations, including
fuel molecules and intermediate combustion products. Kinetics of essential
primary reactions, retro-ene and hydrogen atom abstraction by OH or
HO2, governing the fuel oxidation pathways, were also calculated
quantum-mechanically. Simulation of the developed mechanisms indicates
that the majority of the fuel will decompose into acetic acid and
relevant butenes at elevated temperatures, making their ignition behaviors
similar to butenes. The adaptability of the developed models to high-temperature
pyrolysis systems was tested against newly collected high-pressure
shock experiments; the simulated CO mole fraction time histories have
a reasonable agreement with the laser measurement in the shock tube.
This work reveals the high-temperature oxidation chemistry of butyl
acetates and demonstrates the validity of predictive models for biofuel
chemistry established on accurate thermochemical and kinetic parameters.
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