Low-temperature combustion chemistry of biofuels: pathways in the initial low-temperature (550 K–750 K) oxidation chemistry of isopentanol

Abstract

The branched C(5) alcohol isopentanol (3-methylbutan-1-ol) has shown promise as a potential biofuel both because of new advanced biochemical routes for its production and because of its combustion characteristics, in particular as a fuel for homogeneous-charge compression ignition (HCCI) or related strategies. In the present work, the fundamental autoignition chemistry of isopentanol is investigated by using the technique of pulsed-photolytic Cl-initiated oxidation and by analyzing the reacting mixture by time-resolved tunable synchrotron photoionization mass spectrometry in low-pressure (8 Torr) experiments in the 550-750 K temperature range. The mass-spectrometric experiments reveal a rich chemistry for the initial steps of isopentanol oxidation and give new insight into the low-temperature oxidation mechanism of medium-chain alcohols. Formation of isopentanal (3-methylbutanal) and unsaturated alcohols (including enols) associated with HO(2) production was observed. Cyclic ether channels are not observed, although such channels dominate OH formation in alkane oxidation. Rather, products are observed that correspond to formation of OH viaβ-C-C bond fission pathways of QOOH species derived from β- and γ-hydroxyisopentylperoxy (RO(2)) radicals. In these pathways, internal hydrogen abstraction in the RO(2)⇄ QOOH isomerization reaction takes place from either the -OH group or the C-H bond in α-position to the -OH group. These pathways should be broadly characteristic for longer-chain alcohol oxidation. Isomer-resolved branching ratios are deduced, showing evolution of the main products from 550 to 750 K, which can be qualitatively explained by the dominance of RO(2) chemistry at lower temperature and hydroxyisopentyl decomposition at higher temperature.

VUV Photoionization Cross Sections of HO2, H2O2, and H2CO

“…[8][9] They assigned a 20% systematic uncertainty in methanol cross sections due to the uncertainty in the cross section of propene. 5 The same 20% systematic uncertainty also applies to our results. We measured the methanol spectrum several times; the scatter in the methanol cross section measurements results in typical cross section errors of ~5%, likely caused by uncertainties in the manometric preparation of the methanol tanks as well as uncertainties in delivery of the sample to the reaction tube.…”

“…The absolute methanol photoionization spectrum was measured relative to the propene spectrum following the procedure outlined in Welz et al, 5 and compared to previous reports. The photoionization spectrum of propene is well-known 6 and has been used previously as a reference compound for determining photoionization cross sections.…”

“…The photoionization spectrum of propene is well-known 6 and has been used previously as a reference compound for determining photoionization cross sections. 5,[7][8] Experiments were conducted by introducing propene (2 sccm of 1.00% propene in He) and methanol (1 sccm of 4.667% methanol in He) into the flow tube. Propene was Matheson Tri-Gas, 1.00% in Ar.…”

Automated exploration of the mechanism of elementary reactions

“…For the current, 1.0 version of the code, we focused on the chemistry that occurs during lowtemperature autoignition processes [12], illustrated in Figure 1. This reaction system represents a wide variety of chemical transformations, which play a role also in atmospheric chemistry.…”

Combustion Characteristics of C5 Alcohols and a Skeletal Mechanism for Homogeneous Charge Compression Ignition Combustion Simulation

“…19 In general, the octane ratings of C 5 and larger alcohols are lower than those of C 1 -C 3 alcohols; this higher propensity for ignition (increased cetane number) makes larger alcohols suitable for compression-ignition (CI) engine applications. 1 20 Attention to alcohol combustion research on a C 5 family of alcohols, including npentanol [21][22][23][24][25] , iso-pentanol (3-methyl-1-butanol, ) [26][27][28][29][30] , and 2-methylbutanol (2-methyl-1-butanol, ) [31][32][33][34] has increased in recent years because longer-chain alcohols are better suited for combustion engines. However, there have been limited studies on C 5 alcohol combustion.…”