Analysis of Important Chemical Pathways of n-Heptane Combustion in Small Skeletal Mechanisms

Abstract

Reduced mechanisms for n-heptane combustion have been constructed using the novel ACR method, with the complex mechanism from CRECK, including low-temperature chemistry, as a starting point. Tailored mechanisms for each part of the combustion process, ignition, flame propagation, and extinction, were created to identify differences and common trends in mechanism composition. The simulations were carried out for n-heptane/air mixtures for zero-dimensional homogenous reactors, one-dimensional freely propagating flames, and counter-flow diffusion flames at temperature, pressure, and equivalence ratio conditions relevant to engine combustion. The smallest mechanism, 28 species, only targets laminar burning velocity, while the largest single-property mechanism is for ignition over a wide temperature range, with 48 species. A compound mechanism covering all conditions consists of 65 species, this mechanism includes reaction paths describing important subchemistries like the peroxyl radical chemistry governing low-temperature ignition and the C/H/O chemistry of importance to flame propagation. Compared to the CRECK mechanism, all the reduced mechanisms have fewer than 2% of the number of reactions.

The effect of poly(oxymethylene) dimethyl ethers (PODE3) on soot formation in ethylene/PODE3 laminar coflow diffusion flames

“…Formaldehyde is then converted into formyl radicals ( • CHO) and finally to carbon monoxide (CO) via H-atom abstraction [81]. Large hydrocarbons such as those present in fossil-based fuels (diesel and kerosene) or surrogate fuels (n-heptane, n-decane, iso-octane, n-decane, methylcyclohexane, and toluene) decompose at flame temperatures into small species such as CH 4 , C 2 H 4 and C 3 H 6 due to the low energy barrier of carboncarbon β-scission of alkyl radicals [82,83,84,85]. For example, H 2 , CH 4 , C 2 H 4 , and C 3 H 6 were found to form in abundance during the pyrolysis of ndodecane, with ethylene (C 2 H 4 ) being the dominant species [86].…”

Maximum reduction in greenhouse gas emissions by complete replacement of natural gas with pure hydrogen as a sole low reactive fuel in a RCCI engine

“…Therefore, the n-heptane oxidation pathways are carefully assessed as depicted in Figure 9. 63 By evaluating most of the reduced mechanisms which use to predict the n-heptane oxidation reactions, 63 methyl radical (CH3) is one of the most well-known species which is resulted from the n-heptane decomposition and has high contribution in the methane (CH4) formation in the RCCI engine run on diesel fuel. Due to the high contribution of unburned methane on global warming, about 23 times compared to CO2, according to the n-heptane oxidation pathways, almost all methyl radical chemical reactions that lead to the methane formation are identified and listed below.…”

“…The present simulation results show that the amount of CO emission is reduced to less than its EURO VI level as listed in Table 12. All methyl radical (CH3) reactions to produce CH4 63…”

Composition of Reduced Mechanisms for Ignition of Biodiesel Surrogates

“…Mechanism reduction was done using the Ant-Colony Reduction (ACR) methodology. ACR has previously been applied to create a small reduced mechanism for methanol combustion at SI-engine conditions [31], mechanisms for various aspects of n-heptane combustion [32], and several skeletal mechanisms for atmospheric chemistry simulations [33]. ACR use a semi-stochastic algorithm that selects reactions and species from a parent mechanism (commonly highly detailed) to form a skeletal mechanism.…”