Qiang Shi, W. Fan, Rongchun Zhang
Feb 8, 2018
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DEStech Transactions on Environment, Energy and Earth Science
Abstract
N-heptane was used as an alternative for biomass fuels research. A simplified mechanistic model of n-heptane oxidation has been studied in this paper. The calculation results reveal the relationship between ambience temperature and components. The environmental temperature acts on the chemical reaction mechanism, thus affecting the distribution of components. High temperature contributes to the formation of CO and C2H2, while low temperature contributes to the formation of CO2 and C2H2, and the influence of temperature on other components is not so obvious, such as C3H6 and so on. The experiment of biomass fuel combustion rate has a good agreement with that from the simulation of n-heptane, so we can conclude that this simplified n-heptane reaction mechanism model is a good alternative to biomass fuel study. Introduction Further research on biomass fuel is a very significant subject. In general, biomass fuel extracted from soybeans or mature seeds mainly contains the following fatty acid esters: methyl oleate, methyl linoleate, methyl palmitate, methyl stearate[1]. It is hardly impossible to directly make numerical simulation on the biomass fuel droplet due to its profound components. Therefor the most common approach is to use alternative molecular formulas that match real fuel characteristics but require relatively less computational requirements to do research[2]. These alternative molecule models are usually methyl butyrate (C5H10O), Methyl fumarate (C5H8O), Ethyl propionate (C5H10O2), n-heptane (C7H16), decane (C10H22). After lots of scholars’ research, n-heptane is well suited for biomass fuel substitution. Chevalier et al proposed a chemical mechanism consisting of 620 components and 2400 reactions to calculate the ignition delay time of n-heptane and air mixing combustion[3]. In recent years, scholars have made a thorough study on the simplification of heptane oxidation mechanism, and the results show that the appropriate simplifications for different research purposes can lead to good calculation results. Muller et al reduced a model of ignition for n-heptane (1130 reactions, 171 components) to four overall steps[4]. Two steps are used for the high temperature mechanism, and the other two for low temperature reactions. M. Bollig et al simplifies the oxidation mechanism involving 52 components and 250 elementary reactions to 10 components and 7 reaction steps[6]. They found that the calculation results of this simplified mechanism were very close to the results of the unsimplified ones when studying the products of the diffusion flame combustion. Numerical Simulation Study Physical Model. The droplets are fired in Two-dimensional column symmetry quasi steady state. We have the following assumptions: (1) The environment around the droplet is infinite, the stationary air and the gas are ideal gases; (2) Fuel is a one-component liquid and has no solubility in any gas; (3) There is phase equilibrium at the junction of liquid and gas, and the boundary layer on the surface of the droplet is quasi steady state and satisfies the Clausius-Clapeyron equation; (4) The pressure is