Investigation into the Influence of the Ethanol Concentration on the Flame Structure and Soot Precursor Formation of the n-Heptane/Ethanol Premixed Laminar Flame

Abstract

The purpose of this work is to investigate the effect of the ethanol blending ratio on the flame structure (species concentrations, heat release rate, and flame temperature profile) and soot precursor (CH 3 , C 2 H 2 , aC 3 H 5 , and C 3 H 3 ) formation of the n-heptane/ethanol premixed laminar flame at the equivalence ratio of 2 and pressure of 3.861 MPa. The results indicate the following: First, n-heptane consumes more rapidly than ethanol for its high dehydrogenation reaction rate under the research temperature range. n-Heptane decomposes completely (over 99% n-heptane is consumed) at about 0.723−0.839 mm above the burner surface, while that of ethanol (over 99% ethanol is consumed) ranges from 1.657 to 8.021 mm. Second, the ethanol addition facilitates the reaction sequences of CH 2 O → HCO → CO → CO 2 by providing reactive radicals, such as O, OH, and H. Third, the thickness of the reaction zone increases by 2.34% when the ethanol blending ratio grows from 0 to 25% because the dehydrogenation reaction rates of ethanol by H/OH radicals are slower than that from n-heptane at the studied flame temperature. However, it decreases by 0.585, 7.018, and 23.0021% at the ethanol blending ratios of 50, 75, and 100% compared to pure n-heptane as a result of the low-temperature heat release inhibition by ethanol. Fourth, even though the ethanol addition reduces the aC 3 H 5 /C 3 H 3 and C 2 H 2 formation, their principles are different. The ethanol addition has no direct impact on the reaction flux of the aC 3 H 5 and C 3 H 3 formation, and their reductions are caused by replacing n-heptane with ethanol. On the contrary, the C 2 H 2 reduction with ethanol addition is attributed to the increasing active radical (such as CH 2 O, OH, and H) concentration. However, the existence of a high concentration of CH 3 and sequential reactions of CH 3 → sC 3 H 5 CO → sC 3 H 5 → C 2 H 2 also facilitate the acetylene formation. Therefore, the decline of acetylene is about 12−43% lower than aC 3 H 5 and C 3 H 3 at the same ethanol blending ratio. The CH 3 concentration increases through C 2 H 5 OH → CH 4 → CH 3 with ethanol addition.

Experimental Study of the Combustion and Emission Characteristics of Lower Alcohols in a Constant Volume Vessel

“…They also investigated the effect of fuel type and blending ratio on combustion characteristics and soot precursor formation on a CVV. 32,33 Lee et al 34−36 studied the flame development, combustion, and gas phase emission characteristics of hydrogen compressed natural gas. Furthermore, the CVV can be used to study the laminar burning velocities of gas phase fuels.…”

“…For instance, a CVV can satisfy the systematic research on fuel combustion characteristics and emission characteristics. They also investigated the effect of fuel type and blending ratio on combustion characteristics and soot precursor formation on a CVV. , Lee et al − studied the flame development, combustion, and gas phase emission characteristics of hydrogen compressed natural gas. Furthermore, the CVV can be used to study the laminar burning velocities of gas phase fuels. − The studies above show that the CVV can meet the requirements of measuring the gas phase emissions and particulate matter from fuel combustion.…”

Effects of Ethanol Blending on the Formation of Soot in n-Heptane/Air Coflow Diffusion Flame

“…us, some oxygen-containing intermediate radicals may be evolved in the combustion, which further promoted the oxidation of basic carbon particles. In addition, particle size is also affected by fuel and the flow rate of oxidizer, since the change in their initial velocity will affect the combustion reaction and the time of the soot particles staying in the flame [16]. Increasing the velocity of the oxidizer can suppress the energy transfer from the annular region producing soot to the flame axis.…”

“…Ergut et al [15] investigated the generation of polycyclic aromatic hydrocarbons (PAHs) in ethylbenzene and ethanol flame at atmosphere pressure and pointed out that the generation rate of PAHs of ethanol was low even under lean oxygen combustion. Previous studies investigated the influence of ethanol doping ratio on the flame structure of n-heptane/ethanol and the formation rate of soot precursor [16]. It was found that the dehydrogenation rate of n-heptane was faster than that of ethanol, while ethanol promotes the reaction by providing active free radicals.…”

Synthesis of Nanomaterials in a Coaxial Flame

“…The authors of [12] studied the impact of ethanol vapor additions into the laminar diffusion flame of n-heptane on the mass yield of soot particles, as well as on their structure and morphology. Research results have shown that the addition of ethanol has a direct effect on the flame height and the size of the resulting soot particles.…”