Vaporization and pyrolysis modelling of a single droplet of heavy fuel oil using continuous thermodynamics

Abstract

This article presents modelling of vaporization and pyrolysis of a single droplet of heavy fuel oil in a high ambient temperature field using the principle of continuous thermodynamics. Continuous thermodynamics reduces the computational simulation load compared with discrete thermodynamics, without compromising the quality of prediction of the complex combustion behaviours of such multicomponent complex fuels. Heavy fuel oil is represented by four fuel fractions and each of these fractions is assigned a separate distribution function. The prediction shows that in the modelling of heavy fuel oil, both heating rate and composition are very important parameters in coke formation. Coke formation can lead to engine degradation and increased exhaust smoke. The developed model shows good agreement with experimental results obtained by other researchers.

A Simple Model of Off-Stoichiometric Premixed Fuel Rich Spray Flames with Droplet Evaporation and Pyrolysis

“…Garaniya and Goldsworthy [16] embellished the work of Baert [15] by using the continuous thermodynamics approach to model evaporation and pyrolysis of a single heavy fuel droplet and obtained good agreement with independent experimental data. Another model and experiments were described by Moskowitz et al [17].…”

“…The vaporization and pyrolysis coefficients are C v and C p , respectively. According to [16] the rate of mass loss after evaporation is less than the rate due to evaporation, which implies here that C p < C v . The reactive pyrolysis products diffuse back into the flame and react there with the oxygen.…”

“…Evaporation continues until the temperature beyond the flame front reaches the value T p at which pyrolysis of the liquid droplets commences. Although there may be some slight overlap region in which evaporation is ceasing whilst pyrolysis is starting this region is deemed negligible based on the evidence in [16], thereby allowing the use of the Heaviside functions in Eq. (5) The source term S dp describes the production of pyrolysis products through pyrolysis of the liquid droplets.…”

“…In these equations ∆ v and ∆ p are vaporization and pyrolysis Damkohler numbers, respectively, whereas L v and L p are the normalized latent heat of vaporization and heat of pyrolysis, respectively, defined by (14) As mentioned before, Garaniya and Goldsworthy [16] state that the rate of mass loss after evaporation is less than the rate due to evaporation. Within our formulation this will imply that ∆ p < ∆ v .…”

Heavy Fuel Oil Combustion Modelling Using Continuous Thermodynamics

“…The more volatile light hydrocarbon molecules continuously vaporise in order of their volatility, leaving the less volatile molecules in the droplet [9]. A continuous thermodynamics vaporisation model [3,11] is used to carry out the spray combustion simulations using CFD package STAR-CD v3.24. In continuous thermodynamics technique fuel components are represented as a series of Probability Density Functions (PDF) rather than a series of discrete components.…”