When modelling multi-component fuel droplet, the surface temperature of the droplet will keep increasing near the end of evaporation time; while the surface temperature of a single-component droplet becomes almost constant near the end of evaporation time.
I can understand that, from a physical point of view, the heavier components stay at the end of evaporation time. These heavy components tend to have higher critical temperature.
However, from modelling point of view, which property can cause the highest affect on this? are they gas properties (such as gas thermal conductivity) or liquid properties (such as enthalpy)?
It could be due to intrinsic interface of the components comprising the fuel.
(I know nothing about this but...) You say the surface temperature is increasing, does this mean the radiative transfer from the environment (plus some conductive from the surrounding gas) heats the droplet surface more rapidly than the evaporative heat loss. In the case of a multi-component liquid, the surface will become enriched with the heavy species since the lighter one will preferentially evaporate and the process of radial diffusion to fully mix the components will be somewhat slow so the evaporation rate will be reduced. This reduction in evaporation rate should allow the high radiative transfer from the flame to cause the surface temperature to rise above the case of the pure material. That's my guess anyway!
Stanley, your answer is very close to my guess which is explained in my question as: "I can understand that, from a physical point of view, the heavier components stay at the end of evaporation time. These heavy components tend to have higher critical temperature".
I should mention that the radiation effect is ignored, since the contribution of this is not higher than 1% to the rapid heating and evaporation process in IC engines.
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