Experimental and numerical spray characterization of biofules and pure components

Abstract

The biodiesel fuelled CI engines are observed to produce higher NOx emission. The emissions depend on spray characteristic along with the composition and physiochemical properties of the biodiesel. The non-evaporating and evaporating spray characteristics are analyzed using numerical models for biodiesel and their pure components. The CFD code is modified to incorporate the physiochemical properties of pure components of biodiesel and model multi-component evaporation. The spray models are validated with experimental data available in the literature for various fuels.The spray characteristics of evaporating spray, liquid length, and vapor length are predicted and compared for pure components of biodiesel and SVO at engine-relevant conditions. The spray tip penetration of karanja biodiesel is found to be similar to that of the methyl oleate. The spray tip penetration of coconut biodiesel is found to be similar to that of methyl laurate. The liquid and vapor length are found to be the function of the fuel properties and ambient gas conditions. The liquid length of methyl oleate is higher than methyl laurate under late-cycle post-injection conditions studied. It may lead to impingement of liquid fuel on the combustion chamber walls. The FAME components studied under near top-dead-center injection conditions are found to have a shorter liquid length, which can avoid wall impingement. A single component representative of biodiesel is found to be sufficient to predict the spray tip penetration of biodiesel and its blend in their respective category.The vapor length for all the biodiesel pure components is similar at near topdead- center conditions. However, at lower ambient gas density and ambient gas temperature conditions methyl oleate is found to produce higher vapor length, which decreases with increase in an ambient gas temperature. The SVO pure components have longer liquid length than that of their corresponding FAME. A linear correlation is observed between the liquid length and the boiling temperature of the biofuels. The vapor distribution for a multi-component surrogate is considerably different than that of single component fuel. The spatial mass fraction distribution of biodiesel is found to be the function of the volatility differential of the pure components and their proportion in the composition. The vapor mass fraction distribution for biodiesel of palm and soybean are found to be similar to that of their single component surrogate due to a similar volatility of components of these biodiesels. The change in the percentage of methyl laurate in coconut composition is found to have a strong impact on vapor distribution. The accurate determination of the biodiesel composition is essential to get correct prediction of combustion characteristics and emission profile for the given engine conditions.