Droplets Combustion Characteristics Comparison of Single Component and Multicomponent Diesel Surrogates With Petroleum-Based Commercial Diesel Fuel
Authors: Parveg A. S. M. Sazzad , Ratner Albert 
Published: February 2024

Abstract
Refined, petroleum-based diesel fuel composes hundreds of hydrocarbons with distinct physio-chemical and combustion characteristics. This range of components leads to difficulties and complexities in accurate computational modeling and experimental investigations. For simplification, different surrogate fuels (single, binary or multi component) are utilized by researchers to satisfactorily mimic the target characteristics of interest (be they physio-chemical, combustion, or both). The present work is focused on combustion characteristics, and particularly those for single droplet combustion. Single component surrogates are n-Dodecane, n-Hexadecane, 2,2,4,4,6,8,8-heptamethylnonane(Iso-cetane), decahydronapth-alene (decalin), and 1-methylnaphthalene, which are representative of the four major hydrocarbon classes (normal-alkanes, iso-alkanes, cyclo-alkanes, and aromatics) found in petroleum-based diesel fuel. The multicomponent surrogate is composed from the single component surrogates with the volume fractions being n-hexadecane = 37.00% v/v, heptamethylnonane = 33.00% v/v, decahydronaphthalene = 18.00% v/v and methylnaphthalene = 12.00% v/v. All of the surrogates are chosen from previous published works based on the availability of the combustion chemical kinetics and through matching target properties include derived cetane number (DCN), hydrogen to carbon (H/C) ratio, molecular weight (MW), and threshold soot index (TSI). Experiments are carried out by suspending a single isolated sub-millimeter sized droplet on three 16 μm silicon carbide wires for different fuel blends as well as neat fuels. The combustion of the single isolated droplet is initiated by utilizing two hot wire loops which are positioned on either side of the droplet for uniform heating. The combustion of the droplet is captured using a high-speed CCD (charge-coupled device) camera and a high-speed CMOS (complementary metal-oxide-semiconductor) camera. These high-speed images are post processed and analyzed to differentiate the combustion characteristics of the single component surrogates, multicomponent surrogates, and petroleum-based commercial diesel fuel. The chosen droplet combustion characteristics are burning rate, ignition delay, burning period, morphological evolution of droplet, and flame dynamics. Different droplet combustion characteristics of both single and multicomponent surrogates are compared with petroleum-based commercial diesel. The outcome shows that the target combustion characteristics of diesel fuel can be reproduced with multicomponent surrogates at the droplet scale and particular aspects can be captured by single component surrogates. In general, Diesel, single component surrogates, and multicomponent surrogate fuel droplets follow the d2 -law combustion. Based on flame shape, size and luminosity, multicomponent surrogate fuel closely resembles diesel while both decalin and multicomponent surrogate resemble the burning rate of diesel. Decalin and multicomponent surrogate fuel resemble the ignition delay trends of diesel while Hexadecane, Decalin, and multicomponent surrogate resemble the burning period of diesel.