The spray characteristics play a crucial role in determining the performance and emissions of compression ignition (CI) engines at the pre-combustion stage. With the advent of many types of alternative fuels and their blends with diesel, it is necessary to investigate the effect of fuel properties and various injection conditions to determine the penetration length, spray cone angle and spray area for a viable fuel with similar or better dispersion characteristics to diesel. Hence, this study reviews and summarizes the spray visualization techniques, along with in depth analysis of macroscopic spray properties of various fuel blends with diesel. It was found that higher injection pressures typically led to higher penetration lengths, better atomization with reduced Sauter mean diameter. Liquid properties such as viscosity, surface tension, and evaporation as well as structural properties play a crucial role in spray formation in fuel blends with various types of alcohols, ethers, biodiesel, aliphatic, aromatic, as well as nanoparticle additives. This review compares these fuel additives and their types to present a comparative study with diesel to determine the ideal conditions with minimal changes to the engine for replacing diesel with a sustainable fuel consisting of better combustion efficiency due to its enhanced spray characteristics.

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Numerical simulations are performed to study the impact of aspect ratio on the micro- and mini-channel heat sink behaviours in the presence of sinusoidal surface roughness. A CFD model is first validated with the relevant reference data for laminar flow conditions using ANSYS-Fluent analysis. The found results of this validation study show that the simulation results agree well with the reference data. The considered channel height, absolute roughness height and diameter are 250 µm, 30 µm and 366 to 374 µm, respectively. The top and bottom rough walls are under constant heat flux conditions, while other walls are adiabatic with air as the working fluid. The micro- and mini-channels with long wetted perimeter and lower aspect ratio have shown more convective heat transfer but with slightly higher frictional resistance. The convective heat transfer and thermal performance factor both improve with the increase in Reynolds number where all the values are higher than 1. The maximum value of the thermal performance factor is noted up to 1.6 for the channel having aspect ratio of 0.038 (Reynolds number = 250). This study shows that micro- and mini-channel heat sinks are sensitive to surface roughness, Reynolds number where varying aspect ratio have influence on both flow and heat transfer performances in laminar regime.

Parallel micro-channel heat sinks linked with a joint are investigated in this paper. Channels are analyzed for laminar flow (water) under constant heat flux. The considered channels with same hydraulic diameter (776 ) are investigated for two different dimensional variations of connecting link with parallel flow and the comparison of parallel and counter flow in the channels. It is found that the varying dimension of joining link has a little influence on the over-all thermal hydraulic performance. Performance index decreases in the cases of either increasing the height (J) or width (W) of the joint at higher Reynolds number (1000 and 1200). Convective heat transfer (Nu) marginally improves with the increasing J. Inter-linked micro-channels with counter flow has given improved convective heat transfer but with an increase in frictional factor. The Nu with counter flow is found almost 15% higher than that with parallel flow at Re = 1200. The design can be further explored based on present calculations for a positive addition of designing micro-channel heat sinks.