Purushothaman Nandagopalan

BSDCBrake-specific diesel consumptionNONitrogen oxideCOCarbon monoxideCO2Carbon dioxideHCHydrocarbonB–OHBoron hydroxideB2O3Diboron trioxideB–OBoron monoxidePpmParts per millionRPMRevolutions per mi...

The combustion dynamics of non-Newtonian gel fuel droplets display a unique behavior influenced by the interaction of viscoelastic properties, rapid vaporization of the base fuel, and surface tension effects. This study offers a detailed experimental investigation of pressure dynamics, phase transitions, and post-explosion behavior of ethanol gel droplets. The investigation elucidates the significance of internal pressure buildup, phase separation due to heat influx leading to bubble generation, and shell rupture in governing combustion phases. It emphasizes the distinctive puffing behavior during the post-phase III regime. The temporal evolution of internal pressure, supported by experimental data, reveals critical dynamics across various phases. During phase II, internal pressure buildup is regulated until it reaches the yield stress of the fluid, thereby delaying droplet rupture and subsequent explosion. Phase III is defined by rapid explosion, which improves fuel–air mixing and facilitates secondary atomization. The regression dynamics following phase III, PIII+, mimics the conventional droplet regression rate of Newtonian fuels. PIII+ is primarily influenced by pressure dissipation, characterized by puffing cycles resulting from transient gellant-based shell formation and depletion, which promotes efficient evaporation. The impact of the decay coefficient (α) on PIII+ pressure dynamics shows that lower values of α prolong puffing, whereas higher values expedite pressure dissipation. These findings provide essential insights into gel droplet combustion, enhancing our understanding of phase-dependent behavior and demonstrating methodologies to optimize gel fuels for high-performance energy systems.

The performance of a supercritical CO2 centrifugal compressor is critically influenced by the backswept angle of the blades. This study investigates the aerodynamic and thermodynamic impacts of varying backswept angles, on the performance parameters such as pressure ratio, isentropic efficiency, flow characteristics, and shaft power requirements. Three-dimensional viscous compressible flow through a centrifugal compressor at steady state is numerically simulated with real gas effects at varying mass flow rate. After the essential grid independency test, the numerical methodology is validated with experimental data. At all mass flow rates, the efficiency and pressure ratio decrease with an increase in the backsweep angle, particularly from 90°. Higher backsweep angle configurations exhibit severe flow separation with energy loss. Due to the larger aerodynamic loading, smaller values of backswept angle require a relatively higher shaft power than configuration with a higher backsweep angle.

For decades, researchers have been exploring alternative fuels to counter the pollution problem caused by burning of fossil fuels. Emulsified fuels have attracted interest in the attempt to replace pure diesel. Water-in-diesel emulsion (WIDE) fuel has shown potential to be used in CI engines because of its reduced emissions and improved net fuel efficiency due to micro-explosions and presence of water content. This paper studies the emulsion's stability and investigates micro-explosion phenomenon by burning a droplet of the emulsion. Sophisticated videography and audiography are deployed to perform in-depth temporal analysis throughout the combustion period of the WIDE droplet.

Jetting in burning gel fuel droplets is an important process which, in addition to pure vaporization, enables the convective transport of unreacted fuel vapors from the droplet interior to the flame envelope. This aids in accelerating the fuel efflux and enhancing the mixing of the gas phase, which improves the droplet burn rates. In this study, Schlieren imaging was used to characterize different jetting dynamics that govern the combustion behavior of organic-gellant-laden ethanol gel fuel droplets. To initiate jetting, the gellant shell of the burning gel fuel droplet was subjected to either oscillatory bursting or isolated bursting, or both. However, irrespective of the jetting mode, the jets interacted with the flame envelope in one of three possible ways. Based on the velocity and the degree to which a jet disrupts the flame envelope, it is classified as either a flame distortion, a fire ball outside the flame or a pin hole jet (localized flame extinction), where the pin hole jets have the highest velocity (1000–1550 mm/s), while the flame distortion events have the lowest velocity (500–870 mm/s). Subsequently, the relative number of the three types of jetting events during the droplet lifetime was analyzed as a function of the type of organic gellant. It was demonstrated that the combustion behavior of gel fuels (hydroxypropyl methylcellulose: HPMC at 3 wt.%) that tend to form thin-weak-flexible shells is dominated by low-velocity flame distortion events, while the gel fuels (methylcellulose: MC at 9 wt.%) that facilitate the formation of thick-strong-rigid shells are governed by high-velocity fire ball and pin hole jets. Overall, this study provides critical insights into the jetting behavior and its characterization, which can help us to tune the droplet gasification and the gas phase mixing to achieve an effective combustion control strategy for gel fuels.