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Guide: Prof. Shamit Bakshi
Mentor: Manas Pal

Presentation by S.Kaushik Ram

Diesel Sprays - Liquid phase axial penetration
Mie scattering used for visualization

Fuel vaporization depends on air entrainment in the cylinder (turbulent mixing)

Liquid length is inversely proportional to fuel volatility
Important in small-bore DI diesel engines - liquid impingement on the piston bowl walls
Liquid length linearly increases with increased injector tip orifice diameter
Liquid length independent of orifice pressure drop change in fuel flow rate due to
changed pressure difference must exactly equal the change in fuel evaporation rate
Liquid length decreases non-linearly with increased ambient gas density & temperature
Liquid length decreases with increased fuel temperature as less energy is required to
vaporize the fuel

Why do we conduct research on spray modelling? sp. Direct Injection Engines

Study and enhance combustion characteristics and control exhaust emissions
Influence of fuel on spray characteristics

Higher fuel density (biodiesel), increased injection pressure, advanced

injection, higher spray velocity, narrower spray and large penetration lengths
Higher viscosity and surface tension effects such as decreased initial spray
velocity and wide cone angle, negligible large nozzle orifice diameter
Larger average droplet size and slower droplet vaporization fuel richness
Primary breakup from the nozzle huge impact on spray macro-characteristics:
turbulence and cavitation induced breakup predominant at nozzle exit
aerodynamic breakup increase significantly as we move away from the nozzle
Breakup parameters had to be tuned by rigorous experimental validation

Increasingly stricter emission regulations and greater demand for fuel

economy makes the injector most critical in modern diesel engines
Fuel temperature and Ambient Gas
Temperature effects on the Diesel Spray
Numerical analysis model RH and KT hybrid breakup model, defining a
hybrid model for the fluid instability problem of the breakup of droplets
Droplet breakup occurs when the inertial force of droplets is larger than the
surface tension force, and the Kinetic + Surface Energy remains constant
Spray tip penetration increases with increased fuel temperature, fuel density
reduces and results in the decrease of spray momentum (also because the
kinematic viscosity and the surface tension of the fuel reduces)
Spray cone angle increases with increased fuel temperature implying that
spray cone angle is inversely proportional to fuel density (spray momentum
decrease in the axial direction, a postulation for the observation)
High ambient gas temperature induces active droplet evaporation and the
spray tip penetration increased with increasing ambient gas temperature
(reduces ambient gas density) while the spray cone angle gradually decreased
Evaporation characteristics of diesel fuel is enhanced above the boiling
temperature and this affects atomization characteristics
Nozzle Orifice Geometry
Base vs Hydroground vs Conical Nozzles

Conicity suppresses cavitation and turbulence within the nozzle and

subsequently the primary breakup, slowing it up producing larger droplets and
increased liquid penetration, mass flow rate reduces too (due to small dia.)
Liquid length increases linearly with orifice diameter and remains
approximately constant with varying pressure drop
Higher flow efficiency (discharge coefficient) for the hydroground nozzle
Least liquid penetration for the base nozzle due to enhanced primary breakup
caused by cavitation and turbulence within the nozzle, smaller SMD
Better spray penetration for the hydroground nozzle in comparison to the
conical nozzle due to the higher fuel injection rate
Spray dispersion increases and peak projection density decreases with
increasing axial distance, with the extrema in both going to the base nozzle
Enhanced liquid breakup leads to smaller droplets and higher dispersion,
enhanced fuel-air leading to earlier injection for the base nozzle
Macroscopic Spray Characterization
Momentum flux and injection rate increase with increased pressure of injection
Momentum coefficient remaining relatively constant in account of cavitation
taking place in the nozzle hole, and decreases with increasing ambient density
Spray tip penetration and spray velocity increases with increased injection
pressure and decreases with increased ambient density (As it loses momentum)
Spray cone angle increases with increased ambient density, as increases the
resistance to spray development in the axial direction, no effect of pressure
Spray volume increases with injection pressure, droplet size decreases and the
probability of air entrainment between the droplets increases
Air-fuel mixing better for higher ambient density for the same penetration,
since the cone angle is higher and the spray volume is higher
As pressure difference in increased, amount of vapour volume fraction
increased due to cavitation, as a result of turbulence generation
Diesel Spray Numerical model validation
No Oxygen at the time of injection spray vaporizes and doesnt ignite
Nuricks model for cavitation within the nozzle
Bag break up (C1) and Stripping break up (C2) tuned breakup model
Eulerian approach for the liquid phase, which is modelled as separate
droplets and Langrangian approach for the gaseous phase
Models for cavitation, droplets primary and secondary break up, coalescence,
turbulence dispersion and evaporation
What I havent understood
Two contradictory theories for the effect of ambient gas temperature on
spray tip penetration:
An increase in ambient gas temperature causes a decrease in the ambient gas
density according to the ideal gas law, and lower ambient gas density leads to
the active development of spray penetration
The entrained higher temperature ambient gas contains more energy and will
heat the liquid fuel to a higher temperature resulting in the overall increase
in the vaporization rate and the shortening of spray required to entrain hot
gas to vaporize the fuel
The fluid instability problem in the high pressure injection of fuel in the
combustion chamber multi-phase flow liquid and gas (fuel and air)
interaction mass, momentum and energy RT and KH hybrid breakup models
Choosing the grid and numerically resolving the setup into a computational
fluid dynamic (CFD) problem and the subsequent numerical analysis
Eulerian-Lagrangian approach in CFD simulations
KH-ACT model for primary breakup and KH-RT model for secondary breakup
Effects of Gas Density and Vaporization on Penetration and Dispersion of Diesel
Sprays - Jeffrey D. Naber and Dennis L. Siebers
Diesel and Biodiesel Fuel Spray Simulations - Primoz Pogorevc, Breda Kegl, and
Leopold Skerget
Comparison of experimental and predicted atomization characteristics of high-
pressure diesel spray under various fuel and ambient temperature - Su Han Park,
Hyung Jun Kim and Chang Sik Lee
under diesel engine conditions - Sibendu Soma, Anita I. Ramirez, Douglas E.
Longman, Suresh K. Aggarwal
Macroscopic spray characterization under high ambient density conditions -
Balaji Mohan, Wenming Yang, Kun Lin Tay, Wenbin Yu
Simultaneous Shadowgraph/Mie Scattering Imaging of Liquid and Vapor Phases of
Diesel Sprays and Validation of a Numerical Model - Alessandro Montanaro, Luigi
Allocca, and Ugo Sorge