ARL-RP-0549 ● SEP 2015

US Army Research Laboratory

High Resolution Numerical Simulations of 

Primary Atomization in Diesel Sprays with 

Single Component Reference Fuels

by L Bravo, D Kim, M Tess, M Kurman, F Ham, and C Kweon

Reprinted from ILASS-Americas. Paper presented at the 27th Annual Conference on Liquid 

Atomization and Spray Systems; 2015 May; Raleigh, NC.

Approved for public release; distribution is unlimited.
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ARL-RP-0549 ● SEP 2015

US Army Research Laboratory

High Resolution Numerical Simulations of 

Primary Atomization in Diesel Sprays with 

Single Component Reference Fuels

by L Bravo, M Tess, M Kurman, and C Kweon

Vehicle Technology Directorate, ARL

D Kim and F Ham

Cascade Technologies Inc, Palo Alto, CA

Reprinted from ILASS-Americas. Paper presented at 27th Annual Conference on Liquid 

Atomization and Spray Systems; 2015 May; Raleigh, NC.

Approved for public release; distribution is unlimited.
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High Resolution Numerical Simulations of Primary Atomization in Diesel 

Sprays with Single Component Reference Fuels

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Reprinted from ILASS-Americas. Paper presented at 27th Annual Conference on Liquid Atomization and Spray Systems;

2015 May; Raleigh, NC.

14. ABSTRACT

A high-resolution numerical simulation of jet breakup and spray formation from a complex diesel fuel injector at diesel engine 

type conditions has been performed. A full understanding of the primary atomization process in diesel fuel injection has not 

been achieved for several reasons including the difficulties accessing the optically dense region. Due to the recent advances in 

numerical methods and computing resources, high resolution simulations of atomizing flows are becoming available to 

provide new insights of the process. In the present study, an unstructured un-split Volume-of-Fluid (VoF) method is employed 

to simulate the injection event with prescribed bulk inflow conditions. An axial single-hole ARL fuel injector was X-ray 

scanned at The Advanced Photon Source Facility from Argonne National Laboratory for this work to define the internal 

geometry. The working conditions correspond to orifice dimensions of 90μm fueled with n-paraffin (n-dodecane) and isoparaffin (iso-octane) reference fuels for a detailed investigation of fuel specific mixing mechanisms. The spray releases into a 

quiescent chamber filled with 100% Nitrogen at ambient conditions at 20 bar, 300K with 6.9x104 < Re < 2.5x104 and 5.4x104 < 

We < 1.25x105 both with Oh > Ohcr setting the spray in the full atomization mode. The simulations provide detailed 

diagnostics in the optically dense region extending from 5 < x/d < 25 jet diameters. The results provide insights on the effect 

of start-of-injection on the velocity and volume fraction fields for each fuel at a range of pressures. High resolution backlit 

imaged data in the near nozzle region recently acquired at the Army Research Laboratory are used to provide validation 

metrics for the spray breakup length and dispersion characteristics.

15. SUBJECT TERMS

multiphase flows, spray, turbulence

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ILASS-Americas 27th Annual Conference on Liquid Atomization and Spray Systems, Rayleigh, NC, May 2015

High Resolution Numerical Simulations of Primary Atomization in Diesel Sprays 

with Single Component Reference Fuels

L. Bravo*1, D. Kim2, M. Tess1, M. Kurman1, F. Ham2and C. Kweon1

1U.S. Army Research Laboratory, APG, MD 21005

2Cascade Technologies Inc, Palo Alto, CA, 94303

A high-resolution numerical simulation of jet breakup and spray formation from a complex diesel fuel injector at 

diesel engine type conditions has been performed. A full understanding of the primary atomization process in diesel 

fuel injection has not been achieved for several reasons including the difficulties accessing the optically dense region. 

Due to the recent advances in numerical methods and computing resources, high resolution simulations of atomizing 

flows are becoming available to provide new insights of the process. In the present study, an unstructured un-split 

Volume-of-Fluid (VoF) method is employed to simulate the injection event with prescribed bulk inflow conditions. 

An axial single-hole ARL fuel injector was X-ray scanned at The Advanced Photon Source Facility from Argonne 

National Laboratory for this work to define the internal geometry. The working conditions correspond to orifice

dimensions of 90μm fueled with n-paraffin (n-dodecane) and iso-paraffin (iso-octane) reference fuels for a detailed 

investigation of fuel specific mixing mechanisms. The spray releases into a quiescent chamber filled with 100% 

Nitrogen at ambient conditions at 20 bar, 300K with 6.9x104 < Re < 2.5x104and 5.4x104 < We < 1.25x105 both with 

Oh > Ohcr setting the spray in the full atomization mode. The simulations provide detailed diagnostics in the optically 

dense region extending from 5 < x/d < 25 jet diameters. The results provide insights on the effect of start-of-injection 

on the velocity and volume fraction fields for each fuel at a range of pressures. High resolution backlit imaged data in 

the near nozzle region recently acquired at the Army Research Laboratory are used to provide validation metrics for 

the spray breakup length and dispersion characteristics. 

________________________________ 

*Corresponding author: luis.g.bravo2.civ@mail.mil
2

Introduction 

 Multiphase flows are of significant interest to the 

engineering and military community as they play an 

important role in several ground/aerial propulsion and 

power generation applications. They are also relevant 

in a broader scientific context in applications ranging 

from aerosol dynamics, fire suppression, and coating 

applications to name a few. For most of these 

applications, an accurate description of the interface 

location is generally difficult to achieve as resolution 

can be limited. In particular for diesel liquid sprays the 

complexity is further compounded by the physical 

attributes present including nozzle turbulence, large 

density ratios, complex evaporation, the 

ligament/droplet formation mechanism and dispersed 

flow transport all in a single injection event. The 

spatio-temporal fluid scales needed for a complete 

description are also very challenging and related to the 

instability length scales (~1μm) and speed of the 

ensuing jet (~100m/s). The multiscale nature of the 

problem requires a high fidelity approach able to 

capture and describe the multiphase dynamics. Of key 

interest here is the need to better understand the liquid 

jet breakup process through a Direct Numerical 

Simulation (DNS) investigation aiming to resolve all 

relevant gas phase flow scales. The intent of DNS 

approach is to present a comprehensive assessment of 

a concurrent experimental measurement [1] and 

ultimately provide more accurate atomization subgrid 

models for engineering level descriptions. A better

understanding of the underlying physics will also drive 

the development of next generation engines featuring 

higher power densities and fuel economy improving 

the efficiency of Army platforms and ensuring military 

power projection superiority. 

 With the continued progress in computing 

technology and numerical algorithms the use of highly 

resolved simulations to study two phase atomizing 

flows has become a viable alternative complementing 

experiments. Early pioneering works have focused on 

developing implicit interface capturing methods such 

as the volume of fluid (VoF) [2] and level set [3] and 

both have attracted significant attention to simulate

interfacial flows involving extensive topology 

changes. In a recent effort [4], complex geometries 

found in realistic gas turbine combustor injectors have 

been simulated using the immersed boundary 

approach. The findings show good experimental 

agreement of the air-assisted breakup of planar and coaxial liquid layers demonstrating the efficacy of the 

first principles approach. Similarly in related works 

[5] simulations of a realistic aerospace combustor 

featuring multi-nozzle swirler injector were carried 

out providing compelling results and insights of the 

primary breakup physics. In diesel spray applications, 

several studies aiming to demonstrate the performance 

of numerical schemes [6-10] have been presented. 

Although canonical, the investigations presented a 

thorough analysis of the hydrodynamic instabilities, 

ligament formation, transport, and droplet statistics. 

Similar works [11] have presented the impact of 

density ratio and injector geometry on the atomization 

physics predicting the influence of the k-factor on the 

droplet number count and jet spread. As a results, 

subsequent efforts have focused on application of the 

numerical schemes to realistic injectors using a 

coupled nozzle flow and spray DNS approach [12]. 

The study correctly captured the spray parameters and 

dispersion characteristics when compared to 

experimental images carried at similar conditions. The 

effort also presented a database containing droplet 

histograms for future comparison with laboratory 

characterization. 

 Also of interest are the recent efforts targeting at

developing more accurate subgrid scale models. In

atomizing flows, the need to correctly identify the 

spray liquid structures has lead to recent algorithmic 

developments [13] using a tagging strategy. The 

method joins linear segments defining the interface 

and discriminates between bubbles, ligaments, 

droplets or sheets. The capability was tested and 

demonstrated in a hydraulic jump application (wave 

breaking region) by computing interfacial statistics 

yielding compelling results. More fundamental work 

was carried out [14-15] to study the interaction of

decaying homogenous isotropic turbulence (HIT) with 

an interface under tension. They reported on the scales 

of interfacial corrugations recognizing the role of the 

Kolmogorov critical radius (or Hinze scale) over wide 

range of conditions. The importance of backscatter 

energy arising from the surface tension force was 

recognized motivating the emerging efforts in subgrid 

scale large-eddy simulation models [16]. 

 The proposed body of work aims to demonstrate 

the capability of a recently adopted high fidelity two 

phase flow solver in the context of diesel engine 

sprays. Previous works relating to this approach 

demonstrate the capability of the simulation software 

[17-18] in accurately capturing two phase flow physics

in different configurations. The applications of interest 

here-in are related to high speed fuel injection of 

single-component fuels, namely n-dodecane and isooctane at engine like conditions. More thorough 

description of the working conditions is described in 

the following sections. The objective of the study is to

provide an extensive database for engineering submodel development and to formulate sub-grid 

atomization models specific for diesel high pressure 

fuel injection. In the next section, we will present the 

computational framework and methodology that was 

adopted in this study. 
3

Computational Framework 

The computational framework adopted in this study 

used a novel geometric unsplit VoF method that is 

conservative on unstructured meshes [17-18]. The 

geometric VoF method ensures discrete conservation 

and boundedness of the volume fraction utilizing nonoverlapping flux polyhedral for donor volumes. The 

unstructured VoF scheme is based on the transport of 

the advection equation as follows, 

∂ρ

∂t +

∂ρuj

∂xj

= 0

where ρ is the mass density field and ujis the velocity 

vector. Assuming each phase has constant properties 

the density and viscosity can be defined as a function 

of the advection scalar . 

ρ = ψρ1 + (1 − ψ)ρ2

μ = ψμ1 + (1 − ψ)μ2

where the subscripts refer to the physical properties of 

fluid 1 and 2. 

The VoF methodology uses a piecewise linear 

interface calculation (PLIC) scheme [19-20] to 

describe the interface requiring an interface normal, n. 

In this scheme, the plane is located geometrically 

within a dual volume and oriented in the direction of 

the local surface normal. The surface normal is then 

calculated based on an upwinded advection of the 

previous signed distance field (G) to the interface. The 

interface vector n and the interface curvature k is 

calculated as follows, 

n =

∇G

|∇G|

k = ∇ ∙ n

The curvature is numerically discretized and the 

location of the plane is determined from the signed 

minimum distance G and the normal vector n from the 

node through a bisection algorithm. On updates of the 

VoF scalar, the mass flux is computed from the VoF 

advection and utilized in the momentum equation 

resulting in mass conserving, un-split, monotonic, 

unstructured VoF scheme. Multiple frozen velocity 

advection updates are performed for each momentum 

step to help diminish the strict over flow time step 

requirement of VoF schemes. 

The gas phase flow solver uses a fractional step 

method to advance the momentum equations imposing 

the divergence free condition. This results in a variable 

coefficient Poisson system that is presently solved 

using a multi-grid preconditioned GMRES solver. The 

accuracy of the coupled two phase flow solver has 

been demonstrated in various canonical verification 

test cases including the two dimensional Zalesak disk, 

three dimensional sphere in deformation field, and a 

stationary column in equilibrium presenting accurate

simulation results in an unstructured state-of-the-art 

framework. In addition, several successful validation 

studies have been performed demonstrating the 

applicability of the first principles approach to 

complex flows of interest [17-18]. 

Experiments for Comparison 

Validation efforts are conducted through comparison 

with measurements carried out with our in-house 

database at ARL-VTD, Spray and Combustion 

Research Laboratory (SCRL). This is a state-of-the-art 

facility housing a Constant Pressure Flow (CPF) hightemperature high-pressure vessel able to provide 

diesel engine thermodynamic conditions. Unlike 

Constant Volume Preburn (CVP) vessels this rig does 

not require a pre-burn phase to obtain this condition 

and rather it is comprised of four subsystems 

including: gas compressor, gas heater, test vessel, and 

control system to achieve nearly quiescent and steady 

thermodynamic conditions. The facility can operate 

with various types of fuel injection systems. However, 

for the validation experiments mentioned in this work, 

the facility utilized a common rail fuel injection 

system with a Bosch CRIN3 fuel injector

Table1. Conditions for non-evaporating single-hole 

spray measurements and simulations. 

Ambient gas temperature 303 (K)

Ambien gas pressure 20 bar

Ambient gas density 22.8 (kg/m3)

Ambient gas N2 100%

Nozzle K factor (nominal) 1.5

Nozzle outlet diameter 

(nominal)

90 um

Number of holes 1 axial

Nozzle type sac

Aspect ratio (l/d) 7.4

Fuels (cases 1,2) ndodecane,

isooctane

Fuel injection pressure 95, 150 bar

For this work the spray transient behavior was 

captured by imaging the flow region near the injector 

tip. The injection events were imaged with a Shimadzu 

HPV-X frame transfer CMOS camera and a Navitar 

long-working distance microscope 12× zoom lens [1]. 

The camera was capable of recording a maximum of 

256 full-frame images (400 × 250 pixels) at speeds up 

to 10 million frames per second with a 50 ns exposure. 
4

More details on the optical techniques can be found on

[1]. 

Computational Setup

 An axial single-hole ARL fuel injector was X-ray 

scanned at The Advanced Photon Source Facility from 

Argonne National Laboratory for this work. Figure 1a 

below shows the line of sight in-situ measurement 

used for characterization, the image shows the axial 

nozzle region selection Note the adjacent orifices are 

not selected because they were welded shut in our 

injector. Figure 1b shows the rendered image used in 

the simulation with a description of the fuel passage 

ways, needle valve in the fully open position, sac 

volume, and nozzle passage way. 

Figure1. Single-hole axial BOSCH CRIN3 injector. 

(a) Line of sight X-ray measurement characterization, 

(b) Schematic and rendered image of geometry. 

 In this study the working conditions correspond to 

nominal orifice dimensions of 90μm fueled with nparaffin (n-dodecane) and iso-paraffin (iso-octane) 

reference fuels at two injection pressures of 95 bar and 

150 bar with constant back pressure of 20 bar and 

ambient temperature of 303K as was indicated in 

Table1. Hence there are a total number of four cases 

studied in this work where the aim is to capture the full 

injection event from the start of injection. The physical 

conditions were prescribed based on an estimated fuel 

temperature at 298K as this was an approximation to 

the water-cooled jacket temperature in the 

experiments. Reported properties for n-dodecane [21] 

are as follows, density ρ = 744 kg/m3, viscosity 

μ = 1.36mPa ∙ s, and surface tension σ = 24.7 mN/

m. The isooctane properties reported [22] are density 

ρ = 686 kg/m3, viscosity μ = 0.478mPa ∙ s, and 

surface tension σ = 18.6 mN/m. The chamber 

density was specified for nitrogen at 303K as ρ =

22.8 kg/m3. Note the simulation was initialized with 

the nozzle filled with liquid, this enabled the 

specification of rate-of-injection (ROI) mass flow 

rates as a bulk flow boundary condition. In addition a 

turbulent inflow generation condition was utilized in 

an effort to help transition and capture the nozzle flow 

turbulence. 

 To simulate the fuel rate-of-injection the CMT 

virtual injection generator was utilized. The generator 

is a generic hydraulic model that allows specification 

of orifice diameter, fuel density, injection temperature, 

and ambient conditions to provide accurate ROI 

profiles. It is provided here for reference, 

http://www.cmt.upv.es/ECN03.aspx. 

Figure 2. Computational geometry with hexahedral 

mesh. (a) Grid distribution along fuel passageway, 

nozzle, and spray chamber. Grids at (b) x/d = 5 cross 

sectional plane and (c) inside the nozzle. 

Figure 3. Structure of the diesel spray in the near 

nozzle region from simulations. 
5

 Figure 2a above shows the grid distribution 

including the injector nozzle geometry and the 

chamber region. Note the grid density is higher inside 

the nozzle region to help resolve the flow scales up to 

y

+ ~ 1. In the streamwise and spanwise directions the 

resolution was defined as ∆x

+~50 and ∆z+~20 as 

these are the recommended criteria for a wall-resolved 

pipe flow calculation with total cell size of 77 Million 

grid points. A dynamic Smagorinsky large eddy 

simulation approach was adopted to treat the smallest 

flow structures and for computational efficiency in this 

work. In the near nozzle chamber region as shown in 

Figure 2b at a cross section x/d=5 the distribution is 

fine near the centerline. In the farstream and outflow, 

the grid is coarsened to mitigate instabilities and 

pressure waves flowing back upstream. Figure 3 

shows the developing spray structure during the first 

stages of the injection event. Note the finer grid 

distribution captures the spray atomization region. 

Results and Discussion

To better understand the atomization process in sprays

the simulation was carried out with a realistic diesel 

complex diesel injector geometry. Of interest in this 

work was to capture the spray evolution from start of 

injection to near quasi-steady conditions. Prescribing 

the transient rate-of-injection profile can enable the 

simulation to capture the transition from low-speed 

laminar jet flow to turbulent fully atomized spray. The 

physical conditions for the inflow rate-of-injection 

generator were based on a selection of peak Reynolds 

and Weber numbers providing computationally 

resolvable scales. Scales of interest for wall-resolved 

turbulent pipe flow is the viscous scale, lv, estimated 

as lv~5.0 Re

−7/8

; and the Kolmogorov critical radius

lcr, (Hinze scale) estimated as lcr~(σ

3

/ρ

3

ε

2

)

1/5

. 

Table 2 below illustrates the range of conditions in this 

work, 

Table 2. Fuel specific target conditions studied in 

transient spray injection event and critical lengthscales. 

Note that after start of injection, all jets are in a fully 

atomization regime consistent with Oh > Ohcr.. 

Start-of-Injection Effects (Isooctane) 

The transient mixture formation process of isooctane 

spray is presented here to examine the effects of start 

of injection on the spray structure. Figure 4 below 

shows the evolution the atomizing jet. The formation 

of azimuthal surface instabilities is indicated by the 

Rayleigh type behavior at the spray tip as shown in 

Figure 4(left). The instability growth-rate continues 

then forming crowns and ligaments that turn into the 

surrounding drops, Figure 4 (middle-right).

Figure 4. Transient development of isooctane jet (95 

bar) showing start-of-injection effects. 

Figure 5 shows the behavior of spray at the near nozzle 

location (x/D = 5) at the following time intervals t = 

{0.04, 0.08, 0.12, 0.16} ms. 

Figure 5. Radial distributions of volume fraction 

fields showing start-of-injection effects at x/D = 5.

ndodecane Re We Oh lv (mm)

P=95bar 6990 54656 0.03 2.1

P=150bar 9204 94737 0.03 1.7

Isooctane Re We Oh lv (mm)

P=95bar 19425 72581 0.01 0.88

P=150bar 25573 125806 0.01 0.69
6

Figure 6. Radial distributions of isooctane mean scalar and velocity fields at 95 bar injection pressure. 

(a) x/d = 5, (b) x/d = 10. 

Figure 7. Isooctane instantaneous velocity scalar fields at 95 bar injection pressure at plane location. 

Axial cut showing flow details at x/d =5 at (a) t =0.04 ms, (b) t=0.08 ms, (c) t=0.12 ms, (d) t=0.16 ms. 

(a) (b)

(c) (d)

(a) (b)
7

The jet width behavior is denoted with the f scalar 

clearly showing radial fluctuations as a result of startof-injection. At early times, the jet-width captures a 

FWHM values of ~1.25 R/D decreasing to ~0.6 R/D at 

later times. This is consistent with experimental 

observations of transient results [1]. Radial profiles of 

streamwise velocity at x/d=5 (Fig 6a) and x/d=10 (Fig 

6b) also show the spray start-of-injection behavior. 

Similarly it shows the decrease in radial signal

distribution at later times consistent with Figure 5. 

Note the simulation captures the linear increase in 

centerline velocity and jet width at x/d=10. To provide 

more details of the spray structure during start-ofinjection Figure 7 presents the cross-sectional contour 

plots at x/d=5 of the instantaneous streamwise velocity 

fields. The contours shows details of the velocity field 

and also captures the velocity increase and jet growth 

behavior in time. These diagnostics are valuable in 

proving insights into the mixing mechanism of the 

spray during start-of-injection. 

Fuel Effects on Spray Statistics

 The simulations were integrated to a common 

solution time of 100 μs (0.1 ms) for both n-dodecane 

and isooctane fuels. Note that at this time the spray is 

close to reaching steady operating conditions with 

respect to the ROI profiles. Note this also represents a 

fully open needle valve position. The conditions 

included two injection pressures, 95 and 150bar, for 

each fuel as this was specified in Table 2. The velocity 

and VoF, f, scalar fields were averaged in the 

azimuthal direction to account for dispersion effects, 

and the results are presented at several downstream 

axial locations. 

 Figure 8 compares the fuel specific radial 

distributions for both of the prescribed injection 

pressures. Peak velocity values captured compare well 

with the theoretical Bernoulli nozzle exit velocity (vel 

~ 125 m/s, 165 m/s). Figure 8a shows that due to its 

lower density, isooctane penetrates along the 

centerline slower than n-dodecane. This effect is 

strongly pronounced at the spray centerline and 

decreases radially. Similar behavior is seen on Figure 

8b, for higher injection pressure. Also note the 

simulated jet captures the jet growth at three axial 

locations marked at 5, 15, 25 diameters downstream of 

the injector nozzle. For both cases presented Fig 8a 

and 8b isooctane shows marginally wider jet-width 

than n-dodecane. Although this was observed, it is 

concluded that the overall spreading behavior is 

similar for both conditions at this time interval. 

However due to the strong transients in this problem 

longer simulation times are required to ensure that the 

inflow boundary is in equilibrium. Figure 9 compares 

the jet mixing behavior through f scalar. 

Figure 8. Radial distribution of mean velocity fields 

at t = 100 μs (0.1 ms) at three axial locations. Solid 

lines represent dodecane, dashed lines isooctane.(a) 95 

bar (b) 150 bar injection pressures. 

At 5 diameters downstream the liquid core remains 

nearly intact at both lower and higher pressures for ndodecane. This is an indication of a full liquid core 

region and no disintegration of the spray at this 

location. Note that isooctane does not retain its intact 

core at higher pressures. As it is expected, at 15 and 25 

diameters both fuels show strong evidence of spray 

disintegration along the centerline and radially. Note 

n-dodecane tends to retains more of the liquid 

structure. The differences between injection pressures

are also clear, as the lower pressure spray is able to 

retain more of its liquid mass, see Figure 9. 

(a)

(b)
8

 

 

Figure 10. Detailed spray structure at isocontours of f=0.5 at t=100 us for (a) ndodecane and (b) isooctane 

at injection pressure of 95 bar. 

 Figure 11. Detailed spray structure at isocontours of f=0.5 at t=100 us for (a) ndodecane and (b) isooctane 

 at injection pressure of 150 bar.

(a)

(b)

(a)

(b)
9

Figure 9. Radial distribution of mean VoF,f, fields at 

t = 100 μs (0.1 ms) at three axial locations. Solid lines 

represent n-dodecane, dashed lines isooctane

Figure 10-11 shows visualization of the spray surface 

features through isocontours of VoF f=0.5 scalar, the 

green and brown color represent n-dodecane and 

isooctane respectively. The figures show the detailed 

structure of the atomizing spray showing the upstream 

azimuthal and radial surface instabilities leading to 

crown, ligament and a fully atomized spray. Figure 10 

compares the spray structure at the lower pressure and 

shows the impact of the lighter fuel in obtaining a 

shorter breakup length. This behavior continues at the 

higher pressure case as seen on Figure 11 which is also 

consistent with the findings on Figure 9. Comparison 

with same fuel between the injection pressures also 

demonstrate shorter breakup lengths. In general, it is 

seen that the breakup length is controlled by the (i) fuel 

mass-density, lighter fuels feature shorter lengths, and 

(ii) injection pressure, higher pressure spray also 

feature shorter lengths at this working conditions.

Figure 12. Comparison with high resolution images at 

P=95bar using n-dodecane fuel. Top row transient 

spray event at 0.2265 ms (a) experiment (b) 

simulation. Bottom row quasi-steady condition 0.364 

ms (c) experiment (d) simulation. 

Figure 12 presents comparisons with experimental 

images for n-dodecane fuel at start of injection and 

quasi-steady condition. The comparison with 

experiments remain qualitative presently, this is due to 

(b)

(d)

(a)

(c)
10

the lack of internal nozzle flow features that are not 

present in the simulation. This includes sustained pipe 

flow turbulence, potential cavitation effects and needle 

fluid-structure interaction. At lower injection pressure 

(95bar) the simulation shows a breakup length at 

approximately 8 diameters downstream which is twice 

as long as the images. Note also that the simulation is 

sensitive to the inflow conditions, hence variations in 

the inflow can clearly affect the solution. 

Conclusion

In this work, a novel numerical scheme was utilized to 

simulate primary atomization for diesel sprays using 

realistic complex injectors. The fuels utilized were nparaffin (n-dodecane) and iso-paraffin (iso-octane) 

reference fuels as they are typical constituents for 

liquid JP8 surrogate fuels. The computational scheme 

is implemented within a conservative unstructured 

Cartesian volume of fluids solver that employs state of 

the art interface transport techniques ideally suited for 

simulating multiphase flows. The methodology 

applied was detailed numerical simulation of liquid 

fueled sprays using bulk inflow conditions from 

community-wide injector generator module to capture 

the start-of-injection events and qualitatively 

compared to experiments. To understand the effect of 

injection pressure on the fuel’s atomization behavior, 

two conditions were selected obtaining observations 

about the breakup length, dispersion characteristics, 

and instantaneous velocity fields. The effects of the 

bulk condition to capture start-of-injection condition 

on the multiphase simulation were discussed.

Future works will be targeted at developing models 

that incorporate more of the nozzle material features, 

i.e., surface roughness. This will be useful in capturing 

more realistic flow features and to study the full 

injection event from start to end of injection across the 

selected fuels. Numerical diagnostics will be further 

developed following similar procedures as the 

experimental imaging to enable direct comparison. In 

addition, the effect of higher grid resolution on the 

detailed flow statistics will be pursued. 

Acknowledgement

 This work was supported in part by high 

performance computer time and resources from the 

DoD High Performance Computing Modernization 

Program (HPCMP) FRONTIER Award. The Army 

project is titled “Petascale High Fidelity Simulation of 

Atomization and Spray/Wall Interactions at Diesel 

Engine Conditions”. The simulations were run on the 

DoD Garnet Cray XE6 computing platform.

 The author is also very thankful to Dr. Christopher 

Powell for characterizing the Army injector 

geometries at The Advanced Photon Source Facility at 

Argonne National Laboratory for this work.

References

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