12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022

LEAN, HIGH EGR RATE TRF-AIR TURBULENT COMBUSTION WITH
TUMBLE FLOW IN A CONSTANT VOLUME VESSEL AT ELEVATEDPRESSURE

Ryoichi Urasaki
Yuki Minamoto
Department of Mechanical Engineering
Department of Mechanical Engineering
Tokyo Institute of technology
Tokyo Institute of technology
2-12-1 Ookayama, Meguro-ku, Tokyo, Japan 2-12-1 Ookayama, Meguro-ku, Tokyo, Japanurasaki.r.aa@m.titech.ac.jp
minamoto.y.aa@m.titech.ac.jp

Masayasu Shimura
Mamoru Tanahashi
Department of Mechanical Engineering
Department of Mechanical Engineering
Tokyo Institute of technology
Tokyo Institute of technology
2-12-1 Ookayama, Meguro-ku, Tokyo, Japan 2-12-1 Ookayama, Meguro-ku, Tokyo, Japanshimura.m.aa@m.titech.ac.jp
tanahashi.m.aa@m.titech.ac.jp

ABSTRACT

flame propagation characteristics of methane and n-heptane air
mixtures under IC engine-relevant combustion condition were
investigated. However, the unburnt species residue also need
to be addressed since since flame-wall interaction can cause
wall heat loss, and this effect on overall engine efficiency increases with leaner, diluted and high pressure thermochemical conditions. Also, Yenerdag et al. (2016) have been examined fundamental insights into turbulence-flame interactions
and heat loss characteristics of hydrogen-air mixture under aelevated pressure condition. However, hydrogen and hydrocarbon fuel yield different combustion characteristics.
Therefore, in this study, a three-dimensional DNS of ignition in a turbulence with a tumble flow has been perfromed
considering TRF-air combustion with more than 100 species
and 400 elemetary reactions for a high EGR rate and lean premixed mixture in a constant volume vessel at elevated pressure. The DNS results are analysed to clarify the transition
mechanism from ignition to flame propagation, flame propagation and flame-wall interaction.

To investigate the flame characteristics and flame-wall interaction (FWI) in lean burn spark ignition engine relevant
combustion, a direct numerical simulation (DNS) of forced ignition has been performed in a constant volume vessel with atumble flow. A lean toluene reference fuel (TRF)-air mixture
is ignited at the elevated pressure. During the combustion process, a ring-like eddy is generated around the unburnt mixtureisland which is separated from the main reaction zone. It isshown that the baroclinic torque contributes to the enstrophy
production around the unburnt mixture island. In the near-wallregion, the low-temperature oxidation reaction becames dominant, and the CO concentration shows a relatively high valueeven after the flame quenching. In the present study, some statistical properties related to the FWI is also investigated.

INTRODUCTION
Due to the environmental regulations for various combustion devices, high efficiency internal combustion engines are
required. To realize highly efficient spark ignition (SI) engines, establishment of combustion technology for lean, highexhaust gas recirculation (EGR) rate, and high compression
ratio is required. Under these conditions, decrease of flame
propagation speed is a problem. It is considered that the flame
speed can be increased by using a high intensity turbulence.
However, under such combustion conditions, there are several issues such as ignition difficulty and flame extinction. In
addition, high efficient SI engines tend to be smaller. This
trend leads the increasing the surface to volume ratio of theengine, and the effect of flame-wall interaction on engine efficiency and emissions will become more significant. However, the characteristics of flame behavior in near wall region
under highly efficient SI engines combustion conditions havenot been fully understood. Therefore, flame propagation andflame-wall interaction are addressed in the present study considering the spark ignition engines conditions.
In a previous study (Saito et al., 2018), the ignition and

DIRECT NUMERICAL SIMULATIONSThe DNS code used in this study is called Tokyo Tech
Combustion Simulation (TTX) that has been developed in previous studies (Tanahashi et al., 2000; Minamoto et al., 2011).
A fully-compressible combustion DNS with temperature dependence of transport and thermal properties is performed ina three-dimensional domain in an isochoric condition. The
governing equations are for conservation of mass, momentum,
energy and species. These equations are discretized using afourth order central finite difference scheme. The third order
explicit Runge-Kutta scheme is used for the time integration.
A reduced mechanism for TRF-air combustion (111 species
and 416 reactions) (Ogura et al., 2007) is used. The multitimescale (MTS) method (Gou et al., 2010) is applied for integration of reaction source terms and the correlated dynamic
adaptive chemistry and transport (CO-DACT) method (Sun &Ju, 2017) is applied for the chemical and transport properties

1

12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022

Figure 2. Turbulent combustion conditions of the present
DNS (red circle).
Figure 1.

Schematic of the computational domain.
overlaying the velocity fluctuation obtained from DNS of homogeneous isotropic turbulence on the initial mean velocity.
Figure 2 shows turbulent combustion condition of the present
study on the combustion regime diagram (Peters, 1999). The
turbulence intensity is set to 28.0 times the unstrained laminarflame speed SL and the integral length scale lE is set to 38.7
times the diffusive thickness δF . These turbulent combustion
conditions is classified in the thin reaction zones regimes asshown in Fig. 2.

for further reduction of computational cost. In the present
DNS, iso-thermal no-slip wall condition formulated based on
NSCBC (Poinsot & Lelef, 1992; Baum et al., 1995) is applied on the wall surfaces in the x and y directions and periodic
boundary condition in the z direction.
Figure 1 shows a schematic of the computational domain.
The dimensions of computational domain is Lx × Ly × Lz =4.8 × 2.4 × 1.2 mm3 , which are discretized by the uniform
mesh of Nx × Ny × Nz = 1152 × 575 × 288.
Initially, the vessel is filled with a fully premixed unburnt
TRF-air mixture at a uniform preheated temperature of 700 K.
The TRF-air mixture is diluted with an exhaust gas consistingof O2 , N2 , H2 O and CO2 from burnt gas, and the EGR rate isdefined as the mass ratio of burnt gas to the mass of unburnt
gas. Equivalence ratio of the mixture is set to be 0.6, the EGR
rate is set to be 20 %, the initial pressure is set to be 5 atm andthe wall temperature is set to 700 K.
Under these thermochemical conditions, the laminarflame speed SL is 0.277 m/s, the diffusive thickness δF is46.3 µm, the laminar flame thermal thickness δL = (Tb −Tu )/|∇T |max is 0.201 mm. Here, Tb and Tu are the temperature of burnt and unburnt gas mixture in a corresponding onedimensional laminar flame, respectively. The ignition source isgiven by placing the one-dimensional laminar flame in a cylindrical shape around the ignition region and kept in the computation to mimic a relatively long-time spark duration in realengines. Considering energy input by spark plug discharge,
the temperature at this ignition kernel is fixed to 2000 K. Here,the position of the ignition region is set to the center in the x
direction, and the distance from the top wall is set to 0.6 mm
in the y direction. The ignition region spans in the z direction.
Also, to simulate the tumble flow, the initial mean velocity is
set as follows:

Ψ=

 

u0 p
1
x2 + y2
Lx Ly exp
1−
4
2
Lx Ly /16

utarg =

∂Ψ
∂Ψ
,−
∂y
∂x

LOCAL MIXTURE ISLAND AND BAROCLINICTORQUEThe temporal evolution of the maximum pressure in theconstant volume vessel is shown in Fig. 3. The maximum
pressure increases with the spatial development of the turbulent flame. The maximum pressure rises to approximately
1.3 MPa. Figure 4 shows flame structures indicated by isosurfaces of temperature at 1600K. As shown in Fig. 4, themixture ignites at the high temperature region and the reaction zone is advected by the tumble flow at the same time as
the flame propagates. In the early stage of the flame propagation process, the flame propagates in a direction different fromthat of the tumble flow. Under the conditions that expected forlean and high-EGR SI engine, unburnt mixture islands are expected to be generated in the transition process from ignition
to flame propagation due to the influence of turbulence relatively intense compared to flame scales. In Fig. 4, from 986 to
1116 µs, such an unburnt mixture island exists and its size becomes smaller as the combustion progresses. Also, at the endof the reaction, the flame front approaches to the four walls.
Figure 5 shows iso-surfaces of temperature at 1600 K andthe second invariant of gradient of velocity tensor at 10 % of
its maximum value at t = 1116 µs. Here, the second invariant
in a incompressible limit is used for the visualization of eddies.
At this time, more than 70 % of the fuel (in mass) is consumed
and mean pressure is elevated to approximately 10 atm. The
unburnt mixture remains only in the near wall region expect
for the unburnt mixture island which is an interesting flame
feature in the present study and denoted as A in Fig. 5.
Here, the eddy structure around the unburnt mixture island is discussed. As shown in Fig. 5, a ring-like eddy (i.e.
genus 1 closed surface) appears around the unburnt mixtureisland. Although this island is created by the separation of themain flame which is sustained by continuous energy input, thering-like eddy is not observed in the early stage.
Figure 6 shows distributions of velocity fluctuation vector

(1)


(2)

where, Ψ is the stream function assuming tumble flow, utarg
is the initial mainstream velocity and u0 is the maximum initial mainstream velocity. The initial velocity field is given by2

12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022

Figure 5. Iso-surfaces of temperature at 1600K and the second invariant of gradient of velocity tensor (in the incompressibility limit) at 10 % of its maximum value at t = 1116 µs.

Figure 3. Temporal development of the maximum pressurein the constant volume vessel.

(a) t = 206µs(b) t = 596µs(c) t = 778µs(d) t = 986µs(e) t = 1116µs(a) Temperature(b) Heat release rate(c) Mass fraction of CH2 O(d) Mass fraction of fuelFigure 6. Distributions of velocity fluctuation vector and(a)temperature, (b)heat release rate, (c)mass fraction of CH2 O
and (d)fuel (show in Fig.5) on a x − y plane (z = 0.0 mm)
around the unburnt mixture island at 1116 µs.

(f) t = 1376µs

Figure 4. Temporal developments of iso-surfaces of temperature at 1600 K at (a)t = 206 µs, (b)t = 596 µs, (c)t = 778 µs,(d)t = 986 µs, (e)t = 1116 µs, (f)t = 1376 µs. Arrows indicate
the unburnt mixture island.
Dω 21= ω · (ω · ∇) u + ω · ν∆ω − ω 2 (∇ · u ) + ω · 2 ∇ρ × ∇P,
Dtρ
(3)
where ω and ν indicate vorticity and kinetic viscosity respectively. Figure 7 shows distribution of the baroclinic torqueterm on a x − y plane around region A shown in Fig.5. Intense baroclinic torque exists around the unburnt mixture island, and the baroclinic torque contributes to both destruction
and production of enstrophy in this region. Figure 8 shows
the conditional average of the enstrophy transport terms conditioned based on the reaction progress variable. The samples collected around the unburnt mixture island, and reaction
progress variable is based on the temperature. On an averagesense, the baroclinic torque contributes to the enstrophy destruction while both destruction and production exist locallyas shown in Fig. 7.
Therefore, the evolution of the ring-like eddy tends to bedissipative, although it yields some local fluctuations. The existence of this destruction and production mechanisms of theand temperature, heat release rate, mass fraction of CH2 O andfuel around the unburnt mixture island (show in Fig. 5) on ax − y plane (z = 0.0 mm) at 1116 µs. Here, heat release rate
shows a high value around the unburnt mixture island, where
the fuel species still exist. Also, the temperature at the unburnt
mixture island is approximately 1300 K which is higher than
the initial temperature of 700 K and the CH2 O is produced.
From the velocity fluctuation vector, it can be seen that a ringlike eddy is generated around this unburnt mixture island.
Since there may be a link between the creation of suchan unburnt mixture island and the ring-like eddy, the enstrophy transport equation is analyzed to investigate the origin of
the ring-like eddy. The enstrophy transport equation can be
written as:3

12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022(a) Heat release rate(b) Mass fraction of fuelFigure 7. Distributions of baroclinic torque on a x − y plane(z = 0.0 mm) around the unburnt mixture island at 1116 µs.
Contour line corresponds to the unburnt mixture island.

(c) Mass fraction of CO(d) Mass fraction of C7 H14 OOHFigure 9. Distributions of (a)heat release rate, mass fraction of (b)fuel, (c)CO, (d)C7 H14 OOH on a x − y plane (z =0.55 mm) at 1324 µs.

only when there is a local maximum exist in the heat release
rate distribution in the region within the laminar flame thermal
thickness δL from the wall surface. The distance between the
flame front and the wall defined by the maximum heat release
rate is defined as dw , which is the flame-wall distance.
Figure 10 shows the conditional average of the maximum
heat release rate ∆Hmax that is used in the identification of theflame front, conditioned based on dw . The conditional average was also conditioned based on the mean pressure in thedomain, 0.9 < ⟨p⟩ < 1.0, 1.0 < ⟨p⟩ < 1.1, 1.1 < ⟨p⟩ < 1.2,
and 1.2 < ⟨p⟩ (MPa). When dw is large, log10 (∆Hmax ) deviates approximately 0.3 for different ⟨p⟩, while the deviation
increases to be approximately 0.8 at flame quenching distance(e.g. dw ≈ 35 µm).
Figure 11 shows the conditional average of the wall heat
flux Φ conditioned based on the flame distance dw from thewall and the mean pressure of the vessel ⟨p⟩. The heat loss
through the wall increases with the decrease of the flame distance from the wall, and this trend is independent on ⟨p⟩.
When the flame-wall distance becomes smaller than
100 µm, the wall heat flux increases rapidly, and the maximum
heat flux exceeds 1.8 MW/m2 . The minimum flame-wall distance is about 50 µm and this distance is also independent on
the pressure. It is interesting that for the 1.2 < ⟨p⟩ samples the
maximum heat flux tends to decrease near the wall, while forthe other samples the heat flux monotonically increases withthe decrease of dw . This non-monotonic behaviour of Φ forthe 1.2 < ⟨p⟩ samples is still unclear.
Figure 12 shows the conditional average of the meanvalue of ⟨ρYCO ⟩ conditioned based on the flame distance fromthe wall. Here, ⟨ρYCO ⟩ is obtained by averaging ρYCO overthe distance between the wall and the identified flame front
location.
Figure 12 shows that the CO concentration near the wall
increases as the flame approaches the wall until dw ≈ 50 µm.
However, for dw < 50 µm, the CO concentration decreases.

Figure 8. Enstrophy transport budget conditioned with theprogress variable based on temperature in the unburnt mixtureisland.

ring-like eddy suggests that the eddy may enhance the scalar
mixing between hot and fresh mixtures near the unburnt mixture island to promote combustion processes.

NEAR-WALL FLAME BEHAVIOR
To realize high efficiency and low emission engines, nearwall behaviors of lean and diluted flame are important. Figure
9 shows near-wall distributions of heat release rate and massfraction of fuel species, CO and C7 H14 OOH on a typical x − yplane. Here, the flame-wall interaction region is enlarged. The
right side of the shown region corresponds to downstream of
the tumble flow.
As shown in Figs. 9(a) and (b), small heat release rate
value is observed in the downstream region (x > −0.2 mm),and this is because the fuel is already consumed almost completely. In the downstream region, the CO concentration showsa moderate value, and the CO consumption process is believed
to yield a relatively large timescale in this region. In the upstream region (x < −0.4 mm), concentration of C7 H14 OOH,
which is an indicator of the low-temperature oxidation reaction, shows a relatively high value in the near-wall region and
CO concentration is high between the wall and high heat release rate region.
In the present study, statistical properties related to the
FWI is also investigated. The local flame front is identified

4

12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022

Figure 10. The conditional average of the maximum heat release rate that is used in the identification of the flame front
based on the flame distance from the wall.

Figure 12. The conditional average of the mean value of⟨ρYCO ⟩ conditioned based on the flame distance from the wall.

Figure 11. The conditional average of the wall heat flux conditioned based on the flame distance from the wall.

Figure 13. The conditional average of the convection (C),diffusion (D) and reaction (R) terms in the CO transport equation on the wall conditioned based on the flame distance fromthe wall.

Figure 13 shows the conditional average of the convection(C), diffusion (D) and reaction (R) terms in the CO transport
equation conditioned based on dw . The samples are taken fromthe second mesh point inside the wall. Figure 13 shows that
diffusion term dominate to the transport of CO near the wallcompared with other terms. The large CO concentration in
the region of dw > 50 µm in Fig. 12 is due to the diffusion
contribution. However, for dw < 50 µm, the diffusion termyields negative values, indicating that CO is transported awayfrom the wall by diffusion.

flux tends to decrease near the wall, but this mechanism is still
unclear. The concentration of CO in near-wall region is dominated by the diffusion process.

ACKNOWLEDGEMENTS
This study is the result of a collaborative research program with the Research association of Automotive Internal
Combustion Engines (AICE) for fiscal year 2020 and 2021.

CONCLUSIONSREFERENCES

A direct numerical simulation (DNS) of forced ignition
in a constant volume vessel with a tumble flow has been performed for a lean TRF-air mixture at high EGR rate at elevatedpressure. During the combustion process, a ring-like eddy is
generated around the unburnt mixture island which is separated from the main flame. It is shown that the baroclinic
torque term contributes to the enstrophy production and destruction around the unburnt mixture island.
In the near wall region, the low-temperature oxidation reaction is increased, and the CO concentration shows a relatively high value even after the flame quenching. The wall heat
flux increases with the decrease of the flame distance from thewall, which is independent on the averaged pressure for low
pressure samples. For the high pressure samples, the wall heat

Baum, M., Poinsot, T. & Thevenin, D. 1995 Accurate boundary conditions for multicomponent reactive flows. Journalof Computational Physics 116, 247–261.
Gou, X., Sun, W., Chen, Z. & Ju, Y. 2010 A dynamic multitimescale method for combustion modeling with detailed
and reduced chemical kinetic mechanisms. Combustion and
Flame 157, 1111–1121.
Minamoto, Y., Fukushima, N., Tanahashi, M., Miyauchi,T., Dunstan, T. & Swaminathan, N. 2011 Effect of flowgeometry on turbulence-scalar interaction in premixed
flames. Physics of Fluids 23, 125107.
Ogura, T., Sakai, Y., Miyoshi, A., Koshi, M. & Degaut, P. 2007
Modeling of the oxidation of primary reference fuel in the512th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022
Sun, W. & Ju, Y. 2017 A multi-timescale and correlated dynamic adaptive chemistry and transport (co-dact) method
for computationally efficient modeling of jet fuel combustion with detailed chemistry and transport. Combustion and
Flame 184, 297–311.
Tanahashi, M., Fujimura, M. & Miyauchi, T. 2000 Coherent
fine-scale eddies in turbulent premixed flames. Proceedingsof the Combustion Institute 28, 529–535.
Yenerdag, B., Minamoto, Y., Naka, M. & Tanahashi, M. 2016
Flame propagation and heat transfer characteristics of ahydrogen-air premixed flame in a constant volume vessel.
International Journal of Hydrogen Energy 41, 9679–9689.

presence of oxygenated octane improvers: Ethyl tert-butyl
ether and ethanol. Energy & Fuels 21, 3233–3239.
Peters, N. 1999 The turbulent burning velocity for large-scaleand small-scale turbulence. Journal of Fluid Mechanics
384, 107–132.
Poinsot, T. & Lelef, S. 1992 Boundary conditions for direct
simulations of compressible viscous flows. Journal of Computational Physics 101, 104–129.
Saito, N., Minamoto, Y., Yenerdag, B., Shimura, M. &Tanahashi, M. 2018 Effects of turbulence on ignition of
methane–air and n-heptane–air fully premixed mixtures.
Combustion Science and Technology 190, 451–469.

6