Post on 18-Mar-2018
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Toyota’s High Efficiency Diesel Combustion Concept
Toyota’s High Efficiency Diesel Combustion Concept
Toyota Motor Corporation
Takeshi HASHIZUME
2015 Engine Research Center Symposium University of Wisconsin-Madison
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Toyota’s High Efficiency Diesel Combustion Concept
1. Introduction
2. Combustion Concept
4. Conclusion
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
Content
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Toyota’s High Efficiency Diesel Combustion Concept
Input Energy
Brake thermal
efficiency
Develop a new combustion concept which improves
thermal efficiency by reducing cooling heat loss.
*)Turbo Charger
Exhaust Gas Treatment
Most of the energy was wasted in heat loss
Large part of this waste energy
Example of heat balance of diesel engine
Heat
Loss
Exh
au
st
Co
oli
ng
Fri
cti
on
Pu
mp
ing
Ou
tpu
t
43%
For T/C, EGT*
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Toyota’s High Efficiency Diesel Combustion Concept
1. Introduction
Content
2. Combustion Concept
4. Conclusion
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
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Toyota’s High Efficiency Diesel Combustion Concept
Factors of cooling heat loss in diesel engine
Cylinder head
Cyli
nd
er
blo
ck
Co
ola
nt
In-cylinder flow
Injection nozzle
Heat loss to
coolant
Heat loss
to engine oil
Radiation
Convective
heat transfer Luminous flame
To clarify the influence of each heat transfer. We measured
the radiant and convective heat flux using a RCM
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Toyota’s High Efficiency Diesel Combustion Concept
Rapid Compression Machine (RCM)
Thermocouple and radiant heat flux sensor were equipped.
Convective and Radiant heat flux can be measured.
Combustion chamber
Cam
Piston Air cylinder
Fuel spray
Thin film thermocouple Radiant heat flux sensor
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Toyota’s High Efficiency Diesel Combustion Concept
Radiant and total heat flux measured using RCM Injection quantity : 40mm3
15
Lo
cal
heat
flu
x
(M
W/m
2)
0
10
5
-10 0 10 20
Time after compression end (end)
250
Heat
rele
ase r
ate
(kJ
/s)
0
200
150
-10 0 10 20
100
50
Total heat flux Radiant
heat flux Small amount
The main cause of cooling heat loss is
convective heat transfer in diesel engine
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Toyota’s High Efficiency Diesel Combustion Concept
Approach to reduce the cooling heat loss
The local heat flux transfer from in-cylinder gas to the chamber wall
Heat flux = α × (Tg -Tw) α : heat transfer coefficient
Tg : in-cylinder gas temp.
Tw : chamber wall temp.
To reduce the cooling heat loss Toyota applied
Diesel engine has a strong swirl and squish flow
to improve mixture formation
(Heat loss)
Strategy Method Engine design
Reduction of in-cylinder gas velocity
Reducing heat transfer coefficient
Lower swirl flow Lower squish flow
α is high
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Toyota’s High Efficiency Diesel Combustion Concept
Low cooling heat loss combustion concept
Lowering cooling heat
loss Increase
in-cylinder temp.
Promote
fuel-air mixing
Adopting a weak in-cylinder flow, highly dispersed sprays
and lower comp. ratio realized maximized advantage.
Maximized advantage, minimized disadvantage
Advancing
injection timing
+ Maximum torque
- Cold startability
Low comp. ratio
+ Smoke reduction
- Maximum torque
(weaken penetration)
Highly dispersed sprays
+ Cooling loss reduction
- Fuel-air mixing (Smoke)
Weaken in-cylinder flow
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Toyota’s High Efficiency Diesel Combustion Concept
Analyzed using STAR-CD
With the low flow combustion gas velocity is lower than conventional.
This result indicates cooling heat loss is decreased
Conventional combustion Low flow combustion
Re-entrant chamber Lip-less shallow dish chamber
Swirl ratio = 2.2 Swirl ratio = 0.3
2400rpm Pme=1.1MPa
Results at 20°ATDC
Estimation of in-cylinder gas velocity
20 0 10 Gas velocity m/s
φ0.10mm x 10hole φ0.08mm x 16hole
Lowering gas flow
・swirl
・squish
cooling heat loss
was reduced
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Toyota’s High Efficiency Diesel Combustion Concept
1. Introduction
2. Combustion Concept
4. Conclusion
Content
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
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Toyota’s High Efficiency Diesel Combustion Concept
Specifications of test engine
With low flow concept, swirl ratio is 0.3, combustion chamber is lip-less
shallow, injection nozzle with smaller diameter and larger number of holes.
Engine type 4 cylinder DI diesel
Conventional Low flow combustion
Displacement L
Bore x stroke mm
Swirl ratio
Combustion chamber
diameter mm
Compression ratio
Nozzle specification
2.231
86 x 96
2.2 0.3
(Straight port)
Re-entrant
φ 58
Lip-less shallow
φ 61
15.8 : 1 14.0 : 1
580 cc φ 0.10 mm x 10 hole
spray angle 155゚
580 cc φ 0.08 mm x 16 hole
140°
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Toyota’s High Efficiency Diesel Combustion Concept
Engine system
In order to reduce in-cylinder gas flow, straight port
and lip-less cavity piston were equipped.
DPF
EGR valve HPL-EGR
EGR cooler Turbo charger
Inter
cooler
EGR valve
Highly dispersed spray
Lip-less cavity
LPL-EGR
Straight port
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Toyota’s High Efficiency Diesel Combustion Concept
With low flow combustion, the in-cylinder gas flow can be restricted
without deteriorating smoke emission.
Start of main injection Conventional: TDC, New concept: 3 BTDC
A large amount of luminous flame forms luminous flame disappears
4 ATDC 10 ATDC 20 ATDC 30 ATDC 40° ATDC Crank angle
Conv.
Low flow
Eventually, reaches an equivalent low level of smoke.
Summary of the combustion photograph
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Toyota’s High Efficiency Diesel Combustion Concept
1. Introduction
2. Combustion Concept
4. Conclusion
Content
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
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Toyota’s High Efficiency Diesel Combustion Concept
Crank angle ( ATDC)
RO
HR
(J
/ )
Cooling loss depends on combustion timing
Under same combustion timing. Conventional
Low flow
Same ignition timing
Conventional N
Ox (
pp
m)
20
Co
olin
g
hea
t lo
ss
(J
)
Low flow
10
0
200
0
50
100
150
80
-10
0
10
20
30
40
50
60
70
-30 30 20 10 0 -10 -20
40%
Cooling heat loss 1600rpm-0.3MPa
Low flow combustion concept can be reduced 40%
of cooling heat losses without increase in NOx emission
Under same smoke emission
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Toyota’s High Efficiency Diesel Combustion Concept
The following section describes this mechanism
and ways to reduce the cooling heat loss further
BMEP MPa
Co
olin
g l
oss r
ed
ucti
on
rate
%
(Co
mp
are
d t
o c
on
ven
tio
nal)
0 0.5 1 1.5
60
0
10
20
50
40
30
Larger cooling loss reduction
at low load
Reduction rate decreases
at high load conditions
Effect of load on cooling heat loss reduction
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Toyota’s High Efficiency Diesel Combustion Concept
If the reverse squish flow can be restricted, the heat transfer
coefficient will decrease, and the heat loss can be improved.
Calculated by STAR-CD
2100rpm-1.1 MPa
The gas flow was restricted by
Lip-less cavity
Near zero swirl ratio.
The low flow combustion High heat flux region
Heat flux MW/m2 0 25
High temperature gas moves
close to the side wall.
Flow at upper portion of the
piston side wall was still high
20 0 Velocity m/s
Reason for a cooling heat loss increase at high load
2800 600 Temperature K
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Toyota’s High Efficiency Diesel Combustion Concept
1. Introduction
Content
2. Combustion Concept
4. Conclusion
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
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Toyota’s High Efficiency Diesel Combustion Concept
Motoring
Engine speed Crank angle
: 1600 rpm : 10deg. ATDC
12
0
Ve
loc
ity (
m/s
)
Tapering piston bowl restricts the reverse squish flow
from the piston wall side to cylinder head .
Wider gap
(Case1)
Stepped
piston
(Case2)
Tapered
piston
(Case3)
Standard
Restrict the reverse
squish flow by
・Allowing wider gap
between piston
and cylinder head.
In-cylinder gas
velocity
The method to restrict the reverse squish flow
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Toyota’s High Efficiency Diesel Combustion Concept
Heat flux
(squish area)
Measured at
cylinder head
RO
HR
J/°
0 -20 20 40 60
Crank angle ° ATDC
Heat
flu
x M
W/m
2
at
sq
uis
h a
rea
0
10
20
0
50
100
150
reduced
less taper
with taper
2100rpm-1.1MPa under the same heat release rate
Tapered piston bowl reduced the heat flux in the squish area,
which makes a large contribution to the cooling heat loss reduction.
Heat flux measurement of the tapered piston
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Toyota’s High Efficiency Diesel Combustion Concept
Low flow combustion reduced the fuel consumption by 3% .
The adoption of taper shallow dish reduced fuel
consumption by 5% under equivalent emissions.
Equivalent NEDC
NOx (g/km)
Fu
el
co
nsu
mp
tio
n
(L/1
00 k
m)
0 0.02 0.04 0.08
5.1
4.5
4.6
4.7
5.0
4.9
4.8
0.06
5% 3%
Improvement of fuel economy in NEDC
Low flow combustion
Conventional combustion
Low flow combustion
w/ tapered shallow dish
Under same smoke emission
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Toyota’s High Efficiency Diesel Combustion Concept
1. Introduction
Content
2. Combustion Concept
4. Conclusion
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine (mass production)
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Toyota’s High Efficiency Diesel Combustion Concept
Specifications of smaller bore engine
Low flow combustion concept was applied
to Mass-produced small engine with 2 valves
Engine type 4 cylinder DI diesel 2 valves
Conventional Low flow combustion
Displacement L
Bore x stroke mm
Swirl ratio
Combustion chamber
Compression ratio
Nozzle specification
1.364
73 x 81.5
2.2
Re-entrant Lip-less shallow
16.9 : 1 16.4 : 1
525 cc φ 0.10 mm x 8 hole
525 cc φ 0.10 mm x 8 hole
2.2
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Toyota’s High Efficiency Diesel Combustion Concept
Application of low flow concept to two valve engine
Effect of low flow chamber in 2 valves engine
NOx g/h
Co
oli
ng
hea
t lo
ss
%
Re-entrant
Lip-less shallow dish
Sm
ok
e F
SN
NOx g/h
Velocity m/s
Gas flow is fast
in large squish area
15 0 φ
Rich mixture is remained
in small squish area
Rich Lean
Center of bore Center of chamber
Large squish area
For 2 valves engine
Injection nozzle
Large squish area
Gas flow is fast
Increase of cooling heat loss
Small squish area
Rich mixture is remained
Increase of smoke emission
Small squish area
Lip-less shallow dish
Lip-less shallow dish
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Toyota’s High Efficiency Diesel Combustion Concept
Lip-less chamber + Bore-centered taper
(Eccentric tapered shape)
Improvement of combustion chamber for 2 valves
Improved combustion chamber with eccentric tapered shape
is applied to lower squish flow and fuel distribution
Center of bore Center of chamber
Small
squish area
Large taper Small taper
Large
squish area
Reducing heat
transfer coefficient
Weaken squish flow
1. Reduction of heat loss
Improve the mixture
formation
Mixture introduction
to large squish area
2. Decrease of smoke
Reduction of fuel at
squish area
Keep the squish
flow
3. Decrease of smoke
Center of bore Center of chamber
Chamber Taper
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Toyota’s High Efficiency Diesel Combustion Concept
Simulated distribution of gas flow velocity
Taper could weaken the gas flow velocity in large squish area.
The cooling heat loss was reduced with Eccentric tapered chamber.
Velocity m/s
0 20
15 TDC 5 10
Low flow velocity
Taper could weaken gas flow velocity
Re-entrant
High flow velocity
Eccentric
Tapered
shape Small
squish area Large
squish area
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Toyota’s High Efficiency Diesel Combustion Concept
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Simulated distribution of equivalence ratio
The lower squish flow and the improvement of air-fuel mixing
can be realized simultaneously with eccentric tapered chamber.
Eccentric
Tapered
shape
TDC 7 15
Re-entrant
Taper could spread fuel mixture gas
φ
0 2
Small
squish area Large
squish area
Spread to whole cylinder area
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Toyota’s High Efficiency Diesel Combustion Concept
Effect of the eccentric tapered chamber
Both reduction of cooling heat loss and smoke emission
could be realized using conventional nozzle spec. and swirl ratio
NOx g/kWh
Co
olin
g h
eat
loss %
Conventional
New chamber (0.5g/kWh)
1800rpm/0.1MPa
18%
Sm
oke F
SN
NOx g/kWh
2000rpm/0.7MPa
(0.5FSN)
(0.5g/kWh) New chamber
Conventional
Smoke 0.5FSN
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Toyota’s High Efficiency Diesel Combustion Concept
1. Introduction
Content
2. Combustion Concept
4. Conclusion
3. Results
• Combustion characteristics
• Cooling heat loss analysis
• Cooling heat loss reduction
• Application to smaller bore engine
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Toyota’s High Efficiency Diesel Combustion Concept
This research aimed to reduce cooling heat loss.
The heat transfer coefficient was reduced by lowering gas flow.
As a result, the cooling heat loss was reduced.
A large amount of cooling heat loss was generated by strong squish
flow. The cooling heat loss was reduced further by tapered piston bowl
For application of this concept to a small engine with two valves,
providing an eccentric tapered combustion chamber achieved a proper
squish flow.
Simultaneous reduction of cooling heat loss and smoke emission can
be achieved without micro multi-hole injector with eccentric tapered
combustion chamber.
Conclusion
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Toyota’s High Efficiency Diesel Combustion Concept
Thank you for your attention