Toyota’s High Efficiency Diesel Combustion Concept Toyota’s High Efficiency Diesel Combustion...

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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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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

3


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*

4


1. Introduction

Content


4. Conclusion

3. Results





5


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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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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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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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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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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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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1. Introduction


4. Conclusion

Content

3. Results





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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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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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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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1. Introduction


4. Conclusion

Content

3. Results





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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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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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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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1. Introduction

Content


4. Conclusion

3. Results





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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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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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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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1. Introduction

Content


4. Conclusion

3. Results




• Application to smaller bore engine (mass production)

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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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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



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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


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


Chamber Taper

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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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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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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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1. Introduction

Content


4. Conclusion

3. Results





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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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Thank you for your attention

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