towards sustainable fuels and clean combustion concepts: progress in combustion...

Towards sustainable fuels and clean combustion

concepts: Progress in Combustion Control and Advanced

Optical Diagnostics

Prof. Dr.-Ing. Michael Wensing

Lehrstuhl für Technische Thermodynamik LTT

Friedrich-Alexander Universität Erlangen-Nürnberg FAU

FAU is one of the ten largest universities in Germany

and one of the leading universities in Europe.

FAU is ranked as the second most innovative university

in Germany by absolute numbers of patents and

publications on innovative technologies,

per professor it is number one.

Of the 39.780 students (winter semester 2017/2018)

at FAU, 19,663 are female and 4,890 are international students.

FAU currently offers 265 degree programmes, including 80 Bachelor’s degree

programmes, 94 Master’s degree programmes and 91 Staatsexamen (state

examinations) degree programmes (in subjects such as teaching, law and

medicine).

In 2016, 7,274 students graduated from FAU, in 2016 766 completed their doctoral

degrees and 51 post-doctoral students completed their habilitation. FAU has a total

of 579 professors. With a total of 177,6 million euros (2016), FAU has one of the

highest volumes of third-party funding of all the universities in Germany.

FAU Key figures at a glance:

275 Years of FAU

Knowledge in Motion

23.08.2018 3

• In Germany now we have 35% of wind and solar electricity

(cumulative)

• CO2 reduction limited due to very limited flexibility

• Volatility and limitations of transfer (between times, areas

and intersectional) have been underestimated an

increasingly come in force

• E-mobility is only a part of a solution

• Thermal energy sector is very important

• Pressure of fossil and nuclear energy carriers

• The use of CO2 as feedstock rather than as waste is

demonstrated in nature in large scales

• Energy can be stored/handled in two ways: free electrons or

chemical bonds

Energy situation in Germany

Energy density in comparison

0

2

4

6

8

10

12

14

12,2

0,08 0,003

10,3

0,07 0,003

Potentials: Energy density of different storage possibilities

• Power of a single filling station at 35l/min: 21,6 MW

• One ship can supply 10 power stations

• The wind and solar power installed in Germay equivals to the Peak-

consumption

Energy density kWh/l

Energy density kWh/kg

Chemical

Storage (Diesel)Elektr.

Battery (BMW i3)

Hydro

Power (1000m)

Task: Sustainable Fuels, low emission, competitive price

23.08.2018 5

Carnot & Pischinger

Motorische

Brennverfahren und

Kraftstoffe

SI engines CI engines

source:

Boschsource:

Bosch

1

2

4

3

p

v

T=const

T=const

s=

const

s=co

nst

Q0

Q

T

s

Q

Q0

4

3TH

T0

23.08.2018 6

Topics

New fuels in mixing controlled combustion concepts

Enhanced combustion control by reduced chemical

complexity

New Ignition Concepts for homogeneous lean combustion

concepts

Enabler for efficiency improvement in a low emission

combustion concept

Hydrogen and LOHC

Possibilities and challenges of an carbon free energy

carrier

23.08.2018 7

Mixing controlled combustion

Atomization investigated by X-Rays

Region of interest

Cooperation with Dr. Jin Wang,

Argonne National Labs, USA

Cooperation with Dr. Edouard

Berrocal, Lund Univ. Sweden

0,5

mm

1,0 mm

8

Primary Breakup of Diesel SprayspFuel = 1000 bar / pGas = 1 bar

X-Ray High Speed Investigation Diesel

300 μm 300 μm

Masse density*velocity spray strukture

* © Density Evaluations Gröger, Dinkelacker, ITV Hannover

23.08.2018 9

Fundamentals of Disel sprays

Momentum balance, Wakuri (1960), Siebers (1996 – 1999)

entrained ambient gas ρa, Ta, pa

θ

Fuel

ρf, Tf,

pa mix

ture

Assumptions:

• Rectangular velocity profile

• Exclusively radial air movement

outside the spray (Zhu 2013: LIF/PIV)

• Stationary injection conditions, i.e.

constant nozzle exit velocity and cone

angle θ

• No-slip-condition between fuel and

ambient gas

• Constant density of ambient gas

mf

ma=

2

1 + 16 x2 − 1

mf = ρf0 ∙ A0 ∙ u0

ma = ρa ∙ A x ∙ u x

mf ∙ u0 = mf + ma ∙ u x

x =ρaρf

∙x

Ca ∙ d∙ tan

θ

2

20 mm

23.08.2018 10

MotivationHow much air is entrained during the mixing process?

0,0

0,5

1,0

1,5

2,0

0 200 400 600 800

mass r

ati

o f

uel/air

t avSoI / µs

0

20

40

60

80

100

0

500

1000

1500

2000

2500

0 200 400 600 800

VF

uel/ m

m³

VS

pra

y/ m

m³

t avSoI / µs

spray plume

fuel

How does it look like locally?

using Raman-spectroscopy

Investigated with 3-hole research injector from Continental

d = 115 μm used fuels: GtL-Diesel

mFuel = 12.3 mg n-Decane

θ = 22°, cA ≈ 0.95 Ethanol

23.08.2018 11

Geometrical relationship between spray plume and measuring

heightsExemplary spectrum above the nozzle tip

H20

H10

H7

H5

H2

a < bx

y025

Laser

beam

locations

0

50

100

150

200

250

2200 2400 2600 2800 3000 3200 3400 3600 3800

Inte

nsity

[counts

]

Raman shift [cm-1]

N2

CH

OHlo

cation

x

wavelength

IR = signal intensity n = number density

kA = setup influences 𝜎R = scattering cross section

𝐼𝑅 ~ 𝑘𝐴∙𝜎𝑅∙𝑛

45°

ICH =

i=2700

3100

IR i

23.08.2018 12

Molar and mass fraction for different fuelspa = 6 MPa, Ta = 923 K, pf = 120 MPa, Tf = 363 K, tavSoI = 700 μs

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0,45

0,5

0 1 2 3 4 5

nf/

na

location / mm

ethanol

decane

GtL-diesel

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0 1 2 3 4 5

mf/ m

a

location / mm

ethanol

decane

GtL-diesel

Height: 5 mm

23.08.2018 13

Air-entrainmentClassification within limits of possible air-entrainment situations

0

0,5

1

1,5

2

2,5

3

0 10 20 30

mf/m

a/ -

x / mm

Schlieren penetration

Mass ratio based on measured spray front penetration:

Derived spray front velocities from Schlieren

measurements

Following momentum conservation

Stationary spray: tavSoI = 700 μs

mf

ma(x)=

1u0u(x)

− 1

0

0,5

1

1,5

2

2,5

3

0 10 20 30

mf/m

a/ -

x / mm


momentum conservation(ideal)

Ideal mass ratio based on total momentum conservation

mf

ma(x)=

2

1 + 16 ⋅ρaρf⋅xd

2⋅ tan2

θ2

− 1

Measured ratios are fitted with Gaussian distribution

Peak value defines spray axis

Using hyperbola fit function

0

0,5

1

1,5

2

2,5

3

0 10 20 30

mf/m

a/ -

x / mm


momentum conservation(ideal)

Raman Fit

Raman measurements

23.08.2018 14

Transformation from 1D measurements to

2D image

0.5

0.4

0.3

0.2

0.1

0.0

mf

ma

mm

mm

23.08.2018 15

Results



complexity

• Diesel sprays mainly consist of air

• Droplets are not important in Diesel Sprays

• Mass distribution is governed by momentum balance

• Molar distribution and air fuel ratios depend on molar

masses

=> Mixture formation (parameters of the injection system)

and combustion (chemical properties of the fuel) can

be handled separately

23.08.2018 16

Topics



complexity


concepts


combustion concept

Hydrogen and LOHC

Possibilities and challenges of an carbon free energy

carrier

23.08.2018 17

SI Combustion concepts, Eta (Epsilon, Kappa)

Efficiency of SI engines limited

• Knocking tendency

• Ignitability of diluted or lean mixtures

• Stoichiometric combustion concept, 3-way-

Catalyst

• NOx Emissions 1.05>λ>1.6

Higher ignition energy needed for λ>1.6 !

Pre-Chamber Ignition

source:

Bosch

23.08.2018 18

SI Combustion concepts

2. New ignition concepts

Main differences and tasks

• Higher power density and speed

• Small space available

• Only liquid fuel available

Large gas engine Race car

19Pre-Chamber Ignition System – Moritz Schumacher

Results

λ-Variation

Low load operating point with

4.5 bar IMEP - 1500 rpm

Two Pre-Chamber designs with

small / large volume and transfer ports

• Ability to ignite mixture up to λ=2

• Lean misfire limit increased to λ≈1.8

• Losses in efficiency due to large PC

• Reduced compression ratio

• Higher heat losses

• Higher fuel consumption of PC

• Engine out NOx emissions at lean limit

below 20 ppm

• Further reduced burn duration

-0,5

0,0

0,5

1,0

1,5

2,0

0

5

10

15

20

25

-360 -300 -240 -180 -120 -60 0 60 120 180 240 300 360

PC

Fue

l pre

ssu

re /

bar

Cyl

ind

er

pre

ssu

re /

bar

Crank Angle /°

PCPr2

PCoPr2

CylPr2

PCValve2

PCFuelPr


Results

Variation of EGRLow load operating point with 4.5 bar IMEP -

1500 rpm

• Variation of inlet phase (EGR rate) @ λ = 1

• Tubmble flaps open (low tumble)

• With / without additional air scavenging of PC

• EGR tolerance much higher with air scavenging

Gasoline

vapourAir


Results – Volume Ignition / Stratification

Stratified Combustion

• Injector position and targeting NOT

optimized for stratified injection

• Typical side injector position and targeting

• EOI near ignition timing at 18°BTDC

• PC fuel only from PC fuelling system,

no fuel from combustion chamber in PC

• Stable stratified combustion

Pre-chamber jets ignite stratified charge

“Volume Ignition”


Results

Cylinder / Pre-Chamber Pressure Analysis

• Overpressure in Pre-chamber

increased to 7.5 bar compared to

1.8 bar with old design

• Improved measurement

technique with real-time

evaluation of PC combustion

• Overpressure

• Timing and Duration

• Stability

New Pre-chamber design with

larger volume at λ=1.6

4.5 bar IMEP and 1500 rpm

Cylinder pressure

PC pressure

Overpressure in PC

SoC

Pmax, Pmax Cov

23.08.2018 23

Results


concepts


combustion concept

• Homogeneous lean combustion with <20ppm NOx is

possible

• Active pre-chamber ignition enables high efficiency

diluted charge combstion concepts

• Ultra Lean Combustion

• High EGR Stochiometric Combustion

=> High efficiency potenzial for SI combustion

23.08.2018 24

Inhalt


recent results using advanced diagnotics like High Speed

(HS) X-Ray imaging, HS-Schlieren, HS-Mie and Raman

Spectroscopy


concepts:

efficiency potentials for SI engines

Hydrogen and LOHC

possibilities and challenges of an carbon free energy

carrier

23.08.2018 25

Hydrogen

Example MAN 2876

• Available for different fuels

• 6-cylinder inline engine

• 12,8 l displacement

Property Unit Diesel CH4 H2 (2G)

Power kW 330 210 130

BMEP bar 20,6 13,1 8,1

Lambda 1,6 3

Compression 15,5 13,5 11

Eff. Efficiency % 41,8 39 39,3

Power density

of fuelMJ/l 38,7 0,0317 0,0108 Source: MAN

• Hydrogen is a very special fuel for internal combustion engines

• Low density and high wall heat losses during combustion

Boosted lean operation with low pressure direct injection

Good power density, high efficiency and low emissions

23.08.2018 26

• LOHCs store hydrogen

from fluctuating renewable

energies

• Storage of LOHCs

possible like diesel fuel

• Release of hydrogen by

means of catalyst and

heat

Hydrogen

23.08.2018 27

Inhalt

Hydrogen and LOHC

possibilities and challenges of an carbon free energy

carrier

Energy

Therm.

Engines

Fuel Cells

Drop-In

Strategies

Chemical

Nox-Reduction

Improve

Waste-to-

Diesel

HQ-Fuels

Heavy Oils

Biofuels

23.08.2018 28

Summary

Thanks for your

Attention!

The Internal Combustion Engines Group

Gasoline

Sprays

Diesel

Sprays Combustion

Concepts

Thanks for your

Attention!

23.08.2018 31

Experimental setupAssembly on spray chamber

beam forming optics

laser @ 532nm

spectograph with

EMCCD camera

Raman

signal

spray

plumes

beam waist

ØBW ~ 200µm

Galilean telescope

ØLB = 50mm

Laser beam

ØLB = 12mm

heig

ht

23.08.2018 32

CalibrationHow to calibrate on a permanently scavenged chamber?

Fuel

N2 0

0,2

0,4

0,6

0,8

1

0 1 2 3 4 5

I f/I

a/ -

location inside the beam waist / mm

v̇a = 0.173 m³/h v̇f = 5.39 ml/minv̇a = 0.172 m³/h v̇f = 5.39 ml/minv̇a = 0.172 m³/h v̇f = 5.39 ml/min

R² = 0,9995

0,0

1,0

2,0

3,0

4,0

5,0

6,0

0,00 0,02 0,04 0,06 0,08

I f/I

a/ -

nf/na / -

IfuelIambient

nfuelnambient

𝑘 =

𝑛𝑓𝑢𝑒𝑙𝑛𝑎𝑚𝑏𝑖𝑒𝑛𝑡

𝐼𝑓𝑢𝑒𝑙𝐼𝑎𝑚𝑏𝑖𝑒𝑛𝑡

⇒𝑛𝑓𝑢𝑒𝑙

𝑛𝑎𝑚𝑏𝑖𝑒𝑛𝑡=

𝐼𝑓𝑢𝑒𝑙

𝐼𝑎𝑚𝑏𝑖𝑒𝑛𝑡 ⋅ 𝑘

23.08.2018 33

Molar and mass fraction within the spray

plumepa = 6 MPa, Ta = 923 K, pf = 120 MPa, Tf = 363 K, tavSoI = 700 μs

fuel: ethanol

0

0,2

0,4

0,6

0,8

1

1,2

1,4

0 1 2 3 4 5

nf/

na

location / mm

H = 2mm

H = 5mm

H = 7mm

H = 10mm

H = 20mm

0

0,2

0,4

0,6

0,8

1

1,2

1,4

1,6

1,8

2

0 1 2 3 4 5

mf/ m

a

location / mm

H = 2mm

H = 5mm

H = 7mm

H = 10mm

H = 20mm

23.08.2018 34

Wavele

ng

th[n

m]

location

N2

CH

-0,1

0,0

0,1

0,2

0,3

0,4

800 1200 1600 2000 2400 2800 3200

no

rmalisie

rte I

nte

nsit

ät

[ -

]

Raman-Shift ΔωR [cm-1]

normalisiertesSpektrumFit CH-Peak

Fit N2-Peak

Mixing controlled Combustion

3. Raman Detail, Bio-EFuels

towards sustainable fuels and clean combustion concepts: progress in combustion...

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