Impacts of molecular
structure on the combustion
and emissions characteristics
of future diesel fuels
Paul Hellier and Nicos Ladommatos
University College London
Brunel University Biodiesel Workshop 21.11.2013
Outline
1. Future fuels
2. Experimental methodology
−
Ultra low volume fuel system
3. Features of alkyl chains
−
Ignition delay
−
Emissions
4. Fatty acid ester alcohol moiety
5. Genetically modified microorganisms
6. Conclusions
Approach
Liquid fuel
Feedstock
Process
Product
Fossil fuel
Organic matter
Intense heat and
pressure over
millions of years
Refined to meet
performance and
environmental
requirements in
ICE
Current bio-fuels
Agricultural crops
with food value
Conversion of
sugars, starch,
and fatty acids
with varying net
CO2 performance
Designed to
emulate existing
fossil fuels
Future fuels
Lignocellulosic
biomass,
photosynthetic
micro-organisms,
waste streams
Various possible
routes of
biological and
thermo-chemical
conversion
?
Experimental approach
−
Testing logical series of chemistries in which a specific
molecular structural property is incrementally altered while
others are kept constant.
1 double
bond
H3C
CH2
Carbon chain length = 12
−
High assay single component fuels may be of limited supply
or require expensive synthesis.
Engine facility
−
Single cylinder
diesel engine.
−
Ricardo Hydra with Ford
Duratorq 2.0 L head.
−
Common rail (Bosch CP3)
with solenoid valve DI
injector (Delphi DFI 1.3).
−
Gaseous emissions: Horiba MEXA 9100 HEGR.
−
Particulate emissions: Cambustion DMS 500 Spectrometer.
research
Solution
Bypass
Free moving
pistons
High pressure valve
Fossil diesel
Test fuel
Diesel
reservoir
Pressure
vessel
Filter
Common rail
Exhaust
Injector
High
pressure
pump
Pressure
sensor
DAQ
Emissions Particulates
analysis
analysis
Engine
Experimental conditions
− Constant injection timing:
−
−
−
−
1200 rpm and 450 bar fuel injection pressure
4 bar IMEP (variable injection timing ~700 – 900
μs)
SOI = 7.5 CAD BTDC
Variable SOC
− Constant ignition timing:
−
−
−
−
1200 rpm and 450 bar fuel injection pressure
4 bar IMEP (variable injection timing ~700 – 900
μs)
Variable SOI
SOC = TDC
Experimental conditions
−
Constant ignition delay timing:
− Addition of 2 EHN to control duration of ignition delay
− 1200 rpm and 450 bar fuel injection pressure
− 4 bar IMEP (variable injection timing ~700 – 900 μs)
−
Fixed SOI
− SOI = 7.5 CAD BTDC
− Variable SOC
−
SOC at TDC
− Variable SOI
− SOC at TDC
SOI
n-alkane carbon chain length
Constant injection timing
Constant ignition timing
Increased alkyl chain length → reduced peak in-cylinder pressures
n-alkane carbon chain length
Constant injection timing
Constant ignition timing
Increased alkyl chain length → reduced peak heat release rate
Alkyl chain saturation
Decrease in saturation → increase in ignition delay
Alkyl chain methyl branching
Increased branching within alkyl chain → increased ignition delay
Relative impacts of alkyl chain
features
% Shift in ID relative to the base fully
saturated straight chain molecule (C10)
60
50
40
Straight Carbon chain
length
Double bonds
Branching
30
20
10
0
10
20
-10
-20
% Increase in structural property
Ignition delay kinetics
−
Initial alkyl chain low temperature branching reactions:
A. CxHy → CxHy-1 + H*
B. R + O2 → RO2
C. R + O2 → QOOH
CH3
H3C
CH3
Primary
Secondary
CH3
C-H bond strengths:
1.
Primary - C-H of a methyl group
2.
Secondary - C-H of C bonded to a further 2 C
3.
Tertiary - C-H of a C bonded to a further 3 C
Strength
Carbon-carbon double bond
−
Increased double bonds → reduced secondary C-H atoms →
reduced potential for isomerisation
−
Six and seven member transition state rings require:
−
Alkyl chain length of at least 3
−
All carbons to be saturated
H3C
CH3
No. of potential transition
rings decreases by 1/3
H3C
CH2
Effect of ignition delay on combustion
phasing
Peak heat release rate
Premixed burn fraction
Duration of ignition delay → premixed burn fraction → peak heat release
NOx and particulate emissions
NOx emissions
Particulate mass
Increased ignition delay → increased NOx + reduced particulates
Double bond position
trans-1-octene
trans-2-octene
trans-3-octene
cis-3-octene
Double bond position
trans-3-octene
cis-3-octene
−
Double bond 1 → 2 increases ignition delay, 2 → 3 does not
−
Contrary to studies with heptene isomers
Double bond ignition kinetics
permits internal H abstraction and isomerisation across a double bond
net reactivity
Fatty acid ester alcohol moiety
Thermo-gravimetric analysis
O
O
CN = ~ 100
OH
O
CN = 61.7
Alcohol moiety particulates
Boiling point, viscosity
Oxygen content
Genetic modification for future fuels
Courtesy of Lamya Al-Haj and Dr. Saul Purton, UCL Institute of
Structural and Molecular Biology
−
Photosynthetic
cyanobacteria
−
Compounds
secreted from
cells
OH
Geraniol
OH
O
Geranial (Citral-A)
H
OH
Nerol
OH
Linalool
Citronellol
Citronellene
O
O
OH
Citral dimethyl acetal
O
3,7-dimethyloctan-1-ol
Farnesene
O
Geranyl acetate
H
H
H
OH
Squalene
Menthol
cis vs trans
Alcohol
group
position
Degree of
saturation
Functional
group
Alkenyl chain
length
Microbial terpene fuels
trans
1 DB
cis
2 DB
0 DB
C30
C15
-OH→=O
Fuel viscosity
Squalene high viscosity → poorer mixing → increased particulates
Design of future fuels in terms of molecular structure
−
Fuel molecular structure determines ignition delay through low
temperature reaction kinetics.
−
Ignition delay is most strongly influenced by the reactivity of long alkyl
chains.
−
Other elements of molecular structure can:
−
−
Result in molecule breakdown prior to vaporisation.
Impact significantly on ignition delay where the alkyl moiety is of
poor ignition quality.
−
Emissions of NOx are thermal and dictated by heat release rates
determined primarily by duration of ignition delay.
−
Levels of soot produced increases with removal of fuel O and
increasing fuel viscosity.
−
Understanding of effects of molecular structure will inform development
of future fuels, eg. from genetically modified organisms
Thank you for listening
Questions?
[email protected]
Acknowledgements: EPSRC
UCL Institute of Structural and Molecular Biology
All f igures and results in this presentation have previously been published in the f ollowing journal articles:
P. Hellier, L. Al-Haj, M. Talib, S. Purton and N. Ladommatos, “Combustion and emissions characterisation of terpenes as biof uels produced by the microalgae Synechocystis”, Fuel, Volume 111, September 2013, Pages 670-688.http://dx.doi.org/10.1016/j.f uel.2013.04.042
P. Hellier, N. Ladommatos, R. Allan, S. Filip and J. Rogerson, "The importance of double bond position and cis trans isomerisation in diesel combustion
and emissions", Fuel, Volume 105, March 2013, Pages 477-489. http://dx.doi.org/10.1016/j.f uel.2012.08.007
P. Hellier, N. Ladommatos, R. Allan, M. Payne and J. Rogerson, "The Inf luence of Fatty Acid Ester Alcohol Moiety Molecular Structure on Diesel
Combustion and Emissions", Energy and Fuels, 2012, 26 (3), pp 19121927. http://dx.doi.org/10.1021/ef 2017545
P. Hellier, N. Ladommatos, R. Allan, M. Payne and J. Rogerson, "The Impact of Saturated and Unsaturated Fuel Molecules on Diesel Combustion and
Exhaust Emissions", SAE Int. J. Fuels Lubr. 5(1):106-122, 2012. http://dx.doi.org/10.4271/2011-01-1922