1. World Biodiesel Congress & Expo 2016, San Antonio, USA
Numerical Study of Soot Formation Using Phenomenological Soot Modelling Approach in a Biodiesel-fueled Compression Ignition Engine
Dr. Zhao Feiyang
Research fellow
Department of Mechanical Engineering
National University of Singapore

2. National University of Singapore
Founded in 1905
Ranked as one of Asia's top Universities
Faculty of Engineering is the largest faculty in the university

3. Content Background A Semi-Detailed Soot Model for Engine Simulation
Numerical Investigation of Soot Formation in Biodiesel-fueled Compression Ignition Engine
Conclusion

4. Content Background A Semi-Detailed Soot Model for Engine Simulation
Numerical Investigation of Soot Formation in Biodiesel-fueled Compression Ignition Engine
Conclusion

5. Background----PM negative impact
Source of Particulate Matter 2.5
Negative effect
Human health
Respiratory
Cardiovascular
Premature death
Absorbs solar radiation
Vector-borne diseases
such as dengue
Sea level
More energy demand
Rising temperatures
Ecosystems
Haze
Visibility impairment

6. Background---Biodiesel in engines
Renewable and Domestic
Less gas emission
Blend with other energy resource and oil
Used in engine without alternation
Fuel property
Diesel
Biodiesel
Density at 20oC(kg/m3)
840
883
Viscosity at 20oC(mm2/s)
2.8
4.36
Calorific value (MJ/kg) 45 38
Cetane number
40-55
48-65
Carbon (wt%) 87 77
Hydrogen (wt%) 13 12
Oxygen (wt%) 11
Biodiesels have a higher cetane number than diesel  shorter ignition delay time
Viscosity is higher for Biodiesels  poorer evaporation and atomization  longer ignition delay
Oxygen content of biodiesel is 11% as compared to 0% for diesel
Challenge in seeking clean combustion in engines

7. Background---what we have done in NUS
Physical and chemical model of biodiesel
Viscosity
Thermal conductivity
Latent heat of vaporization
Fatty acid methyl esters (FAMEs) composition
…..
3D combustion simulation in diesel engine
Diesel engine test
Emissions / Fuel consumptions
Performance
Flexible ECU control system
Injection timing/duration
Split injection, multiple injections
Common Rail Pressure
…..

8. Content Background A Semi-Detailed Soot Model for Engine Simulation
Numerical Investigation of Soot Formation in Biodiesel-fueled Compression Ignition Engine
Conclusion

9. Soot forming process
Soot formation experience the most complicated physical and chemical progress in fuel combustion

10. A semi-detailed soot model for engine simulation---Methodology
GAS PHASE CHEMISTRY
Semi-Detailed Soot Particle Model
Soot inception through precursor
𝑷𝒓𝒆𝒄𝒖𝒓𝒔𝒐𝒓𝒔 𝑹𝟏 𝑪 𝑺 + 𝑯 𝟐
𝑪 𝟐 𝑯 𝟐 assisted surface growth
HACA mechanism
Soot coagulation
𝒏𝑪(𝒔) 𝑹𝟑 𝑪(𝒔) 𝒏
O2 related surface oxidation
𝑪 𝒔 + 𝟏 𝟐 𝑶 𝟐 𝑹𝟒 𝑪𝑶
5. OH related surface oxidation
𝑪 𝒔 +𝑶𝑯 𝑹𝟓 𝑪𝑶+ 𝟏 𝟐 𝑯 𝟐

11. A semi-detailed soot model for engine simulation----Validation
Gas Phase Validation
Soot Particle Validation
n-heptane flame
iso-octane flame
Test data from: Soot formation in a shock tube under elevated pressure conditions. Combustion Science and Technology, 1996(113):67–80

12. Content Background A Semi-Detailed Soot Model for Engine Simulation
Numerical Investigation of Soot Formation in Biodiesel-fueled Compression Ignition Engine
Conclusion

13. Numerical Investigation of Soot Formation in Biodiesel-fueled Compression Ignition Engine
CFD model under kiva4-chemkin platform
Engine specification and operating conditions
Engine speed
2400 rpm
Load
50%
Bore
9.2 cm
Stroke cm
Volume
2.5L
Compression ratio
18.5
Fuel injection holes 6
Mass of injected fuel g
Initial Temperature
390 K
Initial Pressure
1.638 bar
Start of injection timing
-20,-15,-10deg ATDC
Multi-component biodiesel skeletal chemical mechanism
Methyl decanoate (MD) Saturated FAMEs
Methyl-5-decenoate (MD5D)
Methyl linoleate (ML) Unsaturated
FAMEs
N-decane Diesel fuel surrogate
Types of fuel were tested
Rapeseed and Sunflower
Biodiesel and diesel fuel blend
Diesel fuel
Phenomenological soot particle modelling
Soot characteristic in mass and size

14. Numerical Investigation of Soot Formation in Biodiesel-fueled Compression Ignition Engine
Soot mass emission
Biodiesel(Sunflower and Rapeseed) have longer ignition delay (for mixing)
-> produces lower soot emission

15. Numerical Investigation of Soot Formation in Biodiesel-fueled Compression Ignition Engine
Soot particle size distribution
@ 0 ATDC
@ 30 ATDC
Lower particle sizes are much more prominent as the nucleation of precursors forms the smaller nuclei at the outset of combustion
Larger size particles are formed by coagulation between the small nuclei

16. Numerical Investigation of Soot Formation in Biodiesel-fueled Compression Ignition Engine
Soot particle size distribution
@ 0 ATDC
@ 30 ATDC
Diesel produces more soot particles in total
It causes more surface to be available for soot precursor to be added, thus promotes the soot mass growth.

17. Numerical Investigation of Soot Formation in Biodiesel-fueled Compression Ignition Engine
Factors influencing soot formation
Higher temperature in Diesel fuel combustion that facilitates reactions rate
More C2H2 accumulated in shorter ignition delay of diesel combustion that accelerates particle nuclei and surface growth
Oxygen content in Biodiesel favors soot oxidation
Soot/Time
Fixed -15deg ATDC

18. Conclusion
Knowledge-based platform on biodiesel application in Compression Ignition Engine were set up in our research group (NUS), investigating physical and chemical model of biodiesel fuel and engine performance fueled with biodiesel.
With the semi-detailed soot particle model, numerical study of soot characteristics were carried on in a biodiesel-fueled compression ignition engine
Differences in physical and chemical properties between diesel and biodiesel leading significant difference in combustion and emission characteristics. Compared with diesel fuel, biodiesel produce less soot both in mass and number.

19. Thank you for your attention