SESAM i60 FTIR unit. ⢠AVL smoke meter measuring ... not being fully utilized. (more efficient ULSD expansion event). 450. 500. 550. 600. 650. 700. 0. 0.5. 1. 1.5.
N-heptane as a Fuel Surrogate for n-alkane Components of Diesel and Biodiesel Fuels H. Lai1, C. Depcik2, E. Peltier3, M. Mangus2, and C. Ragone2, University of Kansas 1. Department of Chemical Engineering, University of Tulsa 2. Department of Mechanical Engineering, University of Kansas 3. Department of Civil, Environmental & Architectural Engineering, University of Kansas
KU “Feedstock to Tailpipe” Systems Approach Sustainable Fuel Production from Biomass Alternative Fuel Assessment
Chris Depcik, Mechanical Engineering Dennis Lane and Edward Peltier, Environmental Engineering Susan Stagg-Williams, Chemical Engineering Ray Taghavi, Aerospace Engineering
Biomass Production
Belinda Sturm, Environmental Engineering Val Smith and Jerry DeNoyelles, Ecology and Evolutionary Biology
Chemical Transformation of Biomass
Laurence Weatherley and Susan Stagg-Williams, Chemical Engineering Belinda Sturm, Environmental Engineering
Pre-Processing of Biomass
Belinda Sturm, Environmental Engineering Val Smith, Ecology and Evolutionary Biology, Aaron Scurto, Susan Stagg-Williams and Laurence Weatherley, Chemical Engineering
Importance of Fuel Modeling • Understanding fuel behavior and properties can aid in analysis of alternative fuels • Reaction kinetics modeling is an important and effective tool for simulating fuel combustion processes – Aids development of low emissions, high power internal combustion engines – Helps comprehend emissions production pathways during combustion
Biodiesel • Oxygenated fuel made from vegetable oil or animal fats – Straight chain alkyl esters – Low aromatic content – Low sulfur content
O
O
Methyl oleate (C19H36O2)
• Relatively small number of compounds – Feedstock dependent – Dominated by C16 and C18 compounds
• Normally blended with petroleum diesel (B5 or B20) – Reaction modeling must account for both components
Biodiesel Fuels Relatively Simple 14000000
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Abundance
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Retention T ime (min)
• WCO Biodiesel Chromatogram; Guo et al. (2009) • Note: Replace with Jatropha biodiesel spectrum before presentation
Petroleum Diesel Contains Significantly More Compounds
• Representative spectrum of #2 diesel fuel from Topal et al. (2004)
Need for Fuel Surrogates • Full kinetic diesel fuel models too complex • Fundamental data not available • Fuel surrogates can be used to: – Model chemical reaction pathways – Perform basic combustion experiments – Understand emissions formation
• Surrogates can be one, two, or three fuel component mixtures • Most diesel fuel surrogates start with nalkane as primary constituent
• Examples of surrogate mixtures for biodiesel? • Biodiesel blended as B5 or B20 (neat biodiesel not expected to be main player) • Hence, kinetic understanding of biodiesel combustion must include diesel kinetics • Therefore, KU first investigating diesel surrogates for kinetic modeling simulations • Will add biodiesel surrogates as next step
N-heptane as Diesel Surrogate • Used as foundation for many diesel combustion kinetic models (LLNL) • Cetane Number (CN) similar to diesel fuel Property Density at 288 K Kinematic Viscosity at 313 K Dynamic Viscosity Lower Heating Value Cetane Number
kg/m3 mm2/s cP MJ/kg
ULSD 840 2.48 2.08 42.9 43
N-heptane 688 0.61 0.42 44.6 56
Combustion and Emissions Tests • Single cylinder, direct injection engine • Mechanical pump-line fuel injector • Constant engine speed of 3600 RPM • Load provided by DyneSystems AC Dynamometer • Data collected at 5 engine loads: 0%, 25%, 50%, 75% and 100% of generator output
Emissions Data Collection • Emissions and performance data collected at steady-state conditions • Gas-phase emissions data collected with AVL SESAM i60 FTIR unit • AVL smoke meter measuring particulate emissions • All emissions results reported as brakespecific emissions
Combustion Analysis 60
– Start of Injection ~15.5⁰ Before TDC – Start of Combustion
55
In-Cylinder Pressure (bar)
• In-cylinder pressure traces (average of 60 cycles, 0.5-degree resolution) • Motoring curve useful comparison between motoring and firing curves
50 45 40 35 Motoring ULSD 0% ULSD 25% ULSD 50%
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Crank Angle (Degrees ATDC) Cylinder Pressure vs. Crank Angle for ULSD for Various Percentages of Rated Torque
Combustion Analysis • N-heptane has longer ignition delay, despite higher CN • Late injection may be occuring • Strong correlation between combustion phasing and engine performance – Fuel consumption – (NOx – PM Tradeoff)
In-Cylinder Pressure (bar)
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50 45
40 ULSD 0% n-heptane 0% ULSD 25% n-heptane 25% ULSD 50% n-heptane 50%
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30 25 -10
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Crank Angle (Degrees ATDC) Cylinder Pressure vs. Crank Angle for ULSD and n-heptane for Various Percentages of Rated Torque
Exhaust Temperatures 700
Exhaust Temperature (K)
• Verify in-cylinder pressure analysis • n-heptane has higher exhaust temperature as a result of later combustion • Indicates that combustion energy is not being fully utilized (more efficient ULSD expansion event)
ULSD n-heptane 650
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Brake Power (kW) Exhaust Temperature vs. Engine Power for ULSD and n-heptane
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Brake-Specific Fuel Consumption 4
BSFC (g/kW-hr)
• BSFC increased above no-load conditions despite higher CN and energy content • Due to very late combustion • Low viscosity could also cause leaking through fuel pump • Phasing also important for emissions
1.1 10 4 1 10 9000 8000 7000 6000 5000 4000
ULSD n-heptane
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Brake Power (kW) Brake-Specific Fuel Consumption vs. Engine Power for ULSD and n-heptane
NOx Emissions 35 ULSD n-heptane
30 25 20 15
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NO (g/kW-hr)
• NOx reduced for nheptane • Caused by late combustion as a result of lower incylinder temperatures • Thermal NO production mechanism
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Brake Power (kW) Brake-Specific NOx Emissions vs. Engine Power for ULSD and n-heptane
Partial Combustion Products
– In-complete combustion due to lower in-cylinder pressures – Shorter combustion event before exhaust valve opening
160 ULSD-THC n-heptane-THC ULSD-CO n-heptane-CO
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Emission (g/kW-hr)
• CO and THC increases for nheptane • Caused by:
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Brake Power (kW) Brake-Specific THC and CO Emissions vs. Engine Power for ULSD and n-heptane
Particulate Matter Emissions 0.5 ULSD n-heptane
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PM (g/kW-hr)
• PM emissions reduced for n-heptane despite late combustion • Due to comparatively simpler chemical structure of only a single bond; does not contain any aromatic, cyclic, nor unsaturated compounds.
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Brake Power (kW) Brake-Specific PM Emissions vs. Engine Power for ULSD and n-heptane
Conclusions • The density and viscosity effects of n-heptane outweigh the similarities in combustion properties – Use as an experimental surrogate is likely very limited – Use in reaction calculations may also suffer – Disconnect between modeling community and engine experimentalists
• Particulate matter is mostly affected by chemical structure and component of a fuel • The effects of fuel properties are greatly nonlinear
Recommendations • Efforts to find a good diesel and biodiesel fuel surrogate should continue – Based on existing literature, n-dodecane is the best initial choice for a single surrogate
• Methyl butanouate (I think this is the wrong spelling) can serve as starting point for unsaturated biodiesel compounds – Unsaturated options are few, and often price limited – Representative oils (e.g. coconut or safflower oil) are potential alternatives
Acknowledgement University of Kansas – Jay Barnard, Ray Carter, Students of the KU Biodiesel Initiative Funding provided by • University of Kansas Transportation Research Institute (USDOT Grant #DTOS59-06-G-00047) • REU acknowledgement
