Chemical properties: aromatics & cycloparaffins ~ 50%. H/C ratio 1.93. â Cetane Number: 55. â Chemistry: 899 species,. 6053 reactions. HCCI Engine Results.
Accurate Predictions of Fuel Effects on Combustion and Emissions in Engines Using CFD Simulations With Detailed Fuel Chemistry 1 Naik ,
1 Puduppakkam ,
Chitralkumar V. Karthik V. 1 Reaction Design, San Diego, CA, USA; Background
Our Approach
● Recent advancements in combustion science and new methods for CFD enable study of advanced engine concepts
● Use accurate fuel models in advanced CFD
Advanced numerical methods
Fuel combustion science
Complex design involvingdesign changing Complex involving fuels and kineticschanging fuels and controlled kinetics-controlled combustion combustion
Dynamic adaptive chemistry
Advanced nozzleflow and spraybreakup dynamics
Multi-core & faster processors
Fuel model
Spray/droplet break-up models
Fuel droplet vaporization model
Fuel-air combustion chemistry model
Tailored, multi-component surrogate fuel Nozzle flow, cavitation Primary, secondary break-up Droplet collision models Mesh-independent models Flash boiling Multi-component fuel-vaporization Detailed kinetics of combustion Detailed emissionsformation models
– 40+ fuel components (thousands of chemical species) aromatics olefinsand – Combustion c-paraffins emissions chemistry
Generate smaller but accurate fuel models -
Fuel specific Surrogate blend formulation Reduction of detailed reaction mechanism
Automated mesh generation
Model Fuels Consortium
Grid-independent spray-jet model
Can Predict: • Effects of fuel variability o Ignition timing o Combustion phasing o Efficiency • Behavior of a new fuel • Engine design and concepts o HCCI, LTC • Emissions details o CO, UHC, NOx o Soot precursors o Aldehydes, phenols
Scope of this work
Fuel Models Used in CFD
Diesel Engine Results
● PRF-ethanol: Exactly match composition of the experimental mixture (3-components)
● Combustion phasing and trends in emissions predicted well for n-heptane
– RON/MON: 104/96 (estimated) – Chemistry: 428 species, 2378 reactions
Hundreds of species
n-paraffins
2 Bunting
Ellen Bruce 2 Oak Ridge National Laboratory, Oak Ridge, TN, USA
i-paraffins
● Detailed fuel models provide predictions that are otherwise unattainable Accurate Model Components
Library of detailed reaction mechanisms
1 Meeks ,
● n-Heptane: Exactly match composition of the experimental mixture (1-component) – Chemistry: 84 species, 523 reactions
● FACE 5 diesel: Surrogate fuel (4-component) to match the experimental diesel – Chemical properties: aromatics & cycloparaffins ~ 50% H/C ratio 1.93 Component Vol.% – Cetane Number: 55 n-Tetradecane 44.8 n-Propylbenzene 10.9 – Chemistry: 899 species, Heptamethylnonane 16.3 6053 reactions
Use accurate fuel models with advanced CFD
Decalin
● A surrogate blend can match any combination of fuel properties
HCCI Engine Results
● Several methods available to reduce a detailed reaction mechanism
● Accurate prediction of combustion phasing
– Skeletalization and severe reduction methods – Reduces a large detailed surrogate fuel mechanism from thousands of chemical species to several hundreds
● Majority of CO is produced in the bowl, and still hot & reactive at EVO
Master mechanism contains 3981 species & 16607 reactions
● Surrogate Blend Optimizer and Automated mechanism reduction methods implemented in Reaction Workbench software
● Simulations for FACE diesel fuels are in progress
Surrogate Blend Optimizer
Desired Fuel Properties
Set target characteristics Class composition Heating value Octane / Cetane # H/C ratio, O content Boiling points Threshold Sooting Index
28.0
● Accurate prediction of emissions and speciation Optimized Surrogate fuel composition
Summary
n-heptane Iso-octane
● Combustion, emissions, and fuel effects predictions in HCCI and diesel engines ● Fuels – PRF with 30% ethanol in an HCCI engine – n-Heptane in a diesel engine – FACE 5 diesel in a diesel engine ● Engines – HCCI engine CR
(Compression Ratio): 14.5 Overall equivalence ratio: 0.32-0.34 (0.15 g/s fuel rate) Intake temperature varied: 448-470 K
– Diesel engine CR: 16 Start of Injection: -8 degree TDC (0.08-0.2 g/s fuel rate) Air intake temperature: 330 K
19%
1-pentene
45%
Match with fuel palette Select surrogate components optimize blend
● An advanced approach to use accurate fuel chemistry for engine simulation has been devised and validated
mc-hexane
15%
m-xylene
3%
ethanol
1%
● Detailed reaction mechanisms for 40+ components for surrogate formulation for gasoline, diesel, and other fuels available
15%
FORTÉ CFD Simulation Package ● FORTÉ couples advanced fuel-sprays with multicomponent fuel vaporization and advanced chemistry
● Only accurate fuel models in CFD can predict all emissions
● Very fast simulation, even with 400+ species model
● Reaction Workbench software used to optimize surrogate blends and accurately reduce fuel models ● Combustion and emissions (speciation) have been accurately captured in an HCCI engine by exactly matching the composition of the experimental fuel in FORTE simulations ● Surrogate for diesel fuels should provide accurate predictions of combustion and emissions in a diesel engine
– 4 to 6 hours for this ~10,000 cell problem , w/ 8 CPUs ● FORTÉ uses advanced chemistry-solution techniques – 100-1000x faster than conventional CFD (Liang et al., SAE 2010-01-0178) From: K. Puduppakkam, et al., SAE2010-01-0362 (Data from B. Bunting, ORNL)
