PowerPoint Presentation
Rapid compression machineComputational model by Fluent
N. Loveldi, X.Gao, A. Marchese,
Outline
What is RCM?
RCM stroke
MotivationCetane numberGold StandardUltimately Cetane number is
an indication what is the quality of ignition delayCompared Mixture
of n-cetane(left) and 1-methylaphthalene(right),Every fuel has
different ignition time, so why do we compare it with only 2
reference fuels?
Ignition Delay
Time required for fuels to evaporate (if liquid) and diffuse
before it reactsCan be defined as Temperature inflection pointFor
Compression Ignition
Ignition delay
How do we measure Ignition Delay?What we want is a 0-D chamber
(homogeneous) that can instantly raise the temperature and
pressure. (impossible)This is where RCM comes in If we cant do it
instantly, lets do it as fast as we canProblems with RCM:It is not
instant, so there is a very high pace movement that might cause
non-homogeneity It is not adiabatic, which cause temperature
gradient
Our Job is to figure out how non-uniform it is? And if it is
non-uniform, where does the combustion actually starts?
How did we do it? Case Setup Drawings of Piston Head
crevisshaft
Piston head surface
Case SetupMesh
Edge sizing structured mesh for dynamic layeringUnstructured
meshQuality:N of cells =17922Orthogonal(min) = 0.796Aspect
ratio(max)= 10.95AxisymmetricClear ?
Case SetupPiston Velocity profileExperiment displacement
data
Total time ~ 42 msDisplacement ~157mm
Case Setup
Case SetupPiston Velocity profile result
At the end of 42 ms, dynamic mesh is turned off to avoid
sinusoidal motion
Adiabatic caseNon-reactiveLaminar ModelHeat flux to wall =
0Green-Gauss node basedInitial conditions:P = 25000 Pa
(experiments)T = 288 K (experiments)No fuel
Adiabatic CasePressure vs time
Temperature vs time
Adiabatic CasePressure Contour @ 21ms
Temperature Contour @ 21 ms
As we expected, both temperature and pressure are
homogeneous
Adiabatic CaseVelocity contour at 91 ms
What we want to show is that there is a movement of fluid inside
the cylinder long after the end of stroke which show
non-homogeneity
Isotherm CaseNon-reactiveLaminar ModelIsotherm wall at 300K with
10mm wall thicknessGreen-Gauss node basedInitial conditions:P =
25000 Pa (experiments)T = 288 K (experiments)No fuel
Pressure Plot
Experimental Pressure plotFluentMax Pressure ~ 2.5MPaAt 27msMax
Pressure ~ 2.5MpaAt 35msIsotherm model is a good representation of
the experimental case,
Temperature Plot
This is a good case representation because We clearly see the
heat transfer from the decreasing temperature after 42 ms
Temperature Contour Isotherm21 ms42 ms63 msMax = 375KMin = 300
KMax = 1030KMin = 302 KMax = 974KMin = 300 K
Temperature ProfileWhat did we see?It is definitely not
homogeneousThere are some temperature vortexBoundary Layer might be
thin enough for approximation?
Velocity Contour Isotherm21 ms42 ms
35 msMax = 10.4 m/sMin = 0 m/sMax = 29 m/sMin = 0 m/sMax = 17.4
m/sMin = 0 m/s
Velocity ProfileThe Crevis on the piston was created to reduce
vortex in the main cylinder and distributing it into another
chamberIt is consistent with the adiabatic case.
Combustion of single step Hydrogen
Combustion of single step HydrogenTemp vs timePressure vs
time
Contour of Temperature
Contour of H2O
Contour of H2
Contour of H2
Conclusion from CombustionVery Inaccurate because it reacts at
300 KThis is where I got stuck because CSU does not have the
license for pre-processor of detail chemistry inputs from
Chem-KinHowever, there are something that can be learned from
hereWe know now that the combustion does not start everywhere at
the same timeWe are able to see where is the flame propagating by
the consumption of hydrogen fuel
Future WorkDetail Chemistry inputs for the whole mechanism
should give us a better resultsSimulation Using Converge
Can RCM really be used as a good measurement to find a
standardized ignition delay?
Referencehttp://www.eecl.colostate.edu/facility/equipment.php?equipment=7J.
Li, Z. Zhao, A. Kazakov, F.L. Dryer, Int. J. Chem.Kinet. 36 (2004)
566575.Computational fluid dynamics modeling of hydrogenignition in
a rapid compression machineGaurav Mittal , Mandhapati P. Raju,
Chih-Jen Sung
