Abstract: Improving the performance of internal combustion
engines is one of the major concerns of researchers. Experimental
studies are more expensive than computational studies. Also using
computational techniques allows one to obtain all the required data
for the cylinder, some of which could not be measured. In this study,
an axisymmetric homogeneous charged spark ignition engine was
modeled. Fluid motion and combustion process were investigated
numerically. Turbulent flow conditions were considered. Standard k-
ε turbulence model for fluid flow and eddy break-up model for
turbulent combustion were utilized. The effects of valve angle on the
fluid flow and combustion are analyzed for constant air/fuel and
compression ratios. It is found that, velocities and strength of tumble
increases in-cylinder flow and due to increase in turbulence strength,
the flame propagation is faster for small valve angles.
Abstract: The objective of this study is to investigate fire
behaviors, experimentally and numerically, in a scaled version of an
underground station. The effect of ventilation velocity on the fire is
examined. Fire experiments are simulated by burning 10 ml
isopropyl alcohol fuel in a fire pool with dimensions 5cm x 10cm x 4
mm at the center of 1/100 scaled underground station model. A
commercial CFD program FLUENT was used in numerical
simulations. For air flow simulations, k-ω SST turbulence model and
for combustion simulation, non-premixed combustion model are
used. This study showed that, the ventilation velocity is increased
from 1 m/s to 3 m/s the maximum temperature in the station is found
to be less for ventilation velocity of 1 m/s. The reason for these
experimental result lies on the relative dominance of oxygen supply
effect on cooling effect. Without piston effect, maximum temperature
occurs above the fuel pool. However, when the ventilation velocity
increased the flame was tilted in the direction of ventilation and the
location of maximum temperature moves along the flow direction.
The velocities measured experimentally in the station at different
locations are well matched by the CFD simulation results. The
prediction of general flow pattern is satisfactory with the smoke
visualization tests. The backlayering in velocity is well predicted by
CFD simulation. However, all over the station, the CFD simulations
predicted higher temperatures compared to experimental
measurements.