Fuel Unmixedness Effects in a Gasoline HCCI Engine

1
Fuel Unmixedness Effects in a Gasoline HCCI Engine
Students R.E. Herold, R.J. Iverson (MS, 2004)
Faculty D.E. Foster, J.B. Ghandhi
Objective
Effects at Varied Fueling Rates
Level of Fuel Unmixedness

• Level of fuel unmixedness created when using the
  port, prevaporized fuel injection was
  investigated optically using fuel tracer planar
  laser-induced fluorescence (PLIF).
• Injection crank angle locations (detailed below)
  corresponded to those detailed in metal engine
  experiments.

• Quantify the effect fuel unmixedness has on
  gasoline HCCI combustion.

Experimental Facilities
Cylinder Head
Quartz Cylinder Window


Sapphire Piston Window

Bowditch Piston Extention

• No changes in combustion observed between
  premixed and port fueling.
• Significant NOx emissions increases only observed
  in 10 mg/cycle fueling. NOx emissions were near
  zero for the 7 and 5 mg/cycle fueling conditions
  due to high EGR.
• The difference in CO emissions between premixed
  and port fueling increases with decreasing
  fueling rate.

Drop-down Liner

• A significant level of unmixedness is created
  with prevaporized port fueling.
• Fuel unmixedness increases with retarded
  injection timings except for the EoPI 256 bTDC
  injection timing, which is less unmixed than the
  EoPI 364 bTDC injection timing.
• For the most retarded injection timing, regions
  exist in the cylinder with equivalence ratios
  that differ from the mean by /- 50.

Engine Properties Engine Properties
CR 10.95
Bore 86 mm
Stroke 94.6 mm
EVO 131? aTDC
IVO 350? aTDC
EVC 375? aTDC
IVC 595? aTDC
Effects at Varied Equivalence Ratios

Imaging Mirror
Engine Test Cell Setup
Optical Engine
Injection Timing Effects

• No changes in combustion observed between
  premixed and port fueling.
• NOx emissions were near zero for all conditions
  because of high EGR rate at the 5 mg/cycle
  fueling condition
• Decreasing the equivalence ratio (increasing air
  flow, decreasing EGR at constant fueling rate)
  leads to an increase in CO emissions but a
  decrease in the difference in CO emissions
  between premixed and port fueling.

To Engine
f 1000 mm Plano-Convex Spherical Lens
f -500 mm Plano-Concave Cylindrical Lens
Conclusions
UG5 Schott Glass Filter

• Fuel unmixedness in the absence of thermal and
  residual unmixedness had no effect on the HCCI
  combustion.
• Small changes in CO and NOx emissions were
  observed for the port fueling, which were
  attributed to the regions in the charge that were
  either locally richer or leaner than the mean
  equivalence ratio.
• At a given operating condition the CO and NOx
  emissions are the lowest for a fully homogeneous
  fuel distribution. Regions locally richer and
  leaner than the mean equivalence ratio lead to
  increases in NOx and CO and therefore should be
  avoiding in an HCCI engine.
• Fuel unmixedness in the absence of thermal and
  residual unmixedness does not appear to be a
  viable method for gasoline HCCI combustion
  control.

Dichroic Mirror

• Variations with respect to intake charge
  temperature due to heat transfer in intake port.
• All combustion metrics investigation (i.e., peak
  pressure, combustion efficiency) show that at a
  given combustion phasing (CA50) premixed and
  prevaporized port injection are
  indistinguishable.
• NOx emissions increase with fuel unmixedness,
  resulting from regions richer than the mean which
  burn hotter after autoignition.
• CO emissions show a slight increase with fuel
  unmixedness, possibly a result of regions richer
  than stoichiometric or quenching in regions
  leaner than the mean.

Beam Stop
90 Turning Prism
NdYAG Laser
Pellin-Broca Prism
Optical Setup for PLIF Experiments