Measurements and Characterization of Gasoline HCCI Combustion

1
Measurements and Characterization of Gasoline
HCCI Combustion
Angelo P. Chialva, Randy E. Herold, David E.
Foster, Jaal B. Ghandhi
Lab Objective
Engine Intake Charge Imposed Unmixedness
Combustion and Emissions Results
Temperature Stratification Baseline cases vs.
Temperature Stratification (T_strat_e1) cases.

• To quantify the effects fuel/air, thermal, and
  residual gas unmixedness have on gasoline HCCI
  combustion

Investigating in-cylinder mixture charge bulk
unmixedness -Using dual intake surge tank,
split runner setup, investigate the in-cylinder
flow field evolution from 330 bTDC (intake)
through 30 bTDC (compression) using PLIF.
GM HCCI Lab Experiments Chart
COV of IMEPImprovement of COV of IMEP is found
at stages with high cycle to cycle variations.
Engine Load IMEPAn increase in engine IMEP is
observed as deltatemperature between runners
mixture increases.
Emissions Index COEffects of intake charge
temperature stratificationprovide trends with
higher combustion burning efficiencies.
Emissions Index HCEffects of intake charge
temperature stratificationprovide trends with
higher combustion burning efficiencies.
Increasing delta temperature at a fixed mass
averaged temperature. Maximum temperature delta
80 degrees Celsius.
EGR Stratification Baseline cases vs. EGR
Stratification (EGR_unmixedness) cases.
- Bulk stratification is created by feeding
each port independently. However, that
initially stratified charge is mixed throughout
the induction and compression processes,
resulting in a uniform unmixedness at 30 bTDC.
window shift
window shift
Combustion Efficiency Similar burning
efficiencies are achieved atlower intake charge
temperatures.
Emissions Index HC High combustion efficiency at
lower intake chargetemperatures results in lower
HC emissions.
Approach to Unmixedness Experiments
HCCI Combustion Performance Baseline
-Definition of HCCI combustion temperature
window - Low Temperature End COV of
IMEP (1). - High Temperature End Knock
index (2). - Engine IMEP through out
temperature window (3). - Homogeneous EGR
andintake charge temperature.
Unmixedness Experiments Lab setup
Combustion Phasing CA50 Combustion phasing
approaching TDC occursat lower intake charge
temperatures.
Emissions Index NO Levels of NO emissions
increases as intake chargetemperature increases
with an offset of 20 degrees respect to baseline
data points.
Engine intake port / intake manifold design-
Dual and independent intake charge runners.-
Extended intake port septum.- Two independently
heat controlled dual intake charge mixtures
(air, fuel and external EGR)
Temperature offset on engine data between cases
with homogeneous and unmixed EGR 20 degrees
Celsius.
Future Work

• Conduct experiments in optical engine to test
  different intake port/ intake manifold setups for
  the purpose of maintaining charge bulk
  unmixedness.
• Run HCCI combustion tests in metal engine to
  characterize the effects of thermal and EGR
  unmixedness as different levels of uniform
  unmixedness are obtained in the mixture charge.
• Analyze combustion and emissions performance in
  HCCI engine tests while introducing thermal and
  EGR unmixedness at lighter engine loads and
  leaner air-fuel mixture conditions.
• Study the combined effects of thermal and EGR
  unmixedness in engine combustion and emissions
  while implementing rebreathing cams and varying
  effective CRs.

Temperature Stratification
Intake Charge Temperature Sweeps -Imposed intake
charge thermal unmixedness by - Varying
intake charge temperature at each runner. -
Targeting in-cylinder mass averaged temperatures
within HCCI window. - Maximum temperature
delta up 80 degrees Celsius.
Case1 T_strat_d
Split runner / splitport setup
Case2 T_strat_e
Intake valves lift profile targetminimizati
on of charge mixing inintake port due to
back-flow.
EGR Stratification
stock profile
Case1
Case2
Pressure Balanced Intake System EGR Air
Fuel -Imposed intake charge EGR unmixedness by
- Varying EGR distribution between split
intake charges.
current profile