University of Wisconsin Engine Research Center Future Work Approach to Unmixedness Experiments Measurements and Characterization of Gasoline HCCI Combustion Angelo P. Chialva, Randy E. Herold, David E. Foster, Jaal B. Ghandhi To quantify the effects fuel/air, thermal, and residual gas unmixedness have on gasoline HCCI combustion Lab Objective Engine Intake Charge: Imposed Unmixedness Combustion and Emissions Results GM HCCI Lab Experiments Chart 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) 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. Unmixedness Experiments: Lab setup Intake valves lift profile target: “minimization of charge mixing in intake port due to back-flow.” 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. - 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. Split runner / split port setup 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 and intake charge temperature. Temperature Stratification EGR 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. Pressure Balanced Intake System: EGR + Air + Fuel - Imposed intake charge EGR unmixedness by: - Varying EGR distribution between split intake charges. Case#1Case#2 Case#1 – T_strat_d Case#2 – T_strat_e Engine Load IMEP An increase in engine IMEP is observed as delta temperature between runners mixture increases. Temperature Stratification: Baseline cases vs. Temperature Stratification (T_strat_e1) cases. COV of IMEP Improvement of COV of IMEP is found at stages with high cycle to cycle variations. Emissions Index CO Effects of intake charge temperature stratification provide trends with higher combustion burning efficiencies. Increasing delta temperature at a fixed “mass averaged temperature.” Maximum temperature delta ~ 80 degrees Celsius. Emissions Index HC Effects of intake charge temperature stratification provide trends with higher combustion burning efficiencies. EGR Stratification: Baseline cases vs. EGR Stratification (EGR_unmixedness) cases. Combustion Efficiency Similar burning efficiencies are achieved at lower intake charge temperatures. Emissions Index HC High combustion efficiency at lower intake charge temperatures results in lower HC emissions. Combustion Phasing CA50 Combustion phasing approaching TDC occurs at lower intake charge temperatures. Emissions Index NO Levels of NO emissions increases as intake charge temperature increases with an offset of 20 degrees respect to baseline data points. Temperature offset on engine data between cases with homogeneous and unmixed EGR ~ 20 degrees Celsius. stock profile current profile window shift