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. Case#1 – T_strat_d Split runner / splitport setup Case#2 – T_strat_e Intake valves lift profile target:“minimization of charge mixing inintake port due to back-flow.” EGR Stratification stock profile Case#1 Case#2 Pressure Balanced Intake System: EGR + Air + Fuel -Imposed intake charge EGR unmixedness by: - Varying EGR distribution between split intake charges. current profile