Fuel Unmixedness Effects in a Gasoline HCCI Engine

1. Fuel Unmixedness Effects in a Gasoline HCCI Engine IVC (855°) IVO (358°) IVC (135°) = Intake Valve Open 245° 140° EGR 301° 196° 361° 256° Inline Heater AIR 469° 364° Premixed Fuel Injection Point 829° 724° Surge Tank 1 720° (TDC – Previous Cycle) 360° (TDC Exhaust) 180° (BDC) 0° (TDC – Cycle of Interest) Surge Tank 2 Crank Angle (° bTDC) Port Fuel Injection Point Exhaust Engine Vaporized Fuel Intake Valve Heated Air + EGR 2.3 mm ID Tube Port, Prevaporized Fuel Injector Students: R.E. Herold, R.J. Iverson (MS, 2004) Faculty: D.E. Foster, J.B. Ghandhi Objective Level of Fuel Unmixedness Effects at Varied Fueling Rates • 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%. 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. f = -500 mm Plano-Concave Cylindrical Lens f = 1000 mm Plano-Convex Spherical Lens To Engine 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 Nd:YAG Laser Pellin-Broca Prism Optical Setup for PLIF Experiments