1. University of Wisconsin Engine Research Center Spray Targeting to Minimize Soot & CO Formation in Premixed Compression Ignition (PCI) Combustion with a HSDI Diesel Engine SANGSUK LEE & Rolf D. REITZ Motivation  Stringent future emission regulations require low emission strategies.  PCI (Premixed Compression Ignition) is a practical way to achieve near zero levels of soot and NOx trade-off even under fairly rich conditions. Objectives  To investigate key factors which determine the characteristics of PCI and Conventional Diesel Combustion.  To find the best way to realize low emissions.  To understand how the spray targeting affects on emission formation. Start of Burn & Burn Duration Burn Duration  10–90 % burn durations about 5 degree regardless of SOI and nozzle within the PCI regime.  In Conventional regime, duration increased as SOI was retarded since fuel burnt within the mixing controlled varies with SOI. Start of Burn  The Combustion starts around -11 o ATDC in PCI. ; Similar Combustion Characteristics with different soot formation  What makes the difference in soot & CO emissions? ; Pre-ignition mixing with squish and swirl flow. Spray Targeting 10-90% Burn Duration Details for 120 o Nozzle Operation Conditions Engine Speed2000 rpm Load4.8bar IMEP Boost Pressure151 kPa EGRabout 55% Intake Air Temp.90 o C Injection Pressure1500 bar Start of 10% Burn Single Injection _ Soot & CO  Three combustion regimes (MK, Conventional, PCI) were identified with respect to SOI. MK (SOI > -5°) Conventional diesel combustion ; Soot & CO increase as SOI retarded. No big difference in levels except 50 °nozzle. PCI (SOI < -20°) ; No simple rule to describe the emission trends in PCI combustion.  No significant NOx emission difference observed under high levels of EGR. CO Soot Split Injections  Hard to find an advantage of split injections compared to single injection optimum in PCI.  Results of Pickett (SAE2005-01-0921) explained that soot emission increased when the spray interacted with the burnt gas due to a shortened lift-off length. Spray Targeting Soot CO  Spray Targeting at a piston bowl edge gave the minimum emissions both soot and CO.  Soot was minimized when the spray was targeted at the bottom of the piston bowl.  Targeting at the inner surface of the piston gave optimized CO emissions. Spray Targeting _ Squish Flow Soot CO  Optimum spray targeting near the edge of the piston bowl was observed regardless of spray angles.  Optimum spray targeting moved up piston bowl as spray angle became narrower. Conclusions  Burn durations are good indicator to classify the PCI combustion in diesel engines.  Spray Targeting at the edge of the piston bowl is a key factor to minimize emissions in PCI combustion.  Soot could be optimized when spray was targeted at the bottom of piston which provided the longest spray travel distance. However, CO emission increased.  CO was significantly reduced when spray was targeted at the inner surface of the bowl, with a corresponding increase in soot emission. NOx Why Targeting? Optimum Targeting (SOI = - 43 o )  Fuel can be dispersed more effectively when the spray is targeted at a spot where the interaction between the spray and the squish flow is enhanced. Worst Targeting (SOI = - 30 o ) 120° Nozzle