Abstract
Key words:
PZEV(Partial zero emission vehicle), ULEV(Ultra low emission vehicle), TWC(Three way catalyst ), A/F(Air fuel ratio), PGM(Platinum group metal), Spec.(Specification), EOS(Exhaust Oxygen Sensor), LOT(Light off- Temp), LOt(Light off time), NMHC(Non-Methane Hydrocarbon), CCC(Close coupled converter), UCC(Underfloor converter),CPSI(cell per square inch)
Abstract
PZEV emission regulation which is tighter than current ULEVII requires state-of-art aftertreatment technology. Improvement of Engine mainly reducing engine out emission need significant development fee and could adversely impact to the engine performance and fuel economy. This means that converter technology can be good solution for this matters. If the backpressure of converter can be minimized, the effect will be best with respect to lower cost and little compromise to engine performance. TWC system has been used to meet TIER-II/LEV-II regulation. As well known, technology to reduce LOT is still hot issue. Advanced aftertreatment systems had been proposed. Active system still offer complicate mechanization and need high cost control system. Passive system has been investigated in order to substitute conventional TWC but need more study. In this paper the allowable limit value of LOt of TWC will be focused. GMDAT’s recent calculation program (AU-53) showed good correlation with current ULEVII system. This program can be extended to apply to PZEV especially predicting in LOt behavior. In this program cold start region can be divided into three areas, i.e., region 1, 2 and 3. Region 1 was hard to simulate with any other engine factors because it is open loop control which only depend on RPM and intake boost pressure. Region 2, from initiation point of EOS to before 20 second, can be calculated mainly by the RPM, A/F and catalyst oxidation energy. Region 3, from 20 second to the top of 1st peak (30sec), used factors like RPM and catalyst oxidation energy as A/F had merged to stoichiometric value. In calculating catalyst oxidation energy we assumed propane as a model gas in NMHC. Only CCC type catalyst (even though CCC+UCC system may be the production solution) was used in calculation due to little contribution of UCC on cold start. In program AU-53, lots of factors were requested as input data like engine RPM, A/F, engine displacement, catalyst loading , ratio and even cell density. By the modulating these values, we could take on final LOt which met target value set down from previous vehicle program. In this regard we could finally propose optimized configuration of catalyst system in cost and detail spec. like PGM loading, ratio and cell density. Further programming study including more specs. of catalyst elements can give rise to an opportunity to enhance better prediction.