Development of a New Engine Control Concept to Help Achieve Light-Duty Euro V Emissions, 03-9387Printer Friendly Version
Inclusive Dates: 04/01/03 - 04/01/04
Background - Light-duty diesel engine powered vehicles will rely on catalysts and traps working synergistically with in-cylinder controls to achieve future emissions regulations in Europe and the United States. Lean NOx traps (LNT) and diesel particulate filters (DPF) have shown much promise to reduce oxides of nitrogen (NOx) and particulate matter (PM) emissions from this class of diesel engines. However, during a small fraction of the operating cycle (perhaps 5 percent) of a light-duty diesel vehicle, both the NOx and PM exhaust treatment systems require higher than typical exhaust temperatures for regeneration and removing unwanted stored sulfur species. Further, for LNTs, fuel-rich operation is required for a small fraction of the time to release and convert the NOx and sulfur trapped in the catalyst. The standard approach of achieving these conditions, spraying fuel into the exhaust, has many disadvantages.
Approach - This project focused on in-cylinder controls to achieve the necessary conditions for regeneration of the exhaust treatment devices (rich and high temperatures). The objective of this internal research project was to establish a new combustion technology that provides high exhaust gas temperatures and rich air-fuel ratios for an exhaust treatment system of a light-duty diesel engine. A PSA DW10 2L engine under full-authority control with the Institute rapid prototyping electronic control system (RPECS) was used for this development program. A strategy using a single advanced injection and high levels of exhaust gas recirculation (EGR), called low-temperature combustion (LTC), was used at light loads for lean and rich operation. Rich combustion was obtained at mid loads with corresponding low smoke by using a variant of diesel combustion called premixed controlled compression ignition (PCCI).
Accomplishments - SwRI demonstrated the LTC concept and documented the advantages of LTC lean and LTC rich control at light loads for clean combustion (NOx-less and smoke-less) and high exhaust temperatures needed to maintain the LNT in the optimal temperature range (250 to 400 °C). Minimizing the excess air and providing suitable amounts of CO and HC during LTC lean operation result in an exotherm over the oxidation catalyst and DPF, thereby providing high temperature gases for the LNT. Refinement of the PCCI concept allowed for periodic rich combustion at mid loads without use of a post injection. A dual-loop EGR system, for which an invention disclosure was filed, allowed for sufficient EGR flow and temperature control. These combustion concepts, while partly reducing engine-out emissions, also provided the proper air-fuel ratio and gas temperatures to allow effective use of LNT and DPF exhaust treatment devices required for future European and domestic emissions regulations. A new approach to determine the amount of excess fuel required for a given NOx conversion on a LNT was demonstrated based upon the unique operating characteristics of LTC lean operation in which the engine-out NOx levels are nearly zero.