Holistic Engine and EAT Development of Low NOx and CO2 Concepts for HD Diesel Engine Applications
The latest legislative tendencies for on-highway heavy duty vehicles in the United States such as the feasibility assessment of low NOX standards of CARB or EPA?s memorandum forecast further tightening of the NOX emissions limits. In addition, the GHG Phase 2 legislation and also phased-in regulations in the EU enforce a continuous reduction in CO2 emissions resp. fuel consumption. In order to meet such low NOX emission limits, a rapid heat-up of the exhaust after-treatment system (EATS) is inevitable. However, the required thermal management results in increased fuel consumption, i.e. CO2 emissions as shown in numerous previous works also by the authors. A NOX-CO2 trade-off for cumulative cycle emissions can be observed, which can be optimized by using more advance technologies on the engine and/or on the EATS side.
In the present study a systematic investigation is carried out by means of model-based holistic approach targeting the definition of a high efficiency engine layout and optimal thermal management calibration. First, the potentials of combustion process optimization (compression ratio, peak firing pressure) and of turbocharger efficiency increase are quantified aiming engine efficiency increase. Afterwards, using holistic engine and EAT concept development approach, conventional and advanced EATS layouts are tested. The advanced EATS layout consist of a close-coupled dual-stage SCR system. In order to explore the benefits of each layouts, the engine heat-up calibrations are varied and the resulting, cumulative NOX-CO2 emissions of the investigated cycle are compared and evaluated. Multiple improvement measures for both engine and EAT system are discussed and an outlook of future powertrain concepts is given.