Holistic Engine and EAT Development of Low NOx and CO2 Concepts for HD Diesel Engine Applications

Abstract

The latest legislative tendencies for on-highway heavy duty vehicles in the United States such as the feasibility assessment of low NO_X standards of CARB or EPA?s memorandum forecast further tightening of the NO_X 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 NO_X 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 NO_X-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 NO_X-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.