The low-NOx standard for heavy duty trucks proposed by the California Air Resources Board will require rapid warm-up of the aftertreatment system. Several different engine technologies are being considered to meet this need. In this study, a 1-D engine model was first used to evaluate several individual control strategies capable of increasing the exhaust enthalpy and decreasing the engine-out NOx over the initial portion of the cold FTP cycle. The additional fuel consumption resulting from these strategies was also quantified with the model. Next, several of those strategies were combined to create a hypothetical aftertreatment warm-up mode for the engine. The model was then used to evaluate potential benefits of an air gap manifold (AGM) and two different turbine by-pass (TBP) architectures. The geometry of the AGM model was quite detailed, having been constructed from a real prototype design. An equally detailed manifold model consisting of a single thick layer with the thermal properties of cast iron served as the baseline. The AGM provided ~30°C increase in temperature and a 13% increase in enthalpy over the first 300 seconds of the cold FTP, which is only about 20% of the impact of the warm-up mode, but is achieved with no additional fuel consumption. The turbine by-pass concepts were not as effective as the AGM, primarily because the by-pass flow rate must be limited during the early loaded periods of the FTP in order to meet the torque demand of the test.
David Kovacs, Hendrik Rauch, Reza Rezaei, Yinyan Huang, Thomas Harris