Diesel Dynamic Skip Fire (dDSF®): Simultaneous CO₂ and NOₓ Emissions Reduction

Authors

L. Farrell PhD, T. Frazier PhD, Cummins Inc., Columbus, USA;
M. Younkins PhD, J. Fuerst, MBA BSME, Tula Technology Inc., San Jose, USA

Year

2020

Print Info

Fortschritt-Berichte VDI, Reihe 12, Nr. 813

Summary

Reductions in CO₂ and NO_x tailpipe emissions present conflicting challenges for diesel engines as worldwide standards continue to become more stringent. Dynamic Skip Fire (DSF^®), in production on SI V8 engines, has potential in diesel commercial vehicles as dDSF to provide benefits in reducing both CO₂ and NO_x emissions simultaneously.
DSF is an advanced cylinder deactivation technology which enables any number of cylinders to be dynamically selected to operate on an event by event basis. Noise, vibration and harshness (NVH) is proactively mitigated by manipulating the firing sequence and cylinder loading to avoid vehicle resonances.
Cummins and Tula embarked on a development project to demonstrate the benefits of dDSF technology for diesel engines in commercial vehicle applications to reduce emissions and control NVH. The development work has been carried out on a 15-liter Cummins X15 6-cylinder diesel engine. The engine and controller have been modified to integrate Tula’s Dynamic Skip Fire control algorithms, to command combustion or deactivation, on a cylinder event basis. Test data has been collected on a wide range of steady-state conditions which was used to evaluate transient operation in simulation. Evaluations of CO₂ and NO_x tailpipe emissions benefits have been conducted on both a Heavy-Duty FTP test cycle and the Low-Load Cycle (LLC #7) proposed by California Air Resources Board (CARB) for their upcoming rulemaking. dDSF is under development for possible future product application. Further work is required to determine whether the technology can meet durability, reliability and cost targets for future products.
On the HD FTP cycle, dDSF technology modeling predicted reductions of NO_x emissions by 45% while simultaneously reducing CO₂ by 1.5%. On the proposed LLC #7, dDSF technology modeling predicted reductions of tailpipe NO_x emissions by 66% while simultaneously reducing by CO₂ by 4%. Further reductions in NO_x emissions should be achievable with the addition of increased conventional thermal management over the cycles with a reduction in the CO₂ benefit. The reduction of tailpipe NO_x is achieved primarily by optimized exhaust temperature control, resulting in improved conversion efficiency of the Selective Catalytic Reduction after-treatment system. The CO₂ reductions are achieved primarily through reductions in pumping losses. Cylinder deactivation thus allows for additional trade-off opportunities for reductions of CO₂ and NO_x emissions.