Southwest Research Institute engineers have developed the next generation of clean diesel engine technology to reduce hazardous nitrogen oxides (NO_x) and carbon dioxide emissions while minimizing fuel consumption.

Working with regulatory agencies, vehicle manufacturers and suppliers, SwRI combined engine modifications with integrated aftertreatment technology and control strategies to reach near-zero emissions levels (0.02 g/hp-hr NO_x emissions). SwRI developed the technology for the California Air Resources Board (CARB). The work is described in a pair of SAE Technical Papers.

SwRI combined engine modifications with integrated aftertreatment technology and control strategies to reach near-zero emissions levels.

Through the continued efforts of a multidisciplinary team, SwRI has developed one of the most fuel-efficient, low-emission diesel engines in the world. Created to address California’s pollution challenges, this technology could be a solution for communities around the globe dealing with the effects of NO_x.

—SwRI Research Engineer Bryan Zavala, a member of the low NO_x development team

According to the Environmental Protection Agency, nitrogen oxides are harmful to human health and the environment. The State of California plans to enact tighter emissions standards in 2024 and will require that heavy-duty engines produce less pollutants. Taking a systems approach to address the problem, SwRI engineers met CARB’s stringent emissions goals to reduce NO_x by 90% while simultaneously lowering carbon dioxide emissions.

The low NO_x technology developed at SwRI illustrates significant strides toward improving today’s heavy-duty engines and lowering greenhouse gas emissions. These types of simultaneous NO_x and greenhouse gas solutions are key to creating sustainable heavy-duty transportation and meeting our public health obligations.

—CARB Vehicle Program Specialist Dr. William Robertson

In 2013, CARB contracted SwRI to investigate potential approaches for achieving an ultra-low NO_x target in three stages.

• The Stage 1 program focused on achieving the Ultra-Low NO_x (ULN) levels utilizing a turbo-compound (TC) engine, which required the integration of novel catalyst technologies and a supplemental heat source. While the aftertreatment configuration provided a potential solution to meet the ULN target, a complicated approach was required to overcome challenges from low temperature exhaust.

• In stage two, SwRI engineers developed a low-load certification cycle to gauge the performance of engine aftertreatment systems in low-load conditions, such as while idling.

• The Stage 3 program leverages a different engine architecture more representative of the broader heavy-duty industry to meet Greenhouse Gas (GHG) targets and to simplify the ULN aftertreatment solution. Stage three, which is ongoing, has consisted of developing the near-zero emissions technology and evaluating it. Engineers modified a 2017 Cummins X15 engine architecture, integrated aftertreatment technology and enhanced controls to produce the desired results.

  SwRI had implemented a model-based controller for the Selective Catalytic Reduction (SCR) system in the CARB Stage 1 program. The chemical kinetics for the model-based controller were further tuned and implemented in order to accurately represent the reactions for the catalysts used in Stage 3. Novel dosing, and ammonia storage management strategies augmented with the model-based controls was critical in achieving the objectives.

Making a relevant impact on pollutants requires a whole system approach. Throughout the program, we have had an open dialogue with regulatory agencies, vehicle manufacturers and suppliers to evaluate the feasibility of a new low NO_x standard.

—Bryan Zavala

SwRI continues to evaluate the system and its NO_x reduction performance under realistic operating conditions such as hydrothermal stress and catalyst contamination to validate real-world performance. Final results are expected in summer 2020.

Resources

• Zavala, B., Sharp, C., Neely, G., and Rao, S. (2020) “CARB Low NO_x Stage 3 Program - Aftertreatment Evaluation and Down Selection,” SAE Technical Paper 2020-01-1402 doi: 10.4271/2020-01-1402.

• Rao, S., Sarlashkar, J., Rengarajan, S., Sharp, C. et al. (2020) “A Controls Overview on Achieving Ultra-Low NO_x,” SAE Technical Paper 2020-01-1404 doi: 10.4271/2020-01-1404.