Assessment of Water Injection in a Heavy-Duty Diesel Engine for NOx Reduction Potential 2019-26-0145
Diesel engine pollutants include Oxides of Nitrogen (NOx) and Particulate Matter (PM) which are traditionally known for their trade-off characteristics. It has been a challenge to reduce both pollutants at the source simultaneously, except by efforts through low temperature combustion concepts. NOx formation is dependent on the combustion temperature and thus the in-cylinder reduction of NOx formation remains of utmost importance. In this regard, water injection into the intake of a heavy-duty diesel engine to reduce peak combustion temperature and thereby reducing NOx is found to be a promising technology.
Current work involves the use of 1-D thermodynamic simulation using AVL BOOST for modeling the engine performance with water injection. Mixing Controlled Combustion (MCC) model was used which can model the emissions. Initially, the model validation without the water injector was carried out with experimental data. Further to this, the water injector module was integrated and the simulation model was used to derive the injection quantity of water to give a targeted NOx reduction of 15%. 3D CFD analysis using CONVERGE was carried out in-order to assess the water spray characteristics. A selection of water injector based on the required injection quantity was carried out and engine experiments were carried out based on the recommendations of the simulation results. European Steady-state Cycle (ESC) and European Transient Cycle (ETC) emissions were carried out using water injection to assess the potential emission reduction.
Water to fuel ratio was varied from 3 to 16% in-order to study the impact on NOx reduction. Results of CFD study showed placement of water injector in the intake air pipe down-stream the EGR mixing point helps to improve the evaporation characteristics of water spray. Engine experiment results show reduction of up to 13% NOx by use of 16% water to fuel ratio in ESC cycle and up to 7% reduction in ETC cycle. Use of higher quantity of water is limited by droplet size of water spray and thus tends to increase the soot emissions. It is recommended to use water to fuel ratio in the range of 3-16% in-order to avoid the NOx-PM trade off.