*Article* **Numerical Analysis of NOx Reduction Using Ammonia Injection and Comparison with Water Injection**

### **María Isabel Lamas Galdo 1,\*, Laura Castro-Santos 1 and Carlos G. Rodriguez Vidal 2**


**\*** Correspondence: isabel.lamas.galdo@udc.es; Tel.: +34-881013896

Received: 8 January 2020; Accepted: 7 February 2020; Published: 11 February 2020

**Abstract:** This work analyzes NOx reduction in a marine diesel engine using ammonia injection directly into the cylinder and compares this procedure with water injection. A numerical model based on the so-called inert species method was applied. It was verified that ammonia injection can provide almost 80% NOx reduction for the conditions analyzed. Furthermore, it was found that the e ffectiveness of the chemical e ffect using ammonia is extremely dependent on the injection timing. The optimum NOx reduction was obtained when ammonia is injected during the expansion stroke, while the optimum injection timing using water is near top dead center. Chemical, thermal, and dilution e ffects of both ammonia and water injection were compared. The chemical e ffect was dominant in the case of ammonia injection. On the other hand, water injection reduces NOx through dilution and, more significantly, through a thermal e ffect.

**Keywords:** CFD; NOx; engine; ammonia; water injection
