Modified selective non-catalytic reduction system to reduce NOx gas emission in biodiesel powered engines

•A combination of SCR and SNCR systems was designed, manufactured and tested.•The aftertreatment system was tested with distilled water and AdBlue.•Water injection reduced CO and NO gases by ~9% and ~7% for biodiesel fuels.•Urea-water injection reduced CO and NO gases by ~60% and ~13% for fossil diesel.•Urea-water injection reduced CO and NO gases by ~45% and ~15% for biodiesel fuels. Biodiesel fuels releases higher NOx emissions than fossil diesel. The Selective Catalytic Reduction (SCR) technique used in the OEM industry is not suitable for application in small engines due to back pressure and clogging problems. Selective Non-Catalytic Reduction (SNCR) is used in relatively large combustion operations. This study introduces a new design by combining SCR and SNCR systems, for use in low power density diesel engines. The system composed of injection-expansion pipe and swirl chamber. The working principle is maximum mixing of the injected fluid and exhaust gas in the expansion chamber, then creating a maximum turbulence in the swirl chamber. This way NOx emission can be reduced at relatively lower exhaust temperatures without using any catalyst. The CFD models of three design candidates were examined in terms of velocity magnitudes, turbulence intensity and particle residence time. The selected design was manufactured and tested. Distilled water and urea-water solution were injected separately at the same flow rate of 375 ml/min. Exhaust emissions of fossil diesel, sheep fat biodiesel – waste cooking oil biodiesel blend and chicken fat – cottonseed biodiesel blend were tested. No significant changes in CO2 and HC gases were observed. Distilled water injection reduced CO and NO emissions by about 10% and 6% for fossil diesel; and by about 9% and 7% for biodiesels operation respectively. The urea-water injection led to reductions in CO and NO emissions by about 60% and 13% for fossil diesel; and by about 45% and 15% for biodiesels respectively.