Modified Selective Non-Catalytic Reduction System to Reduce NOx Gas Emission in Biodiesel Powered Engines

Biodiesel is considered as one of the attractive alternatives to fossil diesel fuel. Although biodiesels reduces most of the harmful gas emissions, they normally releases higher NOx emissions compared to fossil diesel. The Selective Catalytic Reduction (SCR) is a well-known technique used in the OEM industry to mitigate NOx emission. However, this technique may not be suitable for application in low power density engines due to back pressure and clogging issues. On the other hand, Selective Non-Catalytic Reduction (SNCR) is used in relatively large combustion operations ie. boilers and incinerators. The main disadvantage of SNCR technique is the high temperature window for diesel engine exhaust temperature. This study introduces a new design concept, which is a combination of SCR and SNCR systems, for low power density diesel engines. The developed after-treatment system composed of two main parts, injection-expansion pipe and swirl chamber. The working principle is providing maximum mixing of the injected fluid and exhaust gas in the expansion chamber, then creating a maximum turbulence in the swirl chamber. In this regard, 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 to select the optimum physical dimensions. The selected design was manufactured and installed to exhaust system of a 1.3 litre diesel engine. Two fluids distilled water and urea-water solution were injected separately at the same flow rate of 375 ml/min. Exhaust gas 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 emissions were observed. However, it was found that 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.