NOx Selective Catalytic Reduction (SCR)-Emission
Technology for India 2009-26-0015
Diesel engines have higher efficiency, better Specific Fuel Consumption (SFC) and lower Hydrocarbon (HC), Carbon monoxide (CO) and Carbon dioxide (CO2) emissions than the gasoline engines owing to higher compression ratios. However, these advantages come with a penalty of higher nitrogen oxides (NOx) generation. NOx is reduced usually by retarding the injection timings at the cost of SFC and higher Particulate Matter (PM) emissions.
Moving towards Bharat Stage-IV (BS-IV) and tighter norms in the subsequent years, the NOx regulations for mobile heavy-duty diesel engines is becoming stringent. This paper presents the work done to meet BS-IV emission norms for its vehicle applications with NOx Selective Catalytic Reduction (SCR) technology.
The influence of SCR system on engine SFC and CO2 levels are investigated along with the effect of high sulphur fuel on system performance. Major PM reduction is carried out through combustion optimisation. SCR system used in the case study injects a eutectic (32.5%) aqueous urea solution in the engine exhaust using an air-assisted dosing system . Tailpipe NOx emissions from the 152 kW BS-III engine were reduced below the BS-IV limits for NOx (3.5 g/kWh) with the SCR system.
The results obtained for the BS-IV engine with SCR show 6% SFC improvement over base BS-III engine. 50% reduction in PM and 70% reduction in the tailpipe NOx was found in European Stationary Cycle (ESC) and European Transient Cycle (ETC) across SCR.
The SCR system was found to be rugged and efficient in operation over a long time. The system performance was not affected with the high sulphur fuel, unlike Diesel Particulate Filters (DPF). Consumption of urea solution for various cycles was investigated. It was observed that the cost of urea over a cycle was offset by the gain in fuel economy due to lower SFC for on-road operating conditions. From the results it was found that SCR technology is an attractive and feasible option for moving towards the upcoming BS-IV and BS-V standards.