A LOW PRESSURE PUMPLESS DEF DOSING SYSTEM BY USING COMPRESSED AIR AND AN AIR ASSISTED DEF INJECTION NOZZLE

This study emphasizes on development of Diesel Exhaust Fluid (DEF) dosing system specifically used in Selective Catalytic Reduction (SCR) of diesel engine for emission control ,where a low pressure pumpless DEF dosing system is developed, utilizing compressed air for pressurizing the DEF tank and discharging DEF through air assisted DEF injection nozzle. SCR systems utilize Diesel Exhaust Fluid (DEF) to convert harmful NOx emissions from diesel engines into harmless nitrogen and water vapor. Factors such as improper storage, handling, or refilling practices can lead to DEF contamination which pose significant operational challenges for SCR systems. Traditional piston-type, diaphragm-type, or gear-type pumps in DEF dosing systems are prone to mechanical failures leading to frequent maintenance, repairs, and costly downtimes for vehicles. To overcome the existing challenges and to create a more reliable and simple DEF delivery mechanism the pumpless DEF Dosing system is developed. The system includes a completely sealed DEF tank, pressurized to a calibrated system pressure, by connecting the tank entry line to compressed air. Signal from the Engine Control Unit is provided to the metering valve positioned in the delivery line which controls the quantity to be dosed. Pressure reducing valve , quick relief valve and pressure sensor for feedback are integrated, with the tank and metering valve to develop a completely reliable DEF dosing system. This system is designed to vent out excess air if pressure is increased and purging of excess DEF during vehicle ignition off condition. The system has been modelled in MATLAB and tested for different operating pressure, height and volume of the tank and by varying the signals provided to the metering unit. Overall we can conclude that the pumpless DEF dosing system is a simplified version among the existing DEF dosing practices. When implemented it provides significant reduction in cost, complexity, repair and maintenance of the system eliminating the challenges and failures posed by the existing pump based dosing systems.