Non-thermal Plasma System for Marine Diesel Engine Emission Control

Abstract

A non-thermal plasma reactor (NTPR) using two 2.45 GHz Microwave (MW) generators for the abatement of Nitrogen Oxides (NOx) and Sulphur (SOx) contained in the exhaust gas of a 200 kW marine diesel engine was built and tested. Numerical analysis based on a non-thermal plasma kinetics model for the abatement of NOx and SOx from marine diesel engine exhaust gas was performed. A generic kinetic model that implements electron collisions and plasma chemistry has been developed for applications involving low temperature (50K – 100K) non-thermal plasma. Abatement efficiencies of NOx and SOx were investigated for a range of mean electron energies which directly impact on the rate constants of electron collisions. The simulation was conducted using the expected composition of exhaust gas from a typical two-stroke slow speed marine diesel engine. The simulation results predict that mean electron energy of 0.25eV-3.2eV gives abatement efficiency of 99% for NOx and SOx. The minimum residence time required was found to be 80ns for the mean electron energy was 1eV. Multi-mode cavity was designed using COMSOL multi-physics. The NTPR performance in terms of NOx and SOx removal was experimentally tested using the exhaust from a 2 kW lab scale two stroke diesel engine. The experimental results also show that complete removal of NO is possible with the microwave plasma (yellow in color) generated. However it was found that generating right Microwave plasma is a challenging task and requires further investigation.