Kwang Min Chun

Plasma/catalyst system for reduction of NOx in diesel engine exhaust

PURPOSE: A plasma catalytic system is provided to efficiently remove NOx from exhaust gas discharged from a diesel engine by using a plasma reactor and a catalytic reactor. CONSTITUTION: A plasma catalytic system is comprised of a plasma reactor(11) supplied with DC pulse power and a catalytic reactor(12) filled with Ag and Al2O3. Exhaust gas generated from a diesel engine is treated by sequentially passing through the plasma reactor and the catalytic reactor. The plasma reactor consists of an anode and a cathode and supplies energy of 10-100J/L per unit flux of exhaust gas. The catalytic reactor is filled with a catalyst prepared by impregnating AgNO3 aqueous solution in gamma-Al2O3. The plasma reactor is operated in a normal pressure while the catalytic reactor is operated at 200-450deg.C of temperature. In the plasma reactor, NO in the exhaust gas is converted to NO2. In the catalytic reactor, NO2 is reduced to N2. Therefore, NOx in the exhaust gas is reduced.

Plasma/catalyst system for reduction of NOx in lean conditions

NOx conversion to N2 was investigated by a plasma/catalyst system in rich oxygen similar to a lean-burn engine exhaust. Catalytic activity was enhanced by the assistance of plasma, and the plasma/catalyst system showed higher NOx conversion over a wider temperature window than did catalyst alone. The plasma/catalyst (Ag/Al2O3) system showed a remarkable improvement in NOx conversion in the lower temperature range under 400 °C. The NOx conversion of plasma/catalyst (Ag/Al2O3) was 40%–50%, and its selectivity to N2 was over 96% under the conditions that the hydrocarbon (C1 base) to NOx ratio was about 3 and 10% O2 existed over the temperature range of 300–500 °C. Ag/Al2O3 showed a better performance than Al2O3 when assisted by plasma. Helium was used as a balance gas to measure N2 formation by gas chromatography, and NOx conversion was measured by a chemiluminescence NOx analyzer in N2 balance as well as He balance. The result in N2 balance gas was compared with the result in helium balance gas at the 300 °C where the largest enhancement by plasma was observed. The NOx conversion in N2 balance gas was similar to that in helium balance gas, which verified that the plasma effect obtained in helium balance gas is consistent with that of N2 balance gas, which is the largest component of the real exhaust gas.

Development of a Real-Time, In-Situ Particle Sizing Technique: Real-Time Light Transmission Spectroscopy (RTLTS)

We developed an improved particle measurement spectroscopic technique, real-time laser transmission spectroscopy (RTLTS), to detect the number-weighted distribution of particles in real time. The measurement system used a deuterium–tungsten lamp for the light source and a spectrometer as the detector. The operating wavelength range was 300–810 nm. To obtain a physically reasonable number concentration from the experimental results, a sequential regularization method was used during the calculations. To verify the feasibility and reliability of RTLTS, the number-weighted distribution of polystyrene particle suspensions was determined over diameters ranging from 0.005 to 2.000 μm in 0.005-μm increments. The measured concentration error was 0.67–32.67%. A mean diameter of the smallest particle we had detected was 0.09 μm, with a 16% oversizing. The measurable concentration range was ∼108 #/cc to ∼1011 #/cc for 0.895-μm-diameter particles. The measurable concentration range could be adjusted simply by changing the system configuration. This technique is available for both waterborne and airborne particles. Copyright 2013 American Association for Aerosol Research

An Experimental Investigation on Low Temperature CDPF Regeneration Utilizing Hydrogen

Soot particles accumulated in a DPF should be removed after a certain service time due to high pressure drop. The most common method is oxygen active regeneration which causes high fuel penalty and sometimes DPF cracking or melting. In this study, the authors aim to investigate the low temperature regeneration with hydrogen, which could prolong the DPF lifespan and facilitate CDPF regeneration efficiency. The DPF used in this research was coated with Pt/Al₂O₃ 25g/ft³ and all experiments were performed on engine test bench. Results showed that hydrogen in exhaust gas can be ignited at about 120℃ and regeneration can be realized at about150℃ or even lower. There was a large temperature drop (about 40℃) at the front end of DPF after hydrogen oxidized. DPF maximum inside temperatures depend on the hydrogen concentration. Therefore, the DPF maximum inside temperature can be controlled by the supplied hydrogen concentrations.

An Experimental Study on the Possibility of Biogas Reforming using the Waste Heat of a Small-Sized Gas Engine Generator

This study has been carried out the experiment for the possibility of biogas reforming using waste heat. The source of this waste heat is the exhaust gas from a small-sized gas engine generator. For recovering the waste heat, Two-stage heat exchanger is manufactured. The two-stage heat exchanger is composed of a heat exchanger for the exhaust gas and a heat exchanger for the water. This two-stage heat exchanger is used for reforming the biogas by means of on-site hydrogen production at the small-sized gas engine generator. The two-stage heat exchanger is coupled with the biogas reformer which is a kind of catalytic reformer. To confirm a heat recovery efficiency of the two-stage heat exchanger, temperature differences of inlet and outlet locations are measured. Also, the variations of syngas concentrations with various biogas flow rates are investigated. As a result using manufactured two-stage heat exchanger, the biogas can be reformed from waste heat recovery. This experiment suggests that the exhaust gas heat exchanger is available for reforming the biogas.