Optimization of soot deposition by high-temperature prepolarization of a resistive particulate matter sensor

For the purposes of the onboard diagnosis (OBD) of diesel particulate filters (DPFs) in diesel exhaust treatment systems, a particulate matter (PM) sensor is applied downstream from the DPFs to detect small amounts of diesel soot that passed through the filter. The state-of-the-art technology is a sensor based on the resistive measurement principle, i.e., charged soot particles are attracted by electrophoretic forces, deposited on an interdigital electrode (IDE) structure and conductive soot bridges that reduce the overall resistance are formed. This paper reports how the response time of a resistively working particulate matter sensor can be shortened up to 30 % by the optimization of soot deposition that is initiated by a change in the sensor operation strategy. The measurement voltage is applied for prepolarization during the sensor regeneration phase rather than during the cooling phase before the measurement is commonly done. Experiments were performed at diesel engine test benches to examine this context and simulations of the electric field above and below the IDE structure. The data are used to deduct a model, including the solid state chemistry of the sensor's ceramic materials, the effect of impurities on the electric field properties and the interconnection with the soot deposition, which defines the sensor's response.

New Experiment of Diesel Exhaust Treatment by Atmospheric Pressure Plasma–Wood Fiber Combination

Herein, a novel process of diesel exhaust purification by non-thermal plasma combined with wood fiber has been investigated to understand the effect of purification efficiency on the emission. The dielectric barrier discharge (DBD) and wood fiber (WF) improved removal efficiency of nitrogen oxide (NOx) owing to the positive activity of oxygen-containing functional groups (such as O–H groups or C–O groups) on the wood surface, which promoted the removal of NOx by 10%–13%. The mechanism to remove NOx in the presence of wood fibers was also deduced through FTIR spectra. When carbon black was loaded on the wood fiber, there was simultaneous removal of carbon soot and NOX. Although complete purification was not achieved, a high purification efficiency was obtained under the conditions of room temperature and no catalysts. These advantages highlight the importance of use of wood and non-thermal plasma (NTP), and this research work opens new avenues in the field of emissions treatment.

Heat pump drying of industrial wastewater sludge

The popularity of heat drying of wastewater sludge has increased over the past several years because it can reduce sludge mass and volume, and hence disposal costs. However, drying sludge using conventional combustion-heated dryers is energy-intensive. Heat pump dryers can be efficient and offer significant energy savings by recycling the drying heat. This paper describes a heat pump dryer designed for continuous drying of industrial wastewater sludge. The dryer constructed was essentially a closed-loop air system. The air used for drying is dehumidified to recover the latent heat of vaporization, re-heated using the recovered heat, and recirculated in a closed environment. The closed-loop layout eliminates emissions of dust, malodorous gases, and volatile compounds, obviating the need for exhaust treatment otherwise required to meet environmental regulations. Data on the moisture extraction rate, specific moisture extraction rate, and specific energy consumption are presented and discussed.