Regeneration of diesel particulate filter using sliding discharge
Diesel particulate filter (DPF) is widely used to trap fine soot particles emitted from diesel engines. It can collect particles as small as submicron but it is necessary to oxidize accumulated particles by heating the filter. Temperatures of 600 degree C or higher is required to oxidize the soot but it is difficult to maintain stable reaction because this is exoergic reaction. The filter is sometimes damaged due to thermal runaway of the reaction. To address this trade-off problem, we have studied low temperature regeneration of DPF using sliding discharge, which can be generated on the surface of DPF and produces oxidative species at room temperature. Diesel soot collected by DPF was used. Simulated air consisting of N2 and O2 and not including CO2 or CO was used and CO and CO2 concentration was monitored by real time FTIR to estimate the soot oxidation. All the experiment was carried out at temperatures between 100 and 190 degree C to simulate exhaust temperature under low load. Experimental results show that soot was oxidized by generating sliding discharge on the DPF. No thermal damage of the DPF was found. Energy efficiency, denoted by the amount of oxidized soot per electric energy dissipated in the sliding discharge, increased with increasing the temperature as well as oxygen concentration in the test gas. Small amount of Ag2O supported by the DPF significantly increase the energy efficiency of soot oxidation. On the contrary, excessive amount of Ag2O resulted in energy efficiency lower than that of DPF without Ag2O probably because the sliding discharge was not generated favorably due to high conductivity resulted from metal Ag. These results suggest that sliding discharge can induce soot oxidation and that Ag2O possibly catalyzes soot oxidation.
Impact of Non-Thermal Plasma on Particulate Emissions in Application in a Diesel Engine Exhaust Duct
Particulates and nitrogen oxides comprise the main emission components of the Diesel combustion and therefore are subject to exhaust emission legislation. Yet, with more stringent emission standards and test-procedures, such as in passenger vehicle applications, resulting exhaust gas after-treatment systems are complex and costly. Hence, new technologies for emission control have to be explored. The application of non-thermal plasma (NTP) as a means to perform exhaust gas after-treatment is one such promising technology. One way to generate a NTP is by a corona high-frequency discharge. Apart from few other publications dealing with NTP exhaust gas aftertreatment where a NTP was generated via dielectric barrier discharges (DBD), the experiments in this publication were conducted on an operated series-production Diesel engine with an industrial pilot-type corona ignition system. Originally developed as an alternative for a spark-plug system in SI engines its attributed properties, such as large penetrated volume and high radical concentration, may also be utilized in the exhaust gas stream as it has been done in this publication. To investigate the effects of a corona discharge on Diesel engine emissions, four igniters were integrated in the exhaust duct of a CRDI 2.0 liter engine equipped with DPF. The impact on particle number, size distribution as well as on nitrogen oxides has been studied for various operational parameters of the corona system. The particle number was measured downstream of the DPF to observe the level of improvement for remaining unfiltered nanoparticles. In this first series of tests, a reduction in particle number of up to 10 % was achieved depending on engine load. Particle size distribution was measured upstream of the DPF. In this case, the highest reduction of 10 % was observed in the mid-range particle size of about 60 nm. No increase in other particulate size ranges has been observed.
A comment on thyrotoxic pericarditis.
We read with great pleasure the work by Inami et al. published in a recent issue of the International Journal of Cardiology [1]. The authors have described an interesting case of acute pericarditis triggered by thyrotoxic crisis in Graves' disease. The authors attribute the causation of acute pericarditis to likely an autoimmune mechanism. This has been supported by a comprehensive review of the existing literature (mostly case reports). Autoimmune forms of pericarditis are often recurrent [2]. Non-recurrent forms of acute pericarditis (as previously described by several reports) occurring only during acute thyrotoxic phase may potentially need another causative explanation. In addition to the possible autoimmune or viral causes as authors have described, we believe that a direct metabolic impact exerted by acute thyrotoxicosis possibly also plays an independent contributory role by leading to an alteration in the pericardial fat metabolism. The hypothesis is supported by the fact as the role of cholesterol-laden effusions in hypothyroidism/myxedema is previously well described [3]. In addition to the described ECG findings, we would also like to highlight yet another valuable ECG finding on the provided ECG illustration i.e. a concave JT-segment elevation with a slightly downsloping TP-segment, also now referred to as the Spodick's sign [4–6]. Spodick's sign is present in about 80% of the patients affected with acute pericarditis and is often a give-away to the diagnosis [5,6]. This finding is best visualized in the lead II and sometimes lateral precordial leads. When used along with PR-segment depression, it often serves as an important electrocardiographic tool for distinguishing the acute pericarditis from acute coronary syndrome.