Search Results

Exhaust stream from automotives and trucks will be subjected to new and more stringent emissions standards. In the case of Diesel engine the lowering of carbon particulates emission (soot) is based on a filtration system in which trapped soot is periodically removed by controlled oxidation with O2 at 550°C or above. It is known that in presence of NO2 the carbon-O2 reaction is significantly speeded-up. Since NO2 may be formed in the gas stream by catalytical oxidation of NO present in the exhaust stream, it is thought that small amounts of NO2 (500 ppm by vol) will promote the continuous oxidation of the deposited carbon particulates in the temperature range 200 - 500°C. The behaviour of the CRT™ system is based on this principle. Very little is known about the reactivity of soot with NO2. Moreover, the effect of other species present in the exhaust stream like O2 and H2O is also not well established.

Particulates (soot) were sampled from the regenerative trap of an automotive diesel engine run under three speed/load conditions. The fuel was doped with a cerium-based catalyst to promote oxidation of the soot bed. The soots were subjected to combustion testing in a DTG under both temperature ramping and isothermal conditions, and under temperature ramping in a small fixed bed. The combustion gas was 10% oxygen in nitrogen, which was supplemented in the case of the fixed bed with other gases found in diesel exhausts. The temperatures of initiation of combustion Tin were measured in the DTG and in the fixed bed. The kinetic rates of oxidation were calculated from the DTG results taking into account the influence of oxygen transport. The effect of gas composition on ignition and burnout in the fixed bed was determined. Ignition did not occur in the DTG, but rather burning progressed steadily.