(123f) Low Temperature Oxidation of Carbon Monoxide Produced By Diesel-Ignited Methane Dual Fuel Low Temperature Combustion in a Single-Cylinder Diesel Engine
A persisting challenge in diesel engine combustion is the simultaneous reduction of NOX and smoke emissions. Dual fuel combustion in diesel engines is a promising strategy to that can address this challenge within the engine cylinders. Although this strategy is able to considerably reduce NOX and smoke emissions, it also leads to substantially higher engine-out carbon monoxide (CO) and total unburned hydrocarbons (THC) emissions. Catalytic oxidation of CO and THC in the exhaust tailpipe is further constrained by significantly lower exhaust temperatures compared to conventional diesel combustion. With dual fuel low temperature combustion (LTC), a primary fuel (e.g., methane) is premixed with air and introduced into the combustion chamber. The homogeneous mixture of primary fuel and air is ignited by a small quantity of diesel, the ‘pilot’ or secondary fuel. In general, under certain conditions (optimum injection timing, boost pressure, rail pressure, and percent energy substitution of the primary fuel) we can get better performance and lower NOXand smoke emissions with dual fuel LTC; however, under the same conditions it is also important to minimize the CO and THC emissions.
In the first part of this study, a single-cylinder research engine (SCRE) was operated with methane at an engine load ranging from 2.5 to 10 bar BMEP with a step size of 2.5 bar. The minimum and maximum exhaust temperatures were recorded as 180 °C and 400 °C for 2.5 and 10 bar BMEP, respectively. The highest CO and THC emissions were observed at an exhaust temperature of 180 °C. In the second part of this study, the catalytic oxidation of CO at the temperature range from 180 °C to 400 °C was investigated.With the knowledge that gold nanoparticles with diameters of less than 5nm are very active for the oxidation, a highly active gold catalyst supported on silica was synthesized. The relevant catalyst characterization was conducted using X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Study of the catalytic activity of silica coated gold nanoparticles was carried out by oxidation of CO at the exhaust temperature. We expect to observe high level of CO oxidation (more than 90% conversion) at the minimum exhaust temperature (180 °C) when the exhaust stream contains only CO. The conversion rate will be decreased by adding methane in the exhaust stream. As a result, to have the same level of CO conversion, we have to increase the temperature of the exhaust gas flow.
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