Comprehensive Characterization of the Behavior of a Diesel Oxidation Catalyst Used on a Dual-Fuel Engine

Abstract

Aim of this work is the evaluation of thermal behavior and performance of a conventional diesel oxidation catalyst (DOC) installed on an engine operating in dual-fuel diesel-methane conditions following a well-defined methodology conceived ad hoc. A catalyst was sized, realized, and instrumented with five thermocouples. Once mounted along the engine exhaust line, the test was run in order to determine several parameters characterizing the DOC behavior, such as downstream emission levels, conversion efficiency, thermal behavior, and light-off temperature. Tests have been performed varying the engine speed and substitution ratio in order to analyze the effect of these operating parameters on the behavior of the catalyst. The results indicate that, in dual-fuel conditions, the oxidation of species takes place in zones closer to the exit section, determining temperatures higher than those measured in conventional diesel combustion conditions at the same engine load. The light-off temperatures related to the conversion efficiency of unburned hydrocarbons and carbon monoxide both increase in dual-fuel conditions. The effect of substitution ratio results from the combined effects on combustion development together with engine-out concentration of long-chain and short-chain unburned hydrocarbons. The resulting effect is, on one hand, the reduction of unburned hydrocarbons light-off temperature as methane increases. On the other hand, carbon monoxide light-off temperature increases as methane increases due to the increased amount of engine-out hydrocarbons emissions. The reduction of engine speed determines the reduction of the temperature of the exhaust gases to the extent that the light-off conditions are sometimes not reached. Finally, a sensitivity analysis base on neural networks showed that, while less variables are sufficient for describing the behavior, in terms of carbon monoxide conversion efficiency, of a DOC mounted on an engine working in dual-fuel diesel-methane conditions, in case of unburned hydrocarbons conversion a set of more variables is required.