Homogeneous oxidation of light alkanes in the exhaust of turbocharged lean-burn gas engines

Abstract

This study investigates hydrocarbon abatement from exhaust of lean-burn gas engines through homogeneous oxidation reactions by combining experiments and modeling under ambient pressure and pre-turbine conditions. The effect of pressure, temperature, net concentration of NOx, and NO/NO2 ratio were studied experimentally over the temperature range of 450–650 °C with gas compositions, which are typical for lean-burn gas engines, representing either a high methane or a high NOx slip. The results obtained by the lab-bench experiments and modeling revealed, that high pressure up to 5 bar and elevated temperatures (>550 °C) are imperative to exploit gas phase reactions for exhaust gas after-treatment. The presence of the exhaust gas component NOx significantly promotes the homogeneous oxidation of light alkanes.The experimental results were interpreted in terms of two different detailed kinetic models. Comparison of simulated concentration profiles with the experimental measurements indicate that the homogeneous kinetics can be modeled using both mechanisms with reasonable accuracy to find the convenient exhaust conditions needed for minimized hydrocarbon emissions. The reactor model used for this study is evaluated based on results derived from a CSTR-cascade approach, which accounts for nonideal conditions in practical applications.Moreover, it was found that typical catalyst poisons such as SO2 do not affect the gas phase reaction. Hence, the results presented in this study demonstrate, that an accurate choice of proper reaction conditions make oxidation catalysts partially redundant. This is of tremendous importance for stationary and large-bore gas engines typically operated under the conditions investigated.