Impact of Novel Bio-fuel Components on the Performance of Three-Way Catalysts for Control of SI Engine Emissions

Sreshtha  Sinha Majumdar, Oak Ridge National Laboratory

In conjunction with the design of highly efficient engines, novel biofuel components are being developed to reduce petroleum consumption and lower the carbon footprint of spark ignition (SI) engines. The rigorous environmental regulations for criteria pollutants such as nitrogen oxides (NO_x), non-methane organic gases (NMOG) and carbon monoxide are successfully met by three-way catalysts (TWCs) operating under stoichiometric conditions. Precisely tuned TWCs convert NO_x, NMOG and CO into N₂, CO₂ and H₂O very efficiently. However, TWCs are only active above a critical temperature called the light-off temperature. Below this temperature, during cold-start, the abovementioned regulated pollutants escape from the vehicle exhaust into the atmosphere. As these species are harmful to the environment and are considered as green-house gases, these cold-start emissions are highly undesirable. Therefore, any novel bio-fuel component under consideration must be evaluated in terms of its light-off characteristics on a commercial TWC to ensure that these pollutants do not slip into the environment from the exhaust under the vehicle operating conditions.

In this study, prior to performance evaluation, a commercial three-way catalyst has been hydrothermally aged as per industry guidelines. The light-off behavior of the novel bio-fuel components, down-selected based on their compatibility with existing engine architecture, on the aged TWC has been investigated. A LabVIEW controlled automated reactor fitted with a vapor delivery module, Fourier transform infra-red (FTIR), flame ionization detector (FID) and a mass spectrometer (MS) has been used to conduct and analyze these experiments as per protocol set by industry.  The effect on the catalyst light-off temperature, depending on the functional groups of the fuel components such as alkanes, alkenes, alcohols, ketones, esters, ethers and aromatic hydrocarbons, has been examined. Furthermore, we have explored the effect of the chemical structure of these fuels, whether straight-chained, branched or cyclic, on its light-off profile. The impact on the CO and NO_x conversions based on the specific fuel light-off characteristics has also been investigated.

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