HC Emissions and Diesel Oxidation Catalyst Characterization when Burning a Low RON Gasoline Fuel in a Compression Ignition Engine
Christophe Chaillou, Aramco
To improve both criteria pollutants and GHG emissions in the transport sector, many researches are conducted on fuel and internal combustion engine. Burning gasoline-like fuels in compression ignition engines is an encouraging way for both NOx and particulate emissions abatement while keeping lower tailpipe CO2 emissions. These gains are obtained from combustion process, physical and chemical properties of the low RON gasoline.
New fuel/engine technology needs investigations of both pollutants and after-treatment systems. Previous works studied soot behavior to define the rules of the Diesel Particulate Filter (DPF) design when used with a low RON gasoline in a compression ignition engine. This new study objective is to assess the impact of such fuel/engine technology on the Diesel Oxidation Catalyst (DOC). Hydrocarbon (HC) speciation is performed upstream and downstream of the DOC. DOC light-off during warm-up conditions and efficiency for stabilized engine operating conditions are investigated. To finish, exothermal capacities of the DOC are considered to guarantee sufficient temperature levels for DPF soot regeneration.
Upstream and downstream DOC HC speciation showed heavier molecules for Diesel fuel compared to low RON gasoline. Carbon balance is higher for low RON gasoline. These two results are consistent with HC fuel composition and impact DOC HC storage. Upstream DOC main HC family is olefin for Diesel while it appears to be paraffin from low RON gasoline. Regardless of the fuel, upstream DOC HC species are mainly C1 to C4 and methane is the major downstream molecule.
For steady hot conditions, conversion efficiency of HC and CO for both fuels are quite similar. Warm-up tests show different DOC behavior between the two fuels. Due to high amounts of HC and CO for low RON gasoline combustion, the catalyst appears to be poisoned and light-off temperatures are higher than Diesel ones. Moreover, the HC storage period, during the light-off phase, is shorter when using low RON gasoline. Both HC species difference and higher HC levels could explain this lower storage performance.
Lastly, DPF soot regeneration is possible through DOC exotherm with low RON gasoline post-injections. For a same fuel quantity injection, low RON gasoline generates higher upstream DOC HC amount and higher exotherms than Diesel.
Even with some differences in the fuel composition and in the HC species between Diesel and low RON gasoline fuels, steady conversion efficiency and DOC exotherm for soot regeneration are comparable. However, for warm-up and light-off characteristics, differences are highlighted between both fuels. HC-storage during a warm-up phase appears to be different and more investigations are needed to design an optimal DOC used with gasoline-like fuels burned in a compression ignition engine.