Enhancing the NO2/NOx ratio in compression ignition engines by hydrogen and reformate combustion, for improved aftertreatment performance

Enhanced NO2 production (without raising total NOx) in a diesel engine combustion chamber can improve the performance of several catalytic aftertreatment systems. Thus this can facilitate a further reduction in key regulated emissions such as nitrogen oxides (NOx) and particulate matter (PM) emissions. The oxidation of NO to NO2 is an important intermediate step involved in all current aftertreatment systems that are designed for NOx and PM catalytic removal. The performance of both NOx control systems and catalysed particulate filters depend highly on the NO2 concentration. In this work we have examined the influence of using hydrogen (H2) and simulated reformate (H2, CO and EGR gases) as a supplement to diesel fuel on NO2 production. In actual engine applications a reformer will be integrated within the engine EGR system. This will not only provide the engine with recirculated exhaust gas (i.e. EGR), but will enrich it with H2 and CO. The effects of adding H2 or reformate results in a significant decrease in total engine-out NOx emissions, as well as an increase in both NO2 concentration and NO2/NOx ratio. The influence of the simulated reformate combustion on the NO2 production is dependent on the engine load and in-cylinder conditions. It was observed that both reformate composition and concentration significantly influence the NO2/NOx ratio of the exhaust gas. Air/fuel ratio, combustion efficiency and in-cylinder temperatures were the most influential parameters in this study. The NO2 production was dependent on the EGR addition and air/fuel ratio

Effect of composite aftertreatment catalyst on alkane, alkene and monocyclic aromatic emissions from an HCCI/SI gasoline engine

Designing automotive catalysts for effective control of NOx, HC and CO emissions under both lean and stoichiometric engine operation is a challenging task. The present work assesses the performance efficiency of a three-zone prototype catalytic convertor in reducing exhaust emissions from a gasoline engine, operating in Homogeneous Charge Compression Ignition (HCCI) and Spark Ignition (SI) mode under lean and stoichiometric conditions. The performance of the convertor for HC oxidation follows the order: lean HCCI > stoichiometric SI > stoichiometric HCCI. The study mainly focused on the quantitative analysis of C1–C7 hydrocarbon compounds before and after the catalytic convertor. The results show that monocyclic aromatic hydrocarbons such as toluene are present at higher concentrations in the exhaust under HCCI operation than in the SI case. On the other hand, benzene concentrations are higher in the SI exhaust. The most common exhaust products of the two engine operating modes are methane, ethylene, propylene, benzene, and toluene. The prototype catalytic convertor eliminates most of the hydrocarbon species in the exhaust under both combustion modes, especially with a lean mixture. Conversion efficiencies for the different hydrocarbon species over the catalyst were in the order of alkenes > alkanes > aromatics. Hydrogen was added upstream of the catalyst primarily to assess its ability to promote NOx reduction, however it was also found to influence the oxidation characteristics of the catalyst. During H2 addition, the methane concentration was higher downstream of the catalyst