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An experimental study was performed to develop a more fundamental understanding of the effects of secondary air injection (SAI) on exhaust gas emissions and catalyst light-off characteristics during cold start of a modern SI engine. The effects of engine operating parameters and various secondary air injection strategies such as spark retardation, fuel enrichment, secondary air injection location and air flow rate were investigated to understand the mixing, heat loss, and thermal and catalytic oxidation processes associated with SAI. Time-resolved HC, CO and CO₂ concentrations were tracked from the cylinder exit to the catalytic converter outlet and converted to time-resolved mass emissions by applying an instantaneous exhaust mass flow rate model. A phenomenological model of exhaust heat transfer combined with the gas composition analysis was also developed to define the thermal and chemical energy state of the exhaust gas with SAI.

Diesel particulate filters are designed to reduce the mass emissions of diesel particulate matter and have been proven to be effective in this respect. Not much is known, however, about their effects on other unregulated chemical species. This study utilized source dilution sampling techniques to evaluate the effects of a catalyzed diesel particulate filter on a wide spectrum of chemical emissions from a heavy-duty diesel engine. The species analyzed included both criteria and unregulated compounds such as particulate matter (PM), carbon monoxide (CO), hydrocarbons (HC), inorganic ions, trace metallic compounds, elemental and organic carbon (EC and OC), polycyclic aromatic hydrocarbons (PAHs), and other organic compounds. Results showed a significant reduction for the emissions of PM mass, CO, HC, metals, EC, OC, and PAHs.

Selective catalytic reduction (SCR) of nitrogen oxides (NOx) is used in diesel-fueled mobile applications where urea is an added reducing agent. We show that the Ultera® dual-stage catalyst, with intercooling aftertreatment system, intrinsically performs the function of the SCR method in nominally stoichiometric gasoline vehicle engines without the need for an added reductant. We present that NOx is reduced during the low-temperature operation of the dual-stage system, benefiting from the typically periodic transient operation (acceleration and decelerations) with the associated swing in the air/fuel ratio (AFR) inherent in mobile applications, as commonly expected and observed in real driving. The primary objective of the dual-stage aftertreatment system is to remove non-methane organic gases (NMOG) and carbon monoxide (CO) slip from the vehicle’s three-way catalyst (TWC) by oxidizing these constituents in the second stage catalyst.

The awareness concerning environmental issues and the economical need for fuel savings leads to the introduction of new, highly efficient Diesel engines for passenger cars. An engine with common rail injection system could meet this target and, with the help of an advanced diesel exhaust aftertreatment system also fulfilled the new legislative emission regulations. Besides the efficient oxidation of carbon monoxide (CO), hydrocarbons (HC) and diesel particulates, such a system also requires a moderate reduction efficiency for nitrogen oxides (NOx) under excess oxygen conditions. The present paper illustrates the further progress in catalytic NOx-reduction under excess of oxygen by hydrocarbon enrichment using the common rail injection system.

One possibility to improve the fuel economy of SI-engines is to run the engine with a lean air-fuel-ratio (AFR). Hydrocarbon and carbon monoxide after-treatment has been proven under lean operation, but NOx-control remains a challenge to catalyst and car manufacturers. One strategy that is being considered is to run the engine lean with occasional operation at stoichiometry. This would be in conjunction with a three-way-catalyst (TWC) to achieve stoichiometric conversion of the three main pollutants in the normal way and a NOx trap. The NOx trap stores NOx under lean operation to be released and reduced under rich conditions. The trap also functions as a TWC and has good HC and CO conversion at both lean and stoichiometric AFR's. Under lean conditions NO is oxidised to NO2 on Pt which is then adsorbed on an oxide surface. Typical adsorbent materials include oxides of potassium, calcium, zirconium, strontium, lanthanum, cerium and barium.

About 50-90 percent of the hydrocarbons that escape combustion during flame passage in spark-ignition engine operation are oxidized in the cylinder before leaving the system. The process involves the transport of unreacted fuel from cold walls towards the hotter burned gas regions and subsequent reaction. In order to understand controlling factors in the process, a transient one-dimensional reactive-diffusive model has been formulated for simulating the oxidation processes taking place in the reactive layer between hot burned gases and cold unreacted air/fuel mixture, with initial and boundary conditions provided by the emergence of hydrocarbons from the piston top land crevice. Energy and species conservation equations are solved for the entire process, using a detailed chemical kinetic mechanism for propane.

Measurements were made of exhaust histories of the following species: unburned hydrocarbons (HC), carbon monoxide, carbon dioxide, oxygen, and nitric oxide (NO). The measurements show that the exhaust flow can be divided into two distinct phases: a leading gas low in HC and high in NO followed by a trailing gas high in HC and low in NO. Calculations of time resolved equivalence ratio throughout the exhaust process show no evidence of a stratified combustion. The exhaust mass flow rate is time resolved by forcing the flow to be locally quasi-steady at an orifice placed in the exhaust pipe. The results with the quasi-steady assumption are shown to be consistent with the measurements. Predictions are made of time resolved mass flow rate which compare favorably to the experimental data base. The composition and flow histories provide sufficient information to calculate the time resolved flow rates of the individual species measured.

U.S. and European nonroad diesel emissions regulations have led to the implementation of various exhaust aftertreatment solutions. One approved configuration, a vanadium-based selective catalytic reduction catalyst followed by an ammonia oxidation catalyst (V-SCR + AMOX), does not require the use of a diesel oxidation catalyst (DOC) or diesel particulate filter (DPF). While certification testing has shown the V-SCR + AMOX system to be capable of meeting the nitrogen oxides, carbon monoxide, and particulate matter requirements, open questions remain regarding the efficacy of this aftertreatment for volatile and nonvolatile organic emissions removal, especially since the removal of this class of compounds is generally attributed to both the DOC and DPF.