Search Results

At the current state of diesel engine technology, all diesel engines require some sort of NOx control device to comply with Tier II Bin 5 light-duty or 2010 heavy-duty NOx emission standards. Selective Catalytic Reduction of NOx with hydrocarbons (HC-SCR) to reduce NOx from diesel exhaust emissions is an attractive technology for lean NOx control, especially when diesel fuel is used as the reductant. However, it has been reported that when diesel fuel is used as the reductant catalyst deactivation occurred. Even though this kind of deactivation is reversible at high enough temperatures, it is a deficiency that needs to be overcome for the successful implementation of the technology. We studied the HC-SCR catalyst deactivation using diesel fuel as the reductant. The variables investigated included catalyst temperature, HC:NOx ratio, NOx concentration, and space velocity. The results showed that one single parameter can be used to measure the catalyst deactivation: the HC-SCR activity.

To comply with Tier II Bin 5 light-duty or 2010 heavy-duty NOx emission standards, all diesel engines require some sort of NOx control device. Selective Catalytic Reduction of NOx with hydrocarbons (HC-SCR) to reduce NOx from diesel exhaust emissions is an attractive technology for lean NOx control, especially when diesel fuel is used as the reductant. However, it has been reported that when diesel fuel is used as the reductant catalyst deactivation occurred (1). In a companion paper, we demonstrated that the HC-deactivation is caused by the mismatch of the adsorption and desorption processes of either the reactants or the products of a normal SCR reaction (2). In this paper, we probe the nature of the catalyst deactivation with various reductants. Both hydrocarbons and oxygenates were used as the reductants. The deactivation or the mismatch in adsorption and desorption rates is molecular size or chain length dependent.

Intake valve deposits ( IVD's ) have been found to cause driveability problems in some modern port fuel-injected engines. Due to the poor repeatability and the lengthy time required for the existing testing procedures, only limited information is available on how and why intake valve deposits form. For a better understanding of the deposit forming mechanism, a short IVD sampling procedure was developed to investigate deposit formation in a single-cylinder CFR engine. To facilitate deposit sampling, an intake valve was modified to accommodate removable sampling coupons. A measurable amount of deposits can be accumulated on a coupon in two hours. It was found that both fuel and lubricant can contribute to the formation of deposits on an intake valve. The fuel-derived deposits came from the high-boiling fractions of the fuel and they were derived from liquid phase fuel.

A single cylinder engine was used to collect engine combustion chamber deposits insitu, and to investigate the influence of fuel composition on combustion chamber deposit formation. High-boiling aromatic compounds were found to contribute greatly to deposit formation, while olefinic compounds did not show any significant deposit-forming tendencies. In a low surface temperature regime, deposit formation increased with boiling point of aromatic dopants added to the base fuel. Various analytical techniques (FTIR, GC/MS, EPMA, SEM) were utilized to characterize carbonaceous deposits in an early stage of formation. Oxidized hydrocarbon species (ketones, carboxylic acids, lactones, esters), metal carboxylates, and decomposition products of oil additives were found to be major building blocks of deposits. The oxidized hydrocarbon species formed in a preflame region are condensed/adsorbed on a relatively cold surface to form combustion chamber deposits.

A single-cylinder engine was used to study the effect of engine operating parameters on the early stage of deposit formation (first 8 hours). Deposit samples were collected from the engine cylinder using removable sampling probes. Among the engine operating parameters studied, coolant temperature had the greatest influence on deposit formation. Equivalence ratio of the air-fuel mixture was also important. Other variables such as compression ratio and intake air temperature had minimal effects. Investigations using a temperature controlled probe revealed that surface temperature is a dominant factor in the deposit forming process. Within a temperature range from 98°C to 256°C, there is an inverse relationship between the amount of deposit accumulated and the surface temperature. Extrapolating the experimental data showed that the critical surface temperature for deposit formation is near 310°C, above which no deposit is expected to form.