Search Results

This paper describes an on-vehicle demonstration of a hydrogen-heated catalyst (HHC) system for reducing the level of cold-start hydrocarbon emissions from a gasoline-fueled light-duty vehicle. The HHC system incorporated an onboard electrolyzer that generates and stores hydrogen (H2) during routine vehicle operation. Stored hydrogen and supplemental air are injected upstream of a platinum-containing automotive catalyst when the engine is started. Rapid heating of the catalytic converter occurs immediately as a result of catalytic oxidation of hydrogen (H2) with oxygen (O2) on the catalyst surface. Federal Test Procedure (FTP) emission results of the hydrogen-heated catalyst-equipped vehicle demonstrated reductions of hydrocarbons (HC) and carbon monoxide (CO) up to 68 and 62 percent, respectively. This study includes a brief analysis of the emissions and fuel economy effects of a 10-minute period of hydrogen generation during the FTP.

A typical automotive catalytic converter is constructed with a ceramic substrate and a steel shell. Due to a mismatch in coefficients of thermal expansion, the steel shell will expand away from the ceramic substrate at high temperatures. The gap between the substrate and shell is usually filled with a fiber composite material referred to as “mat.” Mat materials are compressed during assembly and must maintain an adequate pressure around the substrate under extreme temperature conditions. The container deformation measurement procedure is used to determine catalytic converter shell expansion during and after a period of hot catalytic converter operation. This procedure is useful in determining the potential physical durability of a catalytic converter system, and involves measuring converter shell expansion as a function of inlet temperature. A post-test dimensional measurement is used to determine permanent container deformation.

An increasing number of passenger vehicle exhaust systems incorporate catalytic converters that are “close-coupled” to the exhaust manifold to further reduce the quantity of cold-start emissions and increase overall catalyst conversion efficiencies. In general, close-coupled catalytic converters are not necessarily subjected to higher inlet exhaust temperatures than conventional underbody catalytic converters. To establish a foundation of on-vehicle temperature data, several passenger vehicles with close-coupled catalytic converters were studied while operating on a chassis dynamometer. Converter temperatures were measured over a variety of vehicle test conditions, including accelerations and extended steady-state speeds for several throttle positions, at both zero- and four-percent simulated road grades.

In order to further reduce vehicle cold-start emissions, the use of catalytic converters that are “close-coupled” to the exhaust manifold is increasing. To understand the vibrational environment of close-coupled and underbody converters, a laboratory study was conducted on several passenger vehicles. Catalytic converter vibration spectra were measured on a chassis dynamometer with the vehicle operating over a variety of test conditions. Vehicle operating conditions included hard accelerations and extended steady-state speeds at distinct throttle positions over zero-percent and four-percent simulated road grades.

Experimental catalysts for the reduction of oxides of nitrogen (NOx) were evaluated on a 258-horsepower (192 kW) direct-injection heavy-duty diesel engine. An experimental reductant delivery system provided supplementary hydrocarbons for the reduction of NOx. Initially, diesel fuel was used as the supplementary reductant. Early experiments resulted in a 10 to 17 percent reduction in NOx emissions when tested using the heavy-duty engine transient Federal Test Procedure (FTP), and a 30 to 40 percent reduction at selected steady-state catalyst inlet temperatures. A fuel economy penalty of five percent was measured for initial FTP experiments. Emissions of total hydrocarbons (HC), carbon monoxide (CO), and particulate matter (PM) tended to increase during initial experiments with the addition of the supplemental reductant, but these emissions decreased with the incorporation of improved catalyst formulations and reductant fuel spray calibrations.

This paper describes the development and evaluation of an operative catalyst for the reduction of NOx in lean exhaust. A catalyst that incorporates iron (II)-complex impregnated modified mesoporous molecular sieves (MCM-41) has been synthesized and further treated with [pd(NH3)4]Cl2 [1]. Experimental results suggest a hydrocarbon-independent reduction of NOx takes place on the iron center, and oxidation of CO is assisted by the palladium ion. The catalytic activity toward HC CO, and NOx removal was studied with simulated and real engine exhaust in the laboratory and on an engine, respectively. Engine test results demonstrate a reduction of NOx of up to 10 percent at catalyst inlet temperatures in the range of 260°C to 280°C. In this paper, possible NOx reduction pathways are also discussed.

Copper ion exchange procedures were used to prepare zeolite-based catalysts for NOx reduction in lean (oxygen-rich) exhaust. Energy dispersive x-ray fluorescence and scanning electron microscopy analyses confirmed the presence of copper in the zeolite matrix. Zeolites were applied onto honeycomb and foam substrates, and evaluated for catalytic NOx reduction efficiency using engine exhaust. Copper-exchanged zeolite catalysts prepared for this study revealed NOx reduction of 95 percent for a period of seven minutes using previously adsorbed exhaust hydrocarbons as the reducing agent. Experiments using ethylene injection to supplement the exhaust suggest long-term and sustained NOx reduction, initially observed at 52 percent. Experimental results and performance comparisons of ZSM-5, mordenite, and Y-type zeolites are discussed. Zeolite catalysts based on Cu-mordenite showed high levels of initial NOx reduction, while results using Cu-ZSM-5 suggested better long-term activity.

This paper describes the findings of a laboratory effort to demonstrate improved automotive exhaust emission control with a cold-start hydrocarbon collection system. The emission control strategy developed in this study incorporated a zeolite molecular sieve in the exhaust system to collect cold-start hydrocarbons for subsequent release to an active catalytic converter. A prototype emission control system was designed and tested on a gasoline-fueled vehicle. Continuous raw exhaust emission measurements upstream and downstream of the zeolite molecular sieve revealed collection, storage, and release of cold-start hydrocarbons. Federal Test Procedure (FTP) emission results show a 35 percent reduction in hydrocarbons emitted during the cold-transient segment (Bag 1) due to adsorption by the zeolite.

Two different configurations of electrically-heated catalyst systems were installed on two new production vehicles. A 1990 Buick LeSabre was evaluated with a heated catalyst placed directly in front of the main production catalytic converter while a 1990 Toyota Celica was evaluated with an electrically-heated catalyst placed between the main close-coupled catalytic converter and a smaller downstream production catalytic converter. Initial laboratory studies involved examination of heating strategies to minimize electrical energy requirements, a variety of off-board battery and recharging configurations for their effect on emissions, and multiple air injection strategies to achieve minimum hydrocarbon emissions while avoiding a NOx penalty. Final efforts involved installation of optimized, complete on-vehicle electrically-heated catalyst systems for subsequent on-road mileage accumulation.

This paper describes the laboratory effort to determine the emissions benefit of cold-start air injection to a preheated automotive catalyst. Previous experimentation with an electrically-heated catalyst on a gasoline-fueled vehicle with no supplemental air showed little improvement in hydrocarbon emission control. In this study, air was injected ahead of an electrically-heated catalyst during cold-start operation. Analysis of continuously recorded raw exhaust emissions were used to determine air injection calibrations and oxidation-reduction trade-offs. Improved control of non-methane hydrocarbons (NMHC), benzene, and carbon monoxide (CO) emissions was observed. Nitrogen oxides (NOx) emission control was maintained by the use of a carefully controlled air injection flow-rate and schedule. This study determined that heating an auto-motive exhaust emission catalyst prior to cold-start operation may not be sufficient in itself.