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A NOx trap catalyst was evaluated in a light-duty diesel engine bench under steady-state speed/load conditions with alternating lean and rich exhaust streams. The NOx conversion was correlated with several engine operating and control parameters, such as speed, lean / rich timing and catalyst temperature. The NOx conversion is a result of balance between stored NOx in a lean stream and the quantity of reductant applied in a rich transient pulse. The conversion is inversely proportional to the lean / rich ratio, R, (at R< 17) and engine speed. At a given speed and lean/rich ratio, the conversion is proportional to the catalyst inlet temperature. If the temperature is too high, thermal NOx release may decrease the overall NOx conversion. With a fully regenerated NOx trap catalyst, its cumulative NOx storage, at a given trapping period (or an instantaneous NOx trapping efficiency), is proportional to engine speed.

The objectives of this study were 1) to evaluate the characteristics of rich diesel combustion near the stoichiometric operating condition, 2) to explore the possibility of stoichiometric operation of a diesel engine in order to allow use of a three-way exhaust after-treatment catalyst, and 3) to achieve practical operation ranges with acceptable fuel economy impacts. Boost pressure, EGR rate, intake air temperature, fuel mass injected, and injection timing variations were investigated to evaluate diesel stoichiometric combustion characteristics in a single-cylinder high-speed direct injection (HSDI) diesel engine. Stoichiometric operation in the Premixed Charge Compression Ignition (PCCI) combustion regime and standard diesel combustion were examined to investigate the characteristics of rich combustion. The results indicate that diesel stoichiometric operation can be achieved with minor fuel economy and soot impact.

The effect of spray targeting on exhaust emissions, especially soot and carbon monoxide (CO) formation, were investigated in a single-cylinder, high-speed, direct-injection (HSDI) diesel engine. The spray targeting was examined by sweeping the start-of-injection (SOI) timing with several nozzles which had different spray angles ranging from 50° to 154°. The tests were organized to monitor the emissions in Premixed Charge Compression Ignition (PCCI) combustion by introducing high levels of EGR (55%) with a relatively low compression ratio (16.0) and an open-crater type piston bowl. The study showed that there were optimum targeting spots on the piston bowl with respect to soot and CO formation, while nitric oxide (NOx) formation was not affected by the targeting. The soot and CO production were minimized when the spray was targeted at the edge of the piston bowl near the squish zone, regardless of the spray angle.

An emissions and performance study was conducted to explore the effects of exhaust gas recirculation (EGR) and multiple injections on the emission of oxides of nitrogen (NOx), particulate emissions, and brake specific fuel consumption (BSFC) over a wide range of engine operating conditions. The tests were conducted on an instrumented single cylinder version of the Caterpillar 3400 series heavy duty Diesel engine. Data was taken at 1600 rev/min, and 75% load, and also at operating conditions taken from a 6-mode simulation of the federal transient test procedure (FTP). The fuel system used was an electronically controlled, common rail injector and supporting hardware. The fuel system was capable of as many as four independent injections per combustion event at pressures from 20 to 120MPa.

Experiments show that intake flow details have a significant influence on High-Speed Direct-Injection (HSDI) diesel engine soot emissions. Four different intake modes were simulated using the combination of the CFD codes, STAR-CD and KIVA-3V, to investigate spray-intake flow-emission interaction characteristics. The simulation results were compared to steady-state flow bench data and engine experimental data. It was found that it is difficult to accurately predict the timing of the small pilot and main combustion events, simultaneously, with current simplified ignition models. NOx emissions were predicted well, however, an insensitivity of the soot emissions to the details of the intake process was found, mainly due to the deficiencies in predicting the ignition delay. The results show that a strong swirling flow causes the formed soot to remain within the bowl, leading to high soot emissions.

Strategic Materials at Reaction Temperatures (SMART) is an approach used to design washcoat systems for passive 4-way emission control catalysts. Light duty diesel vehicles need to meet the European Motor Vehicle Emissions Group (MVEG) cycle or U. S. Federal test procedure (FTP 75). Emissions that are monitored include hydrocarbon (HC), nitrogen oxides (NOx), carbon monoxide (CO) and total particulate matter (TPM). Low engine-exhaust temperatures (< 200°C during city driving) and high temperatures (> 500-800°C under full load and wide-open throttle) make emission control a formidable task for the catalyst designer Gas phase HC, CO and NOx reactions must be balanced with the removal of the soluble organic fraction for the vehicle to be in compliance with regulations. The SMART approach uses model gases under typical operating conditions in the laboratory to better understand the function of individual washcoat components.

The development of a plasma jet ignition system is described on a 4-cyl, 140 in3 engine. Performance was evaluated on the basis of combustion flame photographs in a single-cylinder engine at 20/1 A/F dynamometer tests on a modified 4-cyl engine, and cold start emissions, fuel economy, and drivability in a vehicle at 19/1 air fuel ratio. In addition to adjustable engine variables such as air-fuel ratio and spark advance, system electrical and mechanical parameters were varied to improve combustion of lean mixtures. As examples, the air-fuel ratio range was 16-22/1, secondary ignition current was varied from 40 to 6000 mA, and plasma jet cavity and electrode geometry were optimized. It is shown that the plasma jet produces on ignition source which penetrates the mixture ahead of the initial flame front and reduces oxides of nitrogen emission, in comparison to a conventional production combustion chamber.

Catalytic reduction of NOx from heavy duty diesel engines via addition of reductant to the exhaust is accompanied by a substantial exotherm in the catalyst bed which does not occur, for example, in a diesel oxidation catalyst. Engine tests show that thermal management in the aftertreatment system is required for optimum reductant use and maximum NOx conversion by the low-temperature (200-300°C) catalyst NSP-5, but of less importance with the high temperature (> 350°C) Catalyst A. Understanding thermal effects is also important for reconciling test results in the near-adiabatic environment of a full-sized catalyst on an engine with the near-isothermal one of a test piece in a laboratory reactor. The effects of reductant type and concentration on NOx conversion on NSP-5 were shown to result in part from non-steady state behavior of the catalyst during steady state engine operation.

Multi-Dimensional modeling was carried out for a Mercury Marine two-stroke DISI engine. Recently developed spray, ignition, and combustion models were applied to medium load cases with an air-fuel ratio of 30:1. Three injection timings, 271, 291 and 306 ATDC were selected to investigate the effects of the injection timing on mixture formation, ignition and combustion. The results indicate that at this particular load condition, earlier injection timing allows more fuel to evaporate. However, because the fuel penetrates further toward the piston, a leaner mixture is created near the spark plug; thus, a slower ignition process with a weaker ignition kernel was found for the SOI 271 ATDC case. The measured and computed combustion results such as average in-cylinder pressure and NOx are in good agreements. The later injection case produces lower NOx emission and higher CO emission; this is due to poor mixing and is in agreement with experimental measurements.

A novel process for coating and assembling metal converters utilizing precoated foil as building blocks has been developed which yields a converter capable of withstanding typical industry specified hot vibration protocols. The precoating process used here results in uniform catalyst coating distributions with coating adhesion to the foil on a par with the coatings' adhesion to ceramic substrates. FTP and MVEG vehicle emission performance of this unique precoated metal converter design versus a more conventional dip-coated metal monolith (parts with the same volume, cell density, and tri-metal catalyst coating), exhibited improved catalyst emission breakthrough efficiencies with respect to HC, CO, and NOx after two different engine-aging protocols. These advantages were observed on three different test vehicles across most phases of these driving cycles.

A previous paper reported (SAE Paper 2002-01-2884) that it was possible to decrease mode-weighted NOx emissions compared to the OEM calibration with corresponding increases in particulate matter (PM) emissions. These PM emission increases were partially overcome with the use of oxygenated diesel fuel additives. We wanted to know if compounds of toxicological concern were emitted more or less using oxygenated diesel fuel additives that were used in conjunction with a modified engine operating strategy to lower engine-out NOx emissions. Emissions of toxicologically relevant compounds from fuels containing triproplyene glycol monomethyl ether and dibutyl maleate were the same or lower compared to a low sulfur fuel (15 ppm sulfur) even under engine operating conditions designed to lower engine-out NOx emissions.

Low-temperature combustion (LTC) strategies for diesel engines are of increasing interest because of their potential to significantly reduce particulate matter (PM) and nitrogen oxide (NOx) emissions. LTC with late fuel injection further offers the benefit of combustion phasing control because ignition is closely coupled to the fuel injection event. But with a short ignition-delay, fuel jet mixing processes must be rapid to achieve adequate premixing before ignition. In the current study, mixing and pollutant formation of late-injection LTC are studied in a single-cylinder, direct-injection, optically accessible heavy-duty diesel engine using three laser-based imaging diagnostics. Simultaneous planar laser-induced fluorescence of the hydroxyl radical (OH) and combined formaldehyde (H2CO) and polycyclic aromatic hydrocarbons (PAH) are compared with vapor-fuel concentration measurements from a non-combusting condition.

Stoichiometric combustion could enable a three-way catalyst to be used for treating NOx emissions of diesel engines, which is one of the most difficult species for diesel engines to meet future emission regulations. Previous study by Lee et al. [1] showed that diesel engines can operate with stoichiometric combustion successfully with only a minor impact on fuel consumption. Low NOx emission levels were another advantage of stoichiometric operation according to that study. In this study, the characteristics of stoichiometric diesel combustion were evaluated experimentally to improve fuel economy as well as exhaust emissions The effects of fuel injection pressure, boost pressure, swirl, intake air temperature, combustion regime (injection timing), and engine load (fuel mass injected) were assessed under stoichiometric conditions.

TECHNIQUES, based on panel estimates, were developed for evaluating the odor and irritation intensities of undiluted diesel-engine exhaust gases or of various dilutions of these gases in air. Along with the estimates, chemical analyses were made to determine the concentrations of total aldehydes, formaldehyde, and oxides of nitrogen. Statistically significant correlations were found between odor or irritation intensity estimates and the analytical data, but these correlations were too weak to permit accurate prediction of odor or irritation from chemical analyses. Effects of some engine variables on diesel odor were studied. Possible means of reducing diesel odor are discussed.

Three different approaches for modeling diesel engine combustion are compared against cylinder pressure, NOx emissions, high-speed soot luminosity imaging, and 2-color thermometry data from a heavy-duty DI diesel engine. A characteristic time combustion (KIVA-CTC) model, a representative interactive flamelet (KIVA-RIF) model, and direct integration using detailed chemistry (KIVA-CHEMKIN) were integrated into the same version of the KIVA-3v computer code. In this way, the computer code provides a common platform for comparing various combustion models. Five different engine operating strategies that are representative of several different combustion regimes were explored in the experiments and model simulations. Two of the strategies produce high-temperature combustion with different ignition delays, while the other three use dilution to achieve low-temperature combustion (LTC), with early, late, or multiple injections.

The desire for improved fuel economy, and lower emissions of green house gases, such as CO2, is projected to increase the demand for diesel and lean-burn gasoline engines throughout the world. Several commercial diesel oxidation catalysts (DOCs) were developed in the last 3-4 years to reduce hydrocarbon, CO, and particulates emitted from the exhaust of diesel passenger cars and trucks. To meet future U.S. and European NOx standards, it is essential to develop catalyst technology that will allow NOx reduction in addition to the other three pollutants. Two materials that attracted great attention as lean NOx catalysts are the Cu/ZSM-5 and Pt based. Cu containing ZSM-5 are active for lean-NOx reduction at temperatures above 350°C, provided sufficient hydrocarbons are present as reductants.

The plasma assisted catalytic reactor (PACR) approach to lean NOx abatement is a two step process. The non-thermal plasma oxidizes the engine out NO to NO2, which is then reduced to N2 over a catalyst using a hydrocarbon reductant. Whereas it was once believed that the plasma itself directly reduces NOx to N2, it has been shown that the plasma's principle function is to oxidize NO to NO2. This is accomplished without oxidizing SO2 to SO3, resulting in lower sulfate particulate when compared to standard lean NOx catalysis using platinum or reducible oxide catalysts. We have performed reactor studies comparing the relative reducibility of NO2 and NO in a synthetic diesel exhaust using diesel fuel as the hydrocarbon reductant, with attention to time-on stream behavior and determination of NOx reversibly adsorbed on the catalyst. We find that at 200°C, 50% of the NO2 disappearance over Na-ZSM5 is attributable to reversible adsorption on the catalyst.

The technical issues related to NOx abatement for diesel applications are summarized. Data on improved catalysts and a novel approach which involves temporarily trapping of NOx before reduction are presented. New high temperature lean NOx materials have been identified which have better hydrothermal stability than the state of the art Cu/ZSM-5. One of these materials, Catalyst A, was shown to reduce the NOx emitted from a 2.5 L diesel engine at temperatures ≥ 350°C using injected diesel fuel as a reductant. Catalyst A also showed reasonably good durability after aging for 500 h at ca. 500°C on a 14 L diesel truck engine. Pt/Al2O3, a low temperature lean NOx reduction catalyst (200-300°C), demonstrated fairly good performance after 125 h of aging on a 4 L diesel truck engine, however sulfate make and N2O formation are high on this material. New low temperature NOx traps show promise for transient removal of NOx below 200-400°C.

Three-way catalysts (TWC) to remove the HC, CO, and NOx pollutants from the exhaust of gasoline powered vehicles employ rhodium in combination with platinum and palladium. Of these precious metals, rhodium is by far the most expensive. Since it is so heavily used for its NOx reduction capabilities, the amount per vehicle approaches and sometimes exceeds the naturally occurring mine ratio. A program was conducted to determine the feasibility of a non-rhodium TWC catalyst. It showed that Pt and Pd in conjunction with other washcoat support materials exhibited relatively good TWC characteristics compared to a Pt/Rh catalyst after engine dynamometer aging. In FTP evaluations this new REDOX type catalyst gave comparable HC and CO efficiency and 85% of the NOx efficiency of a Pt/Rh-containing catalyst. Presently the operating window is being defined but comparisons to conventional Pt/Pd and Pt/Rh catalysts have been made under a number of conditions.