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Technical Paper

The Role of CFD Combustion Simulation in Diesel Burner Development

2009-10-06
2009-01-2878
Diesel burners introduce combustion of diesel fuel to raise exhaust gas temperature to Diesel Oxidization Catalyst (DOC) light-off or Diesel Particulate Filter (DPF) regeneration conditions, thereby eliminating the need of engine measures such as post-injections. Such diesel combustion requirement nevertheless poses challenges to burner development especially in combustion control and risk mitigation of DPF material failure. In particular, burner design must satisfy good soot distribution and heat distribution at DPF front face after meeting minimum requirements of ignition, heat release, and backpressure. In burner development, Computational Fluid Dynamics (CFD) models have been developed based on commercial codes for burner thermal and flow management with capability of predicting comprehensive physical and chemical phenomena including turbulence induced mixing, fuel injection, fuel droplet transport, diesel combustion, radiation, conjugate heat transfer and etc.
Technical Paper

Passive Regeneration Response Characteristics of a DPF System

2013-04-08
2013-01-0520
This study investigates the passive regeneration behavior of diesel particulate filters (DPFS) with various PGM loadings under different engine operating conditions. Four wall-flow DPFs are used; one uncoated and three wash-coated with low, medium, and high PGM loadings, with and without an upstream diesel oxidation catalyst (DOC). DPFs with variable pre-soot loads are evaluated at two steady state temperatures (300°C and 400°C), as well as across three levels of transients based on the 13-mode ESC cycle. Passive regeneration rates are calculated based on pre and post soot gravimetric measurements along with accumulated soot mass rates for specified exhaust mass flow rates and temperatures. Results illustrate the effect of temperature, NO₂ content, and soot loading on passive regeneration without upstream DOCs or DPF wash coatings.
Technical Paper

Optimization of a Urea SCR System for On-Highway Truck Applications

2010-10-05
2010-01-1938
In order to satisfy tightening global emissions regulations, diesel truck manufacturers are striving to meet increasingly stringent Oxides of Nitrogen (NOx) reduction standards. The majority of heavy duty diesel trucks have integrated urea SCR NOx abatement strategies. To this end, aftertreatment systems need to be properly engineered to achieve high conversion efficiencies. A EuroV intent urea SCR system is evaluated and failed to meet NOx conversion targets with severe urea deposit formation. Systematic enhancements of the design have been performed to enable it to meet targets, including emission reduction efficiency via improved reagent mixing, evaporation, distribution, back pressure, and removing of urea deposits. Multiple urea mixers, injector mounting positions and various system layouts are developed and evaluated, including both CFD analysis and full scale laboratory tests.
Technical Paper

Mixer Development for Urea SCR Applications

2009-10-06
2009-01-2879
2010 and future EPA regulations introduce stringent Oxides of Nitrogen (NOx) reduction targets for diesel engines. Selective Catalytic Reduction (SCR) of NOx by Urea over catalyst has become one of the main solutions to achieve these aggressive reductions. As such, urea solution is injected into the exhaust gas, evaporated and decomposed to ammonia via mixing with the hot exhaust gas before passing through an SCR catalyst. Urea mixers, in this regard, are crucial to ensure successful evaporation and mixing since its liquid state poses significant barriers, especially at low temperature conditions that incur undesired deposits. Intensive efforts have been taken toward developing such urea mixers, and multiple criteria have been derived for them, mainly including NOx reduction efficiency and uniformity. In addition, mixers must also satisfy other requirements such as low pressure drop penalty, mechanical strength, material integrity, low cost, and manufacturability.
Technical Paper

Material Corrosion Investigations for Urea SCR Diesel Exhaust Systems

2009-10-06
2009-01-2883
New emissions standards for oxides of nitrogen (NOx) in on-road diesel vehicles are effective in 2010, and a common approach applies urea selective catalytic reduction (SCR). Urea is injected into the exhaust and decomposes to form ammonia, which chemically reacts with NOx as it passes through an SCR catalyst. Ammonia is corrosive and negatively affects typical stainless steels used in exhaust applications, but these corrosive impacts have not yet been quantified in an exhaust system. Two unique corrosion tests are performed on a number of various stainless steel samples, illustrating such performance concerns with 409, while offering alternatives with much better performance, including cost-effective options. The method applied is described, yielding performance criteria through appearance, weight loss, and corrosion pit depth.
Technical Paper

Low Temperature SCR Catalysts Optimized for Cold-Start and Low-Load Engine Exhaust Conditions

2015-04-14
2015-01-1026
The main objective of this work is to develop a low-temperature SCR catalyst for the reduction of nitrogen oxides at cold start, low-idle and low-load conditions. A series of metal oxide- incorporated beta zeolite catalysts were prepared by adopting incipient wetness technique, cation-exchange, deposition-precipitation and other synthesis techniques. The resulting catalysts were characterized and tested for reduction of NOx in a fixed bed continuous flow quartz micro-reactor using ammonia as the reductant gas. Initial catalyst formulations have been exhibited good NOx reduction activity at low-temperatures. These catalyst formulations showed a maximum NOx conversion in the temperature range of 100 - 350°C. Besides, more experiments were performed with the aim of optimizing these formulations with respect to the metal atomic ratio, preparation method, active components and supported metal type.
Technical Paper

Investigation of Urea Deposits in Urea SCR Systems for Medium and Heavy Duty Trucks

2010-10-05
2010-01-1941
With increasing applications of urea SCR for NOx emission reduction, improving the system performance and durability has become a high priority. A typical urea SCR system includes a urea injector, injector housing, mixer, and appropriate pipe configurations to allow continuous urea injection into the exhaust stream and evaporation of urea solution into gaseous products. Continuous operation at various conditions with high NOx reduction is possible, but one problem that threatens the life and performance of these systems is urea deposit. When urea or its byproducts become deposited on the inner surfaces of the system including walls, mixers, injector housings and substrates it can create concerns of backpressure and material deteriorations. In addition, deposits as a waste of reagents can negatively affect engine operation, emissions performance and DEF economy. Urea deposit behavior is explored in terms of heat transfer, pipe geometry, injector layout and mixing mechanisms.
Journal Article

Investigation of SCR Catalysts for Marine Diesel Applications

2017-03-28
2017-01-0947
Evolving marine diesel emission regulations drive significant reductions of nitrogen oxide (NOx) emissions. There is, therefore, considerable interest to develop and validate Selective Catalytic Reduction (SCR) converters for marine diesel NOx emission control. Substrates in marine applications need to be robust to survive the high sulfur content of marine fuels and must offer cost and pressure drop benefits. In principle, extruded honeycomb substrates of higher cell density offer benefits on system volume and provide increased catalyst area (in direct trade-off with increased pressure drop). However higher cell densities may become more easily plugged by deposition of soot and/or sulfate particulates, on the inlet face of the monolithic converter, as well as on the channel walls and catalyst coating, eventually leading to unacceptable flow restriction or suppression of catalytic function.
Technical Paper

Integration of Diesel Burner for Large Engine Aftertreatment using CFD

2010-10-05
2010-01-1946
Diesel burners recently have been used in Diesel Particulate Filter (DPF) regeneration process, in which the exhaust gas temperature is raised through the combustion process to burn off the soot particles. The feasibility of such process using the burner in large diesel applications is investigated along with a mixer and DPF. For such applications, only partial flow of the exhaust stream is fed into the burner and the resulting hot flow from combustion process is then mixed with the rest of the main stream. The amount of flow into the burner plays a vital role in overall system performance as it determines the amount of hot gas needed for Diesel Oxidation Catalyst (DOC) light-off (to facilitate DPF regeneration) and also oxygen amount needed for secondary combustion. A passive valve plate design is proposed for such flow split applications for the burner.
Technical Paper

Evaluation of a DPF Regeneration System and DOC Performance Using Secondary Fuel Injection

2009-10-06
2009-01-2884
An active diesel particulate filter (DPF) regeneration system is evaluated, which applies secondary fuel injection (SFI) directly within the exhaust system upstream of a diesel oxidation catalyst (DOC). Diesel fuel is oxidized in the presence of a proprietary catalyst system, increasing exhaust gas temperatures in an efficient and controlled manner, even during low engine-out gas temperatures. The exotherms produced by secondary fuel injection (SFI) have been evaluated using two different DOC volumes and platinum catalyst loadings. DOC light-off temperatures were measured using SFI under steady-state conditions on an engine dynamometer. A ΔT method was used for the light-off temperature measurements – i.e., the minimum DOC inlet gas temperature at which the exothermic reaction increases the outlet gas temperature 20°C or greater than the inlet temperature.
Technical Paper

Evaluation of Mixer Designs for Large Diesel Exhaust Aftertreatment Systems

2010-10-05
2010-01-1943
The presented work evaluates several mixer designs being considered for use in large Diesel exhaust aftertreatment systems. The mixers are placed upstream of a diesel oxidation catalyst (DOC) in the exhaust system, where a liquid hydrocarbon fuel is injected. DOC exothermic behaviour resulting from each mixer at different operating conditions is evaluated. A gas flow bench equipped with a XY-Table measurement system is used to determine gas velocity, temperature, and hydrocarbon species uniformity, as well as, pressure drop. Experimental mixer data obtained from a flow bench and an engine dynamometer are compared and discussed. The experimental methodology used in this study can be used to evaluate mixers via comprehensive testing.
Technical Paper

Development of Low Temperature Selective Catalytic Reduction (SCR) Catalysts for Future Emissions Regulations

2014-04-01
2014-01-1520
A series of novel metal-oxide (TiO2, TiO2-SiO2)-supported Mn, Fe, Co, V, Cu and Ce catalysts were prepared by incipient wetness technique and investigated for the low-temperature selective catalytic reduction (SCR) of NOx with ammonia at industrial relevantly conditions. Among all the prepared catalysts, Cu/TiO2 showed superior de-NOx performance in the temperature range of 150-200 °C followed by Mn/TiO2 in the temperature range of 200-250 °C. The Ce/TiO2 catalyst exhibited a broad temperature window with notable de-NOx performance in the temperature regime of 250-350 °C. The phyico-chemical characterization results revealed that the activity enhancement was correlated with the properties of the support material. All the anatasetitania-supported catalysts (M/TiO2 (Hombikat)) demonstrated significantly high de-NOx performance above 150 °C.
Technical Paper

Clean EGR for Gasoline Engines – Innovative Approach to Efficiency Improvement and Emissions Reduction Simultaneously

2017-03-28
2017-01-0683
External Exhaust Gas Recirculation (EGR) has been used on diesel engines for decades and has also been used on gasoline engines in the past. It is recently reintroduced on gasoline engines to improve fuel economy at mid and high engine load conditions, where EGR can reduce throttling losses and fuel enrichment. Fuel enrichment causes fuel penalty and high soot particulates, as well as hydrocarbon (HC) emissions, all of which are limited by emissions regulations. Under stoichiometric conditions, gasoline engines can be operated at high EGR rates (> 20%), but more than diesel engines, its intake gas including external EGR needs extreme cooling (down to ~50°C) to gain the maximum fuel economy improvement. However, external EGR and its problems at low temperatures (fouling, corrosion & condensation) are well known.
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