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Technical Paper

Water-Gas-Shift Catalyst Development and Optimization for a D-EGR® Engine

2015-09-01
2015-01-1968
Dedicated Exhaust Gas Recirculation (D-EGR®) technology provides a novel means for fuel efficiency improvement through efficient, on-board generation of H2 and CO reformate [1, 2]. In the simplest form of the D-EGR configuration, reformate is produced in-cylinder through rich combustion of the gasoline-air charge mixture. It is also possible to produce more H2 by means of a Water Gas Shift (WGS) catalyst, thereby resulting in further combustion improvements and overall fuel consumption reduction. In industrial applications, the WGS reaction has been used successfully for many years. Previous engine applications of this technology, however, have only proven successful to a limited degree. The motivation for this work was to develop and optimize a WGS catalyst which can be employed to a D-EGR configuration of an internal combustion engine. This study consists of two parts.
Technical Paper

Use of Nitric Acid to Control the NO2:NOX Ratio Within the Exhaust Composition Transient Operation Laboratory Exhaust Stream

2020-04-14
2020-01-0371
The Exhaust Composition Transient Operation Laboratory (ECTO-Lab) is a burner system developed at Southwest Research Institute (SwRI) for simulation of IC engine exhaust. The current system design requires metering and combustion of nitromethane in conjunction with the primary fuel source as the means of NOX generation. While this method affords highly tunable NOX concentrations even over transient cycles, no method is currently in place for dictating the speciation of nitric oxide (NO) and nitrogen dioxide (NO2) that constitute the NOX mixture. NOX generated through combustion of nitromethane is dominated by NO, and generally results in a NO2:NOX ratio of <5 %. Generation of any appreciable quantities of NO2 is therefore dependent on an oxidation catalyst to oxidize a fraction of the NO to NO2.
Journal Article

The Role of EGR in PM Emissions from Gasoline Engines

2010-04-12
2010-01-0353
A dilute spark-ignited engine concept has been developed as a potential low cost competitor to diesel engines by Southwest Research Institute (SwRI), with a goal of diesel-like efficiency and torque for light- and medium-duty applications and low-cost aftertreatment. The targeted aftertreatment method is a traditional three-way catalyst, which offers both an efficiency and cost advantage over typical diesel aftertreatment systems. High levels of exhaust gas recirculation (EGR) have been realized using advanced ignition systems and improved combustion, with significant improvements in emissions, efficiency, and torque resulting from using high levels of EGR. The primary motivation for this work was to understand the impact high levels of EGR would have on particulate matter (PM) formation in a port fuel injected (PFI) engine. While there are no proposed regulations for PFI engine PM levels, the potential exists for future regulations, both on a size and mass basis.
Journal Article

The Interaction of Fuel Anti-Knock Index and Cooled EGR on Engine Performance and Efficiency

2012-04-16
2012-01-1149
Experiments were performed on a 2.4L boosted, MPI gasoline engine, equipped with a low-pressure loop (LPL) cooled EGR system and an advanced ignition system, using fuels with varying anti-knock indices. The fuels were blends of 87, 93 and 105 Anti-Knock Index (AKI) gasoline. Ignition timing and EGR sweeps were performed at various loads to determine the tradeoff between EGR level and fuel octane rating. The resulting engine data was analyzed to establish the relationship between the octane requirement and the level of cooled EGR used in a given application. In addition, the combustion difference between fuels was examined to determine the effect that fuel reactivity, in the form of anti-knock index (AKI), has on EGR tolerance and burn rate. The results indicate that the improvement in effective AKI of the fuel from using EGR is constant across commercial grade gasolines at about 0.5 ON per % EGR.
Journal Article

The Impact of Cooled EGR on Peak Cylinder Pressure in a Turbocharged, Spark Ignited Engine

2015-04-14
2015-01-0744
The use of cooled EGR as a knock suppression tool is gaining more acceptance worldwide. As cooled EGR become more prevalent, some challenges are presented for engine designers. In this study, the impact of cooled EGR on peak cylinder pressure was evaluated. A 1.6 L, 4-cylinder engine was operated with and without cooled EGR at several operating conditions. The impact of adding cooled EGR to the engine on peak cylinder pressure was then evaluated with an attempt to separate the effect due to advanced combustion phasing from the effect of increased manifold pressure. The results show that cooled EGR's impact on peak cylinder pressure is primarily due to the knock suppression effect, with the result that an EGR rate of 25% leads to an almost 50% increase in peak cylinder pressure at a mid-load condition if the combustion phasing is advanced to Knock Limited Spark Advance (KLSA). When combustion phasing was held constant, increasing the EGR rate had almost no effect on PCP.
Technical Paper

The Effect of Hydrogen Enrichment on EGR Tolerance in Spark Ignited Engines

2007-04-16
2007-01-0475
Small (up to 1% by volume) amounts of hydrogen (H2) were added to the intake charge of a single-cylinder, stoichiometric spark ignited engine to determine the effect of H2 addition on EGR tolerance. Two types of tests were performed at 1500 rpm, two loads (3.1 bar and 5.5 bar IMEP), two compression ratios (11:1 and 14:1) and with two fuels (gasoline and natural gas). The first test involved holding EGR level constant and increasing the H2 concentration. The EGR level of the engine was increased until the CoV of IMEP was > 5% and then small amounts of hydrogen were added until the total was 1% by volume. The effect of increasing the amount of H2 on engine stability was measured along with combustion parameters and engine emissions. The results showed that only a very small amount of H2 was necessary to stabilize the engine. At amounts past that level, increasing the level of H2 had no or only a very small effect.
Journal Article

Potential and Challenges for a Water-Gas-Shift Catalyst as a Combustion Promoter on a D-EGR® Engine

2015-04-14
2015-01-0784
In light of the increasingly stringent efficiency and emissions requirements, several new engine technologies are currently under investigation. One of these new concepts is the Dedicated EGR (D-EGR®) engine. The concept utilizes fuel reforming and high levels of recirculated exhaust gas (EGR) to achieve very high levels of thermal efficiency. While the positive impact of reformate, in particular hydrogen, on gasoline engine performance has been widely documented, the on-board reforming process and / or storage of H2 remains challenging. The Water-Gas-Shift (WGS) reaction is well known and has been used successfully for many years in the industry to produce hydrogen from the reactants water vapor and carbon monoxide. For this study, prototype WGS catalysts were installed in the exhaust tract of the dedicated cylinder of a turbocharged 2.0 L in-line four cylinder MPI engine. The potential of increased H2 production in a D-EGR engine was evaluated through the use of these catalysts.
Technical Paper

Microwave Enhancement of Lean/Dilute Combustion in a Constant-Volume Chamber

2019-04-02
2019-01-1198
High dilution engines have been shown to have a significant fuel economy improvement over their non-dilute counterparts. Much of this improvement comes through an increase in compression ratio enabled by the high knock resistance from high dilution. Unfortunately, the same reduction in reactivity that leads to the knock reduction also reduces flame speed, leading to the engine becoming unstable at high dilution rates. Advanced ignition systems have been shown to improve engine stability, but their impact is limited to the area at, or very near, the spark plug. To further improve the dilute combustion, a system in which a microwave field is established in the combustion chamber is proposed. This standing electric field has been shown, in other applications, to improve dilution tolerance and increase the burning velocity.
Journal Article

LPL EGR and D-EGR® Engine Concept Comparison Part 2: High Load Operation

2015-04-14
2015-01-0781
The ongoing pursuit of improved engine efficiency and emissions is driving gasoline low-pressure loop EGR systems into production around the globe. The Dedicated EGR (D-EGR®) engine was developed to minimize some of the challenges of cooled EGR while maintaining its advantages. The D-EGR engine is a high efficiency, low emissions internal combustion engine for automotive and off-highway applications. The core of the engine development focused on a unique concept that combines the efficiency improvements associated with recirculated exhaust gas and the efficiency improvements associated with fuel reformation. To outline the differences of the new engine concept with a conventional LPL EGR setup, a turbocharged 2.0 L PFI engine was modified to operate in both modes. The second part of the cooled EGR engine concept comparison investigates efficiency, knock resistance, combustion stability, and maximum load potential at high load conditions.
Journal Article

LPL EGR and D-EGR® Engine Concept Comparison Part 1: Part Load Operation

2015-04-14
2015-01-0783
The ongoing pursuit of improved engine efficiency and emissions are driving gasoline low-pressure loop EGR systems into production around the globe. To minimize inevitable downsides of cooled EGR while maintaining its advantages, the Dedicated EGR (D-EGR®) engine was developed. The core of the D-EGR engine development focused on a unique concept that combines the efficiency improvements associated with recirculated exhaust gas and the efficiency improvements associated with fuel reformation. To outline the differences of the new engine concept with a conventional low-pressure loop (LPL) EGR setup, a turbocharged 2.0 L PFI engine was modified to operate in both modes and also compared to the baseline. The first part of the cooled EGR engine concept comparison investigates efficiency, emissions, combustion stability, and robustness at throttled part load conditions.
Technical Paper

Investigation of Urea Derived Deposits Composition in SCR Systems and Their Potential Effect on Overall PM Emissions

2016-04-05
2016-01-0989
Ideally, complete thermal decomposition of urea should produce only two products in active Selective Catalytic Reduction (SCR) systems: ammonia and carbon dioxide. In reality, urea thermal decomposition reaction includes the formation of isocyanic acid as an intermediate product. Being highly reactive, isocyanic acid can initiate the formation of larger molecular weight compounds such as cyanuric acid, biuret, melamine, ammeline, ammelide, and dicyandimide [1,2,3,4]. These compounds can be responsible for the formation of deposits on the walls of the decomposition reactor in urea SCR systems. Composition of these deposits varies with temperature exposure, and under certain conditions, can create oligomers such as melam, melem, and melon [5, 6] that are difficult to remove from exhaust systems. Deposits can affect the efficiency of the urea decomposition, and if large enough, can inhibit the exhaust flow.
Technical Paper

Investigation of Urea Derived Deposits Composition in SCR Systems

2016-10-17
2016-01-2327
Ideally, complete decomposition of urea should produce only two products in active Selective Catalytic Reduction (SCR) systems: ammonia and carbon dioxide. In reality, urea decomposition reaction is a two-step process that includes the formation of ammonia and isocyanic acid as intermediate products via thermolysis. Being highly reactive, isocyanic acid can initiate the formation of larger molecular weight compounds such as cyanuric acid (CYN), biuret (BIU), melamine (MEL), ammeline (AML), ammelide (AMD), and dicyandimide (DICY). These compounds can be responsible for the formation of deposits on the walls of the decomposition reactor in urea SCR systems. Composition of these deposits varies with temperature exposure, and under certain conditions can create oligomers that are difficult to remove from exhaust pipes. Deposits can affect efficiency of the urea decomposition, and if large enough, can inhibit the exhaust flow and negatively impact ammonia distribution on the SCR catalyst.
Technical Paper

Investigation into Low-Temperature Urea-Water Solution Decomposition by Addition of Titanium-Based Isocyanic Acid Hydrolysis Catalyst and Surfactant

2020-04-14
2020-01-1316
Mitigation of urea deposit formation and improved ammonia production at low exhaust temperatures continues to be one of the most significant challenges for current generation selective catalytic reduction (SCR) aftertreatment systems. Various technologies have been devised to alleviate these issues including: use of alternative reductant sources, and thermal treatment of the urea-water solution (UWS) pre-injection. The objective of this work was to expand the knowledge base of a potential third option, which entails chemical modification of UWS by addition of a titanium-based urea/isocyanic acid (HNCO) decomposition catalysts and/or surfactant to the fluid. Physical solid mixtures of urea with varying concentrations of ammonium titanyl oxalate (ATO), oxalic acid, and titanium dioxide (TiO2) were generated, and the differences in NH3 and CO2 produced upon thermal decomposition were quantified.
Technical Paper

Impact of Operating Parameters on Ignition System Energy Consumption

2014-04-01
2014-01-1233
The use of cooled EGR in gasoline engines improves the fuel efficiency of the engine through a variety of mechanisms, including improving the charge properties (e.g. the ratio of specific heats), reducing knock and enabling higher compression ratio operation and, at part loads conditions in particular, reducing pumping work. One of the limiting factors on the level of improvement from cooled EGR is the ability of the ignition system to ignite a dilute mixture and maintain engine stability. Previous work from SwRI has shown that, by increasing the ignition duration and using a continuous discharge ignition system, an improved ignition system can substantially increase the EGR tolerance of an engine [1, 2]. This improvement comes at a cost, however, of increased ignition system energy requirements and a potential decrease in spark plug durability. This work examines the impact of engine operating parameters on the ignition energy requirements under high dilution operation.
Journal Article

Impact of EGR Quality on the Total Inert Dilution Ratio

2016-04-05
2016-01-0713
A series of tests were performed on a gasoline powered engine with a Dedicated EGR® (D-EGR®) system. The results showed that changes in engine performance, including improvements in burn rates and stability and changes in emissions levels could not be adequately accounted for solely due to the presence of reformate in the EGR stream. In an effort to adequately characterize the engine's behavior, a new parameter was developed, the Total Inert Dilution Ratio (TIDR), which accounts for the changes in the EGR quality as inert gases are replaced by reactive species such as CO and H2.
Technical Paper

Fuel Reforming and Catalyst Deactivation Investigated in Real Exhaust Environment

2019-04-02
2019-01-0315
Increased in-cylinder hydrogen levels have been shown to improve burn durations, combustion stability, HC emissions and knock resistance which can directly translate into enhanced engine efficiency. External fuel reformation can also be used to increase the hydrogen yield. During the High-Efficiency, Dilute Gasoline Engine (HEDGE) consortium at Southwest Research Institute (SwRI), the potential of increased hydrogen production in a dedicated-exhaust gas recirculation (D-EGR) engine was evaluated exploiting the water gas shift (WGS) and steam reformation (SR) reactions. It was found that neither approach could produce sustained hydrogen enrichment in a real exhaust environment, even while utilizing a lean-rich switching regeneration strategy. Platinum group metal (PGM) and Ni WGS catalysts were tested with a focus on hydrogen production and catalyst durability.
Journal Article

Ethanol Flex-fuel Engine Improvements with Exhaust Gas Recirculation and Hydrogen Enrichment

2009-04-20
2009-01-0140
An investigation was performed to identify the benefits of cooled exhaust gas recirculation (EGR) when applied to a potential ethanol flexible fuelled vehicle (eFFV) engine. The fuels investigated in this study represented the range a flex-fuel engine may be exposed to in the United States; from 85% ethanol/gasoline blend (E85) to regular gasoline. The test engine was a 2.0-L in-line 4 cylinder that was turbocharged and port fuel injected (PFI). Ethanol blended fuels, including E85, have a higher octane rating and produce lower exhaust temperatures compared to gasoline. EGR has also been shown to decrease engine knock tendency and decrease exhaust temperatures. A natural progression was to take advantage of the superior combustion characteristics of E85 (i.e. increase compression ratio), and then employ EGR to maintain performance with gasoline. When EGR alone could not provide the necessary knock margin, hydrogen (H2) was added to simulate an onboard fuel reformer.
Technical Paper

Effects of Catalyst Formulation on Vehicle Emissions With Respect to Gasoline Fuel Sulfur Level

1999-10-25
1999-01-3675
Proposed emissions standards will require that emissions control systems function at extremely high efficiency. Recently, studies have shown that elevated gasoline fuel sulfur levels (GFSL) can impair catalytic converter efficiency. In this study, a variety of tri-metal catalysts were evaluated to determine if formulation changes could reduce emissions sensitivity to GFSL. Catalysts with elemental composition similar to an OEM, but with double the precious metal (PM) loading, were evaluated using 38 and 620 ppm GFSL. Doubling the PM loading significantly reduced catalyst sensitivity to sulfur. Doubling the rhodium loading, at the expense of the platinum loading, significantly improved NOx emission sulfur sensitivity.
Journal Article

Effect of EGR on Particle Emissions from a GDI Engine

2011-04-12
2011-01-0636
Gasoline direct injected (GDI) engines are becoming a concern with respect to particulate matter (PM) emissions. The upcoming 2014 Euro 6 regulations may require a drastic reduction in solid particle number emissions from GDI engines and the proposed California Air Resources Board (CARB) LEV III regulations for 2014 and 2017 will also require some PM reduction measures. As a result, it is necessary to characterize PM emissions from GDI engines and investigate strategies that suppress particle formation during combustion. The main focus of this work was on using exhaust gas recirculation (EGR) as a means to reduce engine-out particle emissions from a GDI engine with an overall stoichiometric fuel to air mixture. A small displacement, turbocharged GDI engine was operated at a variety of steady-state conditions with differing levels of EGR to characterize total (solid plus volatile) and solid particle emissions with respect to size, number, and soot or black carbon mass.
Technical Paper

Detailed Characterization of Criteria Pollutant Emissions from D-EGR® Light Duty Vehicle

2016-04-05
2016-01-1006
In this study, the criteria pollutant emissions from a light duty vehicle equipped with Dedicated EGR® technology were compared with emissions from an identical production GDI vehicle without externally cooled EGR. In addition to the comparison of criteria pollutant mass emissions, an analysis of the gaseous and particulate chemistry was conducted to understand how the change in combustion system affects the optimal aftertreatment control system. Hydrocarbon emissions from the vehicle were analyzed usin g a variety of methods to quantify over 200 compounds ranging in HC chain length from C1 to C12. The particulate emissions were also characterized to quantify particulate mass and number. Gaseous and particulate emissions were sampled and analyzed from both vehicles operating on the FTP-75, HWFET, US06, and WLTP drive cycles at the engine outlet location.
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