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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.

A turbocharged 2.0 L PFI engine was modified to operate in a low-pressure loop and Dedicated EGR (D-EGR®) engine configuration. Both engine architectures were operated with a low and high octane gasoline as well as three ethanol blends. The core of this study focused on examining combustion differences at part and high loads between the selected fuels and also the different engine configurations. Specifically, the impact of the fuels on combustion stability, burn rates, knock mitigation, required ignition energy, and efficiency were evaluated. The results showed that the knock resistance generally followed the octane rating of the fuel. At part loads, the burn rates, combustion stability, and EGR tolerance was marginally improved with the high ethanol blends. When combustion was not knock or stability limited, the efficiency differences between the fuels were negligible. The D-EGR engine was much less sensitive to fuel changes in terms of burn rates than the LPL EGR setup.

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.

A recent collaborative research project between Southwest Research Institute® (SwRI®) and the University of Texas at San Antonio (UTSA) has demonstrated that a ruthenium (Ru) catalyst is capable of converting oxides of nitrogen (NOX) emissions to nitrogen (N2) with high activity and selectivity. Testing was performed on coated cordierite ceramic cores using SwRI’s Universal Synthetic Gas Reactor® (USGR®). Various gas mixtures were employed, from model gas mixes to full exhaust simulant gas mixes. Activity was measured as a function of temperature, and gaseous inhibitors and promoters were identified. Different Ru supports were tested to identify ones with lowest temperature activity. A Ru catalyst can be used in the exhaust gas recirculation (EGR) leg of a Dedicated-EGR (D-EGR) engine [1,2], where it uses carbon monoxide (CO) and hydrogen (H2) present in the rich gas environment to reduce NOX to N2 with 100% efficiency and close to 100% selectivity to N2.

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.

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.

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.

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.

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.

The drive to more fuel efficient vehicles is underway, with passenger car targets of 54.5 mpg fleet average by 2025. Improving engine efficiency means reducing losses such as the heat lost in the exhaust gases. However, reducing exhaust temperature makes it harder for emissions control catalysts to function because they require elevated temperatures to be active. Addressing this conundrum was the focus of the work performed. The primary objective of this work was to identify low temperature limiters for a variety of catalyst aftertreatment types. The ultimate goal is to reduce catalyst light-off temperatures, and the knowledge needed is an understanding of what prevents a catalyst from lighting off, why, and how it may be mitigated. Collectively these are referred to here as low temperature limiters to catalyst activity.

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.

SwRI has developed the DCO® ignition system, a unique continuous discharge system that allows for variable duration/energy events in SI engines. The system uses two coils connected by a diode and a multi-striking controller to generate a continuous current flow through the spark plug of variable duration. A previous publication demonstrated the ability of the DCO system to improve EGR tolerance using low energy coils. In this publication, the work is extended to high current (≻ 300 mA/high energy (≻ 200 mJ) coils and compared to several advanced ignition systems. The results from a 4-cylinder, MPI application demonstrate that the higher current/higher energy coils offer an improvement over the lower energy coils. The engine was tested at a variety of speed and load conditions operating at stoichiometric air-fuel ratios with gasoline and EGR dilution.

This paper forms the third of a series and presents results obtained during the testing and development phase of a dedicated range extender engine designed for use in a compact class vehicle. The first paper in this series used real world drive logs to identify usage patterns of such vehicles and a driveline model was used to determine the power output requirements of a range extender engine for this application. The second paper presented the results of a design study. Key attributes for the engine were identified, these being minimum package volume, low weight, low cost, and good NVH. A description of the selection process for identifying the appropriate engine technology to satisfy these attributes was given and the resulting design highlights were described. The paper concluded with a presentation of the resulting specification and design highlights of the engine. This paper will present the resulting engine performance characteristics.

Nitrous Oxide (N2O) is a greenhouse gas with a Global Warming Potential (GWP) of 298-310 [1,2] (298-310 times more potent than carbon dioxide (CO2)). As a result, any aftertreatment system that generates N2O must be well understood to be used effectively. Under low temperature conditions, N2O can be produced by Selective Catalytic Reduction (SCR) catalysts. The chemistry is reasonably well understood with N2O formed by the thermal decomposition of ammonium nitrate [3]. Ammonium nitrate and N2O form in oxides of nitrogen (NOx) gas mixtures that are high in nitrogen dioxide (NO2)[4]. This mechanism occurs at a relatively low temperature of about 200°C, and can be controlled by maintaining the nitric oxide (NO)/NO2 ratio above 1. However, N2O has also been observed at relatively high temperatures, in the region of 500°C.

Selective catalytic reduction (SCR) catalysts will be used to reduce oxides of nitrogen (NOx) emissions from internal combustion engines in a number of applications [1,2,3,4]. Southwest Research Institute® (SwRI)® performed an Internal Research & Development project to study SCR catalyst thermal deactivation. The study included a V/W/TiO2 formulation, a Cu-zeolite formulation and an Fe-zeolite formulation. This work describes NOx timed response to ammonia (NH3) transients as a function of thermal aging time and temperature. It has been proposed that the response time of NOx emissions to NH3 transients, effected by changes in diesel emissions fluid (DEF) injection rate, could be used as an on-board diagnostic (OBD) metric. The objective of this study was to evaluate the feasibility and practicality of this OBD approach.

Nitrous Oxide (N₂O) is a greenhouse gas with a Global Warming Potential (GWP) of 298-310 (298-310 times more potent than carbon dioxide (CO₂)). As a result, any aftertreatment system that generates N₂O must be well understood to be used effectively. Under low temperature conditions, N₂O can be produced by Selective Catalytic Reduction (SCR) catalysts. The chemistry is reasonably well understood with N₂O formed by the thermal decomposition of ammonium nitrate. Ammonium nitrate and N₂O form in oxides of nitrogen (NOx) gas mixtures that are high in nitrogen dioxide (NO₂). This mechanism occurs at a relatively low temperature of about 200°C, and can be controlled by maintaining the nitric oxide (NO)/NO₂ ratio above 1. However, N₂O has also been observed at relatively high temperatures, in the region of 500°C.

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.

Selective Catalytic Reduction (SCR) catalysts are used to reduce NOx emissions from internal combustion engines in a variety of applications. Southwest Research Institute (SwRI) performed an Internal Research & Development project to study SCR catalyst thermal deactivation. The study included a V/W/TiO₂ formulation, a Cu-zeolite formulation and a Fe-zeolite formulation. This work describes NH₃ storage capacity measurement data as a function of aging time and temperature. Addressing one objective of the work, these data can be used in model-based control algorithms to calculate the current NH₃ storage capacity of an SCR catalyst operating in the field, based on time and temperature history. The model-based control then uses the calculated value for effective DEF control and prevention of excessive NH₃ slip. Addressing a second objective of the work, accelerated thermal aging of SCR catalysts may be achieved by elevating temperatures above normal operating temperatures.

Selective catalytic reduction (SCR) catalysts will be used to reduce oxides of nitrogen (NOx) emissions from internal combustion engines in a number of applications. Southwest Research Institute® (SwRI)® performed an Internal Research & Development project to study SCR catalyst thermal deactivation. The study included a V/W/TiO₂ formulation, a Cu-zeolite formulation and an Fe-zeolite formulation. This work describes NOx timed response to ammonia (NH₃) transients as a function of thermal aging time and temperature. It has been proposed that the response time of NOx emissions to NH₃ transients, effected by changes in diesel emissions fluid (DEF) injection rate, could be used as an on-board diagnostic (OBD) metric. The objective of this study was to evaluate the feasibility and practicality of this OBD approach.

OBD requirements for aftertreatment system components require monitoring of the individual system components. One such component can be an NH3-SCR catalyst for NOx reduction. An OBD method that has been suggested is to generate positive or negative spikes in the inlet NH3 concentration, and monitor the outlet NOx transient response. A slow response indicates that the catalyst is maintaining its NH3 storage capacity, and therefore it is probably not degraded. A fast response indicates the catalyst has lost NH3 storage capacity, and may be degraded. The purpose of the work performed at Southwest Research Institute was to assess this approach for feasibility, effectiveness and practicality. The presentation will describe the work performed, results obtained, and implications for applying this method in test laboratory and real-world situations. Presenter Gordon J. Bartley, Southwest Research Institute