Diesel Emission Control in Review

<div class="section abstract"><div class="htmlview paragraph">The challenge for decreasing the emissions of compression ignition engines now remains mainly on NOx control. If the Lean NOx Trap (LNT) and Selective Catalytic Reduction by Urea (Urea-SCR) are very efficient, their extra-cost and management are a major issue for the OEMs. In that context, the selective catalytic reduction by hydrocarbons (HC-SCR) appears to be an interesting alternative solution, with a more limited NOx conversion efficiency but an easier packaging (diesel fuel as a reductant) and a limited price (reasonable coating cost / no PGM).</div><div class="htmlview paragraph">In the framework of the RedNOx project, a prototype catalyst made of 2% silver on Alumina coated on cordierite was manufactured and tested on a synthetic gas bench. In parallel, an exhaust implementation study has been led to ensure the most suited conditions for injection. Thanks to SGB and simulation results, adapted engine tests have been designed and performed.</div><div class="htmlview paragraph">If the results on SGB are consistent with the literature with a maximum NOx conversion reaching about 70% and an operating range between 300 and 500°C, first engine results were very disappointing showing efficiencies lower than 15% for all the operating points. Three guidelines for improving these results were identified and studied: <ul class="list disc"><li class="list-item"><div class="htmlview paragraph">The way the reductant is introduced in the exhaust, especially the discontinued HC delivery due to the injection pattern</div></li><li class="list-item"><div class="htmlview paragraph">The gas velocity: unusual small GHSV values for automotive applications are needed to ensure a good NOx conversion rate.</div></li><li class="list-item"><div class="htmlview paragraph">The nature of the used reductant. Diesel fuel (ULSD) compared with decane lowers the efficiency, but synthetic Diesel fuel (SD) and, moreover, ethanol, largely improve it, especially for high GHSV.</div></li></ul></div></div>

<div class="section abstract"><div class="htmlview paragraph">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.</div><div class="htmlview paragraph">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. This paper describes the work performed to identify low temperature limiters to catalyst activity for gasoline Three Way Catalyst (TWC), Diesel Oxidation Catalyst (DOC), Cu-Z Selective Catalytic Reduction (SCR), Fe-Z SCR and V SCR, Lean NOx Trap (LNT), Ammonia Oxidation Catalyst (AMOx) and Natural Gas Oxidation Catalyst (NGOx).</div></div>

<div class="htmlview paragraph">Effective implementation of lean NOx trap (LNT) technologies requires the development of desulfation strategies to prevent significant degradation of LNT performance as a result of sulfur poisoning. Key to desulfation investigations is the requirement for a controllable and realistic sulfur loading model.</div> <div class="htmlview paragraph">The use of market based fuels can give inconsistent results due to variation of sulfur levels, and increased engine development times. Traditionally, increasing the sulfur level in the fuel via a specific sulfur based dopant has been used to accelerate the sulfation. This research used a different approach, in which sulfur dioxide was rapidly injected immediately prior to the LNT. The ability to replicate slow sulfur accumulation, as well as the benefits of injection control are demonstrated on a gasoline direct injection spark ignition (DISI) engine with LNT aftertreatment, tested on a dynamic dynamometer facility.</div> <div class="htmlview paragraph">The development of the sulfation injection technique enabled a series of sulfur loads and desulfation (DeSOx) experiments to be run. This study investigated the effect of sulfur loading, LNT temperature, and air:fuel ratio (AFR) on the DeSOx efficiency. The study shows that LNT DeSOx rate is fundamentally linked to the LNT temperature; and that other parameters, such as sulfur load, are far less critical to desorption rate.</div>

<div class="htmlview paragraph">Driven mainly by tightening of regulations, advance diesel emission control technologies are rapidly advancing. This paper will review the field with the intent of highlighting representative studies that illustrate the state-of-the-art. First, the author makes estimates of the emission control efficiency targets for heavy and light duty applications. Given the emerging significance of ultrafines to health, and to emission control technologies, an overview of the significant developments in ultrafine particulate science is provided, followed by an assessment of filter technology. Major deNOx catalyst developments, in addition to SCR and LNT progress is described. Finally, system integration examples are provided.</div> <div class="htmlview paragraph">In general, progress is impressive and studies have demonstrated that high-efficiency systems are within reach in all sectors highway vehicle sectors. Engines are making impressive gains, and will increase the options for emission control. Regarding ultrafines, evidence suggests the aerosol nanoparticles come from lube oil. Filter technology is focusing on optimization, with work being done on better ways to regenerate the filter and improving system back pressure. SCR NOx control is focusing on urea injection algorithms, and system optimization, while NOx adsorbers are showing marked improvements in performs and durability. System integration of filters and NOx control is moving into heavy-duty systems, albeit mainly on the bench.</div>

<div class="section abstract"><div class="htmlview paragraph">Selective Catalytic Reduction (SCR) operation depends strongly on both heat and ammonia availability (stored or incoming). These requirements make high efficiency SCR challenging in lower temperature cycles where SCR is relatively cold, and Diesel Exhaust Fluid (DEF) injection is largely absent due to deposit risks. Examples include low temperature cycles such as low-idling, stop-and-go or low-load cycles such as city driving or local delivery cycles.</div><div class="htmlview paragraph">An Electrically Heated Mixer/ EHM™ is utilized to address these challenges in a single component. EHM simultaneously provides heat for rapid SCR heat-up during the cold phase or in other low-temperature operations, steady or transient. Second, its heating mechanism makes deposit risks nearly non-existent. Third, EHM enables DEF injection at 130 °C, markedly enhancing the low temperature SCR impact. It is shown that these capabilities collectively make EHM a promising pathway for meeting ultra-stringent NOx targets including California 2027 (0.02 gr/hp.hr). Via rapidly heating the SCR catalyst during cold-start, EHM enables substantially lowering the cold-phase NOx. For instance, it is shown this lowers the cold FTP and cold WHTC NOx emission by 2 – 2.5 fold and in Low-Load Cycle by 22-fold.</div><div class="htmlview paragraph">EHM also allows DEF injection in low exhaust temperatures such as in 70 - 80 °C, for instance for rapidly filling the SCR catalyst with ammonia, if needed.</div><div class="htmlview paragraph">Unlike adding other exhaust flow heating devices where an additional component is ultimately integrated in the aftertreatment architecture, EHM is a mixer, already present in emission control systems. These flexibilities, along with its lower cost and ease in fitting, make EHM an enabling pathway for Diesel emission control systems meeting very low NOx regulations.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Diesel aftertreatment (AT) systems are critical for controlling emissions of CO, HC, NO<sub>X</sub>, and PM in the on-road transportation sector. Ensuring compliance with regulatory standards throughout the AT system's lifespan requires precise prediction of various degradation mechanisms under real-world operating conditions and mitigating their impact through proper catalyst sizing and advanced controls. In the SwRI A2CAT-II consortium, a medium-duty diesel engine production aftertreatment system was subjected to full useful life aging, involving chemical poisoning with phosphorus (P) and sulfur (S) species, along with hydrothermal aging following the DAAAC protocol. This study was aimed to model and predict the aging trajectory of this production AT system thereby capturing changes in system dynamics under both steady-state and transient conditions. The system, designed to meet the 0.2 g/bhp-hr standard, comprised a Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR), and Ammonia Slip Catalyst (ASC). It was aged to 3600 hours equivalent to the DAAAC protocol and tested across a series of steady-state and regulatory cycles (HFTP, RMC, and LLC) at degreened, 33%, 66%, and 100% aging points. A linear decrease in system NOx conversion was observed between 0% to 66% aging, followed by a nonlinear drop from 66% to 100%. The cumulative decline in NOx conversion was 0.8%, which could significantly impact systems designed to meet a 0.05 g/bhp-hr target.</div><div class="htmlview paragraph">IntroductionAftertreatment durability demonstration is a mandatory validation exercise for on-road medium and heavy-duty diesel engine certification. This requirement ensures that the emission compliance can be achieved for the intended full useful life (FUL) of the engine system or multiple vehicle families. Conventional Deterioration Factor (DF) approach considers linear effect of sulfur and phosphorous poisoning on the catalysts over the entire useful life based on performance from 33% of aging the catalysts and extrapolating them to FUL. However, based on various studies, the impact of fuel derived Sulfur on diesel aftertreatment components was found to be exponentially significant particularly on the SCR due to the sulfur poisoning effect which require an active means to liberate sulfur to maintain appropriate SCR NOx conversion performance. Phosphorous from lubricating oil is known to adversely affect the activity of the oxidation catalyst in a catalyzed DPF thereby reducing the passive regenerative performance of DPF. For these reasons, an extensive understanding of chemical poisoning (particularly Sulfur and Phosphoros) and hydrothermal aging are warranted to design, validate and demonstrate the durability of aftertreatment components that are subjected to the prolonged chemical exposure.</div><div class="htmlview paragraph">To address the extensive challenges in durability demonstration, the Diesel Aftertreatment Accelerated Aging Protocol, or DAAAC, was developed by Southwest Research Institute as a part of consortium effort that includes input from diesel engine manufacturers [<span class="xref">1</span>, <span class="xref">2</span>, <span class="xref">3</span>]. DAAAC is an accelerated aging cycle developed for each application based on the available field data. It includes the exposure from hydrothermal aging, sulfur and lubricant derived poison at accelerated rates. The protocol also requires the entire aftertreatment system to be aged as a complete system, since the upstream components, such as DOC, can impact the chemical makeup of sulfur derived constituents.</div><div class="htmlview paragraph">The protocol does not introduce chemical constituents not normally observed in the field. The accelerated chemical exposure rate is limited only to a degree that has previously demonstrated successful correlation to normal, unaccelerated aging. The Protocol also requires that chemical aging mechanisms are to be introduced and / or consumed in a manner representative of the engine’s defined consumption pathways. Examples include sulfur exposure via high sulfur fuel or gaseous SO<sub>2</sub> and oil consumption via pre-combustion / post-combustion pathways. The Protocol also does not introduce chemical components that are not normally present in oil or fuel (other than doping the fuel with higher concentrations of sulfur, but this amount is relatively small). A comprehensive step by step breakdown of DAAAC protocol is presented elsewhere [<span class="xref">2</span>].</div><div class="htmlview paragraph">The primary objective of this paper is to disseminate the observation of long-term impacts of chemical poisoning and hydrothermal aging on a production aftertreatment catalyst subjected to FUL DAAAC protocol. The results of this experimental campaign were used to develop and validate a model capable of predicting hydrothermal and chemical aging mechanisms of conventional diesel aftertreatment to optimize long term emissions reduction performance. The paper is divided into following sections: <ol class="list nostyle"><li class="list-item"><span class="li-label">1</span><div class="htmlview paragraph">Introduction: An overview of the system</div></li><li class="list-item"><span class="li-label">2</span><div class="htmlview paragraph">Background: A review of literature in the field of diesel AT aging</div></li><li class="list-item"><span class="li-label">3</span><div class="htmlview paragraph">Test Campaign: Description of experimental setup used for collection of both steady state and transient data.</div></li><li class="list-item"><span class="li-label">4</span><div class="htmlview paragraph">Experimental setup: Description of burner stand used for data collection.</div></li><li class="list-item"><span class="li-label">5</span><div class="htmlview paragraph">Results and Discussion: Description of experimental results followed by discussion about underlying degradation mechanism identified through simulation work.</div></li><li class="list-item"><span class="li-label">6</span><div class="htmlview paragraph">Summary and conclusion</div></li></ol></div></div>

<div class="section abstract"><div class="htmlview paragraph">Various engine platforms employ Selective Catalytic Reduction (SCR) technology to reduce the tail pipe emissions of oxides of nitrogen (NOx) from diesel engines as part of an overall strategy to comply with the emission regulations in place in various countries. High levels of NOx conversion (greater than 98%) in SCR aftertreatment may provide operating margin to increase overall fuel efficiency. However, to realize the potential fuel efficiency gains, the SCR technology employed should achieve high NOx conversion with limited reductant slip over transient application cycles in addition to steady state operation.</div><div class="htmlview paragraph">A new approach to SCR controls was developed and implemented. This approach does not rely on any maps to determine the amount of urea solution to be dosed, thus significantly reducing calibration and development time and effort when implementing the SCR technology on multiple engine platforms and applications.</div><div class="htmlview paragraph">In addition, the controls technique is completely model based and was able to achieve high NOx conversion efficiencies through the SCR system, while ensuring limited ammonia slip due to sharp transient events in the application cycle. This ability allows the system to extract the maximum performance from the SCR catalyst, enabling the catalyst size to be optimized for space and cost constraints.</div><div class="htmlview paragraph">The successful implementation of this control technique requires an SCR model with prediction accuracies greater than that typically achieved in practical implementation. Therefore, a real time correction technique was used to enhance the model accuracy to the desired levels for use in the controls algorithm.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Small commercial vehicles (SCV) with Diesel engines require efficient exhaust aftertreatment systems to reduce the emissions while keeping the fuel consumption and total operating cost as low as possible. To meet current emission legislations in all cases, a DOC and DPF and some NOx treatment device (e,g. lean NOx trap or SCR) are required.</div><div class="htmlview paragraph">Creating a cost-effective SCV also requires keeping the cost for the exhaust aftertreatment system as low as possible because the contribution to total vehicle cost is high. By using more sophisticated and more robust operating strategies and control algorithms, the hardware cost can be reduced. To keep the calibration effort at a low level, it is necessary to apply only algorithms which have a time-efficient calibration procedure.</div><div class="htmlview paragraph">This paper will focus on the active regeneration of the DPF. For safe and efficient DPF regeneration, a very reliable and stable DOC out temperature control is required. DOC characteristics and design are often limited by cost and available space but also strongly influence the control requirements and thus the performance. This leads to more sophisticated and more robust control algorithms.</div><div class="htmlview paragraph">In this paper an advanced control algorithm for DOC outlet temperature control for a SCV is presented. The control algorithm applies model-based control and gain-scheduling techniques. An overview over the control algorithm is given and its performance is evaluated on engine test bench, chassis dynamometer and on the public road and compared to the traditional concept which was used before. The results and experiences are presented and analyzed.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Selective Catalytic Reduction (SCR) catalysts used in Lean NO<sub>x</sub> Trap (LNT) - SCR exhaust aftertreatment systems typically encounter alternating oxidizing and reducing environments. Reducing conditions occur when diesel fuel is injected upstream of a reformer catalyst, generating high concentrations of hydrogen (H₂), carbon monoxide (CO), and hydrocarbons to deNO<sub>x</sub> the LNT. In this study, the functionality of an iron (Fe) zeolite SCR catalyst is explored with a bench top reactor during steady-state and cyclic transient SCR operation.</div><div class="htmlview paragraph">Experiments to characterize the effect of an LNT deNO<sub>x</sub> event on SCR operation show that adding H₂ or CO only slightly changes SCR behavior with the primary contribution being an enhancement of nitrogen dioxide (NO₂) decomposition into nitric oxide (NO). Exposure of the catalyst to C₃H₆ (a surrogate for an actual exhaust HC mixture) leads to a significant decrease in NO<sub>x</sub> reduction capabilities of the catalyst. A degradation mechanism is proposed to account for the decrease in NO<sub>x</sub> conversion efficiency, highlighted by reactions between NO₂ and C₃H₆ to make NO at a rate of similar order of magnitude as the Fast SCR reaction. This inhibits SCR reactions when the NO:NO<sub>x</sub> ratio favors NO, but can increase NO<sub>x</sub> conversion when the NO:NO<sub>x</sub> ratio favors NO₂.</div><div class="htmlview paragraph">Ammonia (NH₃) storage is only marginally affected by the presence of H₂, CO, or C₃H₆; but significant amounts of C₃H₆ can be stored on the catalyst. Further observation reveals that the oxidation effects of C₃H₆ are non-negligible and C₃H₆ strongly influences the oxidation of NH₃. The degradation mechanism includes seven proposed reactions to model the experimental results of adding H₂, CO, and C₃H₆ to the SCR feed gas during steady-state and transient operation.</div></div>

<div class="section abstract"><div class="htmlview paragraph">This paper focuses on measuring particle emissions of a representative light-duty diesel vehicle equipped with different engine exhaust aftertreatment in close-coupled position, including one designed to meet the upcoming Euro 6 emission standards. The latter combines a lean NOx trap (LNT) and a diesel particulate filter (DPF) in series to simultaneously reduce NOx and PM.</div><div class="htmlview paragraph">Particle Matter (PM) and particle number emissions are measured throughout testing procedure and instrumentation which are compliant with the UN-ECE Regulation 83 proposals. Specifically measuring devices for particle number emissions, provided by two different suppliers, are alternatively used. No significant differences are observed due to the different system employed. On the other hand particle size distributions are measured by means of a specific experimental set-up including a two stage dilution system and an electrical low pressure impactor (ELPI).</div><div class="htmlview paragraph">Particle emissions are evaluated over New European Driving Cycles (NEDCs) in cold start conditions with different amount of soot loaded into the DPF. Additionally, effect of different aftertreatment used are also registered and the impact of rich phase during DeNOx events is also evaluated with respect to this type of emissions.</div><div class="htmlview paragraph">Traditional particle mass gravimetric measurements and particle counting emissions are compared to highlight differences and effectiveness of both measurement methods.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Selective Catalytic Reduction (SCR) systems are crucial for automotive emissions control, as they are essential to comply with stringent emissions regulations. Model-based SCR controls are used to minimize NOx emissions in a broad range of real-word driving scenarios, constantly adapting the urea injection to diverse load and temperature operating conditions, also accounting for different catalyst ageing status. In this framework, Neural Networks (NN) based models offer a promising alternative to reduced-order physical models or map-based controls.</div><div class="htmlview paragraph">This study introduces a hybrid modeling approach for SCR systems, leveraging the integration of machine learning techniques with detailed physics-based models. A high fidelity 1D-CFD plant model of a SCR catalyst, previously calibrated on experimental data, was used as digital twin of the real component. A standardized simulation protocol was defined to virtually characterize the SCR thermal and chemical behavior under the full range of operating conditions typically covered during the real operation of the system. The generated dataset, including hard-to-measure physical quantities such as the catalyst wall temperature and the ammonia storage, was used to train and validate the neural network models. In particular, Recurrent Neural Networks (RNN) were used to mimic catalyst wall temperature and ammonia storage temporal trends, while Feed Forward Neural Networks (FFNN) were applied to model SCR outlet temperature and species concentrations such as NOx and NH3.</div><div class="htmlview paragraph">The NN-based SCR model predictive capabilities were assessed against experimental driving cycles data. The results show that the NN model is able to accurately capture the non-linear characteristics of the system behavior, even under the highly transient conditions typical of real-driving scenarios, thus confirming the reliability of the proposed methodology.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The Diesel engine combustion process results in harmful exhaust emissions, mainly composed of Particulate Matter (PM), Hydro Carbon (HC), Carbon monoxide (CO) and Nitrogen Oxides (NO<sub>x</sub>). Several technologies have been developed in the past decades to control these diesel emissions. One of the promising and well matured technology of reducing NO<sub>x</sub> is to implement Selective Catalytic Reduction (SCR) using ammonia (NH<sub>3</sub>) as the reducing agent. For an effective SCR system, the aqueous urea solutions should be fully decomposed into ammonia and it should be well distributed across the SCR. In the catalyst, all the ammonia is utilized for NO<sub>x</sub> reduction process. In the design stage, it is more viable to implement Computational Fluid Dynamics (CFD) for design iterations to determine an optimized SCR system based on SCR flow distribution. And in later stage, experimental test is required to predict the after-treatment system performance based on NO<sub>x</sub> reduction.</div><div class="htmlview paragraph">The SCR model predicts the NH<sub>3</sub> formation from urea decomposition and it is quantified at the SCR inlet, whereas experimental data involves the NO<sub>x</sub> reduction process. In order to validate the numerical predictions, the modeling needs to include surface reactions happening in the SCR catalyst bed. There are many factors that affect NO<sub>x</sub> conversion process, such as exhaust temperature, NO<sub>2</sub>/NO<sub>x</sub> ratio, catalyst coating, oxidation, etc. To model SCR Kinetics, various input parameters are required and also the reaction process needs to be well defined. The objective of this work is to conduct urea SCR spray modeling studies to focus on these input parameters and to observe its influence over NO<sub>x</sub> reduction process.</div></div>

<div class="htmlview paragraph">The tightening legislation in the on-road heavy-duty diesel area means that pollution control systems will soon be widely introduced on such engines. A number of different aftertreatment systems are currently being considered to meet the incoming legislation, including Diesel Particulate Filters (DPF), Diesel Oxidation Catalysts (DOC) and Selective Catalytic Reduction (SCR) systems.</div> <div class="htmlview paragraph">Relatively little is known about the interactions between lubricant-derived species and such aftertreatment systems. This paper describes the results of an experimental program carried out to investigate these interactions within DPF, DOC and SCR systems on a state-of-the-art 9 litre engine.</div> <div class="htmlview paragraph">The influence of lubricant composition and lube oil ash level was investigated on the different catalyst systems. In order to reduce costs and to speed up testing, test oil was dosed into the fuel. Tests without dosing lubricant into the fuel were also run.</div> <div class="htmlview paragraph">Driving distances of up to 115,000 km (based on oil consumption) were simulated in these experiments. Following such treatments, no significant change in the activity of the CR-DPF oxidation catalyst, Diesel Oxidation Catalysts or SCR catalysts were observed. In each case, the distribution of oil-derived species was studied as a function of distance down the catalyst. It was found that the Ca, Zn and P were generally present in higher concentrations at the front of the catalyst, decreasing down the unit. In contrast, sulfur is distributed evenly throughout the length of each catalyst. This is because sulfur can be deposited from the gas phase and is more mobile on the catalyst surface.</div> <div class="htmlview paragraph">Interestingly, when doping high ash oil into the fuel it was found that the back pressure of the DPF system increased rapidly. This is particularly important since it is known that used engine oil is sometimes poured back into the fuel tank for disposal. These results imply that this practice may strongly affect the efficiency of DPF devices.</div> <div class="htmlview paragraph">This rapid increase in back pressure is a consequence of doping the fuel with the high ash oil, since operation of the engine with the high ash oil without doping, or with a low ash oil with doping, resulted in only a gradual increase in back pressure. In addition, the distribution of the ash in the filter was strongly affected when doping the high ash oil into the fuel, in that the ash was uniformly distributed down the length of the filter. In the other experiments carried out here, and in measurements of field-aged filters, the ash thickness increases with distance into the filter. These observations reveal that care needs to be taken when doping oil into the fuel to accelerate the observation of oil-derived effects in DPF systems.</div>

<div class="htmlview paragraph">The implementation and development efforts of lean NOx trap catalysts for heavy-duty applications decreased a number of years ago. Most heavy-duty engine manufacturers realized that the system complexity as well as the durability of such a system does not allow large volume production without significant risk. The current consensus of the heavy-duty community is that for 2010 the SCR system will be the prime path to meet the 0.2 g/bHPhr NO<sub>x</sub> emission standard, although this is subject to adequate infrastructure investment and progress.</div> <div class="htmlview paragraph">As a low volume manufacturer, in order to comply with the 2007 heavy-duty phase-in emission standards, General Engine Products (a subsidiary of AM General LLC) integrated a NO<sub>x</sub> adsorber system on the Optimizer 6500 engine. This engine features split combustion chamber design, rotary fuel injection pump and operates with EGR. The engine meets the 2004 heavy-duty emission standards, but does not allow a NO<sub>x</sub> reduction through engine internal measures that would allow certification to 2007 emission standards. This fact forced the introduction of an exhaust aftertreatment system with NO<sub>x</sub> conversion efficiencies in the 60% range. The developmental results were presented in greater detail in paper 2007-01-0235.</div> <div class="htmlview paragraph">The paper discusses the details of the catalyst system development, the oxygen storage management of the different components and the associated hydrocarbon breakthrough during DNT regenerations as well as the durability results of the DF testing.</div>

<div class="section abstract"><div class="htmlview paragraph">Today turbo-diesel powertrains offering low fuel consumption and good low-end torque comprise a significant fraction of the light-duty vehicle market in Europe. Global CO₂ regulation and customer fuel prices are expected to continue providing pressure for powertrain fuel efficiency. However, regulated emissions for NO</div><div class="htmlview paragraph"> and particulate matter have the potential to further expand the incremental cost of diesel powertrain applications. Vehicle segments with the most cost sensitivity like compacts under 1400 kg weight look for alternatives to meet the CO₂ challenge but maintain an attractive customer offering. In this paper the concepts of downsizing and downspeeding gasoline engines are explored while meeting performance needs through increased BMEP to maintain good driveability and vehicle launch dynamics. A critical enabler for the solution is adoption of gasoline direct injection (GDi) fuel systems. GDi provides the ability to utilize increased scavenging without sacrificing hydrocarbon emissions because fueling and air controls can be separated. In-cylinder injection with GDi also provides charge cooling benefit yielding the knock reduction necessary for turbocharged applications. Several options within GDi are explored including multi-hole and single pintle spray generators, as well as side-mount versus central-mount applications. Both 3-cylinder and 4-cylinder base engine configurations are explored for turbocharged engines downsized to 1.2 L. Improvements in hydrocarbon emissions, heat losses and scavenging favor fewer cylinders. This is re-enforced by packaging and cost considerations. The next system aspect considered is emissions aftertreatment. Stoichiometric turbocharged GDi provides the lowest cost using the established 3-way catalyst. Stratified GDi is expected to require a lean NO</div><div class="htmlview paragraph"> trap (LNT) and diesel Euro 6 systems require addition of a diesel particulate filter (DPF) and possibly NO</div><div class="htmlview paragraph"> aftertreatment. Although the aftertreatment system to meet Euro 6 NO</div><div class="htmlview paragraph"> requirement is not known today, addition of a DPF, DPF with LNT, or DPF with urea selective catalytic reduction (SCR) represent significant cost and packaging challenges. The analysis concludes by comparing the 3-cylinder turbocharged GDi to other offerings in the context of value tradeoff of CO₂ reduction to system on-cost. Stratified 3-cylinder turbocharged GDi systems offer up to 22% CO₂ reduction compared to a baseline port-fuel-injected 4-cylinder engine. CO₂ reduction of 18% is possible for a stoichiometric GDi mechanization that employs variable valve actuation (VVA) and a conventional 3-way catalytic converter. At Euro 6 emission levels, stoichiometric 3-cylinder turbocharged GDi powertrains offer excellent value. The 3-cylinder turbo-diesel offers similar value if it is capable of meeting the NO</div><div class="htmlview paragraph"> emissions standard without lean aftertreatment. Powertrains with higher engine-out NO</div><div class="htmlview paragraph"> levels that require lean aftertreatment are significantly disadvantaged. Based on the price sensitivity of the compact car segment, the value analysis predicts the 3-cylinder turbocharged GDi engine as the powertrain of choice.</div></div>