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It is widely recognized that future NOx and particulate matter (PM) emission targets for diesel engines cannot be met solely via advanced combustion over the full engine drive cycle. Therefore some combination of advanced combustion and aftertreatment technologies will be required. In this study, advanced combustion modes operating with a diesel particulate filter (DPF) and a lean NOx trap (LNT) catalyst were evaluated on a 1.7 liter 4-cylinder diesel engine. The combustion approaches included baseline engine operation with and without exhaust gas recirculation (EGR) and one PCCI-type (premixed charge combustion ignition) combustion mode to enable high efficiency clean combustion (HECC). Five steady-state operating conditions were evaluated. At the low load setting the exhaust temperature was too low to enable LNT regeneration and oxidation; however, HECC (low NOx) was achievable.

Ethanol is a very effective reductant for nitrogen oxides (NOX) over silver/alumina (Ag/Al2O3) catalysts in lean exhaust environments. With the widespread availability of ethanol/gasoline-blended fuel in the U.S., lean gasoline engines equipped with Ag/Al2O3 catalysts have the potential to deliver higher fuel economy than stoichiometric gasoline engines and to increase biofuel utilization while meeting exhaust emissions regulations. In this work a pre-commercial 2 wt% Ag/Al2O3 catalyst was evaluated on a 2.0-liter BMW lean burn gasoline direct injection engine for the selective catalytic reduction (SCR) of NOX with ethanol/gasoline blends. The ethanol/gasoline blends were delivered via in-pipe injection upstream of the Ag/Al2O3 catalyst with the engine operating under lean conditions. A number of engine conditions were chosen to provide a range of temperatures and space velocities for evaluation of catalyst performance.

NOx reduction product speciation during regeneration of a fully formulated lean NOx trap catalyst has been investigated using a bench-scale flow reactor. NH3 and N2O were both observed during the regeneration phase of fast lean/rich cycles that simulated engine operation. Formation of both products increased with higher reductant concentrations and lower temperatures. Steady flow experiments were used to decouple the regeneration reactions from the NOx storage and release processes. This approach enabled a detailed investigation into the reactions that cause both formation and destruction of non-N2 reduction products. Pseudo-steady state experiments with simultaneous flow of NOx and reductant indicated that high concentrations of CO or H2 drive the reduction reactions toward NH3 formation, while mixtures that are stoichiometric for N2 formation favor N2. These experiments also showed that NH3 is readily oxidized by both NO and O2 over the LNT catalyst.

The fueleconomy.gov website provides information such as “window label” fuel economy for city, highway, and combined driving for all U.S.-legal light-duty vehicles from 1984 to present. The site is jointly maintained by the U.S. Department of Energy and the U.S. Environmental Protection Agency (EPA), and also offers a considerable amount of consumer information and advice pertaining to vehicle fuel economy and energy-related issues. Included with advice pertaining to driving styles and habits is information concerning the trend that as highway cruising speed is increased, fuel economy will degrade. An effort was undertaken to quantify this “conventional wisdom” through analysis of dynamometer testing results for 74 vehicles at steady-state speeds from 50 to 80 mph. Using this experimental data, several simple models were developed to predict individual vehicle fuel economy and its rate of change over the 50-80 mph speed range interval.

NOx emissions have traditionally been difficult to control from diesel engines; however, lean NOx trap catalysts have been shown to reduce NOx emissions from diesel engines by greater than 90% under some conditions. It is imperative that lean NOx traps be highly selective to N2 to achieve the designed NOx emissions reduction. If selectivity for NOx reduction to NH3 or N2O is significant then, ultimately, higher levels of pollution or greenhouse emissions will result. Here studies of the N2 selectivity of lean NOx trap regeneration with in-cylinder techniques are presented. Engine dynamometer studies with a light-duty engine were performed, and a lean NOx trap in the exhaust system was regenerated by controlling in-cylinder fuel injection timing and amounts to achieve rich exhaust conditions. NH3 and N2O emissions were analyzed with FTIR spectroscopy.

High Efficiency Clean Combustion (HECC) strategies such as homogenous charge compression ignition (HCCI) and pre-mixed charge compression ignition (PCCI) offer much promise for the reduction of NOx and PM from diesel engines. While delivering low PM and low NOx, these combustion modes often produce much higher levels of CO and HC than conventional diesel combustion modes. In addition, partially oxygenated species such as formaldehyde (an MSAT) and other aldehydes increase with HECC modes. The higher levels of CO and HCs have the potential to compromise the performance of the catalytic aftertreatment, specifically at low load operating points. As HECC strategies become incorporated into vehicle calibrations, manufacturers need to avoid producing MSATs in higher quantities than found in conventional combustion modes. This paper describes research on two different HECC strategies, HCCI and PCCI.

Accurate knowledge of diesel particulate filter (DPF) particulate matter (PM) loading is critical for robust and efficient operation of the combined engine-exhaust aftertreatment system. Furthermore, upcoming on-board diagnostics regulations require on-board technologies to evaluate the status of the DPF. This work describes the application of radio frequency (RF) - based sensing techniques to accurately measure DPF particulate matter levels. A 1.9L GM turbo diesel engine and a DPF with an RF-sensor were studied. Direct comparisons between the RF measurement and conventional pressure-based methods were made. Further analysis of the particulate matter loading rates was obtained with a mass-based total PM emission measurement instrument (TEOM) and DPF gravimetric measurements.

Lean NOx Trap (LNT) catalysts can effectively reduce NOx from lean engine exhaust. Significant research for LNTs in diesel engine applications has been performed and has led to commercialization of the technology. For lean gasoline engine applications, advanced direct injection engines have led to a renewed interest in the potential for lean gasoline vehicles and, thereby, a renewed demand for lean NOx control. To understand the gasoline-based reductant chemistry during regeneration, a BMW lean gasoline vehicle has been studied on a chassis dynamometer. Exhaust samples were collected and analyzed for key reductant species such as H₂, CO, NH₃, and hydrocarbons during transient drive cycles. The relation of the reductant species to LNT performance will be discussed. Furthermore, the challenges of NOx storage in the lean gasoline application are reviewed.

Due to increasingly stringent emissions regulations, Lean NOx Trap (LNT) catalysts are being researched as a potential solution for diesel engine emissions reduction. LNTs are practical for diesel NOx reduction due to their ability to reduce NOx from the O2 rich environment produced by diesel engines. LNTs function by storing NOx on the catalyst surface during efficient lean operation then, under rich conditions, releasing and reducing the trapped NOx. One method of producing this rich environment which regenerates a LNT involves manipulating the fuel injection parameters and throttling the air intake. This process is called in-cylinder regeneration. Experiments will be described here in which a 1.7 L common rail diesel engine has been used to regenerate LNTs at various stages of sulfur exposure, a known poison of the LNT.

A Lean NOx Trap (LNT) regeneration method that has shown promise regarding its ability to effectively regenerate the LNT, while not adversely affecting the PM emissions, involves the use of Low Temperature Combustion (LTC). LTC is accomplished by highly diluting the intake charge with EGR.1-3* If enough EGR is applied, the in-cylinder air:fuel mixture, and ensuing exhaust, will become rich, thereby regenerating the LNT. This type of highly dilute combustion tends to be more premixed than diffusion, which can lower engine-out PM and NOx emissions. LTC regeneration has been characterized and results are presented comparing this approach to other approaches for rich, in-cylinder diesel combustion for LNT regeneration.

Hydrogen (H2) is an excellent reductant, and has been shown to be highly effective when introduced into a variety of catalysts such as three-way catalysts, lean NOx traps (LNTs), and hydrocarbon lean NOx catalysts (also termed hydrocarbon selective catalytic reduction (SCR) catalysts). Furthermore, since lean-burn engines offer improved fuel efficiency yet difficult NOx emission control, H2 production during lean operation for the purpose of NOx reduction could be beneficial. On-board generation of hydrogen is being explored via catalytic or plasma-based reformers. A possible alternative to these add-on systems is generation of the H2 in-cylinder with standard fuel injection hardware. This paper details experiments relating to the production and measurement of H2 under net-lean operation in a common-rail diesel engine. In-cylinder fuel control is used to tailor the combustion process such that H2 is generated while maintaining a lean Air:Fuel ratio in the bulk exhaust gas.

Advanced diesel combustion regimes such as High Efficiency Clean Combustion (HECC) offer the benefits of reduced engine out NOx and particulate matter (PM) emissions. Lower PM emissions during advanced combustion reduce the demand on diesel particulate filters (DPFs) and can, thereby, reduce the fuel penalty associated with DPF regeneration. In this study, a SiC DPF was loaded and regenerated on a 1.7-liter 4-cylinder diesel engine operated in conventional and advanced combustion modes at different speed and load conditions. A diesel oxidation catalyst (DOC) and a lean NOx trap (LNT) were also installed in the exhaust stream. Five steady-state speed and load conditions were weighted to estimate Federal Test Procedure (FTP) fuel efficiency. The DPF was loaded using lean-rich cycling with frequencies that resulted in similar levels of NOx emissions downstream of the LNT.

The combination of advanced combustion with advanced selective catalytic reduction (SCR) catalyst formulations was studied in the work presented here to determine the impact of the unique hydrocarbon (HC) emissions from premixed charge compression ignition (PCCI) combustion on SCR performance. Catalyst core samples cut from full size commercial Fe- and Cu-zeolite SCR catalysts were exposed to a slipstream of raw engine exhaust from a 1.9-liter 4-cylinder diesel engine operating in conventional and PCCI combustion modes. The zeolites which form the basis of these catalysts are different with the Cu-based catalyst made on a chabazite zeolite which has smaller pore structures relative to the Fe-based catalyst. Subsequent to exposure, bench flow reactor characterization of performance and hydrocarbon release and oxidation enabled evaluation of overall impacts from the engine exhaust.

In the current work, a series-hybrid vehicle has been constructed that utilizes a dual-fuel, Reactivity Controlled Compression Ignition (RCCI) engine. The vehicle is a 2009 Saturn Vue chassis and a 1.9L turbo-diesel engine converted to operate with low temperature RCCI combustion. The engine is coupled to a 90 kW AC motor, acting as an electrical generator to charge a 14.1 kW-hr lithium-ion traction battery pack, which powers the rear wheels by a 75 kW drive motor. Full vehicle testing was conducted on chassis dynamometers at the Vehicle Emissions Research Laboratory at Ford Motor Company and at the Vehicle Research Laboratory at Oak Ridge National Laboratory. For this work, the US Environmental Protection Agency Highway Fuel Economy Test was performed using commercially available gasoline and ultra-low sulfur diesel. Fuel economy and emissions data were recorded over the specified test cycle and calculated based on the fuel properties and the high-voltage battery energy usage.

This paper demonstrates the potential for fast absorption spectroscopy measurements in diesel-engine exhaust to track H2O concentration transients. Wavelength-agile absorption spectroscopy is an optical technique that measures broadband absorption spectra between 10 kHz and 100 MHz. From these measured spectra, gas temperature and absorber concentrations can be determined. We introduce a laser spectroscopy system for high speed (10 μs) diesel exhaust measurements in the presence of significant particulate matter. The sensor can be broadly applicable for understanding the dynamics of EGR distribution, cycle-to-cycle stability, cylinder-to-cylinder charge uniformity, and NOX regeneration strategies. The method precision is 10% and 5%, for individual 10-μs measurements and 2-ms averaged measurements, respectively. The sensitivity or detection limit of the measurement is 0.5% H2O.

The use of fuel reformate from catalytic processes is known to have beneficial effects on the spark-ignited (SI) combustion process through enhanced dilution tolerance and decreased combustion duration, but in many cases reformate generation can incur a significant fuel penalty. In a previous investigation, the researchers showed that, by controlling the boundary conditions of the reforming catalyst, it was possible to minimize the thermodynamic expense of the reforming process, and in some cases, realize thermochemical recuperation (TCR), a form of waste heat recovery where exhaust heat is converted to usable chemical energy. The previous work, however, focused on a relatively light-load engine operating condition of 2000 rpm, 4 bar brake mean effective pressure (BMEP). The present investigation demonstrates that this operating strategy is applicable to higher engine loads, including boosted operation up to 10 bar BMEP.

To quantify the fuel economy (FE) effect of some common vehicle accessories or alterations, a compact passenger sedan and a sport utility vehicle (SUV) were subjected to SAE J2263 coastdown procedures. Coastdowns were conducted with low tire pressure, all windows open, with a roof top or hitch-mounted cargo carrier, and with the SUV pulling an enclosed cargo trailer. From these coastdowns, vehicle dynamometer coefficients were developed which enabled the execution of vehicle dynamometer experiments to determine the effect of these changes on vehicle FE and emissions over standard drive cycles and at steady highway speeds. In addition, two minivans were subjected to coastdowns to examine the similarity in derived coefficients for two duplicate vehicles of the same model. The FE penalty associated with the rooftop cargo box mounted on the compact sedan was as high as 25-27% at higher speeds, where the aerodynamic drag is most pronounced.

Aggressive driving is an important topic for many reasons, one of which is higher energy used per unit distance traveled, potentially accompanied by an elevated production of greenhouse gases and other pollutants. Examining a large data set of self-reported fuel economy (FE) values revealed that the dispersion of FE values is quite large and is larger for hybrid electric vehicles (HEVs) than for conventional gasoline vehicles. This occurred despite the fact that the city and highway FE ratings for HEVs are generally much closer in value than for conventional gasoline vehicles. A study was undertaken to better understand this and better quantify the effects of aggressive driving, including reviewing past aggressive driving studies, developing and exercising a new vehicle energy model, and conducting a related experimental investigation.

New regulations requiring increases in vehicle fuel economy are challenging automotive manufacturers to identify fuel-efficient engines for future vehicles. Lean gasoline direct injection (GDI) engines offer significant increases in fuel efficiency over the more common stoichiometric GDI engines already in the marketplace. However, particulate matter (PM) emissions from lean GDI engines, particularly during stratified combustion modes, are problematic for lean GDI technology to meet U.S. Environmental Protection Agency Tier 3 and other future emission regulations. As such, the control of lean GDI PM with wall-flow filters, referred to as gasoline particulate filter (GPF) technology, is of interest. Since lean GDI PM chemistry and morphology differ from diesel PM (where more filtration experience exists), the functionality of GPFs needs to be studied to determine the operating conditions suitable for efficient PM removal.

Lean Gasoline Direct Injection (LGDI) combustion is a promising technical path for achieving significant improvements in fuel efficiency while meeting future emissions requirements. Though Stoichiometric Gasoline Direct Injection (SGDI) technology is commercially available in a few vehicles on the American market, LGDI vehicles are not, but can be found in Europe. Oak Ridge National Laboratory (ORNL) obtained a European BMW 1-series fitted with a 2.01 LGDI engine. The vehicle was instrumented and commissioned on a chassis dynamometer. The engine and after-treatment performance and emissions were characterized over US drive cycles (Federal Test Procedure (FTP), the Highway Fuel Economy Test (HFET), and US06 Supplemental Federal Test Procedure (US06)) and steady state mappings. The vehicle micro hybrid features (engine stop-start and intelligent alternator) were benchmarked as well during the course of that study.