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All high-pressure exhaust gas recirculation (EGR) coolers become fouled during operation due to thermophoresis of particulate matter and condensation of hydrocarbons present in diesel exhaust. In some EGR coolers, fouling is so severe that deposits form plugs strong enough to occlude the gas passages thereby causing a complete failure of the EGR system. In order to better understand plugging and means of reducing its undesirable performance degradation, EGR coolers exhibiting plugging were requested from and provided by industry EGR engineers. Two of these coolers contained glassy, brittle, lacquer-like deposits which were analyzed using gas chromatography-mass spectrometry (GC-MS) which identified large amounts of oxygenated polycyclic aromatic hydrocarbons (PAHs). Another cooler exhibited similar species to the lacquer but at a lower concentration with more soot.

A high-resolution corrosion probe was placed within the airhorn section of the exhaust gas recirculation (EGR) loop of a heavy-duty diesel engine. The corrosion rate of the mild-steel probe elements was evaluated as a function of fuel sulfur level, EGR fraction, dewpoint margin, and humidity. No significant corrosion was observed while running the engine using a No. 2 grade, < 15ppm sulfur diesel fuel; however, high corrosion rates were observed with No. 2 diesel fuel (∼350 ppm sulfur) while condensing water in the EGR loop. The rate of corrosion on the mild steel elements increased with increasing levels of sulfate in the condensate. However, the engine conditions influencing the sulfate level were not clearly identified in this study.

Light-duty chassis dynamometer driving cycle tests were conducted on a Mercedes A170 diesel vehicle with various sulfur-level fuels and exhaust emission control systems. Triplicate runs of a modified light-duty federal test procedure (FTP), US06 cycle, and SCO3 cycle were conducted with each exhaust configuration and fuel. Ultra-low sulfur (3-ppm) diesel fuel was doped to 30- and 150-ppm sulfur so ppm sulfur so that all other fuel properties remained the same. The fuels used in these experiments met the specifications of the fuels from the DECSE (Diesel Emission Control Sulfur Effects) program. Although the Mercedes A170 vehicle is not available in the United States, its emissions in the as tested condition fell within the U.S. Tier 1 full useful life standards with the OEM catalysts installed. Tests with the OEM catalysts removed showed that the OEM catalysts reduced PM emissions from the engine-out condition by 30-40% but had negligible effects on NOx emissions.

Exhaust gas recirculation (EGR) cooler fouling has become a significant issue for compliance with nitrogen oxides (NOx) emissions standards. In order to better understand fouling mechanisms, eleven field-aged EGR coolers provided by seven different engine manufacturers were characterized using a suite of techniques. Microstructures were characterized using scanning electron microscopy (SEM) and optical microscopy following mounting the samples in epoxy and polishing. Optical microscopy was able to discern the location of hydrocarbons in the polished cross-sections. Chemical compositions were measured using thermal gravimetric analysis (TGA), differential thermal analysis (DTA), gas chromatography-mass spectrometry (GC-MS), x-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD). Mass per unit area along the length of the coolers was also measured.

The buildup of deposits in EGR coolers causes significant degradation in heat transfer performance, often on the order of 20-30%. Deposits also increase pressure drop across coolers and thus may degrade engine efficiency under some operating conditions. It is unlikely that EGR cooler deposits can be prevented from forming when soot and HC are present. The presence of cooled surfaces will cause thermophoretic soot deposition and condensation of HC and acids. While this can be affected by engine calibration, it probably cannot be eliminated as long as cooled EGR is required for emission control. It is generally felt that “dry fluffy” soot is less likely to cause major fouling than “heavy wet” soot. An oxidation catalyst in the EGR line can remove HC and has been shown to reduce fouling in some applications. The combination of an oxidation catalyst and a wall-flow filter largely eliminates fouling. Various EGR cooler designs affect details of deposit formation.

Exhaust gas recirculation (EGR) cooler fouling has become a significant issue for compliance with NOx emissions standards. This paper reports results of a study of fundamental aspects of EGR cooler fouling. An apparatus and procedure were developed to allow surrogate EGR cooler tubes to be exposed to diesel engine exhaust under controlled conditions. The resulting fouled tubes were removed and analyzed. Volatile and non-volatile deposit mass was measured for each tube. Thermal diffusivity of the deposited soot cake was measured by milling a window into the tube and using the Xenon flash lamp method. The heat capacity of the deposit was measured at temperatures up to 430°C and was slightly higher than graphite, presumably due to the presence of hydrocarbons. These measurements were combined to allow calculation of the deposit thermal conductivity, which was determined to be 0.041 W/mK, only ∼1.5 times that of air and much lower than the 304 stainless steel tube (14.7 W/mK).

Exhaust gas recirculation (EGR) coolers experience degradation of performance as a result of the buildup of material in the gas-side flow paths of the cooler. This material forms a deposit layer that is less thermally conductive than the stainless steel of the tube enclosing the gas, resulting in lower heat exchanger effectiveness. Biodiesel fuel has a fuel chemistry that is much more susceptible to polymerization than that of typical diesel fuels and may exacerbate deposit formation in EGR coolers. A study was undertaken to examine the fundamentals of EGR cooler deposit formation by using surrogate tubes to represent the EGR cooler. These tubes were exposed to engine exhaust in a controlled manner to assess their effectiveness, deposit mass, and deposit hydrocarbon content. The tubes were exposed to exhaust for varying lengths of time and for varying coolant temperatures. The results show that measurable differences in the response variables occur within a few hours.

Fouling in EGR coolers occurs because of the presence of soot and condensable species (such as hydrocarbons) in the gas stream. Fouling leads to one of two possible outcomes: stabilization of effectiveness and plugging of the gas passages within the cooler. Deposit formation in the cooler under high-temperature conditions results in a fractal deposit that has a characteristic thermal conductivity of ∼0.033 W/m*K and a density of 0.0224 g/cm3. Effectiveness becomes much less sensitive to changes in thermal resistance as fouling proceeds, creating the appearance of “stabilization” even in the presence of ongoing, albeit slow, deposit growth. Plugging occurs when the deposit thermal resistance is several times lower because of the presence of large amounts of condensed species. The deposition mechanism in this case appears to be soot deposition into a liquid film, which results in increased packing efficiency and decreased void space in the deposit relative to high-temperature deposits.

The Office of Heavy Vehicle Technologies supports research to enable high-efficiency diesel engines to meet future emissions regulations, thus clearing the way for their use in light trucks as well as continuing as the most efficient powerplant for freight-haulers. Compliance with Tier 2 emission regulations for light-duty vehicles will require effective exhaust emission controls (aftertreatment) for diesels in these applications. Diesel-powered heavy trucks face a similar situation for the 2007 regulations announced by EPA in December 2000. DOE laboratories are working with industry to improve emission control technologies in projects ranging from application of new diagnostics for elucidating key mechanisms, to development and evaluation of prototype devices. This paper provides an overview of these R&D efforts, with examples of key findings and developments.

An experimental study was performed to understand fuel property effects on low temperature combustion (LTC) processes in a light-duty diesel engine. These types of combustion modes are often collectively referred to as high efficiency clean combustion (HECC). A statistically designed set of research fuels, the Fuels for Advanced Combustion Engines (FACE), were used for this study. Engine conditions of 1500rpm, 2.6bar BMEP was chosen for investigating fuel property effects on HECC operation in a GM 1.9-L common rail diesel engine. The FACE fuel matrix includes nine combinations of fuel properties including cetane number (30 to 55), aromatic content (20 to 45%), and 90% distillation temperature (270 to 340°C). HECC operation was achieved with high levels of exhaust gas recirculation (EGR) and adjusting injection parameters, such as higher fuel rail pressure and single injection event, which is also known as premixed charge compression ignition (PCCI) combustion.

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.

Previously reported work with a full-scale ethanol-SCR system featuring a Ag-Al2O3 catalyst demonstrated that this particular system has potential to reduce NOx emissions 80-90% for engine operating conditions that allow catalyst temperatures above 340°C. A concept explored was utilization of a fuel-borne reductant, in this case ethanol “stripped” from an ethanol-diesel micro-emulsion fuel. Increased tailpipe-out emissions of hydrocarbons, acetaldehyde and ammonia were measured, but very little N2O was detected. In the current increment of work, a number of light alcohols and other hydrocarbons were used in experiments to map their performance with the same Ag-Al2O3 catalyst. These exploratory tests are aimed at identification of compounds or organic functional groups that could be candidates for fuel-borne reductants in a compression ignition fuel, or could be produced by some workable method of fuel reforming.

Compact heat exchangers are commonly used in diesel engines to reduce the temperature of recirculated exhaust gases, resulting in decreased NOx emissions. These exhaust gas recirculation (EGR) coolers experience fouling through deposition of particulate matter (PM) and hydrocarbons (HCs) that reduces the effectiveness of the cooler. Surrogate tubes have been used to investigate the impacts of gas flow rate and coolant temperature on the deposition of PM and HCs. The results indicate that mass deposition is lowest at high flow rates and high coolant temperatures. An oxidation catalyst was investigated and proved to effectively reduce deposition of HCs, but did not reduce overall mass deposition to near-zero levels. Speciation of the deposit HCs showed that a range of HCs from C15 - C25 were deposited and retained in the surrogate tubes.

Advanced diesel combustion modes offer the promise of reduced engine-out particulate and nitrogen oxide emissions, thereby reducing the demand on post-combustion emission control devices. In this activity, a light-duty diesel engine was operated in conventional and advanced combustion modes. The advanced combustion modes investigated correspond to both clean (i.e., low PM and low NOX) and clean efficient combustion. The low-NOX, low-PM mode is considered an intermediate condition and the low-NOX, low-PM efficient mode is referred to as high efficiency clean combustion (HECC). Particulate and gaseous emissions were analyzed during all of these experiments. The detailed exhaust chemistry analysis provided significant new information to improving our understanding of these modes as well as identifying potentially important unregulated emissions.

In-cylinder fuel blending of gasoline with diesel fuel is investigated on a multi-cylinder light-duty diesel engine as a strategy to control in-cylinder fuel reactivity for improved efficiency and lowest possible emissions. This approach was developed and demonstrated at the University of Wisconsin through modeling and single-cylinder engine experiments. The objective of this study is to better understand the potential and challenges of this method on a multi-cylinder engine. More specifically, the effect of cylinder-to-cylinder imbalances and in-cylinder charge motion as well as the potential limitations imposed by real-world turbo-machinery were investigated on a 1.9-liter four-cylinder engine. This investigation focused on one engine condition, 2300 rpm, 5.5 bar net mean effective pressure (NMEP). Gasoline was introduced with a port-fuel-injection system.

The influence of fuel rail pressure (FRP) and urea-selective catalytic reduction (SCR) on particulate matter (PM) formation is investigated in this paper along with notes regarding the NOx and other emissions. Increasing FRP was shown to reduce the overall soot and total PM mass for four operating conditions. These conditions included two high speed conditions (2400 rpm at 540 and 270 Nm of torque) and two moderated speed conditions (1400 rpm at 488 and 325 Nm). The concentrations of CO2 and NOx increased with fuel rail pressure and this is attributed to improved fuel-air mixing. Interestingly, the level of unburned hydrocarbons remained constant (or increased slightly) with increased FRP. PM concentration was measured using an AVL smoke meter and scanning mobility particle sizer (SMPS); and total PM was collected using standard gravimetric techniques. These results showed that the smoke number and particulate concentrations decrease with increasing FRP.

Urea-SCR systems are potentially a highly-effective means of NOX reduction for light-duty diesel vehicles. However, use of urea-SCR technologies at low temperatures presents unique technical challenges. This study was undertaken to provide more knowledge about low temperature urea decomposition and the resulting effects on SCR performance. Data are presented for experiments using two SCR catalysts of differing size with a light-duty diesel engine. Analyses of the NOX reduction efficiency, NH3 storage phenomena, and unregulated emissions are shown. Over production of NO2 by the oxidation catalyst is demonstrated to be problematic at 25,000 hr-1 space velocity for a range of temperatures. This leads to production of N2O by both SCR catalysts that is higher when urea is injected than when NH3 is injected.

Automobile manufacturers strive to minimize oil consumption from their engines due to the need to maintain emissions compliance over the vehicle life. Engine oil can contribute directly to organic gas and particle emissions as well as accelerate emissions degradation due to catalyst poisoning. During the Department of Energy Intermediate Ethanol Blends Catalyst Durability program, vehicles were aged using the Standard Road Cycle (SRC). In this program, matched sets of three or four vehicles were acquired; each vehicle of a set was aged on ethanol-free retail gasoline, or the same base gasoline blended with 10, 15, or 20% ethanol (E0, E10, E15, E20). The primary purpose of the program was to assess any changes in tailpipe emissions due to the use of increased levels of ethanol. Oil consumption was tracked during the program so that any measured emissions degradation could be appropriately attributed to fuel use or to excessive oil consumption.

Exhaust gas recirculation (EGR) cooler fouling has become a significant issue for compliance with NOX emissions standards and has negative impacts on cooler sizing and engine performance. In order to improve our knowledge of cooler fouling as a function of engine operating parameters and to predict and enhance performance, 19 tube-in-shell EGR coolers were fouled using a 5-factor, 3-level design of experiments with the following variables: (1) EGR flow rate, (2) EGR inlet gas temperature, (3) coolant temperature, (4) soot level, and (5) hydrocarbon concentration. A 9-liter engine and ULSD fuel were used to form the cooler deposits. Coolers were run until the effectiveness stabilized, and then were cooled down to room temperature and run for an additional few hours in order to measure the change in effectiveness due to shut down. The coolers were cut open and the mass per unit area of the deposit was measured as a function of distance down the tube.

The source of exhaust gas recirculation (EGR), and consequently composition and temperature, has a significant effect on advanced combustion modes including stability, efficiency, and emissions. The effects of high-pressure loop EGR (HPL EGR) and low-pressure loop EGR (LPL EGR) on achieving high efficiency clean combustion (HECC) modes in a light-duty diesel engine were characterized in this study. High dilution operation is complicated in real-world situations due to inadequate control of mixture temperature and the slow response of LPL EGR systems. Mixed-source EGR (combination of HPL EGR and LPL EGR) was investigated as a reasonable approach for controlling mixture temperature. The potential of mixed-source EGR has been explored using LPL EGR as a ‘base’ for dilution rather than as a sole source. HPL EGR provides the ‘trim’ for controlling mixture temperature and has the potential for enabling precise control of dilution targets.