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To cope with regulatory standards, minimizing tailpipe emissions with rapid catalyst light-off during cold-start is critical. This requires catalyst-heating operation with increased exhaust enthalpy, typically by using late post injections for retarded combustion and, therefore, increased exhaust temperature. However, retardability of post injection(s) is constrained by acceptable pollutant emissions such as unburned hydrocarbon (UHC). This study provides further insight into the mechanisms that control the formation of UHC under catalyst-heating operation in a medium-duty diesel engine, and based on the understanding, develops combustion strategies to simultaneously improve exhaust enthalpy and reduce harmful emissions. Experiments were performed with a full boiling-range diesel fuel (cetane number of 45) using an optimized five-injections strategy (2 pilots, 1 main, and 2 posts) as baseline condition.

The effects of thermal and chemical aging on the performance of cordierite-based and high-porosity mullite-based diesel particulate filters (DPFs), were quantified, particularly their filtration efficiency, pressure drop, and regeneration capability. Both catalyzed and uncatalyzed core-size samples were tested in the lab using a diesel fuel burner and a chemical reactor. The diesel fuel burner generated carbonaceous particulate matter with a pre-specified particle-size distribution, which was loaded in the DPF cores. As the particulate loading evolved, measurements were made for the filtration efficiency and pressure drop across the filter using, respectively, a Scanning Mobility Particle Sizer (SMPS) and a pressure transducer. In a subsequent process and on a different bench system, the regeneration capability was tested by measuring the concentration of CO plus CO2 evolved during the controlled oxidation of the carbonaceous species previously deposited on the DPF samples.

Thermal efficiencies of 54% have been demonstrated by single cylinder engine testing of advanced diesel engine concepts developed under Department of Energy funding. In order for these concept engines to be commercially viable, cost effective and durable systems for insulating the piston, head, ports and exhaust manifolds will be required. The application and development of new materials such as thick thermal barrier coating systems will be key to insulating these components. Development of test methods to rapidly evaluate the durability of coating systems without expensive engine testing is a major objective of current work. In addition, a novel, low cost method for producing thermal barrier coated pistons without final machining of the coating has been developed.

Fuel properties impact the engine-out emission directly. For some geographic regions where diesel engines can meet emission regulations without aftertreatment, the change of fuel properties will lead to final tailpipe emission variation. Aftertreatment systems such as Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) are required for diesel engines to meet stringent regulations. These regulations include off-road Tier 4 Final emission regulations in the USA or the corresponding Stage IV emission regulations in Europe. As an engine with an aftertreatment system, the change of fuel properties will also affect the system conversion efficiency and regeneration cycle. Previous research works focus on prediction of engine-out emission, and many are based on chemical reactions. Due to the complex mixing, pyrolysis and reaction process in heterogeneous combustion, it is not cost-effective to find a general model to predict emission shifting due to fuel variation.

Catalytic converters have become a viable aftertreatment system for reducing emissions from on-highway diesel engines. This paper addresses the development and production qualification of a catalytic converter. The testing programs that were utilized to qualify the converter system for production included emissions performance, emissions durability, physical durability, and field test programs. This paper reports on the specific tests that were utilized for the emissions performance and emissions durability testing programs. An explanation on the development of an accelerated durability test program is also included. The physical durability section of the paper discusses the development and execution of laboratory bench tests to insure the catalytic converter/muffler maintains acceptable physical integrity.

A slipstream of exhaust from a Caterpillar 3126B engine was diverted into a plasma-catalytic NOx control system in the space velocity range of 7,000 to 100,000 hr-1. The stream was first fed through a non-thermal plasma that was formed in a coaxial cylinder dielectric barrier discharge reactor. Plasma treated gas was then passed over a catalyst bed held at constant temperature in the range of 573 to 773 K. Catalysts examined consisted of γ-alumina, indium-doped γ-alumina, and silver-doped γ-alumina. Road and rated load conditions resulted in engine out NOx levels of 250 - 600 ppm. The effects of hydrocarbon level, catalyst temperature, and space velocity are discussed where propene and in one case ultra-low sulfur diesel fuel (late cycle injection) were the reducing agents used for NOx reduction. Results showed NOx reduction in the range of 25 - 97% depending on engine operating conditions and management of the catalyst and slipstream conditions.

Line-imaging of Raman scattered light is used to simultaneously measure the mole fractions of CO2, H2O, N2, O2, and fuel (premixed C3H8) in a modern 4-valve spark-ignition engine operating at idle. The measurement volume consists of 16 adjacent sub-volumes, each 0.27 mm in diameter × 0.91 mm long, giving a total measurement length of 14.56 mm. Measurements are made 3 mm under the centrally-located spark plug, offset 3 mm from the spark plug center towards the exhaust valves. Data are taken in 15 crank angle degree increments starting from top center before the intake stroke (-360 CAD) through top center of the compression stroke (0 CAD).

Our previous work applied LIF measurements of in-cylinder fuel distribution to predict CO2, CO, and HC emissions from an HCCI engine under low-load stratified-charge conditions. The prediction method is based on the premise that local fuel-air packets at a given equivalence ratio (characterized using LIF imaging) burn as if in a homogeneous charge at the same equivalence ratio. Thus, emissions measured during homogeneous operation provide an emission-versus- equivalence-ratio look-up table for predicting stratified-charge emissions. The present paper extends the technique to predict engine-out NOX emissions. Because of operating-range limitations, NOX look-up data for homogeneous operation cannot adequately be determined by experiment. Instead, a CHEMKIN-based model provides this look-up table data instead.

This paper describes two independent studies on γ-alumina as a plasma-activated catalyst. γ-alumina (2.5 - 4.3 wt%) was coated onto the surface of mesoporous silica to determine the importance of aluminum surface coordination on NOx conversion in conjunction with nonthermal plasma. Results indicate that the presence of 5- and 6- fold aluminum coordination sites in γ-alumina could be a significant factor in the NOx reduction process. A second study examined the effect of changing the reducing agent on NOx conversion. Several hydrocarbons were examined including propene, propane, isooctane, methanol, and acetaldehyde. It is demonstrated that methanol was the most effective reducing agent of those tested for a plasma-facilitated reaction over γ-alumina.

NOx reduction efficiency in simulated lean exhaust conditions has been examined for three proprietary catalyst materials using a non-thermal plasma discharge as a pretreatment stage to the catalyst. Using propene as the reducing agent for selective catalytic reduction, 74% reduction of NOx has been observed in the presence of 20 ppm SO2. For sulfur-free simulated exhaust, 84% NOx reduction has been obtained. Results show that the impact of sulfur on the samples examined can vary widely from virtually no effect (< 5%) to more than 20% loss in activity depending on the catalyst. Any loss due to sulfur poisoning appears to be irreversible according to limited measurements on poisoned catalysts exposed to sulfur-free exhaust streams. Catalysts were tested over a temperature range of 473-773K, with the highest activity observed at 773K. Examination of this large temperature window has shown that the optimum C1:NOx ratio changes with temperature.

The objectives of this paper are to describe the ongoing projects in diesel engine combustion research at Sandia National Laboratories' Combustion Research Facility and to detail recent experimental results. The approach we are employing is to assemble experimental hardware that mimic realistic engine geometries while enabling optical access. For example, we are using multi-cylinder engine heads or one-cylinder versions of production heads mated to one-cylinder engine blocks. Optical access is then obtained through a periscope in an exhaust valve, quartz windows in the piston crown, windows in spacer plates just below the head, or quartz cylinder liners. We have three diesel engine experiments supported by the Department of Energy, Office of Heavy Vehicle Technologies: a one-cylinder version of a Cummins heavy-duty engine, a diesel simulation facility, and a one-cylinder Caterpillar engine to evaluate combustion of alternative diesel fuels.

A free piston internal combustion (IC) engine operating on high compression ratio (CR) homogeneous charge compression ignition (HCCI) combustion is being developed by Sandia National Laboratories to significantly improve the thermal efficiency and exhaust emissions relative to conventional crankshaft-driven SI and Diesel engines. A two-stroke scavenging process recharges the engine and is key to realizing the efficiency and emissions potential of the device. To ensure that the engine's performance goals can be achieved the scavenging system was configured using computational fluid dynamics (CFD), zero- and one-dimensional modeling, and single step parametric variations. A wide range of design options was investigated including the use of loop, hybrid-loop and uniflow scavenging methods, different charge delivery options, and various operating schemes. Parameters such as the intake/exhaust port arrangement, valve lift/timing, charging pressure and piston frequency were varied.

A novel direct-fabrication technique (robocasting) was used to produce periodic lattices of ceramic rods. The macrostructure is a three-dimensional mesh with controlled porosity in all dimensions but no line-of-sight pathways. These ceramic lattices can function as catalyst supports for gas combustion, and possibly self-regenerating filters for diesel particulates. Compared to the traditional two-dimensional “honeycomb” structured extrudates, the three-dimensional structures have high surface to volume ratios and highly turbulent flow. The flow behaviors of these ceramic lattices and the resulting enhancements in catalytic performance over traditional supports have been demonstrated for propane and methane combustion. Similar tests are underway for the selective catalytic reduction (SCR) of NOx. The potential utility of these structures for diesel particulate trapping will also be discussed.

Methods of producing non-sooting, low flame temperature diesel combustion were investigated in an optically-accessible, quiescent constant-volume combustion vessel. Combustion and soot formation processes of single, isolated fuel jets were studied after autoignition and transient premixed combustion and while the injector needle was fully open (i.e., during the quasi-steady mixing-controlled phase of heat-release for diesel combustion).The investigation showed that fuel jets that do not undergo soot formation in any region of the reacting jet and that also have a low flame temperature could be produced in at least three different ways during mixing-controlled combustion: First, using a #2 diesel fuel and an injector tip with a 50 micron orifice, a fuel jet was non-sooting in ambient oxygen concentrations as low as 10% (simulating the use of EGR) for typical diesel ambient temperatures (1000 K) and densities.

With stringent emission regulations, aftertreatment systems with a Diesel Particulate Filter (DPF) and a Selective Catalytic Reduction (SCR) are required for diesel engines to meet PM and NOx emissions. The adoption of aftertreatment increases the back pressure on a typical diesel engine and makes engine calibration a complicated process, requiring thousands of steady state testing points to optimize engine performance. When configuring an engine to meet Tier IV final emission regulations in the USA or corresponding Stage IV emission regulations in Europe, this high back pressure dramatically impacts transient performance. The peak NOx, smoke and exhaust temperature during a diesel engine transient cycle, such as the Non-Road Transient Cycle (NRTC) defined by the US Environmental Protection Agency (EPA), will in turn affect the performance of the aftertreatment system and the tailpipe emissions level.

A set of elementary surface reactions is proposed for modeling the chemistry in a lean NOx trap during regeneration (reduction of stored NOx). The proposed reaction mechanism can account for the observed product distribution from the trap over a range of temperatures and inlet gas compositions similar to those expected for realistic operation. The mechanism includes many reactions already discussed in the literature, together with some hypothesized reactions that are required to match observations from temperature programmed reactor experiments with a commercial lean NOx trap catalyst. Preliminary results indicate that the NOx trap regeneration and byproduct formation rates can be effectively captured by using a relatively compact set of elementary reactions.

Methanol is one of the most promising fuels for the decarbonization of the off-road and transportation sectors. Although methanol is typically seen as an alternative fuel for spark ignition engines, mixing-controlled compression ignition (MCCI) combustion is typically preferred in most off-road and medium-and heavy-duty applications due to its high reliability, durability and high-efficiency. In this paper, the potential of using ignition enhancers to enable methanol MCCI combustion was investigated. Methanol was blended with 2-ethylhexyl nitrate (EHN) and experiments were performed in a single-cylinder production-like diesel research engine, which has a displacement volume of 0.83 L and compression ratio of 16:1. The effect of EHN has been evaluated with three different levels (3%vol, 5%vol, and 7%vol) under low- and part-load conditions. The injection timing has been swept to find the stable injection window for each EHN level and load.

It is generally accepted that thermal (Zeldo'vich) chemical kinetics dominate NO formation in diesel engines, so control of temperature is critical for reducing exhaust NOx emissions. Recent optical engine data revealed that when the start of injection (SOI) was retarded to very late timings, combustion luminosity decreased while exhaust NOx emissions increased, causing a “NOx bump.” This data suggested that changes in radiative heat transfer from soot may affect in-cylinder temperatures and subsequent NOx formation. In this study, soot thermometry measurements of in-cylinder temperature and radiative heat transfer were correlated with exhaust NOx to quantify the role of radiative heat transfer on in-cylinder temperatures and NOx formation. The engine was operated at low-load conditions, for which the premixed burn was a significant fraction of the total heat release.

The NOx reduction performance under lean conditions over γ-alumina was evaluated using a micro-reactor system and a non-thermal plasma-equipped bench test system. Various alumina samples were obtained from alumina manufacturers to assess commercial alumina materials. In addition, γ-alumina samples were synthesized at Caterpillar with a sol-gel technique in order to control alumina properties. The deNOx performances of the alumina samples were compared. The alumina samples were characterized with analytical techniques such as inductively coupled plasma (ICP) emission spectroscopy, temperature programmed desorption (TPD) and surface area measurements (BET) to understand physical and chemical properties. The information derived from these techniques was correlated with the NOx reduction performance to identify key parameters of γ-alumina for optimizing materials for lean-NOx and plasma assisted catalysis.

Video imaging has been used to investigate the evolution of liquid fuel films on combustion chamber walls during a simulated cold start of a port fuel-injected engine. The experiments were performed in a single-cylinder research engine with a production, four-valve head and a window in the piston crown. Flood-illuminated laser-induced fluorescence was used to observe the fuel films directly, and color video recording of visible emission from pool fires due to burning fuel films was used as an indirect measure of film location. The imaging techniques were applied to a comparative study of open and closed valve injection, for coolant temperatures of 20, 40 and 60 °C. In general, for all cases it is shown that fuel films form in the vicinity of the intake valve seats.