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Widespread implementation of homogeneous charge compression ignition (HCCI) engines is presently hindered by stability, control, and load range issues. Although the operable HCCI speed/load range is expanding, it is likely that the initial HCCI engines will rely on conventional combustion for part of the operating cycle. In the present study, we have investigated the role of fuel properties and chemistry on the operation of a spark-assisted gasoline HCCI engine. The engine employed is a single cylinder, 500 cc, port fuel injected research engine, operating near lambda = 1.0 and equipped with hydraulic variable valve actuation. HCCI is initiated by early exhaust valve closing to retain exhaust in the cylinder, thereby increasing the cylinder gas temperature. This is also referred to as a ‘negative overlap’ strategy.

The poisoning of diesel oxidation catalysts (DOCs) by the engine oil additive zinc dialkyldithiophosphate (ZDDP) is investigated in the present study. A 517cc single-cylinder diesel engine is used to accelerate the phosphorus poisoning of DOCs by artificially increasing the ZDDP consumption to approximately 700 times normal operation by three different methods. These include lube-oil doped fuel, intake manifold, and exhaust manifold injection with lube-oil containing an elevated level of ZDDP. The deactivation of DOCs under these conditions is characterized by a variety of physical and chemical techniques. Surface composition and structure of the poisoned catalysts analyzed with SEM-EDS show differences depending on the method of ZDDP introduction. Exhaust manifold injection produces a zinc phosphate glaze which masks the surface to species diffusion. Fuel and intake manifold injection methods produce chemically absorbed phosphorus on the catalyst washcoat surface.

The accelerated ash loading of diesel particulate filters (DPFs) with diesel oxidation catalysts (DOCs) mounted upstream by lube-oil derived products was investigated using a single cylinder diesel engine and fuel blended with 5% lube oil. An ash loading protocol is developed which combines soot loading, active soot regeneration, and periodic shutdowns for filter weighing. Active regeneration is accomplished by exhaust injection of diesel fuel, initiated by a backpressure criteria and providing DPF temperatures up to 700°C. In developing this protocol, five DPFs of various combinations of substrates (cordierite, silicon carbide, and mullite) and washcoats (none, low PGM, and high PGM) are used and evaluated. The initial backpressure and rate of backpressure increase with ash varied with each of the DPFs and ash was observed to have an effect on the active soot light-off temperature for the catalyzed DPFs.

In this study, high-temperature deactivation of a fully-formulated lean NOx trap (LNT) is investigated with an accelerated aging protocol where accelerated aging is accomplished by rapid temperature cycling and by higher temperatures. Thermal aging is carried out in a bench-flow reactor at nominal temperatures of 700, 800, 900, and 1000°C using an aging cycle consisting of a 130s lean-phase and a 50s rich-phase. After a prescribed number of lean/rich aging cycles, the NOx conversion of the aged LNT is evaluated at 200, 300, and 400°C. The NOx performance is obtained at a GHSV of 30,000 h−1 using an evaluation cycle consisting of a 60s lean-phase and 5s rich-phase. The effects of aging on the LNT washcoat are determined with EPMA, XRD, STEM/EDS, and BET. Aging at 700 and 800°C has a minimal effect on LNT performance and material properties.

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.

In the present study, a bench-flow reactor is used to perform lean/rich thermal cycling on model “Ba+K” LNT catalysts at temperatures of 700, 800, 900 and 1000°C using simulated diesel exhaust gases. Deterioration of NOx performance is measured and the deactivation mechanisms of thermally-aged “Ba+K” LNTs are identified using characterization techniques such as TEM, XRD and EPMA. Results indicate that the deterioration is minimal at 700 and 800°C, however, at aging temperatures exceeding 800°C the severity of thermal aging depends on aging temperature as well as number of aging cycles.

In this research, small, single cylinder engines have been used to simulate larger engines in the areas of aftertreatment, combustion, and fuel formulation effects. The use of small engines reduces overall research cost and allows more rapid experiments to be run. Because component costs are lower, it is also possible to investigate more variations and to sacrifice components for materials characterization and for subsequent experiments. Using small engines in this way is very successful in some cases. In other cases, limitations of the engines influence the results and need to be accounted for in the experimental design and data analysis. Some of the results achieved or limitations found may be of interest to the small engine market, and this paper is offered as a summary of the authors' research in these areas. Research is being conducted in two areas. First, small engines are being used to study the rapid aging and poisoning of exhaust aftertreatment catalysts.