Bruce G. Bunting

Antiwear performance and mechanism of an oil-miscible ionic liquid as a lubricant additive.

An ionic liquid (IL) trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate has been investigated as a potential antiwear lubricant additive. Unlike most other ILs that have very low solubility in nonpolar fluids, this IL is fully miscible with various hydrocarbon oils. In addition, it is thermally stable up to 347 °C, showed no corrosive attack to cast iron in an ambient environment, and has excellent wettability on solid surfaces (e.g., contact angle on cast iron <8°). Most importantly, this phosphonium-based IL has demonstrated effective antiscuffing and antiwear characteristics when blended with lubricating oils. For example, a 5 wt % addition into a synthetic base oil eliminated the scuffing failure experienced in neat oil and, as a result, reduced the friction coefficient by 60% and the wear rate by 3 orders of magnitude. A synergistic effect on wear protection was observed with the current antiwear additive when added into a fully formulated engine oil. Nanostructure examination and composition analysis revealed a tribo-boundary film and subsurface plastic deformation zone for the metallic surface lubricated by the IL-containing lubricants. This protective boundary film is believed to be responsible for the ILs antiscuffing and antiwear functionality.

Fuel chemistry and cetane effects on diesel homogeneous charge compression ignition performance, combustion, and emissions

Abstract The effects of cetane number (CN) on homogeneous charge compression ignition (HCCI) performance and emissions were investigated in a single-cylinder engine with port fuel injection, using intake air temperature for control. Commercial fuels and blends of the diesel secondary reference fuels were evaluated, covering a CN range from 19 to 76. Sweeps of intake air temperature showed that low-CN fuels needed higher intake temperatures than high-CN fuels to achieve ignition. As a function of intake air temperature, each fuel passed through a point of maximum indicated mean effective pressure (i.m.e.p.). High-CN fuels required a combustion phasing approximately 10 crank angle degrees (CAD) earlier than the lowest CN fuels in order to prevent misfire. The high-CN fuels exhibited a strong low-temperature heat release (LTHR) event, while no LTHR was detected for fuels with CN ≤ 34. All of the fuels yielded comparable NOx emissions (< 6 ppm at 3.5 bar i.m.e.p.) at their respective maximum i.m.e.p. timeing. Low-CN fuels were prone to excessive pressure rise rates and NOx emissions at advanced phasing, while high-CN fuels were prone to excessive CO emissions at retarded phasing. These results suggest that the products of LTHR, which are high in CO, are more sensitive to the quenching effects of cylinder expansion. Engine speed was found to suppress LTHR since higher engine speed reduces the time allowed for the LTHR reactions. In addition to measurements of standard gaseous emissions, additional sampling and analysis techniques were used to identify and measure the individual exhaust HC species including an array of oxygenated compounds. In addition to high concentrations of formaldehyde and other low molecular weight carbonyls, results showed an abundance of organic acids, ranging from formic to nonanoic acid. Concentrations of high molecular weight partially oxidized species were highest for the high-CN fuels at retarded phasing, and are believed to be a direct product of LTHR.

Cetane Number and Engine Speed Effects on Diesel HCCI Performance and Emissions

The effects of cetane number (CN) on homogeneous charge compression ignition (HCCI) performance and emissions were investigated in a single cylinder engine using intake air temperature for control. Blends of the diesel secondary reference fuels for cetane rating were used to obtain a CN range from 19 to 76. Sweeps of intake air temperature at a constant fueling were performed. Low CN fuels needed to be operated at higher intake temperatures than high CN fuels to achieve ignition. As the intake air temperature was reduced for a given fuel, the combustion phasing was retarded, and each fuel passed through a phasing point of maximum indicated mean effective pressure (IMEP). Early combustion phasing was required for the high CN fuels to prevent misfire, whereas the maximum IMEP for the lowest CN fuel occurred at a phasing 10 crank angle degrees (CAD) later. The high CN fuels exhibited a strong low temperature heat release (LTHR) event, accounting for more than 15% of the total heat release in some instances, while no LTHR was detected for fuels with CN ≤ 34. All of the fuels had comparable NOx emissions and pressure rise rates at their respective maximum IMEP timing, with NOx emissions below 6 ppm at 3.5 bar IMEP. At advanced combustion phasing, low CN fuels had significantly higher pressure rise rates and higher NOx emissions than the high CN fuels. At retarded phasing, the CO emissions for the high CN fuels were excessive, with a CO:UHC ratio of up to 8, while these remained <1 for low CN fuels. These results suggest that the products of LTHR, which are high in CO, are more sensitive to the quenching effects of cylinder expansion. Thus high CN fuels, which exhibit significant LTHR, require early combustion phasing, whereas low CN fuels can be retarded to later combustion phasing. Increasing engine speed had the effect of reducing the total LTHR. Further investigation showed that the LTHR rate is constant on a millisecond basis, so the effect of higher engine speed is to reduce the time allowed for the reaction without changing the rate of reaction.

Performance Evaluation and Optimization of Diesel Fuel Properties and Chemistry in an HCCI Engine

The nine CRC fuels for advanced combustion engines (FACE fuels) have been evaluated in a simple, premixed HCCI engine under varying conditions of fuel rate, air-fuel ratio, and intake temperature. Engine performance was found to vary mainly as a function of combustion phasing as affected by fuel cetane and engine control variables. The data was modeled using statistical techniques involving eigenvector representation of the fuel properties and engine control variables, to define engine response and allow optimization across the fuels for best fuel efficiency. In general, the independent manipulation of intake temperature and air-fuel ratio provided some opportunity for improving combustion efficiency of a specific fuel beyond the direct effect of targeting the optimum combustion phasing of the engine (near 5 CAD ATDC). High cetane fuels suffer performance loss due to easier ignition, resulting in lower intake temperatures, which increase HC and CO emissions and result in the need for more advanced combustion phasing. The FACE fuels also varied in T90 temperature and % aromatics, independent of cetane number. T90 temperature was found to have an effect on engine performance when combined with high centane, but % aromatics did not, when evaluated independently of cetane and T90.

Hydrocarbon Selective Catalytic Reduction Using a Silver- Alumina Catalyst with Light Alcohols and Other Reductants

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 microemulsion 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. A second important goal was to improve understanding of the possible reaction mechanisms and other phenomena that influence performance of this SCR system. Test results revealed that diesel engine exhaust NOx emissions can be reduced by more than 80%, utilizing ethanol as the reductant for a space velocity near 50,000/h and catalyst temperatures between 330 and 490 o C. Similar results

Combustion simulations of the fuels for advanced combustion engines in a homogeneous charge compression ignition engine

Numerical simulations of combustion have been performed for a homogeneous charge compression ignition engine operating on multi-component reference diesel fuels. Two surrogate representation methods were used to describe the nine fuels for advanced combustion engines. The first method of surrogates, denoted as physical-surrogate components, was formulated to describe the fuel’s physical properties by matching its distillation profile, specific gravity, lower heating value, hydrogen-to-carbon ratio, and cetane index with measured data. The second method of surrogates, denoted as chemical-surrogate components, was introduced to represent the chemistry of the fuel components using a new group chemistry representation model. In the model, the fuel components in the physical-surrogate components and chemical-surrogate components are related through the classification of chemical structures of the components, i.e. the component in the physical-surrogate components are grouped based on their chemical classes and the chemistry of each group is calculated using a chemical kinetics mechanism (MultiChem) that represents the combustion characteristics of its chemical class. This MultiChem mechanism includes reduced reaction mechanisms for the four main surrogate hydrocarbon chemistry components of diesel fuel, n-paraffins, iso-paraffins, naphthenes, and aromatics, with two n-paraffins to provide the ability to mimic molecular weight effects. The computations were performed using a multi-dimensional computational fluid dynamic code, KIVA-ERC-CHEMKIN, and the results show that the predictions of the present multi-component combustion models are in good agreement with experimental measurements. The combustion characteristics of the fuels for advanced combustion engines are well represented and the present models are well suited for practical engine computations.

KINETIC MODELING OF FUEL EFFECTS OVER A WIDE RANGE OF CHEMISTRY, PROPERTIES, AND SOURCES

Kinetic modeling is an important tool for engine design and can also be used for engine tuning and to study response to fuel chemistry and properties before an engine configuration is physically built and tested. Methodologies needed for studying fuel effects include development of fuel kinetic mechanisms for pure compounds, tools for designing surrogate blends of pure compounds that mimic a desired market fuel, and tools for reducing kinetic mechanisms to a size that allows inclusion in complex CFD engine models. In this paper, we demonstrate the use of these tools to reproduce engine results for a series of research diesel fuels using surrogate fuels in an engine and then modeling results with a simple 2 component surrogate blend with physical properties adjusted to vary fuel volatility. Results indicate that we were reasonably successful in mimicking engine performance of real fuels with blends of pure compounds. We were also successful in spanning the range of the experimental data using CFD and kinetic modeling, but further tuning and matching will be needed to exactly match engine performance of the real and surrogate fuels.

Effect of Narrow Cut Oil Shale Derived Distillates on HCCI Engine Performance

In this investigation, oil shale crude obtained from the Green River Formation in Colorado using Paraho Direct retorting was mildly hydrotreated and distilled to produce 7 narrow boiling point fuels of equal volumes. The resulting derived cetane numbers ranged between 38.3 and 43.9. Fuel chemistry and bulk properties strongly correlated with boiling point.

DOE Project 18545, AOP Task 2.0B, CRADA with Reaction Design

We ran 5 FACE fuels and 8 surrogate blends in diesel combustion with detailed particulate and exhaust chemistry measurements to provide data needed to develop and evaluate a kinetic model for particulate formation. Surrogate blends duplicated engine performance of real fuels. We demonstrated that a simple 2 surrogate blend is capable of duplicating the range of engine response for the FACE fuels, but that further tuning and complexity will be needed to reproduce emissions. We assisted in setting up a Jaguar computer user program for bench marking parallel solvers for chemistry in GPU machine environment. This program has just been approved by the Jaguar user facility and will begin in 2012.

Characterization and Tribological Evaluation of 1-Benzyl-3-Methylimidazolium Bis(trifluoromethylsulfonyl)imide as Neat Lubricant and Oil Additive

Selected physical and chemical properties and tribological data for a newly-developed, imidazolium-based ionic liquid (IL) are presented. The IL is soluble in the SAE 5W-30 oil up to a certain weight percentage, and is as a promising candidate for use in lubrication applications, either in its neat version or as an oil additive. Characterization of the IL included dynamic viscosity at different temperatures, corrosion effects on cast iron cylinder liners, and thermal stability analysis. The tribological performance was evaluated using a reciprocating ring-on-liner test arrangement. When used in neat version this IL demonstrated friction coefficient comparable to a fully formulated engine oil, and when used as an oil additive it produced less wear.Copyright