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Exhaust gas recirculation (EGR) cooler fouling has emerged as an important issue in diesel engine development. Uncertainty about the level of impact that fuel chemistry may have upon this issue has resulted in a need to investigate the cooler fouling process with emerging non-traditional fuel sources to gage their impact on the process. This study reports experiments using both ultra-low sulfur diesel (ULSD) and 20% biodiesel (B20) at elevated exhaust hydrocarbon conditions to investigate the EGR cooler fouling process. The results show that there is little difference between the degradation in cooler effectiveness for ULSD and B20 at identical conditions. At lower coolant temperatures, B20 exhibits elevated organic fractions in the deposits compared with ULSD, but this does not appear to lead to incremental performance degradation under the conditions studied.

In order to meet common fuel specifications such as cetane number and volatility, a refinery must blend a number of refinery stocks derived from various process units in the refinery. Fuel chemistry can be significantly altered in meeting fuel specifications. Additionally, fuel specifications are seldom changed in isolation, and the drive to meet one specification may alter other specifications. Homogeneous charge compression ignition (HCCI) engines depend on the kinetic behavior of a fuel to achieve reliable ignition and are expected to be more dependent on fuel specifications and chemistry than today's conventional engines. Regression analysis can help in determining the underlying relationships between fuel specifications, chemistry, and engine performance. Principal Component Analysis (PCA) is used as an adjunct to regression analysis in this work, because of its ability to deal with co-linear variables and potential to uncover ‘hidden’ relationships between the variables.

Numerous studies have demonstrated that exhaust gas recirculation (EGR) can attenuate knock propensity in spark ignition (SI) engines at naturally aspirated or lightly boosted conditions [1]. In this study, we investigate the role of cooled EGR under higher load conditions with multiple fuel compositions, where highly retarded combustion phasing typical of modern SI engines was used. It was found that under these conditions, EGR attenuation of knock is greatly reduced, where EGR doesn’t allow significant combustion phasing advance as it does under lighter load conditions. Detailed combustion analysis shows that when EGR is added, the polytropic coefficient increases causing the compressive pressure and temperature to increase. At sufficiently highly boosted conditions, the increase in polytropic coefficient and additional trapped mass from EGR can sufficiently reduce fuel ignition delay to overcome knock attenuation effects.

The effects of variable compression ratio (CR) and fuel composition on thermal efficiency were investigated in a homogeneous charge compression ignition (HCCI) engine using blends of n-heptane and toluene with research octane numbers (RON) of 0 to 90. Experiments were conducted by performing CR sweeps at multiple intake temperatures using both unthrottled operation, and constant Φ conditions by throttling to compensate for varying air density. It was found that CR is effective at changing and controlling the HCCI combustion phasing midpoint, denoted here as CA 50. Thermal efficiency was a strong function of CA 50, with overly advanced CA 50 leading to efficiency decreases. Increases in CR at a constant CA 50 for a given fuel composition did, in most cases, increase efficiency, but the relationship was weaker than the dependence of efficiency on CA 50.

Diesel fuels derived from different types of crude oil can exhibit different chemistry while still meeting market requirements and specifications. Oil sands derived fuels typically contain a larger proportion of cycloparaffinic compounds, which result from the cracking and hydrotreating of bitumens in the crude. In the current study, 17 refinery streams consisting of finished fuels and process streams were obtained from a refinery using 100% oil sands derived crude oil. All samples except one met the ULSD standard of 15 ppm sulfur. The samples were characterized for properties and chemistry and run in a simple premixed HCCI engine using intake heating for combustion phasing control. Results indicate that the streams could be equally well characterized by chemistry or properties, and some simple correlations are presented. Cetane number was found to relate mainly to mono-aromatic content and the cycloparaffins did not appear to possess any unique diesel related chemical effects.

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.

This paper describes the simultaneous reduction of nitrogen oxides (NOx) and particulate matter (PM) in a modern light-duty diesel engine under high exhaust gas recirculation (EGR) levels. Simultaneous reduction of NOx and PM emissions was observed under lean conditions at several low to moderate load conditions using two different approaches. The first approach utilizes a throttle to increase EGR rate beyond the maximum rate possible with sole use of the EGR valve for a particular engine condition. The second approach does not use a throttle, but rather uses a combination of EGR and manipulation of injection parameters. A significant reduction in particulate matter size and concentration was observed corresponding to the reduction in particulate mass. This PM reduction was accompanied by a significant shift in the heat release profile. In addition, there were significant cylinder-to-cylinder variations in particulate matter characteristics, gaseous emissions, and heat release.

Mixing controlled compression ignition, i.e., diesel engines are efficient and are likely to continue to be the primary means for movement of goods for many years. Low-net-carbon biofuels have the potential to significantly reduce the carbon footprint of diesel combustion and could have advantageous properties for combustion, such as high cetane number and reduced engine-out particle and NOx emissions. We developed a list of over 400 potential biomass-derived diesel blendstocks and populated a database with the properties and characteristics of these materials. Fuel properties were determined by measurement, model prediction, or literature review. Screening criteria were developed to determine if a blendstock met the basic requirements for handling in the diesel distribution system and use as a blend with conventional diesel. Criteria included cetane number ≥40, flashpoint ≥52°C, and boiling point or T90 ≤338°C.

A minimally invasive spatially resolved capillary inlet mass spectrometer has been used to quantify EGR/air mixing in a Cummins V-8 medium-duty diesel engine. Two EGR-system hardware designs were evaluated in terms of EGR-air mixing at the intake manifold inlet and port-to-port EGR charge uniformity. Performance was assessed at four modalized-FTP engine conditions. One design is found to be considerably better, particularly at three of the four engine conditions. Specific questions such as the effect of maximizing mass air flow on EGR mixing, and if particular cylinders are EGR starved are investigated. The detailed performance characteristics suggest areas to focus improvement efforts, and serve as a foundation for identifying the non-uniformity EGR barriers and origins.

The focus of this paper is to discuss the modeling and control of intake plenum pressure on the Powertrain Control Research Laboratory's (PCRL) Single-Cylinder Engine (SCE) transient test system using a patented device known as the Intake Air Simulator (IAS), which dynamically controls the intake plenum pressure, and, subsequently, the instantaneous airflow into the cylinder. The IAS exists as just one of many devices that the PCRL uses to control the dynamic boundary conditions of its SCE transient test system to make it “think” and operate as though it were part of a Multi-Cylinder Engine (MCE) test system. The model described in this paper will be used to design a second generation of this device that utilizes both continuously and discretely actuating valves working in parallel.

A number of studies have identified a tendency for exhaust gas recirculation (EGR) coolers to foul to a steady-state level and subsequently not degrade further. One possible explanation for this behavior is that the shear force imposed by the gas velocity increases as the deposit thickens. If the shear force reaches a critical level, it achieves a removal of the deposit material that can balance the rate of deposition of new material, creating a stabilized condition. This study reports efforts to observe removal of deposit material in-situ during fouling studies as well as an ex-situ removal through the use of controlled air flows. The critical gas velocity and shear stress necessary to cause removal of deposit material is identified and reported. In-situ observations failed to show convincing evidence of a removal of deposit material. The results show that removal of deposit material requires a relatively high velocity of 40 m/s or higher to cause removal.

A technique for rapid in situ measurement of the fuel dilution of oil in a diesel engine is presented. Fuel dilution can occur when advanced in-cylinder fuel injection techniques are employed for the purpose of producing rich exhaust for lean NOx trap catalyst regeneration. Laser-induced fluorescence (LIF) spectroscopy is used to monitor the oil in a Mercedes 1.7-liter engine operated on a dynamometer platform. A fluorescent dye suitable for use in diesel fuel and oil systems is added to the engine fuel. The LIF spectra are monitored to detect the growth of the dye signal relative to the background oil fluorescence; fuel mass concentration is quantified based on a known sample set. The technique was implemented with fiber optic probes which can be inserted at various points in the engine oil system. A low cost 532-nm laser diode was used for excitation.

Reactivity Controlled Compression Ignition (RCCI) is an approach to increase engine efficiency and lower engine-out emissions by using in-cylinder stratification of fuels with differing reactivity (i.e., autoignition characteristics) to control combustion phasing. Stratification can be altered by varying the injection timing of the high-reactivity fuel, causing transitions across multiple regimes of combustion. When injection is sufficiently early, combustion approaches a highly-premixed autoignition regime, and when it is sufficiently late it approaches more mixing-controlled, diesel-like conditions. Engine performance, emissions, and control authority over combustion phasing with injection timing are most favorable in between, within the RCCI regime.

Reactivity Controlled Compression Ignition (RCCI) is an engine combustion strategy that produces low NO and PM emissions with high thermal efficiency. Previous RCCI research has been investigated in single-cylinder heavy-duty engines. The current study investigates RCCI operation in a light-duty multi-cylinder engine at 3 operating points. These operating points were chosen to cover a range of conditions seen in the US EPA light-duty FTP test. The operating points were chosen by the Ad Hoc working group to simulate operation in the FTP test. The fueling strategy for the engine experiments consisted of in-cylinder fuel blending using port fuel-injection (PFI) of gasoline and early-cycle, direct-injection (DI) of diesel fuel. At these 3 points, the stock engine configuration is compared to operation with both the original equipment manufacturer (OEM) and custom-machined pistons designed for RCCI operation.

In this study we identify components of a typical biodiesel fuel and estimate both their individual and mixed thermo-physical and transport properties. We then use the estimated mixture properties in computational simulations to gauge the extent to which combustion is modified when biodiesel is substituted for conventional diesel fuel. Our simulation studies included both conventional diesel combustion (DI) and premixed charge compression ignition (PCCI). Preliminary results indicate that biodiesel ignition is significantly delayed due to slower liquid evaporation, with the effects being more pronounced for DI than PCCI. The lower vapor pressure and higher liquid heat capacity of biodiesel are two key contributors to this slower rate of evaporation. Other physical properties are more similar between the two fuels, and their impacts are not clearly evident in the present study.

Thermoelectric generators (TEGs) have been researched and developed for harvesting energy from otherwise wasted heat. For automotive applications this will most likely involve using internal combustion engine exhaust as the heat source, with the TEG positioned after the catalyst system. Applications to exhaust gas recirculation systems and compressed air coolers have also been suggested. A thermoelectric generator based on half-Heusler thermoelectric materials was developed, engineered, and fabricated, targeting a gasoline passenger sedan application. This generator was installed on a gasoline engine exhaust system in a dynamometer cell, and positioned immediately downstream of the close-coupled three-way catalyst. The generator was characterized using a matrix of steady-state conditions representing the important portions of the engine map. Detailed performance results are presented.

As the world market develops for biodiesel fuels, it is likely that a wider variety of biodiesels will become available, both locally and globally, and require engines to operate on a wider variety of fuels than experienced today. At the same time, tighter emissions regulations and a drive for improved fuel economy have focused interest on advanced combustion modes such as HCCI or PCCI, which are known to be more sensitive to fuel properties. This research covers two series of biodiesel fuels. In the first, B20 blends of natural methyl esters derived from palm, coconut, rape, soy, and mustard were evaluated at light load in an HCCI research engine to determine combustion and performance characteristics. These fuels showed performance differences between the biodiesels and the base #2 ULSD fuel, but did not allow separation of chemical effects due to the small number of fuels and correlation of various properties.

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).

In prior work, the EGR loop catalytic reforming strategy developed by ORNL has been shown to provide a relative brake engine efficiency increase of more than 6% by minimizing the thermodynamic expense of the reforming processes, and in some cases achieving thermochemical recuperation (TCR), a form of waste heat recovery where waste heat is converted to usable chemical energy. In doing so, the EGR dilution limit was extended beyond 35% under stoichiometric conditions. In this investigation, a Microlith®-based metal-supported reforming catalyst (developed by Precision Combustion, Inc. (PCI)) was used to reform the parent fuel in a thermodynamically efficient manner into products rich in H2 and CO. We were able to expand the speed and load ranges relative to previous investigations: from 1,500 to 2,500 rpm, and from 2 to 14 bar break mean effective pressure (BMEP).

Low temperature combustion (LTC) has been shown to yield higher brake thermal efficiencies with lower NOx and soot emissions, relative to conventional diesel combustion (CDC). However, while demonstrating low soot carbon emissions it has been shown that LTC operation does produce particulate matter whose composition appears to be much different than CDC. The particulate matter emissions from dual-fuel reactivity controlled compression ignition (RCCI) using gasoline and diesel fuel were investigated in this study. A four cylinder General Motors 1.9L ZDTH engine was modified with a port-fuel injection system while maintaining the stock direct injection fuel system. The pistons were modified for highly premixed operation and feature an open shallow bowl design. RCCI operation was carried out using a certification grade 97 research octane gasoline and a certification grade diesel fuel.