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SAE 2015 World Congress

Tuesday, April 21

Partially Premixed Compression Ignition, PPCI (Part 1 of 2)

(Session Code: PFL250)

Room 140 C
9:30 a.m. 2015-01-0831 Use of Multiple Injection Strategies to Reduce Emission and Noise in Low Temperature Diesel Combustion
Wonah Park, Youngchul Ra, Univ. of Wisconsin; Eric Kurtz, Ford Motor Co; Werner Willems, Ford Forschungszentrum Aachen GmbH; Rolf D. Reitz, Univ. of Wisconsin

The low temperature combustion concept is very attractive for reducing NOx and soot emissions in diesel engines. However, it has potential limitations due to higher combustion noise and CO and HC emissions. A multiple injection strategy is an effective way to reduce unburned emissions and noise in LTC. In this paper, the effect of multiple injection strategies was investigated to reduce combustion noise and unburned emissions in LTC conditions. A hybrid surrogate fuel model was developed and validated, and was used to improve LTC predictions. Triple injection strategies were considered to find the role of each pulse and then optimized. The split ratio of the 1st and 2nd pulses fuel was found to determine the ignition delay. Increasing mass of the 1st pulse reduced unburned emissions and an increase of the 3rd pulse fuel amount reduced noise. It is concluded that the pulse split ratio can be used as a control factor for emissions and noise.

Wednesday, April 22

RCCI and Dual-Fuel Low Temperature Combustion (Part 1 of 3)

(Session Code: PFL262)

Room 252 A
8:00 a.m. Oral Only Technical Keynote: Perspective on the Development of Reactivity Controlled Compression Ignition
Rolf D. Reitz, University of Wisconsin
9:00 a.m. 2015-01-0841 Investigation of the Combustion Instability-NOx Tradeoff in a Dual Fuel Reactivity Controlled Compression Ignition (RCCI) Engine
David Klos, Daniel Janecek, Sage Kokjohn

The tradeoff between NOx emissions and combustion instability in an engine operating in the dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion mode was investigated using a combination of engine experiments and detailed CFD modeling. Experiments were performed on a single cylinder version of a General Motors/Fiat JTD 1.9L four-cylinder diesel engine. Gasoline was injected far upstream of the intake valve using an air assisted injector and fuel vaporization system and diesel was injected directly into the cylinder using a common rail injector. The timing of the diesel injection was swept from -70° ATDC to -20° ATDC while the gasoline percentage was adjusted to hold the average combustion phasing (CA50) and load (IMEPg) constant at 0.5° ATDC and 7 bar, respectively. At each operating point the variation in IMEP, peak PRR, and CA50 was calculated from the measured cylinder pressure trace and NOx, CO, soot and UHC were recorded. It was observed that a late injection strategy with start-of-injection (SOI) timings ranging from -30° ATDC to -20° ATDC could significantly reduce cycle-to-cycle variation with only a marginal increase in NOx emissions. To explain the sources of increased combustion stability, detailed computational fluid dynamics (CFD) simulations were used. The CFD simulations confirmed that the late injection timing produced a higher equivalence ratio ignition site that is less sensitive to fluctuations. By optimizing injection timing large improvements in combustion instability can be made while still maintaining low temperature combustion-like emissions.

9:30 a.m. 2015-01-0855 Characterization of Reactivity Controlled Compression Ignition (RCCI) using Premixed Gasoline and Direct-Injected Gasoline with a Cetane Improver on a Multi-Cylinder Engine
Adam B. Dempsey, Scott Curran, Oak Ridge National Laboratory; Rolf D. Reitz, University of Wisconsin

The focus of the present study was to characterize Reactivity Controlled Compression Ignition (RCCI) using a single-fuel approach of gasoline and gasoline mixed with a commercially available cetane improver on a multi-cylinder engine. RCCI was achieved by port injecting a certification grade 96 research octane gasoline and direct injecting the same gasoline mixed with various levels of the cetane improver, 2-ethylhexyl nitrate (EHN). The EHN volume percentage in the direct injected fuel was 10%, 5%, and 2.5%. The engine performance and emissions of the different fueling combinations was characterized at 2300 rpm and 4.2 bar BMEP over a various parametric investigations. Comparisons were made to gasoline/diesel operation on the same engine platform. The experiments were conducted on a four cylinder General Motors 1.9L ZDTH engine that has been 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. The results indicate that the direct injected fuel reactivity increases with EHN concentration, but that successful RCCI operation was achieved with as little as 2.5% EHN mixed with the direct injected gasoline (i.e., controllability of combustion phasing through the premixed percentage and the direct injection timing). It was also observed that the NOx emissions are a strong function of the global EHN concentration in cylinder and significantly elevated compared to gasoline/diesel RCCI operation.

10:00 a.m. 2015-01-0837 Highway Fuel Economy Testing of an RCCI Series Hybrid Vehicle
Reed Hanson, Shawn Spannbauer, Christopher Gross, Rolf D. Reitz, University of Wisconsin; Scott Curran, John Storey, Shean Huff, Oak Ridge National Laboratory

In the current work, a series-hybrid vehicle has been constructed that utilizes a dual-fuel, Reactivity Controlled Compression Ignition (RCCI) engine. The vehicle is a 2009 Saturn Vue chassis and a 1.9L turbo-diesel engine converted to operate with low temperature RCCI combustion. The engine is coupled to a 90 kW AC motor, acting as an electrical generator to charge a 14.1 kW-hr lithium-ion traction battery pack, which powers the rear wheels by a 75 kW drive motor.

Full vehicle testing was conducted on chassis dynamometers at the Vehicle Emissions Research Laboratory at Ford Motor Company and at the Vehicle Research Laboratory at Oak Ridge National Laboratory. For this work, the US Environmental Protection Agency Highway Fuel Economy Test was performed using commercially available gasoline and ultra-low sulfur diesel. Fuel economy and emissions data were recorded over the specified test cycle and calculated based on the fuel properties and the high-voltage battery energy usage.

The results were used to provide estimates of fuel economy and emissions performance with comparisons to a commercially available hybrid vehicle. The estimates also provide guidelines for system improvements to further increase the vehicle performance.

10:30 a.m. 2015-01-0856 Direct Dual Fuel Stratification, a Path to Combine the Benefits of RCCI and PPC
Martin Wissink, Rolf D. Reitz, University of Wisconsin

Control of the timing and magnitude of heat release is one of the biggest challenges for premixed compression ignition, especially when attempting to operate at high load. Single-fuel strategies such as partially premixed combustion (PPC) use direct injection of gasoline to stratify equivalence ratio and retard heat release, thereby reducing pressure rise rate and enabling high load operation. However, retarding the heat release also reduces the maximum work extraction, effectively creating a tradeoff between efficiency and noise. Dual-fuel strategies such as reactivity controlled compression ignition (RCCI) use premixed gasoline and direct injection of diesel to stratify both equivalence ratio and fuel reactivity, which allows for greater control over the timing and duration of heat release. This enables combustion phasing closer to top dead center (TDC), which is thermodynamically favorable. However, the main control mechanism in RCCI is the ratio of the two fuels, and the diesel fraction typically reaches zero before full load is achieved. We propose a new strategy that effectively combines the benefits of RCCI and PPC by injecting both gasoline and diesel directly, enabling control over the in-cylinder distribution of both fuels. We present a comparison of RCCI, PPC, and our new strategy, direct dual fuel stratification (DDFS) at a nominal gross mean effective pressure of 0.9 MPa. DDFS allowed for combustion phasing near TDC with reduced combustion noise. Cyclic combustion instability was reduced significantly with the new strategy and approached levels typical of conventional diesel combustion. Compared to RCCI, there was a reduction in noise and required exhaust gas recirculation (EGR) while maintaining similar efficiency. Compared to PPC, there was a reduction in noise and an increase in efficiency. The new strategy therefore combines the efficiency advantage of RCCI with the load advantage of PPC, while reducing EGR and combustion instability.

Combustion in Compression-Ignition Engines: In-Cylinder Processes (Part 1 of 2)

(Session Code: PFL222)

Room 251 A
10:30 a.m. Oral Only Advanced CFD Diagnostics: Tracking Soot from Originating Fuel Sources through to EVO in a Cummins N14 Optical Engine Utilizing Post Injections
Randy Hessel, Univ. of Wisconsin Madison; Rolf Reitz; Zongyu Yue; Mark Musculus, Sandia National Laboratories; Jacqueline O'Connor, Pennsylvania State University
11:00 a.m. 2015-01-0794 CFD Study of Soot Reduction Mechanisms of Post-Injection in Spray Combustion
Zongyu Yue, Randy Hessel, Rolf D. Reitz, Univ of Wisconsin

The application of close-coupled post injections in diesel engines has been proven to be an effective in-cylinder strategy for soot reduction, without much fuel efficiency penalty. But due to the complexity of in-cylinder combustion, the soot reduction mechanism of post-injections is difficult to explain. Accordingly, a simulation study using a three dimensional computational fluid dynamics (CFD) model, coupled with the SpeedChem chemistry solver and a semi-detailed soot model, was carried out to investigate post-injection in a constant volume combustion chamber, which is more simple and controllable with respect to the boundary conditions than an engine.

A 2-D axisymmetric mesh of radius 2 cm and height 5 cm was used to model the spray. Post-injection durations and initial oxygen concentrations were swept to study the efficacy of post-injection under different combustion conditions. Several factors that influence the evolution of soot were analyzed, including the distribution of temperature, oxygen concentration, and OH radicals. Additionally, newly developed analysis methods, which can quantify and visualize soot formation, soot oxidation, soot from the main-injection and soot from post-injections individually, were also used to provide more insight into the effects of post-injections.

It was observed that both soot formation and soot oxidation are enhanced by post-injection. Soot formation is increased due to the larger amount of fuel injected, especially under low O2 concentration conditions where the high equivalence ratio favors soot formation. Two mechanisms of soot oxidation were seen which are affected by different factors: soot oxidation by O2 is more sensitive to elevated temperatures and soot oxidation by OH is enhanced due to the presence of OH radicals as intermediate products of post-injection combustion.

Fluid flow Measurement & Analysis

(Session Code: PFL140)

Room 413 A
1:00 p.m. 2015-01-1696 Principal Component Analysis and study of port-induced swirl structures in a light-duty optical diesel engine
Federico Perini, University of Wisconsin; Kan Zha, Stephen Busch, Paul Miles, Sandia National Laboratories; Rolf D. Reitz, University of Wisconsin

In this work computational and experimental approaches are combined to characterize in-cylinder flow structures and local flow field properties during operation of the Sandia 1.9L light-duty optical diesel engine. A full computational model of the single-cylinder research engine was used that considers the complete intake and exhaust runners and plenums, as well as the adjustable throttling devices used in the experiments to obtain different intake swirl ratios. The in-cylinder flow predictions were validated against an extensive set of planar PIV measurements at different vertical locations in the combustion chamber for different swirl ratio configurations. Principal Component Analysis was used to characterize precession, tilting and eccentricity, and regional averages of the in-cylinder turbulence properties in the squish region and the piston bowl. Complete sweeps of the port throttle configurations were run to study their effects on the flow structure, together with their correlation with the bulk swirl ratio. Significant deviations between the flows in the piston bowl and squish regions were seen. Piston bowl design, more than the global swirl ratio, was identified to foster flow homogeneity between these two regions. Also, analysis of the port-induced flow showed that port geometry, more than different intake port mass flow ratios, can improve turbulence levels in-cylinder.

RCCI and Dual-Fuel Low Temperature Combustion (Part 2 of 3)

(Session Code: PFL262)

Room 252 A
1:30 p.m. 2015-01-0840 Multi-Dimensional-Modeling-Based Development of a Novel 2-zone Combustion Chamber Applied to Reactivity Controlled Compression Ignition Combustion
Michael Bergin, David Wickman, Christopher Rutland, Rolf D. Reitz, Wisconsin Engine Research Consultants, LLC

A novel 2-zone combustion chamber concept (patent pending) was developed using multi-dimensional modeling. At minimum volume, an axial projection in the piston divides the volume into distinct zones joined by a communication channel. The projection provides a means to control the mixture formation and combustion phasing within each zone. The novel combustion system was applied to reactivity controlled compression ignition (RCCI) combustion in both light-duty and heavy-duty diesel engines. Results from the study of an 8.8 bar BMEP, 2600 RPM operating condition are presented for the light-duty engine. The results from the heavy-duty engine are at an 18.1 bar BMEP, 1200 RPM operating condition. The effect of several major design features were investigated including the volume split between the inner and outer combustion chamber volumes, the clearance (squish) height, and the top ring land (crevice) volume. The results show significant improvements in the peak rate of pressure rise (RoPR), unburned hydrocarbon (uHC) emissions, and carbon monoxide (CO) emissions relative to conventional open chamber RCCI combustion. Ultra-low soot and NOx emissions as well as a significant fuel consumption improvement, relative to conventional diesel combustion, were obtained with the novel 2-zone combustion chamber, similar to RCCI combustion in a conventional open chamber. The novel 2-zone combustion system allows later, ignition controlling, diesel injection timings to be used while maintaining low uHC and CO emissions. Therefore control over combustion phasing and the peak RoPR are enhanced.

2:00 p.m. 2015-01-0860 Load Limit Extension in Pre-Mixed Compression Ignition Using a 2-Zone Combustion System
Michael Bergin, Wisconsin Engine Research Consultants, LLC; Adam Dempsey, Scott Curran, Oak Ridge National Laboratory; Rolf D. Reitz, Christopher Rutland, Wisconsin Engine Research Consultants, LLC

A novel 2-zone combustion system was examined at medium load operation consistent with loads in the light duty vehicle drive cycle (7.6 bar BMEP and 2600 rev/min). Pressure rise rate and noise can limit the part of the engine map where pre-mixed combustion strategies such as HCCI or RCCI can be used. The present 2-zone pistons have an axial projection that divides the near TDC volume into two regions (inner and outer) joined by a narrow communication channel defined by the squish height. Dividing the near TDC volume provides a means to prepare two fuel-air mixtures with different ignition characteristics. Depending on the fuel injection timing, the reactivity of the inner or outer volume can be raised to provide an ignition source for the fuel-air mixture in the other, less reactive volume.

Multi-dimensional CFD modeling was used to design the 2-zone piston geometry examined in this study. For experimental evaluation of the design, the geometry was applied to a GM 1.9L ZDTH in-line 4-cylinder engine equipped for dual fuel RCCI operation. The intake system was modified for port injection of gasoline, and diesel was direct injected. Engine tests showed the load could be increased from 9.3 bar IMEP to 12.2 bar IMEP at equivalent noise level when compared to an open geometry using early injections.

CFD modeling using KIVA-3V was used to explore the operation of the novel concept. Using a validated numerical model, the effects of changes in boundary conditions and load extension were examined. The numerical model was used to provide insight into cyclic variability seen in the experiments.

3:00 p.m. 2015-01-0850 Numerical Study of RCCI Combustion Processes Using Gasoline, Diesel, iso-Butanol and DTBP Cetane Improver
Hu Wang, Univ. of Wisconsin, Tianjin Univ.; Dan DelVescovo, Univ. of Wisconsin; Mingfa Yao, Tianjin Univ.; Rolf D. Reitz, Univ. of Wisconsin

Reactivity Controlled Compression Ignition (RCCI) has been shown to be one of the most competitive combustion concepts to achieve clean and high efficiency combustion. RCCI can be realized as long as the two fuels have quite different reactivities, e.g. diesel and gasoline. This motivates the idea of using a single low reactivity fuel as the premixed fuel and the same fuel blended with a small amount of cetane improver as the direct injected high reactivity fuel. In the current study, numerical investigation was conducted to simulate the RCCI combustion processes and emissions achieved by various fuels, including gasoline/diesel, iso-butanol/diesel and iso-butanol/iso-butanol + di-tert-butyl peroxide (DTBP) (cetane improver). A reduced Primary Reference Fuel (PRF)-iso-butanol-DTBP chemical mechanism was formulated based on available references and mechanisms, and the proposed mechanism was coupled with the KIVA CFD code to predict the combustion characteristics and emissions of the above mentioned fuels under different intake pressure conditions in a heavy duty diesel engine. The results showed that RCCI combustion is achievable by applying a single low reactivity fuel combined with small amount of DTBP cetane improver, and the performance of the iso-butanol-DTBP fuel is comparable to that of gasoline-diesel and iso-butanol-diesel fuels. The essential combustion characteristics, as well as emissions, can be well predicted by the simulations. However, due to the low reactivity of iso-butanol, a relatively high amount of DTBP was needed to enhance the reactivity of the direct-injected iso-butanol + DTBP fuel.

Thursday, April 23

RCCI and Dual-Fuel Low Temperature Combustion (Part 3 of 3)

(Session Code: PFL262)

Room 252 A
8:00 a.m. 2015-01-0843 Comparison of Variable Valve Actuation, Cylinder Deactivation and Injection Strategies for Low-load RCCI Operation of a Light-duty Engine
Anand Nageswaran Bharath, Yangdongfang Yang, Rolf D. Reitz, Christopher Rutland, University of Wisconsin

While Low Temperature Combustion (LTC) strategies such as Reactivity Controlled Compression Ignition (RCCI) exhibit high thermal efficiency and produce low NOx and soot emissions, low load operation is still a significant challenge due to high unburnt hydrocarbon (UHC) and carbon monoxide (CO) emissions, which occur as a result of poor combustion efficiencies at these operating points. Furthermore, the exhaust gas temperatures are insufficient to light-off the Diesel Oxidation Catalyst (DOC), thereby resulting in poor UHC and CO conversion efficiencies by the aftertreatment system. To achieve exhaust gas temperature values sufficient for DOC light-off, combustion can be appropriately phased by changing the ratio of gasoline to diesel in the cylinder, or by burning additional fuel injected during the expansion stroke through post-injection. Alternatively, variable valve actuation (VVA) strategies such as Early Exhaust Valve Opening (EEVO) and cylinder deactivation may be implemented to raise the exhaust gas temperatures for DOC activation, and/or improve fuel economy by firing fewer cylinders at operating points with higher combustion efficiencies. Since each of these strategies has benefits and drawbacks, it is of interest to compare them in terms of engine performance, emissions and catalyst efficiency for low load operation. In this work, coupled GT-Power and KIVA simulations of a multi-cylinder light duty engine operating on RCCI are performed at a near-idle operating point of 1 Bar BMEP at 1,500 rev/min. Five operating strategies are considered: 1. Varying combustion phasing via the gasoline-diesel ratio, 2. Using late fuel injection during the expansion stroke to activate the catalyst, 3. EEVO using a cam phaser, 4. EEVO using a fully flexible variable valvetrain, and 5. Cylinder deactivation. The cylinder-out emissions are compared and explained for each strategy. The effects of exhaust gas temperature on DOC performance, and the impact of each strategy on fuel economy are also studied to determine the most suitable strategy for low load operation.

8:30 a.m. 2015-01-0839 Isobutanol as Both Low Reactivity and High Reactivity Fuels with addition of Di-Tert Butyl Peroxide (DTBP) in RCCI Combustion
Dan DelVescovo, Hu Wang, Martin Wissink, Rolf D. Reitz, University of Wisconsin

Engine experiments and multi-dimensional modeling were used to explore the effects of isobutanol as a high and low reactivity fuel in Reactivity Controlled Compression Ignition (RCCI) Combustion. Three fuel combinations were examined; EEE/diesel, isobutanol/diesel, and isobutanol/isobutanol+DTBP (di-tert butyl peroxide). In order to assess the relative performance of fuel combinations of interest under RCCI operation, the engine was operated under conditions representative of typical RCCI operation. A net load of 6bar IMEP was chosen because it provides a wide operable range of equivalence ratios and combustion phasings without excessively high peak pressure rise rates. To provide a representative set of operating conditions for comparison between fuel combinations, the engine was operated under various intake pressures to adjust the global equivalence ratio from 0.27-0.35 for EEE/diesel operation, and various combustion phasings from a CA50 of about 1.5 to about 10deg ATDC. Each fuel combination was operated with matched combustion phasing (CA50), at the same intake temperature and pressure conditions. Combustion phasing was achieved by scaling the direct injected fuel quantity appropriately until the desired combustion phasing was achieved while maintaining the desired load by correspondingly scaling the port fuel injected quantity. The experimental work demonstrates the need to tailor the direct injection strategy to the specific fuel combination if the fuel properties between the baseline case, in this case EEE/diesel, and the particular fuel combination differ significantly. Due to isobutanol’s high octane number, a significantly larger quantity of direct injected fuel was required to match combustion phasing, resulting in higher NOx emissions and decreased gross thermal efficiency. Tailoring the direct injection strategy for the specific fuel combination however was shown to mitigate the increased emissions and decreased efficiency. Utilizing a triple injection approach instead of the standard double injection approach for RCCI operation was shown to provide decreased NOx emissions and increased thermal efficiency for the isobutanol cases by avoiding overly rich in-cylinder regions.

Emission Control Modeling (Part 3 of 3)

(Session Code: PFL430)

Room 140 E
10:00 a.m. 2015-01-1060 Model Based Study of DeNOx Characteristics for Integrated DPF/SCR System over Cu-Zeolite
Yangdongfang Yang, Univ of Wisconsin; Gyubaek Cho, Korea Institute of Machinery & Materials; Christopher Rutland, Univ of Wisconsin

The SCR Filter simultaneously reduces NOx and Particle Matter (PM) in the exhaust and is considered an effective way to meet emission regulations. By combining the function of a Diesel Particulate Filtration (DPF) and a Selective Catalytic Reduction (SCR), the SCR Filter reduces the complexity and cost of aftertreatment systems in diesel vehicles. Moreover, it provides an effective reaction surface and potentially reduces backpressure by combining two devices into one. However, unlike traditional flow through type SCR, the deNOx reactions in the SCR Filter can be affected by the particulate filtration and regeneration process. Additionally, soot oxidation can be affected by the deNOx process.

A 1-D kinetic model for integrated DPF and NH3-SCR system over Cu-zeolite catalysts was developed and validated with experimental data in previous work[1]. In the current work, the reaction kinetics, and interaction between soot and SCR reactions are analyzed to give a clear review on chemical and physical process inside the filter. Extensive studies on the effect of the NO2/NOx ratio, ANR (ammonia to NOx ratio), temperature, and SV (gas hourly space velocity) on clean filter deNOx efficiency at both steady and transient states are presented, followed by the soot influence on deNOx performance. This soot influence is studied for the wall soot and cake layer cases separately, and the wall soot was found to have a larger effect on SCR reactions compared to the soot inside cake layer. It was also observed that the soot promotes the concentration of adsorbed ammonia.

Alternative and Advanced Fuels

(Session Code: PFL330)

Room 411 B
10:30 a.m. 2015-01-0952 Effects of Fuel Physical Properties on Auto-Ignition Characteristics in a Heavy-Duty Compression Ignition Engine
Michael A. Groendyk, David Rothamer, Univ. of Wisconsin

The effect of fuel physical properties on the ignition and combustion characteristics of diesel fuels was investigated in a heavy-duty 2.52 L single-cylinder engine. Two binary component fuels, one comprised of farnesane (FAR) and 2,2,4,4,6,8,8-heptamethylnonane (HMN), and another comprised of primary reference fuels (PRF) for the octane rating scale (i.e. n-heptane and 2,2,4-trimethylpentane), were blended to match the cetane number (CN) of a 45 CN diesel fuel. The binary mixtures were used neat, and blended at 25, 50, and 75% by volume with the baseline diesel. Ignition delay (ID) for each blend was measured under identical operating conditions. A single injection was used, with injection timing varied from -12.5 to 2.5 CAD. Injection pressures of 50, 100, and 150 MPa were tested. Observed IDs were consistent with previous work done under similar conditions with diesel fuels. The shortest IDs were seen at injection timings of -7.5 CAD. The largest difference in ID between all fuels of 75 ± 18 μs was observed at the earliest injection timing with an injection pressure of 50 MPa. The average difference in ignition delay between individual blends was 35 ± 18 μs. None of the blends tested exhibited significant differences in ignition delay compared to the baseline diesel. The results indicate that for the density and temperature range tested, fuel physical properties have limited influence on the ignition process in a heavy-duty diesel engine. Instead, chemical ignition characteristics, i.e., CN, control the ignition delay.