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Viewing 1 to 30 of 287
2018-04-03
Technical Paper
2018-01-0217
David Vuilleumier, Xun Huan PhD, Tiernan Casey PhD, Magnus Sjöberg
The Octane Index framework and Co-Optimization of Fuels and Engines (Co-Optima) Central Fuels Hypothesis are evaluated using seven fuels operated under stoichiometric, knock-limited conditions in a directly injected spark ignition (DISI) engine. Of the seven tested fuels, three fuels are “Tier III” fuel blends, meaning that they are blends of molecules which have passed two levels of screening, and have been evaluated to be ready for tests in a research engine. These molecules have been blended into a 4-component gasoline surrogate at varying volume fractions in order to achieve a Research Octane Number (RON) rating of 98. The four molecules under consideration are: isobutanol, 2-butanol, and Diisobutylene. Research engine tests measured knock limits at heated and unheated intake temperature conditions, as well as throttled and boosted intake pressures.
2018-04-03
Technical Paper
2018-01-0198
Riccardo Scarcelli, Anqi Zhang, Thomas Wallner, Douglas Breden, Anand Karpatne, Laxminarayan Raja, Isaac Ekoto, Benjamin Wolk
While the spark-ignition (SI) engine technology migrates towards challenging combustion regimes (dilute and boosted operation), advanced ignition technologies generating non-equilibrium types of plasma have continued to receive significant attention from the automotive industry as a potential replacement for conventional spark-plugs. However there are no models currently that can describe the non-thermal plasma ignition process in the computational fluid dynamics (CFD) codes that are widely used in the engine multi-dimensional modeling community. A key question for the engine modelers that are trying to describe the non-equilibrium ignition physics concerns the characteristics of the non-equilibrium plasma. A key challenge is represented by the plasma formation timescale (nanoseconds) that can hardly be resolved within a full engine cycle (milliseconds) simulation.
2018-04-03
Technical Paper
2018-01-0196
Noah Van Dam, Magnus Sjöberg, Sibendu Som
Large-eddy Simulations (LES) have been carried out to investigate spray variability and its effect on cycle-to-cycle flow variability in a direct-injection spark-ignition (DISI) engine under non-reacting conditions. Initial simulations were performed of an injector in a constant volume spray chamber. Detailed measurements of the spray including quantitative mixing data are used to validate a simulation spray set-up for the stepped-bore multi-hole gasoline direct injection (GDI) injector. A random seed perturbation methodology was used to generate shot-to-shot spray variability in the LES, and comparisons of both mean and standard deviations were made for quantities with sufficient experimental data. After validation, the same spray set-up was used to simulate the same injector in an optically accessible DISI engine.
2018-04-03
Technical Paper
2018-01-0228
Stephen Busch, Kan Zha, Eric Kurtz, Alok Warey, Richard Peterson
In light- and medium-duty diesel engines, piston bowl shape influences thermal efficiency, either due to changes in wall heat loss or to changes in the heat release rate. The relative contributions of these two factors are not clearly described in the literature. In this work, two production piston bowls are adapted for use in a single cylinder research engine: a conventional, re-entrant piston, and a stepped-lip piston. An injection timing sweep is performed at constant load with each piston, and heat release analyses provide information about thermal efficiency, wall heat loss, and the degree of constant volume combustion. Zero-dimensional thermodynamic simulations provide further insight and support for the experimental results. The effect of bowl geometry on wall heat loss depends on injection timing, but changes in wall heat loss cannot explain changes in efficiency.
2018-04-03
Technical Paper
2018-01-0230
Kan Zha, Stephen Busch, Alok Warey, Richard C. Peterson, Eric Kurtz
In light-duty, direct injection (DI) diesel engines, combustion chamber geometry influences the complex interactions between swirl and squish flows, spray-wall interactions as well as late-cycle mixing. Because of these interactions, piston bowl geometry significantly affects fuel efficiency and emissions behavior. However, due to lack of reliable in-cylinder measurements, the mechanisms responsible for piston-induced changes in engine performance are not well understood. Non-intrusive, in-situ optical measurement techniques are necessary to provide a deeper understanding of the piston geometry effect on in-cylinder processes and to assist in the development of predictive engine simulation models. This study compares two substantially different piston bowls with geometries representative of existing technology: a conventional re-entrant bowl and a stepped-lip bowl. Both pistons are tested in a single-cylinder optical diesel engine under identical boundary conditions.
2018-04-03
Technical Paper
2018-01-0232
Ted Lind, Gregory Roberts, W. Eagle, Christine Rousselle, Oivind Andersson, Mark PB Musculus
Small closely-coupled post injections of fuel in diesel engines are known to reduce engine-out soot emissions, but the relative roles of various underlying in-cylinder mechanisms have not been established. Furthermore, the efficacy of soot reduction is not universal, and depends in unclear ways on operating conditions and injection schedule, among other factors. Consequently, designing engine hardware and operating strategies to fully realize the potential of post-injections is limited by this lack of understanding. Following previous work [1], several different post-injection schedules are investigated using a single-cylinder 2.34 L heavy-duty optical engine equipped with a Delphi DFI 1.5 light-duty injector. In this configuration, adding a closely-coupled post injection with sufficiently short injection duration can increase the load without increasing soot emissions.
2018-04-03
Technical Paper
2018-01-0233
Scott Skeen, Koji Yasutomi, Emre Cenker, Brian Adamson, Nils Hansen, Lyle Pickett
The formation of soot in high-pressure sprays of n-dodecane is visualized and quantified under conditions relevant to heavy-duty diesel engines. Sprays are injected from a single-hole diesel injector belonging to the family of Engine Combustion Network (ECN) Spray D injectors. Soot optical thickness (KL) and the total soot mass are quantified using a high-speed extinction imaging diagnostic with incident light wavelengths of 632 nm and 850 nm. The total soot mass is derived from KL using a non-dimensional extinction coefficient based on the Rayleigh-Debye-Gans approximation for fractal aggregates (RDG-FA). Previous work showed consistency between the total soot mass measured with incident wavelengths of 406 nm, 520 nm, and 632 nm; however, the present work demonstrates a significant difference for measurements with incident light in the infrared.
2018-04-03
Technical Paper
2018-01-0277
Michele Battistoni, Gina M. Magnotti, Caroline L. Genzale, Marco Arienti, Katarzyna E. Matusik, Daniel J. Duke, Jhoan Giraldo, Jan Ilavsky, Alan L. Kastengren, Christopher F. Powell, Pedro Marti-Aldaravi
In order to improve understanding of the primary atomization process for diesel-like sprays, a collaborative experimental and computational study was focused on the near-nozzle spray structure for the Engine Combustion Network Spray D single-hole injector. These results were presented at the 5th Workshop of the Engine Combustion Network in Detroit, Michigan. Application of x-ray diagnostics to the Spray D standard cold condition (SCC) enabled quantification of mass, phase interfacial area, and droplet size distributions in the near-nozzle region from 0.1 to 10 mm from the nozzle exit. Using these data, several modeling frameworks, from Lagrangian-Eulerian to Eulerian-Eulerian and from Reynolds-Averaged Navier Stokes (RANS) to Large-Eddy Simulation (LES), were assessed in their ability to capture and explain experimentally observed spray details.
2018-04-03
Technical Paper
2018-01-0284
Shane Daly, Emre Cenker, Lyle Pickett, Scott Skeen
This work investigates the impact of injector temperature on the characteristics of high-pressure n-dodecane sprays under conditions relevant to heavy-duty diesel engines. Sprays are injected from a pair of single-hole diesel injectors belonging to the family of “Spray C” and “Spray D” Engine Combustion Network (ECN) injectors. Low and high injector temperature conditions are achieved by activating or de-activating a cooling jacket. We quantify spray spreading angle and penetration using high-speed shadowgraph and long-distance-microscopy imaging. We evaluate differences in fuel/air mixture formation at key timings through one-dimensional modeling. Injections from a cooled injector penetrate faster than those from a higher temperature injector, especially for an injector already prone to cavitate (Spray C).
2018-04-03
Technical Paper
2018-01-1101
Vicente Romero
This paper introduces a “Direct Discrete” (DD) model calibration and uncertainty propagation approach for handling aleatory variability and epistemic uncertainties in replicate tests of stochastic systems and in computational models calibrated to the experimental data. The DD approach appears to have several advantages over Bayesian and other calibration and uncertainty propagation approaches for capturing and utilizing the inference information obtained from the typically small number of experiments in model calibration situations. In particular, the DD approach preserves the fundamental information from the sparse sample data in a way that enables model predictions to represent the sparse-data aleatory-epistemic uncertainty differently according to what best supports inference accuracy for different quantities such as the central 95% of response vs. a small exceedance probability associated with a tail of the response distribution.
2018-04-03
Technical Paper
2018-01-1252
Gerald Gentz, Jeremie Dernotte, Chunsheng Ji, John Dec
Low-temperature gasoline combustion (LTGC) engines can deliver high efficiencies, with ultra-low emissions of nitrogen oxides (NOx) and particulate matter (PM). However, controlling the combustion timing and maintaining robust operation remains a challenge for LTGC engines. One promising technique to overcoming these challenges is spark assist (SA). In this work, well-controlled, fully premixed experiments are performed in a single-cylinder LTGC research engine at 1200 rpm using a cylinder head modified to accommodate a spark plug. Compression ratios (CR) of 16:1 and 14:1 were used during the experiments. Two different fuels were also tested, with properties representative of premium- and regular-grade market gasolines. SA was found to work well for both CRs and fuels. The equivalence ratio (Phi) limits and the effect of intake pressure boost on the ability of SA to compensate for a reduced Tin were studied. For the conditions studied, Phi=0.42 was found to be most effective for SA.
2018-04-03
Technical Paper
2018-01-1249
Isaac Ekoto, Fabrice Foucher
Mechanisms responsible for enhanced compression ignition when ozone (O3) is added into the intake charge were explored in a single-cylinder, optically accessible, research engine configured for low-load advanced compression ignition experiments. Intake O3 concentrations were varied up to 35 ppm, with the intake pressure fixed at 1.0 bar. Cycle resolved measurements of in-cylinder O3 decomposition for both motored and fired operation were performed using an O3 absorption diagnostic that used filtered 266 nm light from a continuous wave arc lamp. For motored operation, it was found that starting at intake valve closure (IVC), O3 gradually decomposed into molecular (O2) and atomic (O) oxygen. Near top dead center (TDC), there was an inflection point where rapid O3 decomposition occurred. The location of the inflection point advanced with increased intake temperature, decreased charge mass O2 content, or when fuel was added.
2018-04-03
Technical Paper
2018-01-1248
Guillaume Petitpas, Russell Whitesides, John Dec, Jeremie Dernotte
This study presents estimates for measurement uncertainties for a Homogenous Charge Compression Ignition (HCCI)/Low-Temperature Gasoline Combustion (LTGC) engine testing facility. A previously presented framework for quantifying those uncertainties developed uncertainty estimates based on the transducers manufacturers’ published tolerances. The present work utilizes the framework with improved uncertainty estimates in order to more accurately represent the uncertainties observed on the specific engine testing facility, concerning both the directly measured (pressures, flow rates…) and the derived quantities (intake temperature, equivalence ratio…). Details of laboratory calibration techniques and commissioning runs are being used to constrain the sensitivities of the transducers relative to manufacturer supplied values. The uncertainty framework is also extended to consider additional sources of uncertainty, including non-ideal engine volume history due to kinematic effects.
2017-10-08
Technical Paper
2017-01-2234
David Vuilleumier, Magnus Sjöberg
Abstract Fundamental engine research is primarily conducted under steady-state conditions, in order to better describe boundary conditions which influence the studied phenomena. However, light-duty automobiles are operated, and tested, under heavily transient conditions. This mismatch between studied conditions and in-use conditions is deemed acceptable due to the fundamental knowledge gained from steady-state experiments. Nonetheless, it is useful to characterize the conditions encountered during transient operation and determine if the governing phenomena are unduly influenced by the differences between steady-state and transient operation, and further, whether transient behavior can be reasonably extrapolated from steady-state behavior. The transient operation mode used in this study consists of 20 fired cycles followed by 80 motored cycles, operating on a continuous basis.
2017-09-04
Journal Article
2017-24-0088
Gregory Roberts, Christine Mounaim Rousselle, Mark Musculus, Martin Wissink, Scott Curran, Ethan Eagle
Abstract 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.
2017-06-05
Journal Article
2017-01-1765
Albert Allen, Noah Schiller, Jerry Rouse
Abstract Corrugated-core sandwich structures with integrated acoustic resonator arrays have been of recent interest for launch vehicle noise control applications. Previous tests and analyses have demonstrated the ability of this concept to increase sound absorption and reduce sound transmission at low frequencies. However, commercial aircraft manufacturers often require fibrous or foam blanket treatments for broadband noise control and thermal insulation. Consequently, it is of interest to further explore the noise control benefit and trade-offs of structurally integrated resonators when combined with various degrees of blanket noise treatment in an aircraft-representative cylindrical fuselage system. In this study, numerical models were developed to predict the effect of broadband and multi-tone structurally integrated resonator arrays on the interior noise level of cylindrical vibroacoustic systems.
2017-03-28
Technical Paper
2017-01-0561
Federico Perini, Kan Zha, Stephen Busch, Rolf Reitz
Abstract In this work, linear, non-linear and a generalized renormalization group (RNG) two-equation RANS turbulence models of the k-epsilon form were compared for the prediction of turbulent compressible flows in diesel engines. The object-oriented, multidimensional parallel code FRESCO, developed at the University of Wisconsin, was used to test the alternative models versus the standard k-epsilon model. Test cases featured the academic backward facing step and the impinging gas jet in a quiescent chamber. Diesel engine flows featured high-pressure spray injection in a constant volume vessel from the Engine Combustion Network (ECN), as well as intake flows in a high-swirl diesel engine. For the engine intake flows, a model of the Sandia National Laboratories 1.9L light-duty single cylinder optical engine was used.
2017-03-28
Journal Article
2017-01-0662
David Vuilleumier, Magnus Sjöberg
Abstract Spark-ignition (SI) engine efficiency is typically limited by fuel auto-ignition resistance, which is described in practice by the Research Octane Number (RON) and the Motor Octane Number (MON). The goal of this work is to assess whether fuel properties (i.e. RON, MON, and heat of vaporization) are sufficient to describe the antiknock behavior of varying gasoline formulations in modern engines. To this end, the auto-ignition resistance of three compositionally dissimilar gasoline-like fuels with identical RON values and varying or non-varying MON values were evaluated in a modern, prototype, 12:1 compression ratio, high-swirl (by nature of intake valve deactivation), directly injected spark ignition (DISI) engine at 1400 RPM. The three gasolines are an alkylate blend (RON=98, MON=97), a blend with high aromatic content (RON=98, MON=88), and a blend of 30% ethanol by volume with a gasoline BOB (RON=98, MON=87; see Table 2 for details).
2017-03-28
Journal Article
2017-01-0674
Benjamin Matthew Wolk, Isaac Ekoto
Abstract Pulsed nanosecond discharges (PND) can achieve ignition in internal combustion engines through enhanced reaction kinetics as a result of elevated electron energies without the associated increases in translational gas temperature that cause electrode erosion. Atomic oxygen (O), including its electronically excited states, is thought to be a key species in promoting low-temperature ignition. In this paper, high-voltage (17-24 kV peak) PND are examined in oxygen/nitrogen/carbon dioxide/water mixtures at engine-relevant densities (up to 9.1 kg/m3) through pressure-rise calorimetry and direct imaging of excited-state O-atom and molecular nitrogen (N2) in an optically accessible spark calorimeter, with the anode/cathode gap distance set to 5 mm or with an anode-only configuration (DC corona). The conversion efficiency of pulse electrical energy into thermal energy was measured for PND with secondary streamer breakdown (SSB) and similar low-temperature plasmas (LTP) without.
2017-03-28
Technical Paper
2017-01-0728
Jeremie Dernotte, John Dec, Chunsheng Ji
Abstract For lean or dilute, boosted gasoline compression-ignition engines operating in a low-temperature combustion mode, creating a partially stratified fuel charge mixture prior to auto-ignition can be beneficial for reducing the heat-release rate (HRR) and the corresponding maximum rate of pressure rise. As a result, partial fuel stratification (PFS) can be used to increase load and/or efficiency without knock (i.e. without excessive ringing). In this work, a double direct-injection (D-DI) strategy is investigated for which the majority of the fuel is injected early in the intake stroke to create a relatively well-mixed background mixture, and the remaining fuel is injected in the latter part of the compression stroke to produce greater fuel stratification prior auto-ignition. Experiments were performed in a 1-liter single-cylinder engine modified for low-temperature gasoline combustion (LTGC) research.
2017-03-28
Journal Article
2017-01-0729
Isaac Ekoto, Benjamin Wolk, William Northrop
Abstract In-cylinder reforming of injected fuel during an auxiliary negative valve overlap (NVO) period can be used to optimize main-cycle auto-ignition phasing for low-load Low-Temperature Gasoline Combustion (LTGC), where highly dilute mixtures can lead to poor combustion stability. When mixed with fresh intake charge and fuel, these reformate streams can alter overall charge reactivity characteristics. The central issue remains large parasitic heat losses from the retention and compression of hot exhaust gases along with modest pumping losses that result from mixing hot NVO-period gases with the cooler intake charge. Accurate determination of total cycle energy utilization is complicated by the fact that NVO-period retained fuel energy is consumed during the subsequent main combustion period. For the present study, a full-cycle energy analysis was performed for a single-cylinder research engine undergoing LTGC with varying NVO auxiliary fueling rates and injection timing.
2017-03-28
Journal Article
2017-01-0731
John E. Dec, Jeremie Dernotte, Chunsheng Ji
Abstract Low-temperature gasoline combustion (LTGC) has the potential to provide gasoline-fueled engines with efficiencies at or above those of diesel engines and extremely low NOx and particulate emissions. Three key performance goals for LTGC are to obtain high loads, reduce the boost levels required for these loads, and achieve high thermal efficiencies (TEs). This paper reports the results of an experimental investigation into the use of partial fuel stratification, produced using early direct fuel injection (Early-DI PFS), and an increased compression ratio (CR) to achieve significant improvements in these performance characteristics. The experiments were conducted in a 0.98-liter single-cylinder research engine. Increasing the CR from 14:1 to 16:1 produced a nominal increase in the TE of about one TE percentage unit for both premixed and Early-DI PFS operation.
2017-03-28
Journal Article
2017-01-0716
Randy Hessel, Zongyu Yue, Rolf Reitz, Mark Musculus, Jacqueline O'Connor
Abstract One way to develop an understanding of soot formation and oxidation processes that occur during direct injection and combustion in an internal combustion engine is to image the natural luminosity from soot over time. Imaging is possible when there is optical access to the combustion chamber. After the images are acquired, the next challenge is to properly interpret the luminous distributions that have been captured on the images. A major focus of this paper is to provide guidance on interpretation of experimental images of soot luminosity by explaining how radiation from soot is predicted to change as it is transmitted through the combustion chamber and to the imaging. The interpretations are only limited by the scope of the models that have been developed for this purpose. The end-goal of imaging radiation from soot is to estimate the amount of soot that is present.
2017-03-28
Journal Article
2017-01-0724
A. S. (Ed) Cheng, Charles J. Mueller
Abstract Experiments conducted with a set of reference diesel fuels in an optically accessible, compression-ignition engine have revealed a strong correlation between hydrocarbon (HC) emissions and the flame lift-off length at the end of the premixed burn (EOPMB), with increasing HC emissions associated with longer lift-off lengths. The correlation is largely independent of fuel properties and charge-gas O2 mole fraction, but varies with fuel-injection pressure. A transient, one-dimensional jet model was used to investigate three separate mechanisms that could explain the observed impact of lift-off length on HC emissions. Each mechanism relies on the formation of mixtures that are too lean to support combustion, or “overlean.” First, overlean regions can be formed after the start of fuel injection but before the end of the premixed burn.
2017-03-28
Journal Article
2017-01-0837
Panos Sphicas, Lyle M Pickett, Scott Skeen, Jonathan Frank, Tommaso Lucchini, David Sinoir, Gianluca D'Errico, Kaushik Saha, Sibendu Som
Abstract Modeling plume interaction and collapse for direct-injection gasoline sprays is important because of its impact on fuel-air mixing and engine performance. Nevertheless, the aerodynamic interaction between plumes and the complicated two-phase coupling of the evaporating spray has shown to be notoriously difficult to predict. With the availability of high-speed (100 kHz) Particle Image Velocimetry (PIV) experimental data, we compare velocity field predictions between plumes to observe the full temporal evolution leading up to plume merging and complete spray collapse. The target “Spray G” operating conditions of the Engine Combustion Network (ECN) is the focus of the work, including parametric variations in ambient gas temperature. We apply both LES and RANS spray models in different CFD platforms, outlining features of the spray that are most critical to model in order to predict the correct aerodynamics and fuel-air mixing.
2017-03-28
Technical Paper
2017-01-0529
Seamus Kane, Xuesong Li, Benjamin Wolk, Isaac Ekoto, William F. Northrop
Abstract Fuel reforming during a Negative Valve Overlap (NVO) period is an effective approach to control Low Temperature Gasoline Combustion (LTGC) ignition. Previous work has shown through experiments that primary reference fuels reform easily and produce several species that drastically affect ignition characteristics. However, our previous research has been unable to accurately predict measured reformate composition at the end of the NVO period using simple single-zone models. In this work, we use a stochastic reactor model (SRM) closed cycle engine simulation to predict reformate composition accounting for in-cylinder temperature and mixture stratification. The SRM model is less computationally intensive than CFD simulations while still allowing the use of large chemical mechanisms to predict intermediate species formation rates.
2016-10-17
Journal Article
2016-01-2295
Chunsheng Ji, John Dec, Jeremie Dernotte, William Cannella
Abstract Previous work has shown that conventional diesel ignition improvers, 2-ethylhexyl nitrate (EHN) and di-tert-butyl peroxide (DTBP), can be used to enhance the autoignition of a regular-grade E10 gasoline in a well premixed low-temperature gasoline combustion (LTGC) engine, hereafter termed an HCCI engine, at naturally aspirated and moderately boosted conditions (up to 180 kPa absolute) with a constant engine speed of 1200 rpm and a 14:1 compression ratio. In the current work the effect of EHN on boosted HCCI combustion is further investigated with a higher compression ratio (16:1) piston and over a range of engine speeds (up to 2400 rpm). The results show that the higher compression ratio and engine speeds can make the combustion of a regular-grade E10 gasoline somewhat less stable. The addition of EHN improves the combustion stability by allowing combustion phasing to be more advanced for the same ringing intensity.
2016-07-18
Journal Article
2016-01-9142
Rebecca S. Levinson, Dawn K. Manley, Todd H. West
Abstract Simulations of the US light duty vehicle stock help policy makers, investors, and auto manufacturers make informed decisions to influence the future of the stock and its associated green house gas emissions. Such simulations require an underlying framework that captures the key elements of consumer purchasing decisions, which can be uncertain. This uncertainty in a simulation’s logic is usually convolved with uncertainty in the underlying assumptions about the futures of energy prices and technology innovation and availability. By comparing simulated alternative energy vehicle (AEV) sales to historical sales data, one can assess the simulation’s ability to capture the dynamics of consumer choice, independent of many of those underlying uncertainties, thereby determining the factors that most strongly impact sales.
2016-04-05
Journal Article
2016-01-0743
W. Ethan Eagle, Louis-Marie Malbec, Mark PB Musculus
Abstract This paper presents new measurements of liquid and liftoff lengths, vapor penetration, and ignition delay using the Engine Combustion Network (ECN) ‘Spray B’ injector in a 2.34 L skip-fired heavy-duty optical engine. The data from the Spray B injector, having three 90-micron holes, are compared with previously existing constant-volume vessel data using both the Spray B injector as well as the ECN Spray A injector, which has a single 90-micron axial hole. The new data were acquired using Mie scattering, OH* chemiluminescence imaging, schlieren imaging, and incylinder pressure measurements. This paper presents data from estimated isentropic-core top-dead-center conditions with ambient densities of 15.2 and 22.8 kg/m3, temperatures of 800, 900, and 1000 K, and for both non-reacting (0% and 7.5% O2) and reacting (13, 15, and 21% O2) injections of n-dodecane at fuel-rail pressures of 500, 1000, and 1500 bar.
2016-04-05
Journal Article
2016-01-0753
Benjamin Wolk, Isaac Ekoto, William Northrop
Abstract Negative Valve Overlap (NVO) is a potential control strategy for enabling Low-Temperature Gasoline Combustion (LTGC) at low loads. While the thermal effects of NVO fueling on main combustion are well-understood, the chemical effects of NVO in-cylinder fuel reforming have not been extensively studied. The objective of this work is to examine the effects of fuel molecular structure on NVO fuel reforming using gas sampling and detailed speciation by gas chromatography. Engine gas samples were collected from a single-cylinder research engine at the end of the NVO period using a custom dump-valve apparatus. Six fuel components were studied at two injection timings: (1) iso-octane, (2) n-heptane, (3) ethanol, (4) 1-hexene, (5) cyclohexane, and (6) toluene. All fuel components were studied neat except for toluene - toluene was blended with 18.9% nheptane by liquid volume to increase the fuel reactivity.
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