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2014-10-22
Article
Charged with overseeing the development and execution of the company’s technology strategy and plans, Dr. Ken Washington will pull from research and advanced engineering experience gained over the course of his 28-year career at Lockheed Martin and Sandia National Laboratories in the areas of nuclear engineering, information systems, super-computing, information privacy, and R&D space technologies.
2014-10-13
Technical Paper
2014-01-2657
Julien Manin, Scott Skeen, Lyle Pickett, Eric Kurtz, James E. Anderson
Abstract The Leaner Lifted-Flame Combustion (LLFC) strategy offers a possible alternative to low temperature combustion or other globally lean, premixed operation strategies to reduce soot directly in the flame, while maintaining mixing-controlled combustion. Adjustments to fuel properties, especially fuel oxygenation, have been reported to have potentially beneficial effects for LLFC applications. Six fuels were selected or blended based on cetane number, oxygen content, molecular structure, and the presence of an aromatic hydrocarbon. The experiments compared different fuel blends made of n-hexadecane, n-dodecane, methyl decanoate, tri-propylene glycol monomethyl ether (TPGME), as well as m-xylene. Several optical diagnostics have been used simultaneously to monitor the ignition, combustion and soot formation/oxidation processes from spray flames in a constant-volume combustion vessel. Ignition delay times, lift-off lengths and soot KL extinction levels for the six fuels have been measured at in-cylinder conditions relevant to modern diesel engines.
2014-10-13
Technical Paper
2014-01-2615
Magnus Sjöberg, Wei Zeng, Daniel Singleton, Jason M. Sanders, Martin A. Gundersen
Abstract Well-mixed lean SI engine operation can provide improvements of the fuel economy relative to that of traditional well-mixed stoichiometric SI operation. This work examines the use of two methods for improving the stability of lean operation, namely multi-pulse transient plasma ignition and intake air preheating. These two methods are compared to standard SI operation using a conventional high-energy inductive ignition system without intake air preheating. E85 is the fuel chosen for this study. The multi-pulse transient plasma ignition system utilizes custom electronics to generate 10 kHz bursts of 10 ultra-short (12ns), high-amplitude pulses (200 A). These pulses were applied to a custom spark plug with a semi-open ignition cavity. High-speed imaging reveals that ignition in this cavity generates a turbulent jet-like early flame spread that speeds up the transition from ignition to the main combustion event. Performance testing shows that lean operation with heated intake air enables a 17% improvement of fuel economy at ϕ = 0.59 for both ignition systems, relative to that of stoichiometric operation.
2014-04-01
Technical Paper
2014-01-1412
Lyle M. Pickett, Julien Manin, Alan Kastengren, Christopher Powell
A full understanding and characterization of the near-field of diesel sprays is daunting because the dense spray region inhibits most diagnostics. While x-ray diagnostics permit quantification of fuel mass along a line of sight, most laboratories necessarily use simple lighting to characterize the spray spreading angle, using it as an input for CFD modeling, for example. Questions arise as to what is meant by the “boundary” of the spray since liquid fuel concentration is not easily quantified in optical imaging. In this study we seek to establish a relationship between spray boundary obtained via optical diffused backlighting and the fuel concentration derived from tomographic reconstruction of x-ray radiography. Measurements are repeated in different facilities at the same specified operating conditions on the “Spray A” fuel injector of the Engine Combustion Network, which has a nozzle diameter of 90 μm. Long-distance microscopy at >100 kHz speeds is used to characterize the opening, steady, and closing phases of injection.
2014-04-01
Technical Paper
2014-01-1423
Shaoping Quan, Meizhong Dai, Eric Pomraning, P. K. Senecal, Keith Richards, Sibendu Som, Scott Skeen, Julien Manin, Lyle M. Pickett
Shock waves have been recently observed in high-pressure diesel sprays. In this paper, three-dimensional numerical simulations of supersonic diesel spray injection have been performed to investigate the underlying dynamics of the induced shock waves and their interactions with the spray. A Volume-of-Fluid based method in the CFD software (CONVERGE) is used to model this multiphase phenomena. An adaptive Mesh Refinement (AMR) scheme is employed to capture the front of the spray and the shock waves with high fidelity. Simulation results are compared to the available experimental observations to validate the numerical procedure. Parametric studies with different injection and ambient conditions are conducted to examine the effect of these factors on the generation of shock waves and their dynamics.
2014-04-01
Technical Paper
2014-01-1429
Joseph Oefelein, Guilhem Lacaze, Rainer Dahms, Anthony Ruiz, Antony Misdariis
Abstract This paper first summarizes a new theoretical description that quantifies the effects of real-fluid thermodynamics on liquid fuel injection processes as a function of pressure at typical engine operating conditions. It then focuses on the implications this has on modeling such flows with emphasis on application of the Large Eddy Simulation (LES) technique. The theory explains and quantifies the major differences that occur in the jet dynamics compared to that described by classical spray theory in a manner consistent with experimental observations. In particular, the classical view of spray atomization as an appropriate model at some engine operating conditions is questionable. Instead, non-ideal real-fluid behavior must be taken into account using a multicomponent formulation that applies to hydrocarbon mixtures at high-pressure supercritical conditions. To highlight the implications and needs related to modeling, we present a series of studies using LES that focus on experiments being conducted in the high-pressure combustion vessel at Sandia National Laboratories.
2013-10-14
Technical Paper
2013-01-2627
Yi Yang, John E. Dec
This paper studies autoignition characteristics and HCCI engine combustion of ketone fuels, which are important constituents of recently discovered fungi-derived biofuels. Two ketone compounds, 2,4-dimethyl-3-pentanone (DMPN) and cyclopentanone (CPN), are systematically investigated in the Sandia HCCI engine, and the results are compared with conventional gasoline and neat ethanol. It is found that CPN has the lowest autoignition reactivity of all the biofuels and gasoline blends tested in this HCCI engine. The combustion timing of CPN is also the most sensitive to intake-temperature (Tin) variations, and it is almost insensitive to intake-pressure (Pin) variations. These characteristics and the overall HCCI performance of CPN are similar to those of ethanol. In contrast, DMPN shows multi-faceted autoignition characteristics. On the one hand, DMPN has strong temperature-sensitivity, even at boosted Pin, which is similar to the low-reactivity ethanol and CPN. On the other hand, DMPN shows much stronger pressure-sensitivity than ethanol and CPN.
2013-10-14
Technical Paper
2013-01-2531
Paul C. Miles, Dipankar Sahoo, Stephen Busch, Johannes Trost, Alfred Leipertz
Measurements of ignition behavior, homogeneous reactor simulations employing detailed kinetics, and quantitative in-cylinder imaging of fuel-air distributions are used to delineate the impact of temperature, dilution, pilot injection mass, and injection pressure on the pilot ignition process. For dilute, low-temperature conditions characterized by a lengthy ignition delay, pilot ignition is impeded by the formation of excessively lean mixture. Under these conditions, smaller pilot mass or higher injection pressures further lengthen the pilot ignition delay. Similarly, excessively rich mixtures formed under relatively short ignition delay conditions typical of conventional diesel combustion will also prolong the ignition delay. In this latter case, smaller pilot mass or higher injection pressures will shorten the ignition delay. The minimum charge temperature required to effect a robust pilot ignition event is strongly dependent on charge O2 concentration. Measured fuel-air ratio distributions, coupled with the homogeneous reactor simulations, show this temperature dependency to be due to both kinetics and over-mixing caused by the long ignition delay associated with dilute mixtures.
2013-10-14
Technical Paper
2013-01-2548
Julien Manin, Lyle M. Pickett, Scott A. Skeen
Despite ongoing research efforts directed at reducing engine-out emissions, diesel engines are known to be one of the largest sources of atmospheric particulate matter (i.e., soot). Quantitative measurements are of primary importance to address soot production during the combustion process in the cylinder of diesel engines. This study presents the capabilities of an extinction-based diagnostic developed to quantitatively measure the soot volume fraction in n-dodecane sprays injected in a high-pressure, high-temperature vessel. Coupled with high-speed imaging, the technique yields time-resolved measurements of the soot field by relying on a diffused back-illumination scheme to improve extinction quantification in the midst of intense beam steering. The experiments performed in this work used two wavelengths, which, when combined with the Rayleigh-Debye-Gans theory, provide information about the optical and physical properties of soot. For validation of the extinction imaging technique and comparison with prior work, the path-averaged soot volume fraction has been simultaneously measured using laser extinction.
2013-09-08
Technical Paper
2013-24-0061
Dipankar Sahoo, Paul C. Miles, Johannes Trost, Alfred Leipertz
Fuel tracer-based planar laser-induced fluorescence is used to investigate the vaporization and mixing behavior of pilot injections for variations in pilot mass of 1-4 mg, and for two injection pressures, two near-TDC ambient temperatures, and two swirl ratios. The fluorescent tracer employed, 1-methylnaphthalene, permits a mixture of the diesel primary reference fuels, n-hexadecane and heptamethylnonane, to be used as the base fuel. With a near-TDC injection timing of −15°CA, pilot injection fuel is found to penetrate to the bowl rim wall for even the smallest injection quantity, where it rapidly forms fuel-lean mixture. With increased pilot mass, there is greater penetration and fuel-rich mixtures persist well beyond the expected pilot ignition delay period. Significant jet-to-jet variations in fuel distribution due to differences in the individual jet trajectories (included angle) are also observed. Increased injection pressure significantly increased the mixing rate, leading to leaner mixture distributions, and with lower ambient temperature modestly richer mixtures are found near the heads of the jets.
2013-09-08
Technical Paper
2013-24-0001
Lyle M. Pickett, Julien Manin, Raul Payri, Michele Bardi, Jaime Gimeno
Transients in the rate of injection (ROI) with respect to time are ever-present in direct-injection engines, even with common-rail fueling. The shape of the injection ramp-up and ramp-down affects spray penetration and mixing, particularly with multiple-injection schedules currently in practice. Ultimately, the accuracy of CFD model predictions used to optimize the combustion process depends upon the accuracy of the ROI utilized as fuel input boundary conditions. But experimental difficulties in the measurement of ROI, as well as real-world affects that change the ROI from the bench to the engine, add uncertainty that may be mistaken for weaknesses in spray modeling instead of errors in boundary conditions. In this work we use detailed, time-resolved measurements of penetration at the Spray A conditions of the Engine Combustion Network to rigorously guide the necessary ROI shape required to match penetration in jet models that allow variable rate of injection. The discrete control-volume jet model of Musculus and Kattke is utilized, and improved to account for variable spreading angle with axial distance, also based upon experimental measurements.
2013-04-08
Technical Paper
2013-01-0502
Garrett E. Barter, David Reichmuth, Todd H. West, Dawn K. Manley
We present a parametric analysis of electric vehicle (EV) adoption rates and the corresponding contribution to greenhouse gas (GHG) reduction in the US light-duty vehicle (LDV) fleet through 2050. The analysis is performed with a system dynamics based model of the supply-demand interactions among the fleet, its fuels, and the corresponding primary energy sources. The differentiating feature of the model is the ability to conduct global sensitivity and parametric trade-space analyses. We find that many factors impact the adoption rates of EVs. These include, in particular, policy initiatives that encourage consumers to consider lifetime ownership costs, the price of oil, battery performance, as well as the pace of technological development for all powertrains (conventional internal combustion engines included). Widespread EV adoption can have noticeable impact on petroleum consumption and GHG emissions by the LDV fleet. However, EVs alone cannot drive compliance with the most aggressive GHG emission reduction targets, even as the electricity source mix shifts away from coal and towards natural gas.
2013-04-08
Technical Paper
2013-01-1105
Federico Perini, Adam Dempsey, Rolf D. Reitz, Dipankar Sahoo, Benjamin Petersen, Paul C. Miles
In a recent study, quantitative measurements were presented of in-cylinder spatial distributions of mixture equivalence ratio in a single-cylinder light-duty optical diesel engine, operated with a non-reactive mixture at conditions similar to an early injection low-temperature combustion mode. In the experiments a planar laser-induced fluorescence (PLIF) methodology was used to obtain local mixture equivalence ratio values based on a diesel fuel surrogate (75% n-heptane, 25% iso-octane), with a small fraction of toluene as fluorescing tracer (0.5% by mass). Significant changes in the mixture's structure and composition at the walls were observed due to increased charge motion at high swirl and injection pressure levels. This suggested a non-negligible impact on wall heat transfer and, ultimately, on efficiency and engine-out emissions. In this work, the extensive and quantitative local information provided by the PLIF experiments was used as the reference for assessing the accuracy of the CFD modeling of the engine.
2013-04-08
Technical Paper
2013-01-0908
Katsufumi Kondo, Tetsuya Aizawa, Sanghoon Kook, Lyle Pickett
For better understanding of soot formation and oxidation processes applicable to diesel engines, the size, morphology, and nanostructure of soot particles directly sampled in a diesel spray flame generated in a constant-volume combustion chamber have been investigated using Transmission Electron Microscopy (TEM). For this soot diagnostics, the effects of the sampling processes, TEM observation methodology and image processing methods on the uncertainty in the results have not been extensively discussed, mainly due to the complexity of the analysis. This study particularly aims to reveal the uncertainties due to sampling methods (mainly the effect of shot-by-shot fluctuation of “identical” single-shot spray flames on the sampled soot properties), TEM observation methods (mainly the fluctuation of soot morphology among different on-grid locations and the number of soot particle samples required to compensate for the fluctuations) and analysis methods (mainly operator-by-operator fluctuation of morphology measurements and the effects of averaged diameter and cutoff number for primary particles in aggregates on the determination of fractal dimension).
2013-04-08
Technical Paper
2013-01-0917
Jacqueline O'Connor, Mark Musculus
This work is a technical review of past research and a synthesis of current understanding of post injections for soot reduction in diesel engines. A post injection, which is a short injection after a longer main injection, is an in-cylinder tool to reduce engine-out soot to meet pollutant emissions standards while maintaining efficiency, and potentially to reduce or eliminate exhaust aftertreatment. A sprawling literature on post injections documents the effects of post injections on engine-out soot with variations in many engine operational parameters. Explanations of how post injections lead to engine-out soot reduction vary and are sometimes inconsistent or contradictory, in part because supporting fundamental experimental or modeling data are often not available. In this paper, we review the available data describing the efficacy of post-injections and highlight several candidate in-cylinder mechanisms that may control their efficacy. We first discuss three in-cylinder mechanisms that have been frequently proposed to explain how post injections reduce engine-out soot.
2013-04-08
Technical Paper
2013-01-0910
Jacqueline O'Connor, Mark Musculus
Partially premixed low-temperature combustion (LTC) using exhaust-gas recirculation (EGR) has the potential to reduce engine-out NO and soot emissions, but increased unburned hydrocarbon (UHC) emissions need to be addressed. In this study, we investigate close-coupled post injections for reducing UHC emissions. By injecting small amounts of fuel soon after the end of the main injection, fuel-lean mixtures near the injector that suffer incomplete combustion can be enriched with post-injection fuel and burned to completion. The goal of this work is to understand the in-cylinder mechanisms affecting the post-injection efficacy and to quantify its sensitivity to operational parameters including post-injection duration, injection dwell, load, and ignition delay time of the post-injection mixture. Three optical diagnostics - planar laser induced fluorescence of OH radicals, planar laser induced fluorescence of formaldehyde, and high-speed imaging of natural combustion luminescence - complement measurements of engine-out UHC with parametric variations of main- and post-injection timing and duration.
2013-04-08
Technical Paper
2013-01-0901
Emre Cenker, Gilles Bruneaux, Lyle Pickett, Christof Schulz
Within the Engine Combustion Network (ECN) spray combustion research frame, simultaneous line-of-sight laser extinction measurements and laser-induced incandescence (LII) imaging were performed to derive the soot volume fraction (fv). Experiments are conducted at engine-relevant high-temperature and high-pressure conditions in a constant-volume pre-combustion type vessel. The target condition, called "Spray A," uses well-defined ambient (900 K, 60 bar, 22.8 kg/m₃, 15% oxygen) and injector conditions (common rail, 1500 bar, KS1.5/86 nozzle, 0.090 mm orifice diameter, n-dodecane, 363 K). Extinction measurements are used to calibrate LII images for quantitative soot distribution measurements at cross sections intersecting the spray axis. LII images are taken after the start of injection where quasi-stationary combustion is already established. In addition, by changing the LII timing relative to the injection, the temporal variation of the soot cloud is ob-served from initial soot formation until soot oxidization.
2013-04-08
Technical Paper
2013-01-0912
Sanghoon Kook, Renlin Zhang, Kevin Szeto, Lyle M. Pickett, Tetsuya Aizawa
In-flame soot sampling based on the thermophoresis of particles and subsequent transmission electron microscope (TEM) imaging has been conducted in a diesel engine to study size, shape and structure of soot particles within the reacting diesel jet. A direct TEM sampling is pursued, as opposed to exhaust sampling, to gain fundamental insight about the structure of soot during key formation and oxidation stages. The size and shape of soot particles aggregate structure with stretched chains of spherical-like primary particles is currently an unknown for engine soot modelling approaches. However, the in-flame sampling of soot particles in the engine poses significant challenges in order to extract meaningful data. In this paper, the engine modification to address the challenges of high-pressure sealing and avoiding interference with moving valves and piston are discussed in detail. Of particular interest is the uncertainty caused by a selection of the on-grid locations for transmission electron microscope imaging and cycle-to-cycle fluctuations of the engine combustion.
2013-04-08
Technical Paper
2013-01-1691
Charles J. Mueller
This study summarizes the peer-reviewed literature regarding the use of raw pyrolysis liquids (PLs) created from woody biomass as fuels for compression-ignition (CI) engines. First, a brief overview is presented of fast pyrolysis and the potential advantages of PLs as fuels for CI engines. Second, a discussion of the general composition and properties of PLs relative to conventional, petroleum-derived diesel fuels is provided, with emphasis on the differences that are most likely to affect PL performance in CI-engine applications. Next, a synopsis is given of the peer-reviewed literature describing experimental studies of CI engines operated using neat PLs and PLs combined in various ways with other fuels. This literature conclusively indicates that raw PLs and PL blends cannot be used as “drop-in replacements” for diesel fuel in CI engines, which is reflected in part by none of the cited studies reporting successful operation on PL fuels for more than twelve consecutive hours. Based on the reported failure modes, some recommendations are offered for improving performance, reliability, and safety when fueling CI engines with PLs.
2013-04-08
Technical Paper
2013-01-0946
Vicente Romero, Joshua Mullins, Laura Swiler, Angel Urbina
This paper discusses the treatment of uncertainties corresponding to relatively few samples of random-variable quantities. The importance of this topic extends beyond experimental data uncertainty to situations involving uncertainty in model calibration, validation, and prediction. With very sparse samples it is not practical to have a goal of accurately estimating the underlying variability distribution (probability density function, PDF). Rather, a pragmatic goal is that the uncertainty representation should be conservative so as to bound a desired percentage of the actual PDF, say 95% included probability, with reasonable reliability. A second, opposing objective is that the representation not be overly conservative; that it minimally over-estimate the random-variable range corresponding to the desired percentage of the actual PDF. The presence of the two opposing objectives makes the sparse-data uncertainty representation problem an interesting and difficult one. The performance of a variety of uncertainty representation techniques is tested and characterized in this paper according to these two opposing objectives.
2012-09-10
Technical Paper
2012-01-1770
Brian Harries, Kenneth Leslie, Townsend Hyatt, Brandon Smith, Kenneth Meierjurgen, Jenna Beckwith, Marc Compere
With a growing need for a more efficient consumer based automotive platform, Embry-Riddle Aeronautical University (ERAU) chose to redesign the 2013 Chevrolet Malibu as a Plug-in Hybrid Electric Vehicle(PHEV). A Series architecture was chosen for its low energy consumption and high consumer acceptability when compared to the Series/Parallel-through-the-road and the Pre-Transmission designs. A fuel selection process was also completed and B20 Biodiesel was selected as the primary fuel due to lower GHG (Greenhouse Gases) emissions and Embry-Riddle's ability to produce biodiesel onsite using the cafeteria's discarded vegetable oil.
2012-09-10
Technical Paper
2012-01-1574
Srivatsava V. Puranam, Richard R. Steeper
Prior studies have shown that fuel addition during negative valve overlap (NVO) can both increase temperature and alter composition of the charge carried over to main HCCI combustion. Late NVO fuel injection, i.e., near top dead center, can cause piston wetting and subsequent localized rich flames. Since acetylene is a product of rich combustion and is known to advance ignition, it is hypothesized that the species could play a chemical role in enhancing main combustion. The objective of this work is to quantify the effects of acetylene on HCCI combustion. While the research topic is specifically relevant to NVO-fueled HCCI operation, the experiments are conducted without NVO fueling to avoid uncertainties of NVO reforming reactions. Instead, a single post-NVO injection of iso-octane fuels the cycle, and acetylene is seeded into the intake flow at varying concentrations to simulate a reformed product of NVO. Total chemical energy is held constant by adjusting injected mass of iso-octane to compensate for added acetylene.
2012-09-10
Technical Paper
2012-01-1643
Magnus Sjöberg, David Reuss
The lean-burn stratified-charge DISI engine has a strong potential for increased thermal efficiency compared to the traditional throttled SI engine. This experimental study of a spray-guided stratified-charge combustion system compares the engine response to injection-timing retard for gasoline and E85. Focus is on engine-out NO and soot, and combustion stability. The results show that for either fuel, injection-timing retard lowers the engine-out NO emissions. This is partly attributed to a combination of lower peak-combustion temperatures and shorter residence time at high temperatures, largely caused by a more retarded combustion phasing. However, for the current conditions using a single-injection strategy, the potential of NO reduction with gasoline is limited by both elevated soot emissions and the occurrence of misfire cycles. In strong contrast, when E85 fuel is used, the combustion system responds very well to injection-timing retard. By using near-TDC injection of E85 ultra-low emissions of NO can be achieved.
2012-06-18
Video
High-load HCCI combustion has recently been demonstrated with conventional gasoline using intake pressure boosting. The key is to control the high combustion heat release rates (HRR) by using combustion timing retard and mixture stratification. However, at naturally aspirated and moderately boosted conditions, these techniques did not work well due to the low autoignition reactivity of conventional gasoline at these conditions. This work studies a low-octane distillate fuel with similar volatility to gasoline, termed Hydrobate, for its potential in HCCI engine combustion at naturally aspirated and low-range boosted conditions. The HCCI combustion with fully premixed and partially stratified charges was examined at intake pressures (Pin) from 100 to 180 kPa and constant intake temperature (60�C) and engine speed (1200 rpm). First, the key parameters for high-load HCCI operation were investigated, including 1) intermediate temperature heat release (ITHR), which determines the potential of using combustion retard to control the HRR, and 2) ?
2012-04-16
Technical Paper
2012-01-1109
Marco Mehl, William Pitz, Mani Sarathy, Yi Yang, John E. Dec
The combustion behavior of conventional gasoline has been numerically investigated by means of detailed chemical-kinetic modeling simulations, with particular emphasis on analyzing the chemistry of the intermediate temperature heat release (ITHR). Previous experimental work on highly boosted (up to 325 kPa absolute) HCCI combustion of gasoline (SAE 2020-01-1086) showed a steady increase in the charge temperature up to the point of hot ignition, even for conditions where the ignition point was retarded well after top dead center (TDC). Thus, sufficient energy was being released by early pre-ignition reactions resulting in temperature rise during the early part of the expansion stroke This behavior is associated with a slow pre-ignition heat release (ITHR), which is critical to keep the engine from misfiring at the very late combustion phasings required to prevent knock at high-load boosted conditions. The experimental results also showed that the amount of ITHR increased with increasing boost and reduced intake temperature.
2012-04-16
Technical Paper
2012-01-0140
Bao-Lin Wang, Michael J. Bergin, Benjamin R. Petersen, Paul C. Miles, Rolf D. Reitz, Zhiyu Han
A generalized re-normalization group (RNG) turbulence model based on the local "dimensionality" of the flow field is proposed. In this modeling approach the model coefficients C₁, C₂, and C₃ are all constructed as functions of flow strain rate. In order to further validate the proposed turbulence model, the generalized RNG closure model was applied to model the backward facing step flow (a classic test case for turbulence models). The results indicated that the modeling of C₂ in the generalized RNG closure model is reasonable, and furthermore, the predictions of the generalized RNG model were in better agreement with experimental data than the standard RNG turbulence model. As a second step, the performance of the generalized RNG closure was investigated for a complex engine flow. The flow field generated by the generalized RNG closure model was compared to particle image velocimetry (PIV) velocity measurements from an optically accessible General Motors Company 1.9L HSDI engine equipped with helical and tangential intake ports.
2012-04-16
Technical Paper
2012-01-0375
Sage Kokjohn, Rolf D. Reitz, Derek Splitter, Mark Musculus
Premixed charge compression ignition (PCI) strategies offer the potential for simultaneously low NOx and soot emissions with diesel-like efficiency. However, these strategies are generally confined to low loads due to inadequate control of combustion phasing and heat-release rate. One PCI strategy, dual-fuel reactivity-controlled compression ignition (RCCI), has been developed to control combustion phasing and rate of heat release. The RCCI concept uses in-cylinder blending of two fuels with different auto-ignition characteristics to achieve controlled high-efficiency clean combustion. This study explores fuel reactivity stratification as a method to control the rate of heat release for PCI combustion. To introduce fuel reactivity stratification, the research engine is equipped with two fuel systems. A low-pressure (100 bar) gasoline direct injector (GDI) delivers iso-octane, and a higher-pressure (600 bar) common-rail diesel direct-injector delivers n-heptane. A sweep of the common-rail injection timing creates a range of fuel reactivity stratification.
2012-04-16
Technical Paper
2012-01-0463
Brian Fisher, Charles J. Mueller
The in-cylinder extent of liquid-phase fuel penetration (i.e., the liquid length) is an important parameter in combustion-chamber design because liquid lengths that are too long can lead to wall impingement and corresponding degradation of engine efficiency, emissions, and durability. Previous liquid-length measurements in constant-volume combustion chambers have shown that the liquid length is nominally independent of injection pressure, but these measurements have employed common-rail fuel systems where injection rate is approximately constant during the entire injection event, and they have been conducted under quasi-steady ambient thermodynamic conditions. The objective of the current work is to better understand the effects of injection-rate shape and injection pressure on the liquid length, including possible effects of unsteady ambient conditions in an engine. Liquid-length measurements under unsteady, non-reacting in-cylinder conditions have been reported recently, with fuel injected using a hydraulically actuated, electronically controlled unit injector (HEUI) with an unsteady injection rate.
2012-04-16
Technical Paper
2012-01-0692
Benjamin Petersen, Paul C. Miles, Dipankar Sahoo
The performance of Partially Premixed Compression Ignition (PPCI) combustion relies heavily on the proper mixing between the injected fuel and the in-cylinder gas mixture. In fact, the mixture distribution has direct control over the engine-out emissions as well as the rate of heat release during combustion. The current study focuses on investigating the pre-combustion equivalence ratio distribution in a light-duty diesel engine operating at a low-load (3 bar IMEP), highly dilute (10% O₂), slightly boosted (P ⁿ = 1.5 bar) PPCI condition. A tracer-based planar laser-induced fluorescence (PLIF) technique was used to acquire two-dimensional equivalence ratio measurements in an optically accessible diesel engine that has a production-like combustion chamber geometry including a re-entrant piston bowl. Equivalence ratio distributions are presented at a single vertical plane and three different horizontal planes within the combustion chamber, including two planes within the bowl of the piston.
2012-04-16
Technical Paper
2012-01-1120
Yi Yang, John E. Dec, Nicolas Dronniou, William Cannella
High-load HCCI combustion has recently been demonstrated with conventional gasoline using intake pressure boosting. The key is to control the high combustion heat release rates (HRR) by using combustion timing retard and mixture stratification. However, at naturally aspirated and moderately boosted conditions, these techniques did not work well due to the low autoignition reactivity of conventional gasoline at these conditions. This work studies a low-octane distillate fuel with similar volatility to gasoline, termed Hydrobate, for its potential in HCCI engine combustion at naturally aspirated and low-range boosted conditions. The HCCI combustion with fully premixed and partially stratified charges was examined at intake pressures (Piⁿ) from 100 to 180 kPa and constant intake temperature (60°C) and engine speed (1200 rpm). First, the key parameters for high-load HCCI operation were investigated, including 1) intermediate temperature heat release (ITHR), which determines the potential of using combustion retard to control the HRR, and 2) φ-sensitivity, which determines the effectiveness of mixture stratification for controlling the HRR.
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