Search Results

Nitric Oxide (NO) can significantly influence the autoignition reactivity and this can affect knock limits in conventional stoichiometric SI engines. Previous studies also revealed that the role of NO changes with fuel type. Fuels with high RON (Research Octane Number) and high Octane Sensitivity (S = RON - MON (Motor Octane Number)) exhibited monotonically retarding knock-limited combustion phasing (KL-CA50) with increasing NO. In contrast, for a high-RON, low-S fuel, the addition of NO initially resulted in a strongly retarded KL-CA50 but beyond the certain amount of NO, KL-CA50 advanced again. The current study focuses on same high-RON, low-S Alkylate fuel to better understand the mechanisms responsible for the reversal in the effect of NO on KL-CA50 beyond a certain amount of NO.

A series of scaled wind tunnel tests are conducted to investigate the aerodynamic benefits of heavy vehicle platooning and the availability of cooling air for trailing vehicles on two- and four-vehicle platoons. To measure the aerodynamic drag, scale models are mounted onto a splitter plate by means of a low-friction linear bearing and a load cell located within each model trailer. In addition to drag, pressure measurements are made with a pitot probe positioned at the center of each model radiator grill. Four homogeneous, two-vehicle platoons are tested for spacings up to 300′ and six heterogeneous, four-vehicle platoons are tested with spacings ranging from 30′ to 50′. For the heterogeneous platoons, configurations are tested with one distinct heavy vehicle or medium duty vehicle, as well as with four distinct heavy vehicles. Over spacings of 15′ to 80′, the best performing homogeneous, two-vehicle platoons are comprised of a Supertruck tractor and straight frame trailer.

Increasingly, travelers are turning to shared mobility and enabling technologies (i.e., smartphone apps) to meet their mobility needs. A consequence of the ever-growing and ever-evolving landscape of shared mobility is the lack of standardized terms and definitions. The shared and digital mobility industry is challenged with discrepancies in use and definition of terms, which often create ambiguity and confusion for policymakers, regulatory agencies, and the broader public. In recognition of this challenge, the SAE Shared and Digital Mobility Committee embarked on the task of developing J3163™ – Taxonomy and Definitions for Terms Related to Shared Mobility and Enabling Technologies. This white paper provides an overview of the rationale, scope, key discussions held in the development of J3163TM, as well as guidance on how to use J3163TM.

Lawrence Livermore National Laboratory (LLNL) has conducted a series of scaled wind tunnel tests to investigate the aerodynamic benefits of heavy vehicle platooning and the availability of cooling air for trailing vehicles on two- and three-vehicle platoons. To measure the aerodynamic drag, scale models are mounted onto a LLNL designed splitter plate by means of a low-friction linear bearing and a load cell located within each model trailer. In addition to drag, pressure measurements are made with a pitot probe positioned at the center of each model radiator grill. Particle Image Velocimetry (PIV) and Infrared Thermography (IRT) measurements are used to map the three-dimensional velocity field and flow structures around the vehicles.

Previous studies have shown that fuels with higher laminar flame speed also have increased tolerance to EGR dilution. In this work, the effects of fuel laminar flame speed on both lean and EGR dilute spark ignition combustion stability were examined. Fuels blends of pure components (iso-octane, n-heptane, toluene, ethanol, and methanol) were derived at two levels of laminar flame speed. Each fuel blend was tested in a single-cylinder spark-ignition engine under both lean-out and EGR dilution sweeps until the coefficient of variance of indicated mean effective pressure increased above thresholds of 3% and 5%. The relative importance of fuel laminar flame speed to changes to engine design parameters (spark ignition energy, tumble ratio, and port vs. direct injection) was also assessed.

Road safety is one of the major concerns for automated vehicles. In order for these vehicles to interact safely and efficiently with the other road participants, the behavior of the automated vehicles should be carefully designed. Liu and Tomizuka proposed the Robustly-safe Automated Driving system (ROAD) which prevents or minimizes occurrences of collisions of the automated vehicle with other road participants while maintaining efficiency. In this paper, a set of design principles are elaborated as an extension of the previous work, including robust perception and cognition algorithms for environment monitoring and high level decision making and low level control algorithms for safe maneuvering of the automated vehicle.

The downsizing of internal combustion engines to increase fuel economy leads to challenges in both obtaining ignition and stabilizing combustion at boosted intake pressures and high exhaust gas recirculation dilution conditions. The use of non-thermal plasma ignition technologies has shown promise as a means to more reliably ignite dilute charge mixtures at high pressures. Despite progress in fundamental research on this topic, both the capabilities and operation implications of emerging non-thermal plasma ignition technologies in internal combustion engine applications are not yet fully explored. In this work, we document the effects of using a corona discharge ignition system in a single cylinder gasoline direct injection research engine relative to using a traditional inductive spark ignition system under conditions associated with both naturally aspirated (8 bar BMEP) and boosted (20 bar BMEP) loads at moderate (2000 rpm) and high (4000 rpm) engine speeds.

Accelerated market penetration of plug-in electric vehicles (PEVs) is presently restricted by the high cost of batteries. Deployment of grid-connected energy storage, which could increase the reliability, efficiency, and cleanliness of the grid, is similarly inhibited by the cost of batteries. Research, development, and manufacturing are underway to reduce cost by lowering material costs, enhance process efficiencies, and increase production volumes. Another approach under consideration is to recover a fraction of the battery cost after the battery has been retired from vehicular service via reuse in other applications, where it may still have sufficient performance to meet the requirements of other energy-storage applications.

Detailed chemical kinetics, although preferred due to increased accuracy, can significantly slow down CFD combustion simulations. Chemistry solutions are typically the most computationally costly step in engine simulations. The calculation time can be significantly accelerated using a multi-zone combustion model. The multi-zone model is integrated into the CONVERGE CFD code. At each time-step, the CFD cells are grouped into zones based on the cell temperature and equivalence ratio. The chemistry solver is invoked only on each zone. The zonal temperature and mass fractions are remapped onto the CFD cells, such that the temperature and composition non-uniformities are preserved. Two remapping techniques published in the literature are compared for their relative performance. The accuracy and speed-up of the multi-zone model is improved by using variable bin sizes at different temperature and equivalence ratios.

We describe a CHEMKIN-based multi-zone model that simulates the expected combustion variations in a single-cylinder engine fueled with iso-octane as the engine transitions from spark-ignited (SI) combustion to homogenous charge compression ignition (HCCI) combustion. The model includes a 63-species reaction mechanism and mass and energy balances for the cylinder and the exhaust flow. For this study we assumed that the SI-to-HCCI transition is implemented by means of increasing the internal exhaust gas recirculation (EGR) at constant engine speed. This transition scenario is consistent with that implemented in previously reported experimental measurements on an experimental engine equipped with variable valve actuation. We find that the model captures many of the important experimental trends, including stable SI combustion at low EGR (~0.10), a transition to highly unstable combustion at intermediate EGR, and finally stable HCCI combustion at very high EGR (~0.75).

Material flammability is an important factor in determining the pressure and composition (fraction of oxygen and nitrogen) of the atmosphere in the habitable volume of exploration vehicles and habitats. The method chosen in this work to quantify the flammability of a material is by its ease of ignition. The ignition delay time was defined as the time it takes a combustible material to ignite after it has been exposed to an external heat flux. Previous work in the Forced Ignition and Spread Test (FIST) apparatus has shown that the ignition delay in the currently proposed space exploration atmosphere (approximately 58.6 kPa and 32% oxygen concentration) is reduced by 27% compared to the standard atmosphere used in the Space Shuttle and Space Station.

We have converted a Caterpillar 3406 natural gas spark ignited engine to HCCI mode and used it as a test bed for demonstrating advanced control methodologies. Converting the engine required modification of most engine systems: piston geometry, starting, fueling, boosting, and (most importantly) controls. We implemented a thermal management system consisting of a recuperator that transfers heat from exhaust to intake gases and a dual intake manifold that permits precise cylinder-by-cylinder ignition control. Advanced control methodologies are used for (1) minimizing cylinder-to-cylinder combustion timing differences caused by small variations in temperature or compression ratio; (2) finding the combustion timing that minimizes fuel consumption; and (3) tuning the controller parameters to improve transient response.

The drag reduction capability of a trailer underbody fairing is investigated using steady Reynolds-averaged Navier-Stokes simulations of a full-scale heavy vehicle traveling at highway speed within a crosswind. The flow field about the vehicle is modeled for two different fairing designs of varying length that yield reductions in the drag coefficient ranging from 0.013 to 0.042. Analysis of the trailer underbody flow field indicates that the fairings decrease the size of a recirculation zone that exists immediately downstream of the tractor drive wheels by providing a surface to which the separated underbody flow can reattach. A comparison of the pressure coefficients across the surface of the fairings demonstrates that the longer fairings produce greater pressure coefficients, hence resulting in a larger reduction in drag than the shorter fairings. One of the fairings is shown to outperform traditional trailer side skirts, which yield a reduction in the drag coefficient of 0.035.

This paper investigates flow and combustion in a full-cycle simulation of a four-stroke, three-valve HCCI engine by visualizing the flow with pathlines. Pathlines trace massless particles in a transient flow field. In addition to visualization, pathlines are used here to trace the history, or evolution, of flow fields and species. In this study evolution is followed from the intake port through combustion. Pathline analysis follows packets of intake charge in time and space from induction through combustion. The local scalar fields traversed by the individual packets in terms of velocity magnitude, turbulence, species concentration and temperatures are extracted from the simulation results. The results show how the intake event establishes local chemical and thermal environments in-cylinder and how the species respond (chemically react) to the local field.

The development of surrogate mixtures that represent gasoline combustion behavior is reviewed. Combustion chemistry behavioral targets that a surrogate should accurately reproduce, particularly for emulating homogeneous charge compression ignition (HCCI) operation, are carefully identified. Both short and long term research needs to support development of more robust surrogate fuel compositions are described. Candidate component species are identified and the status of present chemical kinetic models for these components and their interactions are discussed. Recommendations are made for the initial components to be included in gasoline surrogates for near term development. Components that can be added to refine predictions and to include additional behavioral targets are identified as well. Thermodynamic, thermochemical and transport properties that require further investigation are discussed.

Design for Six Sigma (DFSS) has evolved as a worthy predecessor to the application of Six-Sigma principles to production, process control, and quality. At Lawrence Livermore National Laboratory (LLNL), we are exploring the interrelation of our current research, development, and design safety standards as they would relate to the principles of DFSS and Six-Sigma. We have had success in prioritization of research and design using a quantitative scalar metric for value, so we further explore the use of scalar metrics to represent the outcome of our use of the DFSS process. We use the design of an automotive component as an example of combining DFSS metrics into a scalar decision quantity. We then extend this concept to a high-priority, personnel safety example representing work that is toward the mature end of DFSS, and begins the transition into Six-Sigma for safety assessments in a production process.

It has previously been shown experimentally and computationally that the process of Homogeneous Charge Compression Ignition (HCCI) is very dependent on the pre-combustion gas temperature field. This study looks in detail at how temperature fields can evolve by comparing results of two combustion chamber designs, a piston with a square bowl and a disk shaped piston, and relates these temperature fields to measured HCCI combustion durations. The contributions of combustion chamber surface area and turbulence levels to the gas temperature evolution are considered over the crank angle range from intake valve closure to top-dead-center. This is a CFD study, whose results were transformed into traditional analysis methods of convective heat transfer (q=h*A*ΔT) and boundary layers.

At 70 miles per hour, overcoming aerodynamic drag represents about 65% of the total energy expenditure for a typical heavy truck vehicle. The goal of this US Department of Energy supported consortium is to establish a clear understanding of the drag producing flow phenomena. This is being accomplished through joint experiments and computations, leading to the intelligent design of drag reducing devices. This paper will describe our objective and approach, provide an overview of our efforts and accomplishments related to drag reduction devices, and offer a brief discussion of our future direction.

We have developed a methodology for analysis of Premixed Charge Compression Ignition (PCCI) engines that applies to conditions in which there is some stratification in the air-fuel distribution inside the cylinder at the time of combustion. The analysis methodology consists of two stages: first, a fluid mechanics code is used to determine temperature and equivalence ratio distributions as a function of crank angle, assuming motored conditions. The distribution information is then used for grouping the mass in the cylinder into a two-dimensional (temperature-equivalence ratio) array of zones. The zone information is then handed on to a detailed chemical kinetics model that calculates combustion, emissions and engine efficiency information. The methodology applies to situations where chemistry and fluid mechanics are weakly linked.

Major efforts to control motor vehicle emissions have been made in recent years, both through improved emission control technologies and through gasoline reformulation. Our assessment of the impacts of these efforts was conducted in the San Francisco Bay Area, in lanes of a highway tunnel where heavy-duty vehicles are not allowed. This study focuses on the afternoon rush hour, during which over 4000 vehicles per hour travel uphill through the tunnel. Concentrations of CO, CO2, NOx, and total and speciated non-methane organic compounds (NMOC) have been measured during summers 1994-1997, 1999, and 2001. Emission factors for CO, NMOC, and NOx decreased by factors of 2-3 over the 7-year period between 1994 and 2001, with CO and NMOC showing greater percentage reductions than NOx. From our data, fleet turnover appears to have a greater overall impact on exhaust emissions than fuel changes for most pollutants.