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Technical Paper

Artificial Neural Networks for Prediction of Knock Events

2022-03-29
2022-01-0478
Downsized turbocharged engines have been increasingly popular in modern light-duty vehicles due to their fuel efficiency benefits. However, high power density in such engines is achieved thanks to high in-cylinder pressure-temperature conditions that increase knock propensity. Control strategies could be used to extend the knock limit if an accurate prediction of knock events were possible. Although knock modeling has been investigated with 3D computational fluid dynamics (CFD) simulations, such models are computationally expensive and cannot be executed in real-time for cycle-to-cycle control purposes. Advances in data analytics and machine learning, however, have enabled the development of real-time executable computer models with different levels of complexity. In this study, artificial neural networks (ANN) were used to develop a predictive model for knock events using the in-cylinder pressure data recorded before knock onset.
Technical Paper

Achieving Diesel Powertrain Ownership Parity in Battery Electric Heavy Duty Commercial Vehicles Using a Rapid Recurrent Recharging Architecture

2022-03-29
2022-01-0751
Battery electric vehicles (BEV) in heavy duty (HD) commercial freight transport face challenging technoeconomic barriers to adoption. Specifically, beyond safety and compliance, fleet and operational logistics require both high up-time and parity with diesel system productivity/Total Cost of Ownership (TCO) to enable strong adoption of electrified powertrains. At present, relatively high energy storage prices coupled with the increased weight of BEV systems limit the practicality of HD commercial freight transport to shorter range applications, where smaller batteries will suffice for the mission energy requirements (single operational shift). This paper presents an approach to extend the feasibility of BEV HD trucking for a broad range of applications.
Technical Paper

Evaluation of high-temperature martensitic steels for heavy-duty diesel piston applications

2022-03-29
2022-01-0599
High-temperature commercially available martensitic steels were evaluated for heavy-duty diesel piston application. Finite element analysis (FEA) simulations were performed to predict temperature distribution and fatigue performance at various locations on the piston to aid in the selection of candidate steels. Oxidation performance of each alloy was assessed relative to the predicted maximum operating temperature using coupon samples in a cyclic oxidation furnace. Microstructural characterization was performed on pistons tested in a single-cylinder research engine using current piston materials, quench and tempered martensitic steel 4140 and micro-alloyed steel (MAS) 38MnVS6. Complimentary material testing was conducted to evaluate elevated temperature strength, resistance to aging, and thermal property data for inputs into FEA piston models, as well as processing optimization and long-term oxidation testing of the steel.
Technical Paper

Compatibility of Seven Biologically Derivable Diesel Blendstocks (1-Octanol, 2-Nonanone, Hexyl Hexanoate, n-Undecane, Di-isobutylene, Biodiesel and Renewable Diesel) with Fuel System Plastics

2022-03-29
2022-01-0487
The compatibility of seven bioderivable diesel blendstocks with 21 plastic materials common to fuel storage, dispensing, and delivery systems was evaluated though volume and hardness measurements. The blendstocks included one alcohol (1-octanol), one acid ester (hexyl hexanoate), one ketone (2-nonanone), dibutoxymethane, and three akanes (n-undecane, biodiesel, and renewable diesel). Each blendstock was blended with diesel in concentrations of 0, 10, 20, and 30 wt %. The plastics included resins, nylons, acetals, high density polyethylene, polypropylene, polyetheretherketone, polyphthalamides polyphenylene sulfide, polyethylene terephthalate, polytetrafluoroethylene, ethylene-tetrafluoroethylene, polyvinylidene fluoride, polyetherimide, polyphthalamides, Polyacrylamide, and polybutylene terephthalate. Specimens of each plastic material were immersed in the test fuels for a period of 16 weeks and measured for volume and hardness.
Technical Paper

Advanced finite-volume numerics and source term assumptions for G-Equation modelling of propane/air flames

2022-03-29
2022-01-0406
G-Equation models represent propagating flame fronts with an implicit two-dimensional surface representation (level-set). Level-set methods are fast, as transport source terms for the implicit surface can be solved with finite-volume operators on the finite-volume domain, without having to build the actual surface. However, they carry out several approximations and assumptions whose practical impact on the accuracy of combustion simulations is often not properly understood. In this study, we analyzed all source terms making up the FRESCO CFD code’s G-Equation solver for simulating propane/air flames. We employed three well-established constant-volume configurations: a one-dimensional, freely-propagating laminar flame; a disc-shaped, constant-volume swirl combustor; and torch-jet flame development through an orifice from a two-chamber device. We tested the explicit (sub-cycled) vs. implicit formulation for the standard transport operators (advection, diffusion, compressibility).
Technical Paper

Assessment of the Effectiveness of Aftermarket Fuel Stabilizers in Preventing Gum Formation and Loss of Oxidation Stability

2022-03-29
2022-01-0486
Plug-in hybrid vehicles are growing in popularity. These vehicles may be driven short distances and recharged several times before engine operation is needed. This situation can cause fuel storage in the vehicle fuel tank for much longer periods of time than have been typical for conventional vehicles. Aftermarket fuel stabilizers have long been marketed to consumers with little if any information availbe to help consumers assess their effectiveness. This study examined the oxidation stability and gum formation tendencies for gasoline samples blended using 3 aftermarket additives plus a top-tier fuel sample and baseline gasoline over a period of one year. Analyses of the fuel oxidation stability and gum formation were conducted at the inception of the study, 1, 2,3, 6, and 12 months of aging.
Technical Paper

Performance Comparison of LPG and Gasoline in an Engine Configured for EGR-Loop Catalytic Reforming

2021-09-21
2021-01-1158
In prior work, the EGR loop catalytic reforming strategy developed by ORNL has been shown to provide a relative brake engine efficiency increase of more than 6% by minimizing the thermodynamic expense of the reforming processes, and in some cases achieving thermochemical recuperation (TCR), a form of waste heat recovery where waste heat is converted to usable chemical energy. In doing so, the EGR dilution limit was extended beyond 35% under stoichiometric conditions. In this investigation, a Microlith®-based metal-supported reforming catalyst (developed by Precision Combustion, Inc. (PCI)) was used to reform the parent fuel in a thermodynamically efficient manner into products rich in H2 and CO. We were able to expand the speed and load ranges relative to previous investigations: from 1,500 to 2,500 rpm, and from 2 to 14 bar break mean effective pressure (BMEP).
Technical Paper

Particle Matter Index and Fuel Wall-wetting Relations on Stochastic Pre-ignition

2021-09-21
2021-01-1163
This work explores the effect of the particle matter index (PMI) and aromatic content on fuel wall impingement associated with stochastic pre-ignition (SPI). Statically significant measurements of SPI rates are directly coupled with laser induced florescence (LIF) measurements of fuel dilution from spray-linear impingement. Literature suggests that PMI is could be correlated with the number of SPI events, but the root cause(s) of PMI and SPI are directly causational or are a predicator of SPI. Three fuels have been used in this study with 3 different PMI and two different aromatic contents. The fuels are direct injected at two different injection timings, an earlier injection timing which initially targets the piston crown, 310°CA bTDC, and a later injection timing that the liner, 220°CA bTDC start of injection timings (SOI) respectively. The earlier 310 SOI injection increases soot, whereas the later 220°CA SOI targets the liner and increases wall-wetting.
Technical Paper

The Effect of Spark-Plug Heat Dispersal Range and Exhaust Valve Opening Timing on Cold-Start Emissions and Cycle-to-Cycle Variability

2021-09-21
2021-01-1180
The partnership for advancing combustion engines (PACE) is a US Department of Energy consortium involving multiple national laboratories and includes a goal of addressing key efficiency and emission barriers in light-duty engines fueled with a market-representative E10 gasoline. A major pillar of the initiative is the generation of detailed experimental data and modeling capabilities to understand and predict cold-start behavior. Cold-start, as defined by the time between first engine crank and three-way catalyst light-off, is responsible for a large percentage of NOx, unburned hydrocarbon and particulate matter emissions in light-duty engines. Minimizing emissions during cold-start is a trade-off between achieving faster light-off of the three-way catalyst and engine out emissions during that period.
Technical Paper

Fuel Effects on Advanced Compression Ignition Load Limits

2021-09-21
2021-01-1172
In order to maximize the efficiency of light-duty gasoline engines, the Co-Optimization of Fuels and Engines (Co-Optima) initiative from the U.S. Department of Energy is investigating multi-mode combustion strategies. Multi-mode combustion can be describe as using conventional spark-ignited combustion at high loads, and at the part-load operating conditions, various advanced compression ignition (ACI) strategies are being investigated to increase efficiency. Of particular interest to the Co-Optima initiative is the extent to which optimal fuel properties and compositions can enable higher efficiency ACI combustion over larger portions of the operating map. Extending the speed-load range of these ACI modes can enable greater part-load efficiency improvements for multi-mode combustion strategies.
Technical Paper

Fuel Stratification Effects on Gasoline Compression Ignition with a Regular-Grade Gasoline on a Single-Cylinder Medium-Duty Diesel Engine at Low Load

2021-09-21
2021-01-1173
Prior research studies have investigated a wide variety of gasoline compression ignition (GCI) injection strategies and the resulting fuel stratification levels to maintain control over the combustion phasing, duration, and heat release rate. Previous GCI research at the US Department of Energy’s Oak Ridge National Laboratory has shown that for a combustion mode with a low degree of fuel stratification, called “partial fuel stratification” (PFS), gasoline range fuels with anti-knock index values in the range of regular-grade gasoline (~87 anti-knock index or higher) provides very little controllability over the timing of combustion without significant boost pressures. On the contrary, heavy fuel stratification (HFS) provides control over combustion phasing but has challenges achieving low temperature combustion operation, which has the benefits of low NOX and soot emissions, because of the air handling burdens associated with the required high exhaust gas recirculation rates.
Technical Paper

Impact of Materials Properties on Higher-Temperature Engine Operation

2021-09-21
2021-01-1142
We examine the effects on materials temperatures and engine efficiency via simulations of engines operating at temperatures which exceed the thermal limits of today’s materials. Potential focus areas include high-speed, high-load operation (in the fuel-enrichment zone) as well as conditions of selective cooling at lower speeds and loads. We focus on a light-duty DISI and a heavy-duty CI engine using GT-Power. Temperature distributions within the head, block, piston, and valves were obtained from 3D FEA simulations coupled with 1D GT-Power representations of the engine’s gas flow and combustion regions.
Technical Paper

In Situ Laser Induced Florescence Measurements of Fuel Dilution from Low Load to Stochastic Pre Ignition Prone Conditions

2021-04-06
2021-01-0489
This work employs a novel laser induced fluorescence (LIF) diagnostic to measure fuel dilution in a running single cylinder research engine operated at stochastic pre ignition (SPI) and non-SPI prone conditions. Measurements of LIF based fuel dilution are quantified over a range of engine loads and fuel injection timings for two fuels. The in situ LIF measurements of fuel/lubricant interactions illustrate regions of increased fuel dilution from fuel-wall interactions and is believed to be a fundamental underpinning to generating top ring zone liquid conditions conducive to SPI. A novel level of dye doped in the fuel, between 50 to 500 ppm was used as the fluorescence source, at engine operating speed of 2000r/min from 5 to 18 bar of IMEPg injection timings was swept for two fuels of varying volatility.
Technical Paper

Three-Dimensional CFD Investigation of Pre-Spark Heat Release in a Boosted SI Engine

2021-04-06
2021-01-0400
Low-temperature heat release (LTHR) in spark-ignited internal combustion engines is a critical step toward the occurrence of auto-ignition, which can lead to an undesirable phenomenon known as engine knock. Hence, correct predictions of LTHR are of utmost importance to improve the understanding of knock and enable techniques aimed at controlling it. While LTHR is typically obscured by the deflagration following the spark ignition, extremely late ignition timings can lead to LTHR occurrence prior to the spark, i.e., pre-spark heat release (PSHR). In this research, PSHR in a boosted direct-injection SI engine was numerically investigated using three-dimensional computational fluid dynamics (CFD). A hybrid approach was used, based on the G-equation model for representing the turbulent flame front and the multi-zone well-stirred reactor model for tracking the chemical reactions within the unburnt region.
Journal Article

EGR Dilution and Fuel Property Effects on High-Efficiency Spark-Ignition Flames

2021-04-06
2021-01-0483
Modern spark ignition internal combustion engines rely on fast combustion rates and high dilution to achieve high brake thermal efficiencies. To accomplish this, new engine designs have moved towards increased tumble ratios and stroke-to-bore ratios. Increased tumble ratios correlate positively with increases in turbulent kinetic energy and improved fuel and residual gas mixing, all of which favor faster and more efficient combustion. Longer stroke-to-bore ratios allow higher geometric compression ratios and use of late intake valve closing to control peak compression pressures and temperatures. The addition of dilution to improve efficiency is limited by the resulting increase in combustion instabilities manifested by cycle-to-cycle variability.
Technical Paper

Dilute Combustion Control Using Spiking Neural Networks

2021-04-06
2021-01-0534
Dilute combustion with exhaust gas recirculation (EGR) in spark-ignition engines presents a cost-effective method for achieving higher levels of engine efficiency. At high levels of EGR, however, cycle-to-cycle variability (CCV) of the combustion process is exacerbated by sporadic occurrences of misfires and partial burns. Previous studies have shown that temporal deterministic patterns emerge at such conditions and certain combustion cycles have a significant influence over future events. Due to the complexity of the combustion process and the nature of CCV, harnessing all the deterministic information for control purposes has remained challenging even with physics based 0-D, 1-D, and high-fidelity computational fluid dynamics (CFD) models. In this study, we present a data-driven approach to optimize the combustion process by controlling CCV adjusting the cycle-to-cycle fuel injection quantity.
Technical Paper

Potential Impacts of High-Octane Fuel Introduction in a Naturally Aspirated, Port Fuel-Injected Legacy Vehicle

2020-11-20
2020-01-5117
In recent years there has been an increased interest in raising the octane level of gasoline to enable higher compression ratios (CR) in spark-ignition engines to improve vehicle fuel efficiency. A number of studies have examined opportunities to increase efficiency in future vehicles, but potential impacts on the legacy fleet have not received as much attention. This effort focused on experimental studies on an engine using high-octane fuels without changing the engine’s CR. Spark timing was advanced until maximum torque was reached or knock was encountered for each engine condition, using each individual fuel to maximize engine efficiency. Knock-limited conditions occurred as the output brake mean effective pressure (BMEP) neared the maximum attainable output at a given engine speed. Increasing research octane numbers generally enabled knock-free operation under a greater number of operating conditions.
Technical Paper

Real-Time Dynamic Brake Assessment for Heavy Commercial Vehicle Safety

2020-10-05
2020-01-1646
This paper summarizes initial results and findings of a model developed to determine the braking performance of commercial motor vehicles in motion regardless of brake type or gross weight. Real-world data collected by Oak Ridge National Laboratory for a U.S. Department of Energy study was used to validate the model. Expanding on previous proof-of-concept research showing the linear relationship of brake application pressure and deceleration additional parameters such as elevation were added to the model. Outputs from the model consist of coefficients calculated for every constant pressure braking event from a vehicle that can be used to calculate a deceleration and thus compute a stopping distance for a given scenario. Using brake application pressure profiles derived from the dataset, stopping distances for light and heavy loads of the same vehicle were compared for various speed and road grades.
Journal Article

Knock Mitigation Effectiveness of EGR across the Pressure-Temperature Domain

2020-09-15
2020-01-2053
Exhaust gas recirculation (EGR) has been shown to enable efficiency improvements in SI engines through multiple different mechanisms, including decreasing the knock propensity at high load, which allows higher compression ratio. While many of the benefits of EGR are applicable to both low and high power density engines, including reductions in pumping work and improved specific heat ratio, the knock benefits and corresponding compression ratio increases have been limited to low power density naturally aspirated engines primarily intended for hybrid vehicle architectures. An earlier study [1] indicated that there may be a kinetic limitation for the ability of EGR to mitigate knock under these conditions, but that study only considered a small number of conditions. This investigation expands on that study while also providing data for model validation for the new light-duty combustion consortium from the U.S. Department of Energy: Partnership for Advancing Combustion Engines (PACE).
Journal Article

Advanced Intra-Cycle Detection of Pre-Ignition Events through Phase-Space Transforms of Cylinder Pressure Data

2020-09-15
2020-01-2046
The widespread adoption of boosted, downsized SI engines has brought pre-ignition phenomena into greater focus, as the knock events resulting from pre-ignitions can cause significant hardware damage. Much attention has been given to understanding the causes of pre-ignition and identify lubricant or fuel properties and engine design and calibration considerations that impact its frequency. This helps to shift the pre-ignition limit to higher specific loads and allow further downsizing but does not fundamentally eliminate the problem. Real-time detection and mitigation of pre-ignition would thus be desirable to allow safe engine operation in pre-ignition-prone conditions. This study focuses on advancing the time of detection of pre-ignition in an engine cycle where it occurs.
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