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Technical Paper

Numerical Analysis of Fuel Impacts on Advanced Compression Ignition Strategies for Multi-Mode Internal Combustion Engines

2020-04-14
2020-01-1124
Multi-mode combustion strategies may provide a promising pathway to improve thermal efficiency in light-duty spark ignition (SI) engines by enabling switchable combustion modes, wherein an engine may operate under advanced compression ignition (ACI) at low load and spark-assisted ignition at high load. The extension from the SI mode to the ACI mode requires accurate control of intake charge conditions; e.g., pressure, temperature and equivalence ratio, in order to achieve stable combustion phasing and rapid mode-switches. This study presents results from computational fluid dynamics (CFD) analysis to gain physical insights into mixture charge formation and combustion dynamics pertaining to auto-ignition processes.
Technical Paper

Analytical approach to characterize the effect of engine control parameters and fuel properties on ACI operation in a GDI engine

2020-04-14
2020-01-1141
Advanced compression ignition (ACI) operation in gasoline direct injection (GDI) engines is a promising concept to reduce fuel consumption and emissions at part load conditions. However, combustion phasing control and the limited operating range in ACI mode are a perennial challenge. In this study the combined impact of fuel properties and engine control strategies are investigated. A design of experiments method was implemented using a three level orthogonal array to determine the sensitivity of five engine control parameters on four engine response variables under low load ACI operation for three 98 RON gasoline fuels, exhibiting disparate chemical composition. Furthermore, the thermodynamic state of the compression histories was studied with the aid of the pressure-temperature framework and correlations were drawn to analogous HCCI experiments conducted in an instrumented CFR engine.
Technical Paper

Fuel Property Effects on Spray Atomization Process in Gasoline Direct Injection

2020-04-14
2020-01-0329
This paper presents a computational fluid dynamics (CFD) study of the Engine Combustion Network (ECN) Spray G, focusing on the impacts of fuel properties as well as realistic geometry on the atomization process. The large-eddy-simulation method, coupled with the volume-of-fluid method, was used to model the high-speed turbulent two-phase flow. A moving-needle boundary condition was applied to capture the internal flow boundary condition accurately. The injector geometry was measured with micron-level resolution using x-ray tomographic imaging at the Advanced Photon Source at Argonne National Laboratory, providing detailed machining tolerance and defects from manufacturing and a realistic rough surface. A 2.5-µm fine mesh was used to resolve the details of liquid-gas interface and the breakup process.
Technical Paper

Numerical Evaluation of Gasoline Compression Ignition at Cold Conditions in a Heavy-Duty Diesel Engine

2020-04-14
2020-01-0778
Achieving robust ignitability for compression ignition of diesel engines at cold conditions is traditionally challenging due to insufficient fuel vaporization, heavy wall impingement, and thick wall films. Gasoline compression ignition (GCI) has shown good potential to offer enhanced NOx-soot tradeoff with diesel-like fuel efficiency, but it is unknown how the volatility and reactivity of the fuel will affect ignition under very cold conditions. Therefore, it is important to investigate the impact of fuel physical and chemical properties on ignition under pressures and temperatures relevant to practical engine operating conditions during cold weather. In this paper, 0-D and 3-D computational fluid dynamics (CFD) simulations of GCI combustion at cold conditions were performed.
Technical Paper

Transient internal nozzle flow in transparent multi-hole diesel injector

2020-04-14
2020-01-0830
An accurate prediction of internal nozzle flow in fuel injector offers the potential to improve predictions of spray computational fluid dynamics (CFD) in and engine, providing a coupled internal-external calculation or by defining better rate of injection (ROI) profile and spray angle information for Lagrangian parcel computations. Previous research has addressed experiments and computations in transparent nozzles, but less is known about realistic multi-hole diesel injectors compared to single axial-hole fuel injectors. In this study, the transient injector opening and closing is characterized using a transparent multi-hole diesel injector, and compared to that of a single axial hole nozzle (ECN Spray D shape). A real-size five-hole acrylic transparent nozzle was mounted in a high-pressure, constant-flow chamber. Internal nozzle phenomena such as cavitation and gas exchange were visualized by high-speed long-distance microscopy.
Technical Paper

Analysis of the Spray Numerical Injection Modeling for Gasoline Applications

2020-04-14
2020-01-0330
The modeling of the fuel jet atomization is key in the characterization of Internal Combustion (IC) engines and 3D Computational Fluid Dynamics (CFD) is a recognized tool to provide insights for design and control purposes. Multi-hole injectors with counter-bored nozzle are the standard for Gasoline Direct Injection (GDI) applications and the Spray-G injector from the Engine Combustion Network (ECN) is considered the reference for numerical studies, thanks to the availability of extensive experimental data. In this work, the behavior of the Spray-G injector is simulated in a constant volume chamber, ranging from sub-cooled (nominal G) to flashing conditions (G2), validating the models on Diffused Back Illumination and Phase Doppler Anemometry data collected in vaporizing inert conditions.
Technical Paper

Durability Study of a Light-Duty High Pressure Common Rail Fuel Injection System Using E10 Gasoline

2020-04-14
2020-01-0616
In this study, a 500-hour test cycle was used to evaluate the durability of a prototype high pressure common rail injection system operating up to 1800 bar with E10 gasoline. Some aspects of the hardware were modified from their baseline design in order to accommodate an opposed-piston, two-stroke engine application and mitigate the impacts of exposure to gasoline. Overall system performance was maintained throughout testing as fueling rate and rail pressure targets were continuously achieved. Although evidence of vapor formation in the low-pressure part of the system was observed, there was no significant physical damage to the associated components. Injectors showed no deviation in their flow characteristics after exposure to gasoline and high resolution imaging of the nozzle tips and pilot valve assemblies did not indicate the presence of cavitation damage.
Technical Paper

Experimental Evaluation of Longitudinal Control for Connected and Automated Vehicles through Vehicle-in-the-Loop Testing

2020-04-14
2020-01-0714
Automated driving functionalities delivered through Advanced Driver Assistance System (ADAS) have been adopted more and more frequently in consumer vehicles. The development and implementation of such functionalities pose new challenges in safety and functional testing and the associated validations, due primarily to their high demands on facility and infrastructure. This paper presents a rather unique Vehicle-in-the-Loop (VIL) test setup and methodology compared those previously reported, by combining the advantages of the hardware-in-the-loop (HIL) and traditional chassis dynamometer test cell in place of on-road testing, with a multi-agent real-time simulator for the rest of test environment.
Technical Paper

Internal Nozzle Flow Simulations of the ECN Spray C Injector under Realistic Operating Conditions

2020-04-14
2020-01-1154
The availability of powerful computational resources has largely increased in the recent years and has been largely exploited in the field of high-fidelity numerical simulations of internal combustion engine applications. Among them, numerical modeling of the internal- and near- nozzle injection flows has attracted interest within both academic and industrial communities. The accurate reproduction of the physics occurring at the very small scales that are typical of the injector’s internal geometry can provide undoubtedly useful insights. In particular, phenomena such as fuel cavitation and hydraulic flip can be qualitatively and quantitatively assessed in order to better understand the performance of the injector under well-defined operating conditions.
Technical Paper

Hybrid Powertrain Choices for Emerging Engine Technologies

2020-04-14
2020-01-0440
US department of energy estimates the peak efficiency of a modern spark ignited naturally aspirated Otto cycle engine to be 36%. Atkinson cycle engines are estimated to get 40% peak efficiency. Most engines can achieve this peak efficiency only for a limited operating region. Hybrid powertrains enable engine to operate in this efficiently. Overall efficiency is improved by shutting down engine during idle events and by adjusting the operating speed and load on the engine using electric machines. The choice of the powertrain and component sizes depends on the engine characteristics, drive cycles and vehicle technical requirements. This study examines what type of powertrains will be suitable for more efficient engines that are likely to be available in the near future. Some of these technologies achieve higher efficiency with a trade off on power or by accepting a more restrictive operating region.
Technical Paper

An analytical energy-budget model for diesel droplet impingement on an inclined solid wall

2020-04-14
2020-01-1158
The study of spray-wall interaction is of great importance to understand the dynamics that occur during fuel impingement onto chamber wall or piston surfaces in internal combustion engines. The maximum spreading length after droplet impingement on wall is approved that it can provide a quantitative estimation of heat transfer and energy transformation for spray-wall interaction and further influence air-fuel mixing and hydrocarbon and particle emissions at combusting conditions. In this paper, an analytical model of a single diesel droplet impinging on the wall with different inclined angle (α) under isothermal conditions (liquid droplet and wall with the same temperature) is developed in terms of β_m (the ratio of maximum spreading length to initial droplet diameter) to understand the detailed impinging dynamic process.
Technical Paper

Combustion System Optimization of a Light-Duty GCI Engine Using CFD and Machine Learning

2020-04-14
2020-01-1313
In this study, the combustion system of a light-duty compression ignition engine running on a market gasoline fuel with Research Octane Number (RON) of 91 was optimized using computational fluid dynamics (CFD) and Machine Learning (ML). The focus of this study was to optimize the piston bowl geometry at two compression ratios (CR) (17 and 18:1) and this exercise was carried out at full-load conditions (22bar indicated mean effective pressure (IMEP). CAESES, a commercial software tool, was used to automatically perturb key bowl design parameters and CONVERGE software was utilized to perform all CFD simulations. 128 piston bowl designs were evaluated at each compression ratio. Subsequently, a Machine Learning-Grid Gradient Algorithm (ML-GGA) approach was developed to further optimize the piston bowl design. This extensive optimization exercise yielded significant improvements in the engine performance and emissions compared to the baseline piston bowl designs.
Technical Paper

Performance of a Printed Bimetallic (Stainless Steel and Bronze) Engine Head Operating Under Stoichiometric and Lean Spark Ignited (SI) Combustion of Natural Gas

2020-04-14
2020-01-0770
The purpose of this study was to evaluate the durability and operational performance of a bimetallic (stainless steel and bronze) natural gas engine head. The performance was evaluated against a stock cast iron head for comparison. During manufacturing of the printed head, efforts were made to ensure that the internal features, including the fire deck geometry for the two head were identical. The engine was operated under two engine speeds (1200 rpm and 1800 rpm) and two Brake Mean Effective Pressures (6 bar and 10 bar). For each speed and BMEP combination, two equivalence ratios (0.7 and 1.0) were evaluated. In addition to emissions and engine performance data, the research team also took thermal images of both operating heads to ascertain heat transfer and thermal loss differences between the two head materials. The results showed that the brake efficiency, coolant and exhaust temperature were the same for both heads.
Technical Paper

Detailed Analysis of U.S. Department of Energy Engine Targets Compared To Existing Engine Technologies

2020-04-14
2020-01-0835
The U.S. Department of Energy, Vehicle Technologies Office (U.S. DOE-VTO) has been developing more energy-efficient and environmentally friendly highway transportation technologies that would enable the United States to burn less petroleum on the road. System simulation is an accepted approach to evaluate the fuel economy potential of advanced (future) technology targets. U.S. DOE-VTO defines the targets for advancement in powertrain technologies (e.g., engine efficiency targets, battery energy density, lightweighting, etc.) Vehicle system simulation models based on these targets have been generated in Autonomie, to reflect the different EPA classifications of vehicles for different advanced timeframes as part of DOE Benefits and Scenario Analysis (BaSce). It is also important to evaluate the progress of these component technical targets compared to existing technologies available in the market.
Technical Paper

Improvements to a CFR Engine Three Pressure Analysis GT-Power Model for HCCI and SI Conditions

2020-01-24
2019-32-0608
While experimental data measured directly on the engine are very valuable, there is a limitation of what measurements can be made without modifying the engine or the process that is being investigated, such as cylinder temperature. In order to supplement the experimental results, a Three Pressure Analysis (TPA) GT-Power model of the Cooperative Fuel Research (CFR) engine was previously developed and validated for estimating cylinder temperature and residual fraction. However, this model had only been validated for normal and knocking spark ignition (SI) combustion with RON-like intake conditions (naturally aspirated, <52 °C). This work presents improvements made to the GT-Power model and the expansion of its use for HCCI combustion. The burn rate estimation sub-model was modified to allow for low temperature heat release estimation and compression ignition operation.
Technical Paper

Zero-Dimensional Heat Release Modeling Framework for Gasoline Compression-Ignition Engines with Multiple Injection Events

2019-09-09
2019-24-0083
A zero-dimensional heat release model was developed for compression ignition engines. This type of model can be utilized for parametric studies, off-line optimization to reduce experimental efforts as well as model-based control strategies. In this particular case, the combustion model, in a simpler form, will be used in future efforts to control the combustion in compression ignition engines operating on gasoline-like fuels. To allow for a realistic representation of the in-cylinder combustion process, a spray model has been employed to allow for the quantification of fuel distribution as well as turbulent kinetic energy within the injection spray. The combustion model framework is capable of reflecting premixed as well as mixing controlled combustion. Fuel is assigned to various combustion events based on the air-fuel mixture within the spray.
Technical Paper

Exploration of Cavitation-Suppressing Orifice Designs for a Heavy-Duty Diesel Injector Operating with Straight-Run Gasoline

2019-09-09
2019-24-0126
The occurrence of cavitation inside injectors is generally undesirable since it can cause material erosion and result in deviations from the expected injector performance. Previous numerical work employing an injector geometry measured with x-ray diagnostics and operating with a high-volatility straight-run gasoline (SRG) has shown that: (1) most of the cavitation is generally observed at low needle lifts, (2) needle motion is responsible for asymmetric structures in the internal flow as well as large pressure and velocity gradients that trigger phase transition at the orifice inlets, and (3) cavitation affects the injector discharge coefficient and distribution of injected fuel. To explore the potential for material damage within the injector orifices due to cavitation cloud collapse, the cavitation-induced erosion risk assessment (CIERA) tool has been applied for the first time to the realistic geometry of a heavy-duty injector using the CONVERGE software.
Technical Paper

Identification and Characterization of Steady Spray Conditions in Convergent, Single-Hole Diesel Injectors

2019-04-02
2019-01-0281
Reduced-order models typically assume that the flow through the injector orifice is quasi-steady. The current study investigates to what extent this assumption is true and what factors may induce large-scale variations. Experimental data were collected from a single-hole metal injector with a smoothly converging hole and from a transparent facsimile. Gas, likely indicating cavitation, was observed in the nozzles. Surface roughness was a potential cause for the cavitation. Computations were employed using two engineering-level Computational Fluid Dynamics (CFD) codes that considered the possibility of cavitation. Neither computational model included these small surface features, and so did not predict internal cavitation. At steady state, it was found that initial conditions were of little consequence, even if they included bubbles within the sac. They however did modify the initial rate of injection by a few microseconds.
Technical Paper

Optimizing Thermal Efficiency of a Multi-Cylinder Heavy Duty Engine with E85 Gasoline Compression Ignition

2019-04-02
2019-01-0557
Gasoline compression ignition (GCI) using a single gasoline-type fuel for direct/port injection has been shown as a method to achieve low-temperature combustion with low engine-out NOx and soot emissions and high indicated thermal efficiency. However, key technical barriers to achieving low temperature combustion on multi-cylinder engines include the air handling system (limited amount of exhaust gas recirculation (EGR)) as well as mechanical engine limitations (e.g. peak pressure rise rate). In light of these limitations, high temperature combustion with reduced amounts of EGR appears more practical. Previous studies with 93 AKI gasoline demonstrated that the port and direct injection strategy exhibited the best performance, but the premature combustion event prevented further increase in the premixed gasoline fraction and efficiency.
Technical Paper

FD&E Total Life T-Sample Residual Stress Analytical Predictions and Measured Results

2019-04-02
2019-01-0528
The Society of Automotive Engineers Fatigue Design & Evaluation Committee [SAE FD&E] is actively working on a total life project for weldments, in which the welding residual stress is a key contributor to an accurate assessment of fatigue life. Physics-based welding process simulation and various types of residual stress measurements were pursued to provide a representation of the residual stress field at the failure location in the fatigue samples. A well-controlled and documented robotic welding process was used for all sample fabrications to provide accurate inputs for the welding simulations. One destructive (contour method) residual stress measurement and several non-destructive residual stress measurements-surface X-ray diffraction (XRD), energy dispersive X-ray diffraction (EDXRD), and neutron diffraction (ND)-were performed on the same or similarly welded samples.
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