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Technical Paper

A Review of Current Understanding of the Underlying Physics Governing the Interaction, Ignition and Combustion Dynamics of Multiple-injections in Diesel Engines

2022-03-29
2022-01-0445
This work is intended to be a comprehensive technical review of existing literature and a synthesis of current understanding of the governing physics behind the interaction of multiple fuel injectio ns, ignition and combustion behavior of multiple-injections in diesel engines. Multiple-injection is a widely adopted operating strategy applied in modern compression-ignition engines, which involves various combinations of small pre-injections and post-injections of fuel before and after the main injection and splitting the main injection into multiple smaller injections. This strategy has been conclusively shown to improve fuel economy in diesel engines while achieving simultaneous NOx, soot, and combustion noise reduction in addition to a reduction in the emissions of unburned hydrocarbons and CO by preventing fuel wetting and flame quenching at the piston wall.
Technical Paper

Modeling of regeneration dynamics in gasoline particulate filters and sensitivity analysis of numerical solutions

2022-03-29
2022-01-0556
Gasoline Direct-Injection (GDI) engine technology improves vehicle fuel economy toward future targets and simultaneously decreases CO2 emissions. The main drawback of this technology is the increased emission of particulates (when compared to their indirect injection-based technology counterpart). Thus, aftertreatment devices such as Gasoline Particulate Filters (GPFs) are today considered the most promising and practically adoptable solution to limit PM/PN out of GDI exhaust. The particulate filter traps soot particles resulting from fuel combustion and prevents their release into the atmosphere. Soot oxidation (also known as regeneration) is required at regular intervals to clean the filter, maintain a consistent soot trapping efficiency, and avoid the formation of soot plugs in the GPF channel.
Technical Paper

Title: Numerical optimization of the piston bowl geometry and investigation of the key geometric parameters for the dual-mode dual-fuel (DMDF) concept under a wide load range

2022-03-29
2022-01-0782
Focusing on the dual-mode dual-fuel (DMDF) combustion concept, a combined optimization of the piston bowl geometry with the fuel injection strategy was conducted at low, mid, and high loads. By coupling the KIVA-3V code with the enhanced genetic algorithm (GA), a total of 14 parameters including the piston bowl geometric parameters and the injection parameters were optimized with the objective of meeting Euro VI regulations while improving the fuel efficiency. The optimal piston bowl shape coupled with the corresponding injection strategy was summarized and integrated at various loads. Furthermore, the effects of the key geometric parameters were investigated in terms of organizing the in-cylinder flow, influencing the energy distribution, and affecting the emissions. The results indicate that the behavior of the DMDF combustion mode is further enhanced in the aspects of improving the fuel economy and controlling the emissions after the bowl geometry optimization.
Technical Paper

Identifying Factors that Affect Brake Wear PM Emissions During Real-world Test Conditions

2022-03-29
2022-01-0570
Particulate Matter (PM) is one of the world’s most problematic pollutants in terms of harm to environment and human health. It has been found out that PM emission levels are very high during traffic congestion and thus, PM is considered as the primary pollutants in urban areas. Many literatures suggested that PM emitted during braking sequence from both internal combustion engines and electrified vehicles are considered high and could be the major cause of this issue. Many studies regarding to PM from brake wear were done in the pin disc laboratory setup which might not represent real-world driving scenarios. Various studies of on road non-exhaust PM measurement were mostly focused on driving cycles. Parametric studies to identifying factors that affect brake wear during real-world driving scenarios are still needed for more investigations. The current study focuses on identifying factors that affect brake wear particle emissions from an on-road vehicle in real-time measurements.
Technical Paper

Calculation Methods Impact on Real Driving Emissions Particulate Number Emission Evaluation: Moving Average Window in China vs. Raw Mileage Averaged in Europe

2022-03-29
2022-01-0567
In the Real Driving Emissions (RDE) tests, Particulate Number (PN) emission is specifically restricted with a limit as product of the Conformity Factor (CF) and WLTC PN limit 6.0E11 #/km. The CF value is defined as 1.5 in the Europe 6d and 2.1 in the China 6b. Besides the tighter CF value in Europe, the calculation methods that are employed to evaluate the RDE PN emission are also different, i.e. Moving Averaged Window (MAW) according to the China 6b and Raw Mileage Averaged (RMA) according to the Europe 6d RDE package 4. In our previous studies, the “MAW” method was found to be less stringent than the “RMA” method generally, because the window-based “MAW” method could under-estimate the high PN emission generated in the cold start [1]. In fact, for the “MAW” method, the cold start emissions are less counted compared to emissions from the middle of the RDE test. Meanwhile, the weight of each window is impacted by CO2 emission.
Technical Paper

A Comparison of Isobaric and Conventional Diesel Combustion using High-Speed Optical Imaging

2022-03-29
2022-01-0418
Isobaric combustion can achieve higher thermal efficiency, lower heat transfer losses, and NOx emissions compared to conventional diesel combustion (CDC). Previous studies on isobaric combustion provided a detailed analysis of performance/emissions characteristics with a limited emphasis on the fuel-air mixing process, high-temperature reaction, and soot formation zones. In the present study, high-speed imaging of Mie-scattering, CH* chemiluminescence, and soot luminosity were conducted in an optically accessible single-cylinder heavy-duty diesel engine for CDC and isobaric combustion. The fuel used for both the combustion modes is n-heptane, which is a surrogate of diesel fuel. The engine was equipped with a flat-bowl shaped optical piston to allow bottom-view imaging of the combustion chamber. The peak cylinder pressure (PCP) and the fuel mean effective pressure (Fuel MEP) for both the combustion modes are kept as 70 bar and 19 bar, respectively.
Technical Paper

Ducted Fuel Injection: An Experimental Study on Optimal Duct Size

2022-03-29
2022-01-0450
Ducted fuel injection (DFI) was implemented in a constant flow High Temperature Pressure Vessel (HTPV) at 60bar ambient pressure, 800-1000K ambient temperature, 21% oxygen. The ducts were 14mm long and placed approximately 3mm away from the orifice exit. The duct diameters ranged from 1.6-3.2mm and had a rounded inlet and a tapered outlet. Diesel fuel was used in a single-orifice fuel injector operating at a rail pressure of 250MPa, where the orifice diameters ranged from 150-219µm. The objective of this work was to study soot reduction for various combinations of orifice diameter in relation to duct diameter. Several combinations of orifice and duct diameters were tested. A complete data set was taken using the 150µm orifice. The results clearly show that soot reduction peaks at an optimal duct size of 2-2.25mm and is reduced as the duct diameter is increased or decreased.
Technical Paper

Strategies for Reduced Engine-out HC, CO, and NOx Emissions in Diesel-Natural Gas and POMDME-Natural Gas Dual-Fuel Engine

2022-03-29
2022-01-0460
Dual-fuel engines employ precisely metered amounts of a high reactivity fuel (HRF) such as diesel at high injection pressures to burn a low reactivity fuel (LRF) such as natural gas, which is typically fumigated into the intake manifold. Dual fuel engines have demonstrated the ability to achieve extremely low engine-out oxides of nitrogen (NOx) emissions compared to conventional diesel combustion at the expense of unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. At low engine loads, due to the low in-cylinder temperatures oxidation of HC and CO is challenging. This results in both compromised combustion and fuel conversion efficiencies.
Technical Paper

Modeling Fuel-Air Mixing, Combustion and Soot Formation with Ducted Fuel Injection Using Tabulated Kinetics

2022-03-29
2022-01-0403
Ducted Fuel Injection (DFI) has the potential to reduce soot emissions in Diesel engines thanks to the enhanced mixing rate resulting from the liquid fuel flow through a small cylindrical pipe located at a certain distance from the nozzle injector hole. A consolidated set of experiments in constant-volume vessel and engine allowed to understand the effects of ambient conditions, duct geometry and shape on fuel-air mixing, combustion and soot formation. However, implementation of this promising technology in compression-ignition engines requires predictive numerical models that can properly support the design of combustion systems in a wide range of operating conditions. This work presents a computational methodology to predict fuel-air mixing and combustion with ducted fuel injection. Attention is mainly focused on turbulence and combustion modelling.
Technical Paper

Potential towards CI engines with lower NOx emissions through calibration optimization and low-carbon fuels

2022-03-29
2022-01-0511
The use of electric vehicles will continue to increase as the technology advances, and governments adopt policies that favor their adoption. However, by some projections, the phase-out of the Internal Combustion Engines (ICEs) will occur later than 2050 (the target year to achieve Net Zero emissions), making imperative the continuous improvement of ICEs with strategies that can be -directly or with minor modifications- applied to existing vehicle platforms to improve efficiency and reduce GHG emissions to help achieve Paris climate targets. Low carbon fuels (LCF) as diesel substitutes for light and heavy duty vehicles are currently being considered as a promising alternative to reduce well-to-wheel (WTW) CO2 emissions by taking advantage of the carbon offset their synthesis pathway can promote, which could capture more CO2 than it releases into the atmosphere.
Technical Paper

Particulates in GDI and their relation to wall-film and mixing quality

2022-03-29
2022-01-0430
Particulates from GDI engines are inevitable, but can be kept low by means of various approaches such as high injection pressures, optimization of the spray formation, injection timing etc. It is known that liquid wall film on the piston and mixing are key factors influencing directly or indirectly the formation of particulates. It is almost impossible to completely avoid that the fuel spray impinges on the piston regardless of fuel injection timing which means that non-evaporated fuel can remain on the piston until late in the compression stroke or even further leading to increases in PN caused by pool-fires or rich zones. For a given fuel pressure, the timing of the fuel injection, SOI, is the most influencing factor. In this paper particulates data in numbers and sizes from experiments in single cylinder research engine are presented and used together with data of wall film and mixing quality from CFD simulations for sweeps in SOI timing.
Technical Paper

Nozzle tip wetting in GDI injector and its link with nozzle spray hole length

2022-03-29
2022-01-0498
Fuel film deposited on fuel injectors used in gasoline direct injection engines, otherwise known as nozzle tip wetting, has been identified as an essential source of particle emissions. Attempts has been made to reduce nozzle tip wetting by the optimization design of nozzle geometry parameters. However, relevant investigations are still limited to the indirect analysis of emission performance and operation conditions. Due to the lack of related visualization research, the mechanism of nozzle tip wetting formation and its link with nozzle internal flow is still unclear. To clarify the influence of spray hole length on nozzle tip wetting and the underlying mechanisms, the dynamic formation process and the fuel film area evolution of nozzle tip wetting were visualized directly by means of laser-induced fluorescence technique and photomicrography technique.
Technical Paper

Unregulated Emissions Characterization and Comparison for Two Off-Road Applications: a DPF and a Non-DPF Engine

2022-03-29
2022-01-0587
As governmental agencies focus on low levels of the oxides of nitrogen (NOx) emissions compliance, new off-road applications are being reviewed for both regulated and unregulated emissions to understand the technological challenges and requirements for improved emissions performance. During an off-road low NOX technology demonstration, a detailed assessment of current engine and aftertreatment technologies was performed. This work discusses the emissions characterization from two non-road engine platforms and compares the emissions species from different approaches designed to meet Tier 4 emissions regulations. The engine platforms reflected the available technology for diesel particulate filter (DPF) and non-DPF aftertreatment architectures. A detailed emissions characterization of the gaseous and particulate emissions was performed to measure an extensive list of non-regulated emission measurements.
Technical Paper

Development of Multiple Injection Strategy for Gasoline Compression Ignition High Performance and Low Emissions in a Light Duty Engine

2022-03-29
2022-01-0457
Increasing regulatory demand to reduce CO2 emissions has led to a focus on the development of novel combustion modes such as gasoline compression ignition (GCI). It has been shown by others that GCI can improve the overall engine efficiency while achieving soot and NOx emissions targets. In comparison with diesel fuel, gasoline has a higher volatility and has more resistance to autoignition, therefore, it has a longer ignition delay time which facilitates better mixing of the air-fuel charge before ignition. In this study, a GCI combustion system has been tested using a Hyundai 2.2L engine as part of a US Department of Energy funded project. For this purpose, a multiple injection strategy was developed to improve the pressure rise rates and soot emission levels for the same engine out NOx emissions.
Technical Paper

Assessing the importance of injector cleanliness in minimising particulate emissions in Gasoline Direct Injection engines.

2022-03-29
2022-01-0490
Injector fouling is an important contributory factor to particulate matter (PM) emissions in Gasoline Direct Injection (GDI) engines. Injector deposits can disrupt fuel spray such that it interacts more with the cylinder liner and piston top, and secondly liquid fuel can be adsorbed on porous carbonaceous deposits on the injector tip that later evaporate at non-ideal points in the engine cycle. Deposit Control Additives (DCAs) are often added to gasoline for the purpose of controlling injector deposits in GDI engines, as well as intake valve deposits (IVDs) in Port Fuel Injected (PFI) Engines. The presence of DCA can often be inferred by an increased level of unwashed gums (UWGs) in the fuel, although it is noted that heavy ends in the fuel, and other constituents of the additive package (especially the carrier fluid) can strongly affect the measured gum levels.
Technical Paper

Real World Emissions Analysis Using Sensor-based Emissions Measurement System for Light-duty Direct-Injection Gasoline Vehicle

2022-03-29
2022-01-0572
In recent years, particulate matter (PM) emitted from direct-injection gasoline vehicles has become a problem. In addition, it is often reported that ammonia (NH3) is emitted from gasoline vehicles equipped with a three-way catalyst. These emissions might be largely emitted especially when driving in on-road driving conditions. In this study, we investigated the emissions, NOx, NH3, and PM / PN (particulate number) of a light-duty direct-injection gasoline vehicle when driving on actual roads. Using a small direct-injection gasoline vehicle equipped with a three-way catalyst, we ran nine times on the same route and measured these emissions. Based on these measurements, we analyzed "where" and "how much" NOx, NH3, and PM / PN were emitted. As a result, it was clarified that a large amount of NOx is emitted after the fuel is cut during deceleration, NH3 is emitted when the air-fuel ratio becomes rich, and PM / PN is emitted during rapid acceleration of the vehicle.
Technical Paper

Characteristics of Methanol and Iso-octane Under Flashing and Non-flashing Conditions in ECN-G Spray

2022-03-29
2022-01-0496
This paper investigated the spray characteristics of methanol under the flash and non-flash boiling conditions defined by the Engine Combustion Network (ECN) Spray G. As a counterpart, the spray features of iso-octane were also simulated and compared to methanol. The Void of Fluid (VOF) approach under the Eulerian scheme was employed to model the internal nozzle flow details, which information was used to initialize the spray parcels and taken as input for the Lagrangian simulations, namely, the one-way coupling method. Since the Eulerian high-fidelity simulations allow capturing the effects of the flow inside the non-symmetrical injector, the rate of injection (ROI) profile, discharge coefficient, and plume angle et al. are not required for the Lagrangian simulations. The simulation results show that the flash boiling led to shorter penetrations and better mixing compared to the non-flash boiling condition.
Technical Paper

Simulation Studies on Glow plug Assisted Neat Methanol Combustion in a Diesel Engine

2022-03-29
2022-01-0519
Methanol due to its high latent heat of vaporization and the oxygen content can lower the NOx and soot levels in a compression ignition (CI) engine. Though methanol has a very low cetane number, hot surface ignition (HSI) using a glow plug can be used for combustion in a CI engine. In this work, a CFD simulation model of a glow plug assisted methanol HSI engine was developed and validated using experimental data on cylinder pressure and heat release reported in literature on a glow plug assisted engine with optical access. The SAGE combustion model, simplified GRI- MECH 3.0 reaction mechanism and adaptive grid refinement were employed. Parametric studies on glow plug surface temperature, injection strategies that use split injection at different split ratios and timings, location of the glow plug and the effect of shielding the glow plug were investigated by applying the model to a three cylinder neat methanol HSI engine.
Technical Paper

Continuous Oil Consumption Measurement Using Laser Induced Breakdown Spectroscopy

2022-03-29
2022-01-0581
This paper describes a new method for measuring oil consumption using laser induced breakdown spectroscopy (LIBS). LIBS focuses a high energy laser pulse on a sample to form a transient plasma. As the plasma cools, each element produces atomic emission lines which can be used to identify and quantify the elements present in the original sample. In this work, a LIBS system was used on simulated engine exhaust with a focus on quantifying the inorganic components (termed ash) of the particulate emissions. Because some of the metallic elements in the ash almost exclusively result from lube oil consumption, their concentrations can also be tied to an oil consumption rate. Initial testing was performed in an Exhaust Composition Transient Operation LaboratoryTM (ECTO-LabTM) burner system so that oil consumption and ash mass could be carefully controlled.
Technical Paper

Autoignition and Sooting Characteristics of Iso-Octane and Ethanol in an Optical Rapid Compression Machine

2022-03-29
2022-01-0419
With the introduction of EV technology into the light-duty vehicle market, the demand for gasoline in conventional spark ignition engines is projected to decline in the coming decades. Therefore, researchers have been investigating the use of gasoline and other light fuels in heavy-duty engine applications. In heavy-duty engines, the combustion mode will likely be non-premixed, mixing-controlled combustion, where the rate of combustion is determined by the fuel-air mixing process. This creates a range of mixture conditions inside the engine cylinder at every instance in time. The goal of this research is to experimentally quantify the sooting behaviors of light fuels under a range of compression ignition engine mixture conditions (i.e., a range of equivalence ratios).
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