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Journal Article

Reduction of Cyclic Variations by Using Advanced Ignition Systems in a Lean-Burn Stationary Natural Gas Engine Operating at 10 Bar BMEP and 1800 rpm

2018-12-14
Abstract In stationary natural gas engines, lean-burn combustion offers higher engine efficiencies with simultaneous compliance with emission regulations. A prominent problem that one encounters with lean operation is cyclic variations. Advanced ignition systems offer a potential solution as they suppress cyclic variations in addition to extending the lean ignition limit. In this article, the performance of three ignition systems-conventional spark ignition (SI), single-point laser ignition (LI), and prechamber equipped laser ignition (PCLI)-in a single-cylinder natural gas engine is presented. First, a thorough discussion regarding the efficacy of several metrics, in addition to coefficient of variation of indicated mean effective pressure (COV_IMEP), in representing combustion instability is presented. This is followed by a discussion about the performance of the three ignition systems at a single operational condition, that is, same excess air ratio (λ) and ignition timing (IT).
Journal Article

Modelling of a Variable Displacement Lubricating Pump with Air Dissolution Dynamics

2018-04-18
Abstract The simulation of lubricating pumps for internal combustion engines has always represented a challenge due to the high aeration level of the working fluid. In fact, the delivery pressure ripple is highly influenced by the effective fluid bulk modulus, which is significantly reduced by the presence of separated air. This paper presents a detailed lumped parameter model of a variable displacement vane pump with a two-level pressure setting, in which the fluid model takes into account the dynamics of release and dissolution of the air in the oil. The pump was modelled in the LMS Imagine.Lab Amesim® environment through customized libraries for the evaluation of the main geometric features. The model was validated experimentally in terms of pressure oscillations in conditions of low and high aeration. The fraction of separated air in the reservoir of the test rig was measured by means of an X-ray technique.
Journal Article

Complete Engine Thermal Model, a Comprehensive Approach

2018-04-18
Abstract Upcoming engine generations are characterized by both a general trend of increased specific-power and higher efficiency. This leads to increased thermal loads, compromising reliability, and simultaneously to a limited amount of heat under ordinary engine use. Heat is a valuable resource in providing passenger comfort and emission control. For these reasons the subject of engine thermal management is receiving increasing attention. This work presents a comprehensive study of the complete engine thermal behavior at relevant running conditions: rated-power, peak-torque and ordinary use. The work is further extended to the engine warm-up period. The result is a high-resolution complete engine thermal model, capable of simultaneously reporting the local temperature of any engine part, and the global engine heat balance at any engine load.
Journal Article

Experimental Investigation of the Influence of Engine Operating Parameters on a Rankine Based Waste Heat Recovery System in a SI Engine

2018-04-18
Abstract One of the most promising techniques to reduce carbon dioxide (CO2) emissions of future combustion engines is the use of waste heat from exhaust gas with a Rankine cycle. The target of this study was to investigate the influence of engine operating parameters such as ignition timing, coolant temperature and injection parameters on the efficiency and performance of Rankine based waste heat recovery systems (WHR). This was done to gain basic knowledge about the influences of the engine operating parameters which helps to explain the system behavior under different operating conditions and second to identify the operating parameters with the highest overall system efficiency which can be used to highlight the impact of changes in engine application on the car. These first of a kind tests were performed on a state-of-the-art gasoline engine equipped with a prototype Rankine-system.
Journal Article

A Novel Approach towards Stable and Low Emission Stratified Lean Combustion Employing Two Solenoid Multi-Hole Direct Injectors

2018-04-18
Abstract Stratified lean combustion has proven to be a promising approach for further increasing the thermal efficiency of gasoline direct injection engines in low load conditions. In this work, a new injection strategy for stratified operation mode is introduced. A side and a central-mounted solenoid multi-hole injector are simultaneously operated in a single-cylinder engine. Thermodynamic investigations show that this concept leads to improved stability, faster combustion, reduced particle number emissions, and lower fuel consumption levels compared to using only one injector. Experiments at an optical engine and three-dimensional computational fluid dynamics (CFD) simulations explain the improvements by a more compact mixture and reduced piston wetting with two injectors. Finally, the application of external EGR in combination with the above concept allows NOx emissions to be effectively kept at a low level while maintaining a stable operation.
Journal Article

Comparative Analysis of Performance of Neural Estimators for Diagnostics in Engine Emission System

2018-06-14
Abstract This article describes the results of a comparative performance analysis on the use of neural estimators to accurately estimate the Differential Pressure (DP) signal from diesel engine systems equipped with a Diesel Particulate Filter (DPF) aftertreatment system. For most systems, there are known and modeled relationships between system inputs and outputs; however, in the case of nonlinear, time-varying systems a detailed modeling of the system might not be readily available. Therefore, Artificial Neural Networks (ANNs) have been used for developing critical relationship between system inputs (engine and aftertreatment parameters) and system output (DP signal). Both batch (offline) and online learning ANN estimators have been proposed. A control-oriented engine out DPF-DP model is desirable for on-board applications as a virtual DPF-DP sensor which could be used in parallel as an alternate analytical redundancy-based sensor.
Journal Article

Analysis of Regulated Pollutant Emissions and Aftertreatment Efficiency in a GTDi Engine Using Different SOI Strategies

2018-06-25
Abstract In order to improve performance and minimize pollutant emissions in gasoline turbocharged direct-injection (GTDi) engines, different injection strategies and technologies are being investigated. The inclusion of exhaust gas recirculation (EGR) and the variation of the start of injection (SOI) are some of these strategies that can influence the air-to-fuel (AF) mixture formation and consequently in the combustion process and pollutant emissions. This paper presents a complete study of the engine performance, pollutant emissions and aftertreatment efficiency that produces the SOI variation with a fixed EGR rate in a 4-cylinder, turbocharged, gasoline direct-injection engine with 2.0 L displacement. The equipment used in this study are TSI-EEPS for particle measurement and HORIBA MEXA 1230-PM for soot measurement being HORIBA MEXA 7100-DEGR with a heated line selector the system employed for regulated gaseous emission measurement and aftertreatment evaluation.
Journal Article

Uncertainty in Gravimetric Analysis Required for LEV III Light-Duty Vehicle PM Emission Measurements

2018-06-20
Abstract With the reduction in PM emission standards for light duty vehicles to 3 mg/mi for current Federal and California standards and subsequently to 1 mg/mi in 2025 for California, the required PM measurements are approaching the detection limits of the gravimetric method. A “filter survey” was conducted with 11 laboratories, representing industry, agencies, research institutes, and academic institutions to analyze the accuracy of the current gravimetric filter measurement method under controlled conditions. The reference filter variability, measured within a given day over periods as short as an hour, ranged from 0.61 μg to 2 μg to 5.0 μg for the 5th, 50th, 95th percentiles (n > 40,000 weights, 317 reference objects), with a laboratory average of 2.5 μg.
Journal Article

In-Use Efficiency of Oxidation and Three-Way Catalysts Used in High-Horsepower Dual Fuel and Dedicated Natural Gas Engines

2018-07-01
Abstract Directional drilling rigs and hydraulic stimulation equipment typically use diesel fueled compression ignition (CI) engines. The majority of these engines are compliant with US Environmental Protection Agency (EPA) Tier 2 standards. To reduce fuel costs, industry is investing in dual fuel (DF) and dedicated natural gas (DNG) engines. DF engines use diesel oxidation catalysts (DOCs) to reduce CO and NMHC emissions. DNG engines may be either lean-burn or rich-burn and the latter uses three-way catalysts (TWC) to reduce CO, NMHC, and NOx emissions. This research presents in-use catalyst efficiency data collected pre- and post-catalyst for three DF engines and two DNG engines. One DF engine was converted earlier and did not include a DOC. Data were collected from six Tier 2 engines, two CI drilling engines converted to operate as DF, two CI hydraulic fracturing engines converted to operate as DF, and two SI DNG drilling engines.
Journal Article

Development and Validation Procedure of a 1D Predictive Model for Simulation of a Common Rail Fuel Injection System Controlled with a Fuel Metering Valve

2018-07-10
Abstract A fully predictive one-dimensional model of a Common Rail injection apparatus for diesel passenger cars is presented and discussed. The apparatus includes high-pressure pump, high-pressure pipes, injectors, rail and a fuel-metering valve that is used to control the rail pressure level. A methodology for separately assessing the accuracy of the single submodels of the components is developed and proposed. The complete model of the injection system is finally validated by means of a comparison with experimental high-pressure and injected flow-rate time histories. The predictive model is applied to examine the fluid dynamics of the injection system during either steady-state or transient operations. The influence of the pump delivered flow-rate on the rail-pressure time history and on the injection performance is analysed for different energizing times and nominal rail pressure values.
Journal Article

CFD Modeling of Tailpipe NOx Sensor Accuracy

2018-08-08
Abstract In a modern diesel aftertreatment system, a sensor for nitrogen oxides (NOx) placed downstream of the selective catalytic reduction (SCR) catalyst is necessary to determine if the tailpipe NOx concentration remains below the applicable On-board diagnostic (OBD) threshold. Typically the same NOx sensor also provides feedback to the dosing control module to adjust diesel exhaust fluid (DEF) dosing rate thereby controlling tailpipe NOx and ammonia emissions. However, feedback signal sent by the tailpipe NOx sensor may not always be accurate due to reasons including non-uniformity in NOx and ammonia distributions at SCR outlet. Flow based metrics from computational fluid dynamics (CFD) analyses, that are typically used to qualitatively assess NOx sensor accuracy in different designs are often inadequate. In this work, an improved CFD analysis procedure has been developed for assessing NOx sensor accuracy.
Journal Article

Active Control of Cylinder Charge Motion Using Vortex Generating Jets (VGJs) on Generic Intake Port Geometries

2018-08-08
Abstract Swirl is known to have impact on the combustion process and the engine emission performance. Generally the swirl flows are generated on engines by e.g. helical or tangential intake ports. However, such features of intake ports constrict the airflow, resulting in raising pumping losses and thus higher fuel consumption. This article introduces a further possibility to generate and regulate the swirl flow by injecting air directly into the intake ports using Vortex Generating Jets (VGJs). The effect of air injection was studied by means of experimental investigations regarding swirl generation and flow rate improvement. The optimization of VGJ diameters, positions as well as injection airflow rate was carried out with respect to energy efficiency of swirl generation.
Journal Article

Transient Operation and Over-Dilution Mitigation for Low-Pressure EGR Systems in Spark-Ignition Engines

2018-09-17
Abstract Low-Pressure cooled Exhaust Gas Recirculation (LP-cEGR) is proven to be an effective technology for fuel efficiency improvement in turbocharged spark-ignition (SI) engines. Aiming to fully exploit the EGR benefits, new challenges are introduced that require more complex and robust control systems and strategies. One of the most important restrictions of LP-cEGR is the transient response, since long air-EGR flow paths introduce significant transport delays between the EGR valve and the cylinders. High dilution generally increases efficiency, but can lead to cycle-by-cycle combustion variation. Especially in SI engines, higher-than-requested EGR dilution may lead to combustion instabilities and misfires. Considering the long EGR evacuation period, one of the most challenging transient events is throttle tip-out, where the engine operation shifts from a high-load point with high dilution tolerance to a low-load point where EGR tolerance is significantly reduced.
Journal Article

Gasoline Particulate Filter Wall Permeability Testing

2018-10-29
Abstract With the introduction of particulate matter emissions regulations for gasoline engines, most car manufacturers are considering using gasoline particulate filters (GPFs). Although very similar to diesel particulate filters (DPFs), GPFs operate at higher temperatures and generally have thinner monolith walls. In order to estimate the pressure loss through the filter, filter wall permeability is needed. This presents a number of challenges since wall losses cannot be efficiently isolated from other losses in a full-scale filter or filter core. Thin wall wafers have been used for DPF characterization. However, GPF wafers are generally thinner, which makes the testing less straightforward. This article presents a novel effective methodology for estimation of GPF wall permeability using thin wafers cut from the filter monolith. Both cold and hot flow permeabilities can be estimated, which allows to account for the change of apparent permeability due to the slip effect.
Journal Article

Direct Versus Indirect Acting Piezoelectric CR Injectors: Comparison of Hydraulic Performance, Pollutant Emissions, Combustion Noise, and Fuel Consumption

2018-11-08
Abstract A comprehensive comparison between a direct acting and an indirect acting piezoelectric injector has been carried out both at the hydraulic rig and at the dynamometer cell. The working principle of these injector typologies is illustrated, and their hydraulic performance has been analyzed and discussed on the basis of experimental data collected at a hydraulic test rig. The injector characteristics, nozzle opening and closure delays, injector leakages, injected flow-rate profiles, injector-to-injector variability in the injected mass, injected volume fluctuations with the dwell time (DT), and minimum DT for fusion-free multiple injections have been compared in order to evaluate the impact of the injector driving system on the injection apparatus performance. The direct acting and indirect acting piezoelectric injectors have been installed on a Euro 5 diesel engine, which has been tested at a dynamometer cell.
Journal Article

The Key Role of Advanced, Flexible Fuel Injection Systems to Match the Future CO2 Targets in an Ultra-Light Mid-Size Diesel Engine

2019-01-23
Abstract The article describes the results achieved in developing a new diesel combustion system for passenger car application that, while capable of high power density, delivers excellent fuel economy through a combination of mechanical and thermodynamic efficiencies improvement. The project stemmed from the idea that, by leveraging the high fuel injection pressure of last generation common rail systems, it is possible to reduce the engine peak firing pressure (pfp) with great benefits on reciprocating and rotating components’ light-weighting and friction for high-speed light-duty engines, while keeping the power density at competitive levels. To this aim, an advanced injection system concept capable of injection pressure greater than 2500 bar was coupled to a prototype engine featuring newly developed combustion system. Then, the matching among these features has been thoroughly experimentally examined.
Journal Article

Carbon Monoxide Density Pattern Mapping from Recreational Boat Testing

2018-10-04
Abstract Exposure to carbon monoxide (CO) gas can cause health risks for users of recreational boats and watercraft. Activities such as waterskiing, wakeboarding, tubing, and wakesurfing primarily utilize gasoline engine-driven vessels which produce CO as a combustion by-product. Recent watersports trends show an increase in popularity of activities which take place closer to the stern of the boat (such as wakesurfing) as compared to traditional waterskiing and wakeboarding. Advancements in gas emissions treatment in marine engine exhaust system designs have reduced risks for CO exposure in some boats. This article presents results from on-water testing of three recreational boats, reports average and maximum values of CO levels under various conditions, and exhibits mapping of the density of CO relative to the stern of the test vessels.
Journal Article

On WTW and TTW Specific Energy Consumption and CO2 Emissions of Conventional, Series Hybrid and Fully Electric Buses

2018-04-17
Abstract Making use of a specifically designed dynamical vehicle model, the authors here presented the results of an activity for the evaluation of energy consumption and CO2 emissions of buses for urban applications. Both conventional and innovative (series hybrid, and fully electric) vehicles were considered to obtain interesting comparative conclusions. The derived tool was used to simulate the dynamical behaviour of these vehicles on a number of kinematic profiles measured during real buses operation in different contexts, varying from really congested city centre routes to fast-lane operated services. It was so possible to evaluate the energetic performances of those buses on a Tank-to-Wheel (TTW) basis.
Journal Article

Development of a Catalytic Converter Cool-Down Model to Investigate Intermittent Engine Operation in HEVs

2018-10-29
Abstract Catalytic converters, a primary component in most automotive emissions control systems, do not function well until they are heated substantially above ambient temperature. As the primary energy for catalyst heating comes from engine exhaust gases, plug-in hybrid electric vehicles (PHEVs) that have the potential for short and infrequent use of their onboard engine may have limited energy available for catalytic converter heating. This article presents a comparison of multiple hybrid supervisory control strategies to determine the ability to avoid engine cold starts during a blended charge-depleting propulsion mode. Full vehicle and catalytic converter simulations are performed in parallel with engine dynamometer testing in order to examine catalyst temperature variations during the course of the US06 City drive cycle. Emissions and energy consumption (E&EC) calculations are also performed to determine the effective number of engine starts during the drive cycle.
Journal Article

Toward Material Efficient Vehicles: Ecodesign Recommendations Based on Metal Sustainability Assessments

2018-09-17
Abstract Current End-of-Life Vehicle (ELV) recycling processes are mainly based on mechanical separation techniques. These methods are designed to recycle those metals with the highest contribution in the vehicle weight such as steel, aluminum, and copper. However, a conventional vehicle uses around 50 different types of metals, some of them considered critical by the European Commission. The lack of specific recycling processes makes that these metals become downcycled in steel or aluminum or, in the worst case, end in landfills. With the aim to define several ecodesign recommendations from a raw material point of view, it is proposed to apply a thermodynamic methodology based on exergy analysis. This methodology uses an indicator called thermodynamic rarity to assess metal sustainability. It takes into account the quality of mineral commodities used in a vehicle as a function of their relative abundance in Nature and the energy intensity required to extract and process them.
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