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Technical Paper

Flight Optimization Model on Global and Interval Ranges for Conceptual Studies of MEA Systems

2019-09-16
2019-01-1906
In development of more electric aircraft applications, it is important to discuss aircraft energy management on various level of aircraft operation. This paper presents a computationally efficient optimization model for evaluating flight efficiency on global and interval flight ranges. The model is described as an optimal control problem with an objective functional subjected to state condition and control input constraints along a flight path range. A flight model consists of aircraft point-mass equations of motion including engine and aerodynamic models. The engine model generates the engine thrust and fuel consumption rate for operation condition and the aerodynamic model generates the drag force and lift force of an aircraft for flight conditions. These models is identified by data taken from a published literature as an example. First, approximate optimization process is performed for climb, cruise, decent and approach as each interval range path.
Technical Paper

Gradationally Controlled Voltage Inverter for More Electric Aircrafts

2019-09-16
2019-01-1913
Over recent decades, there has been a lot of progress toward a more electric aircraft (MEA) to reduce emissions and fuel consumption. In MEAs, many subsystems that previously used hydraulic or pneumatic power have been replaced by electrical systems with inverters and electrical machines. Therefore, MEAs reduce the weight, i.e. fuel consumption, and maintenance cost. To achieve advanced electrical systems, the weight of inverters has significant importance. In this work, a gradationally controlled voltage (GCV) inverter is proposed to reduce the weight and enhance reliability. A GCV inverter can supply gradational quasi-sinusoidal voltages combining two different voltages from a 3-phase 3-level (main) inverter and three single-phase H-bridge (sub) inverters. A dc power supply is required only for the main inverter. A main inverter with Si-IGBTs supplies the fundamental voltage by only one switching in the fundamental period.
Technical Paper

Large eddy simulation of an ignition wave front in a heavy duty partially premixed combustion engine

2019-08-15
2019-24-0010
In partially premixed combustion engines high octane number fuels are injected into the cylinder during the late part of the compression cycle, giving the fuel and oxidizer enough time to mix into a desirable stratified mixture. If ignited by auto-ignition such a gas composition can react in an ignition wave-front dominated combustion mode. 3D-CFD modeling of such a combustion mode is challenging as the reaction speed is dependent on both mixing history and turbulence acting on the reaction wave. This paper presents a large eddy simulation (LES) study of the effects of energetic turbulence scale on the fuel/air mixing and on the propagation of reaction wave. The results are compared with optical experiments to validate both pressure trace and ignition location. The studied case is a closed cycle simulation of a single cylinder of a Scania D13 engine running PRF81 (81% iso-octane and 19% n-heptane).
Technical Paper

Development of 1D/0D cycle simulation model for highly lean burn SI engine operation

2019-08-15
2019-24-0004
In the development processes for an engine control scheme and a novel engine configuration, 1D or 0D engine cycle simulation is effective and has been widely utilized, in these years. In SI engines, engine operations with the highly lean air-fuel mixture or highly diluted with EGR gas have been known as one of the most effective strategies to save fuel consumption. Following these situations, it is strongly demanded to develop a predictive combustion model capable of accurately predicting the effects of air-fuel ratio and EGR ratio on combustion characteristics, and thus on engine performance. In this paper, to predict highly lean or EGR diluted combustion with enough accuracy in 1D/0D engine simulation, a spark ignition model capable of predicting spark discharge circuit and a spark discharge channel behavior in the cylinder, and a flamelet concept model were applied into a single cylinder engine performance prediction model.
Technical Paper

Optical diagnostics investigation on the effect of fuel injection timing on Partially Premixed Combustion stratification and soot formation in a single-cylinder optical compression ignition engine

2019-08-15
2019-24-0028
The present work investigates the effect of fuel injection timing on combustion stratification and soot formation in an optically accessible, single cylinder light duty diesel engine. The engine operated under low load and low engine speed conditions, employing a single injection scheme. The conducted experiments considered three different injection timings, which promoted Partially Premixed Combustion (PPC) operation. The fuel quantity of the main injection was adjusted to maintain the same Indicated Mean Effective Pressure (IMEP) value among all cases considered. Findings were analysed via means of pressure trace and apparent heat release rate (AHRR) analyses, as well as a series of optical diagnostics techniques, namely flame natural luminosity, CH* and C2* chemiluminescence high-speed imaging, as well as planar Laser Induced Incandescence (pLII).
Technical Paper

Impact of cooled EGR on performance and emissions of a turbocharged Spark-Ignition engine under low-full load conditions

2019-08-15
2019-24-0021
The stringent worldwide exhaust emission legislations for CO2 and pollutants require significant efforts to increase both the combustion efficiency and the emission quality of internal combustion engines. With this aim, several solutions are continuously produced to improve the combustion efficiency of spark ignition engines. Among the various solutions, EGR represents a well-established technology to improve the gasoline engine performance and the nitrogen-oxides emissions. This work presents the results of an experimental investigation on the effects of the EGR technique on combustion evolution, knock tendency, performance and emissions of a small–size turbocharged PFI SI engine, equipped with an external cooled EGR system. Measurements are carried out at different engine speeds, on a wide range of loads and EGR levels. The standard engine calibration is applied at the reference test conditions.
Technical Paper

Experimental tests on the feasibility of passive regeneration in a catalytic DPF at the exhaust of a light-duty Diesel engine

2019-08-15
2019-24-0045
Diesel engines are attractive thanks to good performance in terms of fuel consumption, drivability, power output and efficiency. Nevertheless in the last years, increasing restrictions have been imposed to particulate emissions, concerning both mass (PM) and number (PN). Different technologies have been proposed to meet emissions standards and the wall-flow Diesel Particulate Filter (DPF) is currently the most common after-treatment system used to trap PM from the exhaust gases. This technology exhibits good features such that it can be regenerated to remove any accumulation of PM. However, this process involves oxidation of the filtered PM at a high temperature through after and post fuel injection strategies, which results in an increase of fuel consumption and may lead to physical damages of the filter in the long term. This work deals with the experimental testing of a catalytic silicon carbide (SiC) wall flow DPF, aiming at decreasing the soot oxidation temperature.
Technical Paper

Driving Cycle and Elasticity Manoeuvre Simulation of a Small SUV Featuring an Electrically Boosted 1.0 L Gasoline Engine

2019-08-15
2019-24-0070
Nowadays, the increasing trend in low voltage electrification promotes the introduction of electrified powertrain. In this context, electric boosting systems are a promising solution to improve the driveability of heavily downsized gasoline engines. The aim of this work is therefore to evaluate, through numerical simulation, the impact of different (12 V or 48 V) electric superchargers (eSC) on an extremely downsized 1.0 L engine in terms of vehicle performance and fuel consumption over different driving cycles. The virtual test rig developed for the analysis integrates a vehicle model representative of a B-SUV segment car with a 1-D CFD fast-running engine model representative of a 1.0 L state-of-the-art gasoline engine, equipped with a dual boost charging system, featuring an eSC in series with the main turbocharger. Vehicle performances were evaluated in terms of vehicle elasticity manoeuvers and in terms of CO2 emissions for type approval and RDE driving cycles.
Technical Paper

Performance and emissions of an advanced multi-cylinder SI engine operating in ultra-lean conditions

2019-08-15
2019-24-0075
Along the design process of a new engine, the calibration phase at the test bench usually involves a relevant percentage of the overall time-to-market. Each control variable, in fact, needs to be properly selected to optimize the performance and emissions, complying with thermal and mechanical stresses limits of the engine. This issue is still more critical for advanced engine architectures, which include additional control variables, such as valve phasing, turbocharger control, EGR level, etc. The aim of this work is the development of a numerically performed calibration procedure, applied to a prototype multi-cylinder Spark Ignition (SI) engine, designed to operate at very lean mixtures. To this aim, an active Pre-Chamber ignition system is considered. The required air flow rate is indeed provided by a Low-Pressure (LP) variable geometry turbocharger group, coupled to a high-pressure e-compressor.
Technical Paper

Description and Application Exercises of an Integrated Complete Engine Performance and Thermal model

2019-08-15
2019-24-0077
In the pursuit of more efficient high performance ICE the interactions between the gas-exchange, the combustion process and the engine thermal behavior becomes increasingly important. This is particularly challenging when aiming simultaneously for high specific power, requiring high cooling effects, and low fuel consumption, requiring appropriate management of the limited heat available at engine part loads. Furthermore, engine ordinary use, in both conventional and hybrid implementations, includes warm-up processes which affect both fuel consumption and emissions and therefore need to be accounted for. In this work a complete detailed engine performance model is integrated with a complete engine thermal model. The integration process and the resulting model are studied in detail. Firstly, the interaction between the models is evaluated by comparing the difference between the results of the models run as standalone with the ones of the integrated model.
Technical Paper

Validation of Using a Steady-State Friction Model for Determining CO2 Emissions in Transient Driving Cycles

2019-08-15
2019-24-0054
MAHLE is conducting extensive parameter studies regarding friction savings on the piston group of fired gasoline and diesel engines to further increase the efficiency of the internal combustion engine. For each tested piston variant, steady-state fired friction measurements are taken across the entire operating range of the engine using the indication method. Based on these measurements, an empirical model is created which describes the Friction Mean Effective Pressure (FMEP) depending on engine speed, engine load and coolant and oil temperature. The friction map is then used in a drive cycle simulation in order to determine fuel consumption and CO2 emissions. A drive cycle corresponds to transient conditions both as a result of the changes in operating point and the engine warm-up. The current legislative drive cycles aim to better reflect real-world driving conditions and thus contain frequent and steep transient events.
Technical Paper

Study of Friction Optimization Potential for Lubrication Circuits of Light-duty Diesel Engines

2019-08-15
2019-24-0056
Over the last two decades, engine research has been mainly focused on reducing fuel consumption in view of compliance with stringent homologation targets and customer expectations. As it is well known, the objective of overall engine efficiency optimization can be achieved only through the improvement of each element of the efficiency chain, of which mechanical constitutes one of the two key pillars (together with thermodynamics). In this framework, the friction reduction for each mechanical subsystems has been one of the most important topics of modern diesel engine development. In particular, the present paper analyzes the lubrication circuit potential as contributor to the mechanical efficiency improvement, by investigating the synergistic impact of oil circuit design, oil viscosity characteristics (including new ultra-low formulations) and thermal management. For this purpose, a combination of theoretical and experimental tools were used.
Technical Paper

Inverted Brayton cycle as an option for waste energy recovery in turbocharged diesel engine

2019-08-15
2019-24-0060
Energy recovery in reciprocating internal combustion engines (ICE) is one of the most investigated options for the reduction of fuel consumption and GHG emissions saving in the transportation sector. In fact, the energy wasted in ICE is greater than that converted in mechanical form. The contribution associated to the exhaust gases is almost one third of the fuel energy, calling for an urgent need to be recovered into mechanical form. An extensive literature is oriented toward this opportunity, strongly oriented to ORC (Organic Rankine Cycle)-based power units. From a thermodynamic point of view, one option, not extensively explored, is certainly represented by the Inverted Brayton Cycle (IBC) concept and by the corresponding components which make possible this recovery.
Technical Paper

Fuel Consumption and Pollutant Emission Optimization at Part and Full Load of a High-Performance V12 SI Engine by a 1D Model

2019-08-15
2019-24-0080
Modern internal combustion engines show complex architectures in order to improve their performance in terms of brake torque and fuel consumption. Concerning naturally-aspirated engines, the arrangement of intake and exhaust systems is crucial to get the prescribed target. An optimization of the intake port geometry, together with the selection of a proper valve timing, allow to improve the cylinder filling and hence the performance. This possibility is enhanced by a variable valve timing, even more with unphased intake and exhaust controls. The identification of an optimal calibration strategy at test bench usually requires long and expensive experimental activities. Focusing on these aspects, numerical tools can help to support engine calibration, especially in the early design phases. In the present work, a 12-cylinder naturally aspirated spark ignition engine is investigated. In a preliminary stage, the engine is experimentally tested under full load operation.
Technical Paper

Validation of Diesel combustion models with turbulence chemistry interaction and detailed kinetics

2019-08-15
2019-24-0088
Detailed and fast combustion models are necessary to support design of Diesel engines with low emission and fuel consumption. Over the years, the important of turbulence chemistry interaction to correctly describe the diffusion flame structure was demonstrated by a detailed assessment with optical data from constant-volume vessel experiments. The main objective of this work is to carry out an extensive validation of two different combustion models which are suitable for the simulation of Diesel engine combustion. The first one is the Representative Interactive Flamelet model (RIF) employing direct chemistry integration. A single flamelet formulation is generally used to reduce the computational time but this aspect limits the capability to reproduce the flame stabilization process. To overcome such limitation, a second model called tabulated flamelet progress variable (TFPV) is tested in this work.
Technical Paper

Potential of 1D Thermo-Fluid Dynamic Modeling in Reducing the Experimental Effort through the comparison of the achievable calibration performance

2019-08-15
2019-24-0013
Over the last decades, internal combustion engines have undergone a continuous evolution to achieve better performance, lower pollutant emissions and fuel consumption. This evolution involved changes in the engine architecture needed to perform advanced management strategies. Therefore, Variable Valve Actuation, Exhaust Gas Recirculation, Gasoline Direct Injection, turbocharging and powertrain hybridization have wide application in the automotive field. However, the effective management of a such complex system is due to the contemporaneous development of the on-board engine electronic control unit (EECU). In fact, the additional degrees of freedom available for the engine regulation highly increased the complexity of engine control and management, resulting in a very expensive and long calibration process. To overcome the drawbacks related to extensive calibration process, this study proposes an effective methodology based on the adoption of 1D thermo-fluid dynamic modelling.
Technical Paper

Emissions Optimization Potential of a Diesel Engine Running on HVO: A Combined Experimental and Simulation Investigation

2019-08-15
2019-24-0039
The present work investigates some recalibration possibilities of a 1.4l common rail turbo-charged diesel engine for the optimal operation in terms of emissions and fuel consumption (FC) with pure Hydrotreated Vegetable Oil (HVO). Initially, steady-state experimental data with nominal engine settings revealed HVO benefits as a drop-in fuel. Under these conditions, pure HVO is associated with lower engine out PM (up to 75%) and CO2 (up to 10%) emissions, and lower mass-based FC (up to 9%), while NOx are similar or slightly higher to diesel fuel. At the next step, a combustion model was developed for the particular engine targeting to identify the optimal IT (Injection Timing) and EGR settings for further emissions (PM, NOx and CO2) and FC reduction with pure HVO. For this purpose, four re-adjusted IT and EGR maps were developed with both conventional diesel and HVO.
Technical Paper

The effect of post injection coupled with extremely high injection pressure on combustion process and emission formation in an off-road diesel engine: a numerical and experimental investigation.

2019-08-15
2019-24-0092
In this paper, a numerical and experimental assessment of post injection potential for soot emissions mitigation in an off-road diesel engine is presented, with the aim of supporting hardware selection and engine calibration processes. As a case study, a prototype off-road 3.4 liters 4-cylinder diesel engine developed by Kohler Engines was selected. In order to comply with Stage V emission standards without a dedicated aftertreatment for NOx, the engine was equipped with a low pressure cooled EGR, allowing high EGR rates (above 30%) even at high load. To enable the exploitation of such high EGR rates with acceptable soot penalties, a two stage turbocharger and an extremely high pressure fuel injection system (up to 3000 bar) were adopted. Moreover, post injections events were also exploited to further mitigate soot emissions with acceptable Brake Specific Fuel Consumption (BSFC) penalties.
Technical Paper

CFD modeling of combustion and soot formation in gasoline direct-injection engines

2019-08-15
2019-24-0095
Gasoline, direct injection engines represent one of the most widely adopted powertrains for passenger cars. However, further development efforts are necessary to meet the future fuel consumption and emission standards imposing an efficiency increase and a reduction of particulate matter emissions. Within this context, computational fluid dynamics is nowadays a consolidated tool to support engine design and development and this work is focused on the development of a set of CFD models for the prediction of combustion and soot formation in modern GDI engines. The one-equation Weller model coupled with a zero-dimensional approach to handle initial flame kernel growth was applied to predict flame propagation. Soot formation was described with a semi-empirical, two-equation model accounting for the most important steps such as nucleation, surface growth, coagulation and oxidation.
Technical Paper

Analysis of Water Injection Strategies to Exploit the Thermodynamic Effects of Water in Gasoline Engines by Means of 3D-CFD Simulations

2019-08-15
2019-24-0102
CO2 emission constraints taking effect from 2020 lead to further investigate technologies to lower knock sensitivity of gasoline engines, main limiting factor to increase engine efficiency and thus reduce fuel consumption. Moreover the RDE cycle demands for higher power operation, where fuel enrichment is needed for component protection. To achieve high efficiency, the engine should be run at stoichiometric conditions in order to have better emission control and reduce fuel consumption. Among others, water injection is a promising technology to improve engine combustion efficiency and to keep high conversion rates of the TWC over the whole engine map. The comprehension of multiple thermodynamic effects of water injection through 3D-CFD simulations and their exploitation to enhance the engine combustion efficiency is the main purpose of the analysis.
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