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Technical Paper

Development and Validation of a Control-Oriented Analytic Engine Simulator

2019-08-15
2019-24-0002
Due to the recent anti-pollution policies, the performance increase in Spark Ignition (SI) engines is currently under the focus of automotive manufacturers. This trend drives the control systems designers to investigate accurate solutions and build more sophisticated algorithms to increase the efficiency of this kind of engines. The development of a control strategy is composed by several phases and steps, and the first part of such process is typically spent to define and validate the logic of the strategy. During this phase a light engine simulator is particularly useful, since it allows producing robust combustion synthetic data with a low calibration and computational effort. In the first part of this paper the description of a control-oriented analytic engine simulator (ANESIM) is carried out.
Technical Paper

Intake manifold primary trumpet tuning options for fuel flow limited high performance ICEs

2019-08-15
2019-24-0005
The 2014 change in Formula 1 power units, from naturally aspirated to highly-downsized and heavily-boosted hybridized power units led to a relevant increase of the internal combustion engine brake specific power output in comparison with former V-8 units. The newly designed “down-sized” engines are characterized by a fuel flow limitation and relevant increase in the thermal loads acting on the engine components, in particular on those facing the combustion chamber. Furthermore, efficiency becomes an equivalent paradigm as performance. In the power unit layout, the air path is defined by the compressor, the intercooler and the piping from the intake plenum to the cylinder. Intake duct length is defined from intake plenum to valve seat and it is a key parameter for engine performance.
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

CFD analysis and knock prediction within the crevices of piston to liner fireland of a high performance I.C.E.

2019-08-15
2019-24-0006
The paper aims at defining a methodology for the prediction and understanding of knock tendency in internal combustion engine piston crevices by means of CFD simulations. The motivation for the analysis comes from a real design requirement which appeared during the development of a new high performance SI unit: it is in fact widely known that, in high performance engines (especially the turbocharged ones), the high values of pressure and temperature inside the combustion chamber during the engine cycle may cause knocking phenomena. “Standard” knock can be easily recognized by direct observation of the in-cylinder measured pressure trace; it is then possible to undertake proper actions and implement design and control improvements to prevent it with relatively standard 3D-CFD analyses.
Technical Paper

Numerical Investigation of Multiple-Injection Strategies of Methanol in a DICI HD Optical Engine

2019-08-15
2019-24-0007
Methanol fuel is a genuine candidate on the alternative fuel market for internal combustion engines within heavy-duty transportation sector. The thermo-physical properties of methanol allow to achieve high thermodynamic efficiency and low emission levels with a good margin below the EURO VI standard using compression ignition (CI) engines with advanced injection strategies. However, due to a low stoichiometric air/fuel ratio and a high latent heat of vaporization there are two challenges that can be mentioned; (a) the tendency to a high pressure rise rate due to the rapid chemical kinetic driven ignition process and, (b) the required high inlet temperature to initiate compression ignition event. These challenges can be tackled for instance by employing multiple-injection strategies, which reduces both the maximal pressure rise rate and the demand on the high inlet temperature.
Technical Paper

CFD Investigation of the Effects of Gas’ Methane Number on the Performance of a Heavy-Duty Natural-Gas Spark-Ignition Engine

2019-08-15
2019-24-0008
Natural gas (NG) is an alternative fuel for spark-ignition engines. In addition to its cleaner combustion, recent breakthroughs in drilling technologies increased its availability and lowered its cost. NG consists of mostly methane, but it also contains heavier hydrocarbons and inert diluents, the levels of which vary substantially with geographical source, time of year, and treatments applied during production or transportation. To investigate the effects of NG composition on engine performance and emissions, a 3D CFD model of a heavy-duty diesel engine retrofitted to spark ignition operations simulated engine operation under lean-combustion, low-speed, and medium load conditions. To eliminate the effect of different gas energy density, three NG blends of similar lower heating value but different H/C ratio have been investigated at fixed spark timing.
Technical Paper

Effects of In-cylinder flow structures on soot formation and oxidation in a swirl-supported light-duty diesel engine

2019-08-15
2019-24-0009
In this paper, computation fluid dynamics (CFD) simulations are performed to describe the effect of in-cylinder flow structures on the formation and oxidation of soot in a swirl-supported light-duty diesel engine. The focus of the paper is on the effect of swirl motion and injection pressure on late cycle soot oxidation. The structure of the flow at different swirl numbers is studied to investigate the effect that varying swirl number imposes on the coherent flow structures. These coherent flow structures are studied to understand the mechanism that leads to efficient soot oxidation in late cycle. Effect of varying injection pressure at different swirl numbers and the interaction between spray and swirl motions are discussed. The complexity of diesel combustion, especially when soot and other emissions are of interest, requires using a detailed chemical mechanism to have a correct estimation of temperature and species distribution.
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

A Computationally Efficient Progress Variable Approach for In-Cylinder Combustion and Emissions Simulations

2019-08-15
2019-24-0011
The use of complex reaction schemes is accompanied by high computational cost in 3D CFD simulations but is particularly important to predict pollutant emissions in in-cylinder simulations. One solution to tackle this problem is to use tabulated chemistry. The approach presented herein combines pre-tabulated progress variable-based source terms for auto-ignition as well as soot and NOx source terms for advanced emission predictions. The method is coupled to CONVERGE v2.4 via user-coding and tested over various speed and load passenger-car Diesel engine conditions. This work includes the comparison between the combustion progress variable (CPV) model and the on-line chemistry solver in CONVERGE 2.4. Both models are also compared against experimental data by means of combustion and emission parameters. A detailed mechanism comprising 190 species, having n-decane/α-methyl-naphthalene as main fuels, is used for both on-line and tabulated chemistry simulations.
Technical Paper

MULTI-LEVEL MODELING OF REAL SYNGAS COMBUSTION IN A SPARK IGNITION ENGINE AND EXPERIMENTAL VALIDATION

2019-08-15
2019-24-0012
Syngas produced from biomass gasification is being increasingly considered as a promising alternative to traditional fuels in Spark-Ignition (SI) Internal Combustion Engines (ICEs). This gaseous fuel, composed by a mixture of CO, CH4, H2, CO2, N2 (and other minor hydrocarbon compounds), is however characterized by an extreme variability of its composition and a low energy density. In order to assure good energy performance and stability of operation as the syngas composition slightly changes, numerical modeling can give an important contribution as a tool to investigate the main parameters affecting the combustion process development and the formation of main pollutants. The present work introduces a multi-level set of numerical approaches to a SI ICE fueled with syngas deriving from biomass gasification.
Technical Paper

Experimental Validation of a Model-based Water Injection Combustion Control System for On-board Application

2019-08-15
2019-24-0015
Water Injection (WI) has become a key technology for increasing combustion efficiency in modern GDI turbocharged engines. In fact, the addition of water mitigates significantly the occurrence of knock, reduces exhaust gas temperatures, and opens the possibility to reach optimum heat release phasing even at high load. This work presents the latest development of a model-based WI controller, and its experimental validation on a GDI TC engine. The controller is based on a novel approach that involves an analytic combustion model to define the SA required to reach a combustion phase target, considering injected water mass effects. The model has been expanded to directly consider air-to-fuel ratio variation effects on combustion phasing, and the same controller structure could integrate other variables that influence 50 percent of Mass Fraction Burned angular position (MFB50), such as EGR.
Technical Paper

Cylinder Pressure based Method for In-Cycle Pilot Misfire Detection

2019-08-15
2019-24-0017
For the reduction of emissions and combustion noise in a internal combustion Diesel engine, multiple injections are normally used. A pilot injection reduces the ignition delay of the main injection and hence the combustion noise. However, normal variations of the operating conditions, component tolerances and aging may result in the lack of combustion (misfire) or even the lack of injection (miss-injection) for short on-times. The result is a lower indicated thermal efficiency, higher emissions and louder combustion noise. Closed-loop combustion control techniques aim to monitor in real-time these variations and act accordingly to counteract their effect. To ensure the in-cycle controllability of the main injection, the misfire diagnosis must be performed before the start of the main injection. This paper focuses on the development and evaluation of in-cycle algorithms for the pilot misfire detection.
Technical Paper

Learning based MPC control of combustion timing in Multi-Cylinder Partially Premixed Combustion Engine

2019-08-15
2019-24-0016
Partially Premixed Combustion has shown to be a promising advanced combustion mode for future engines in terms of efficiency and emission levels. The combustion timing should be suitably phased to realize high efficiency. However, a simple map-based feed-forward control method is not sufficient for controlling the combustion during transient operation. This article proposes one learning-based model predictive control (MPC) approach to achieve controllability and feasibility. Since PPC engines could have unacceptably high pressure-rise rates at different operation points, triple injection is applied as a solvent, with the use of two pilot fuel injection. The controller utilizes the main injection timing to manage the combustion timing, and the first and second injection timing is considered as a function of the engine load and speed. The cylinder pressure is used as the combustion feedback.
Technical Paper

Evaluation of water and EGR effects on combustion characteristics of GDI engines using a chemical kinetics approach

2019-08-15
2019-24-0019
The modern spark ignition engines, due to the introduced strategies for limiting the consumption without reducing the power, are sensitive to both the detonation and the increase of the inlet turbine temperature. In order to reduce the risk of detonation, the use of dilution with the products of combustion (EGR) is an established practice that has recently was improved with the use of water vapour obtained via direct or indirect injection. The application and optimization of these strategies cannot ignore the knowledge of physical quantities characterizing the combustion such as the laminar flame speed and the ignition delay, both are an intrinsic property of the fuel and are function of the mixture composition (mixture fraction and dilution) and of its thermodynamic conditions. The experimental measurements of the laminar flame speed and the ignition delay available in literature, rarely report the effects of dilution by EGR or water vapor.
Technical Paper

Experimental and numerical analysis of a pre-chamber turbulent jet ignition combustion system

2019-08-15
2019-24-0018
The growing demand for more efficient and less polluting internal combustion engine has pushed the development of non-conventional ignition systems. One of the most promising techniques appears to be the so-called Pre-Chamber initiated Turbulent Jet Ignition Combustion system in which a jet of hot combusting gasses is employed to initiate the combustion in the main chamber. In the present study, the combustion process related to this ignition system has been experimentally investigated in an optically accessible single cylinder Spark-Ignition engine. The pre-chamber was composed of a gas injector and a miniaturized spark-plug, embedded in a small annular chamber connected to the cylinder through a 4 holes pipette. A small amount of methane is injected within the pre-chamber for initiating the combustion. The flame reaches the combustion chamber through the four narrow orifices and rapidly consumes a homogeneous mixture of port injected gasoline and air.
Technical Paper

Computational Chemistry Consortium: surrogate fuel mechanism development, pollutants submechanisms and components library.

2019-08-15
2019-24-0020
The Computational Chemistry Consortium (C3) is dedicated to leading the advancement of combustion and emissions modeling in internal combustion engines. The C3 cluster combines the expertise of different groups involved in combustion research aiming to refine existing chemistry models and to develop more efficient tools for the generation of surrogate and multi-fuel mechanisms, and suitable mechanisms for CFD applications. In addition to the development of more accurate kinetic models for different components of interest in real fuels’ surrogates and for pollutants formation (NOx, PAHs, soot), the core activity of C3 is to develop a tool capable of merging high fidelity kinetics from different sources (i.e. different partners), resulting in a high-fidelity model for a specific application.
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 and numerical investigation of the maximum pressure rise rate for an LTC concept in a single cylinder CI engine

2019-08-15
2019-24-0023
In the foreseeable future, the transportation sector will continue to rely on internal combustion engines. Therefore, reduction of engine-out emissions and increase in engine efficiency are important goals to meet future legislative regulations and restricted fuel resources. One viable option, which provides lower peak temperatures and increased mixture homogeneity and thus simultaneously reduces nitric oxide as well as soot, is a low-temperature combustion (LTC) concept. However, this might result in an increase of unburnt hydrocarbon, carbon monoxide, and combustion noise due to early combustion phasing and lower engine efficiency. Various studies show that these drawbacks can be compensated by advanced injection strategies, e.g. by employing multiple injections. The aim of this work is to identify the optimum injection strategy, which enables a wide range of engine operating points in LTC mode with reduced engine-out emissions.
Technical Paper

Potential to reduce nano-particle emission in SG-DISI engine with normal butane.

2019-08-15
2019-24-0022
Under lean stratified combustion, differed from the stoichiometric homogeneous charge combustion, flame could propagate through extremely rich air-fuel mixture. The rich mixture causes considerable amount of particulate matter, but, due to large effect of efficiency improvement, the attractive point is on fuel economy compare to homogeneous charge SI combustion. The easiest way to reduce particulate matter is changing fuel to gaseous hydrocarbon, to minimize evaporating and mixing period. In this study, to reduce the particulate emission and to develop the way to mitigation of emission, the emission data of particulate under low and medium-low load conditions from normal butane fueled research engine are dealt to optimize combustion strategies, with respect to injection and ignition. Especially, particulate number density were collected in the research engine, and the causes of particulate formation were speculated with visualized combustion data.
Technical Paper

Study of fuel octane sensitivity effects on gasoline partially premixed combustion using optical diagnostics

2019-08-15
2019-24-0025
Partially premixed combustion (PPC) is a low-temperature combustion (LTC) concept that could deliver higher engine efficiency, as well as lower NOx and soot emissions. Gasoline-like fuels are beneficial for air/fuel mixing process under PPC mode because they have superior auto-ignition resistance to prolong ignition delay time. In current experiments, the high octane number gasoline fuel E10 (US market used gasoline, RON=91) and low octane number GCI blend fuel (RON=77) were tested respectively in a full-transparent AVL single cylinder optical compression ignition (CI) engine. Aiming at investigating the fuel sensitivity on engine performances under different combustion modes as well as soot particle emissions, the engine operating parameters and emission data were analyzed from CI to HCCI (homogeneous charge compression ignition) via PPC (partially premixed combustion) by changing fuel injection timing.
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