Development of a Lumped Model for the Characterisation of the Intake Phase in Spark-ignition Internal Combustion Engines

Abstract The present work aims to develop a control-oriented lumped model to investigate the fluid dynamic behaviour of multi-valve spark-ignition engines (ICEs). Specifically, the attention has been focused on the intake phase and in-cylinder air charge estimation. To this purpose, a spark-ignition engine has been characterised at a flow rig in terms of flow coefficients. The experimental data have been used to define the fluid dynamic behaviour of the different intake system components and to calibrate and validate the proposed model that has been developed in Matlab/Simulink environment. Furthermore, in order to evaluate the capability of the zero-dimensional code and to estimate the instantaneous in-cylinder mass flow in different operating conditions, the numerical data have been compared to the results of a one-dimensional commercial software. The comparison between numerical and experimental data shows a good agreement. The investigation highlights that the proposed control-oriented lumped model represents a useful and simple tool to evaluate the engine breathability and to define the proper valve timing

Acoustic Optimization of an Intake System by Means of Geometry CAD Modifications

Abstract The intake system of internal combustion engines represents the most prominent noise source at high load and low vehicle speeds because of the de-throttling strategies which are realized in order to maximize the cylinders filling. Therefore, a good acoustic performance of intake systems represents a very important challenge in order to respect the overall noise emission, according to the more strict European standards. In general, the most used method for characterizing the acoustic performances of a system is represented by the Transmission Loss computation. In this study, a 3D numerical analysis by using the Finite Element Method onan intake system for a commercial spark ignition engine has been exploited for the Transmission Loss calculation. The numerical findings of the finite element model have been validated by means of experimental investigations. A very good agreement between numerical and experimental data has been reached. For this reason, an optimization procedure, by implementing different CAD modifications on the system, has been investigated, as well. All the foreseen geometry changes do not modify the overall size of the original system

Development of combustion models for RANS and LES applications in SI engines

Prediction of flow and combustion in IC engines remains a challenging task. Traditional Reynolds Averaged Navier Stokes (RANS) methods and emerging Large Eddy Simulation (LES) techniques are being used as reliable mathematical tools for such predictions. However, RANS models have to be further refined to make them more predictive by eliminating or reducing the requirement for application based fine tuning. LES holds a great potential for more accurate predictions in engine related unsteady combustion and associated cycle-tocycle variations. Accordingly, in the present work, new advanced CFD based flow models were developed and validated for RANS and LES modelling of turbulent premixed combustion in SI engines. In the research undertaken for RANS modelling, theoretical and experimental based modifications have been investigated, such that the Bray-Moss-Libby (BML) model can be applied to wall-bounded combustion modelling, eliminating its inherent wall flame acceleration problem. Estimation of integral length scale of turbulence has been made dynamic providing allowances for spatial inhomogeneity of turbulence. A new dynamic formulation has been proposed to evaluate the mean flame wrinkling scale based on the Kolmogorov Pertovsky Piskunow (KPP) analysis and fractal geometry. In addition, a novel empirical correlation to quantify the quenching rates in the influenced zone of the quenching region near solid boundaries has been derived based on experimentally estimated flame image data. Moreover, to model the spark ignition and early stage of flame kernel formation, an improved version of the Discrete Particle Ignition Kernel (DPIK) model was developed, accounting for local bulk flow convection effects. These models were first verified against published benchmark test cases. Subsequently, full cycle combustion in a Ricardo E6 engine for different operating conditions was simulated. An experimental programme was conducted to obtain engine data and operating conditions of the Ricardo E6 engine and the formulated model was validated using the obtained experimental data. Results show that, the present improvements have been successful in eliminating the wall flame acceleration problem, while accurately predicting the in-cylinder pressure rise and flame propagation characteristics throughout the combustion period. In the LES work carried out in this research, the KIVA-4 RANS code was modified to incorporate the LES capability. Various turbulence models were implemented and validated in engine applications. The flame surface density approach was implemented to model the combustion process. A new ignition and flame kernel formation model was also developed to simulate the early stage of flame propagation in the context of LES. A dynamic procedure was formulated, where all model coefficients were locally evaluated using the resolved and test filtered flow properties during the fully turbulent phase of combustion. A test filtering technique was adopted to use in wall bounded systems. The developed methodology was then applied to simulate the combustion and associated unsteady effects in Ricardo E6 spark ignition engine at different operating conditions. Results show that, present LES model has been able to resolve the evolution of a large number of in-cylinder flow structures, which are more influential for engine performance. Predicted heat release rates, flame propagation characteristics, in-cylinder pressure rise and their cyclic variations are also in good agreement with measurements

Characterisation of flow structures inside an engine cylinder under steady state condition

The in-cylinder flow of internal combustion (IC) engines, formed during the intake stroke, is one of the most important factors that affect the quality of air-fuel mixture and combustion. The inducted airflow through the inlet valve is primarily influenced by the intake port design, intake valve design, valve lift and valve timing. Such parameters have a significant influence on the generation and development of in-cylinder flow motion. In most combustion systems the swirl and tumble motions are used to aid the air-fuel mixing with the subsequent decay of these bulk flow motions generating increased turbulence levels which then enhance the combustion processes in terms of rate of chemical reactions and combustion stability. Air motion formed inside the engine cylinder is three-dimensional, transient, highly turbulent and includes a wide spectrum of length and time scales. The significance of in-cylinder flow structures is mainly reflected in large eddy formation and its subsequent break down into turbulence kinetic energy. Analysis of the large scale and flow motions within an internal combustion engine are of significance for the improvement of engine performance. A first approximation of these flow structures can be obtained by steady state analysis of the in-cylinder flow with fixed valve lifts and pressure drops. Substantial advances in both experimental methods and numerical simulations provide useful research tools for better understanding of the effects of rotational air motion on engine performance. This study presents results from experimental and numerical simulations of in-cylinder flow structures under steady state conditions. Although steady state flow problem still includes complex three-dimensional geometries with high turbulence intensities and rotation separation, it is significantly less complex than the transient problem. Therefore, preliminary verifications are usually performed on steady state flow rig. For example, numerical investigation under steady state condition can be considered as a precondition for the feasibility of calculations of real engine cylinder flow. Particle Image Velocimetry (PIV) technique is used in the experimental investigations of the in-cylinder flow structures. The experiments have been conducted on an engine head of a pent-roof type (Lotus) for a number of fixed valve lifts and different inlet valve configurations at two pressure drops, 250mm and 635mm of H2O that correlate with engine speeds of 2500 and 4000 RPM respectively. From the 2-D in-cylinder flow measurements, a tumbling vortex analysis is carried out for six planes parallel to the cylinder axis. In addition, a swirl flow analysis is carried out for one horizontal plane perpendicular to the cylinder axis at half bore downstream from the cylinder head (44mm). Numerically, modelling of the in-cylinder flow is proving to be a key part of successful combustion simulation. The numerical simulations require an accurate representation of turbulence and initial conditions. This Thesis deals with numerical investigation of the in-cylinder flow structures under steady state conditions utilizing the finite-volume CFD package, STAR CCM+. Two turbulence models were examined to simulate the turbulent flow structure namely, Realizable k-ε and Reynolds Stress Turbulence Model, RSM. Three densities of generated mesh, which is polyhedral type, are examined. The three-dimensional numerical investigation has been conducted on the same engine head of a pent-roof type (Lotus) for a number of fixed valve lifts and both valves are opened configuration at two pressure drops 250mm and 635mm of H2O that is equivalent to engine speeds of 2500 and 4000 RPM respectively. The nature and modelling of the flow structure together with discussions on the influence of the pressure drop and valve lift parameters on the flow structures are presented and discussed. The experimental results show the advantage of using the planar technique (PIV) for investigating the complete flow structures developed inside the cylinder. It also highlighted areas where improvements need to be made to enhance the quality of the collected data in the vertical plane measurements. Based on the comparison between the two turbulence models, the RSM model results show larger velocity values of about 15% to 47% than those of the Realizable k-ε model for the whole regions. The computational results were validated through qualitative and quantitative comparisons with the PIV data obtained from the current investigation and published LDA data on both horizontal and vertical cross sections. The calculated correlation coefficient, which is above 0.6, indicated that a reasonable prediction accuracy for the RSM model. This verifies that the numerical simulation with the RSM model is a useful tool to analyse turbulent flows in complex engine geometries where anisotropic turbulence is created

Powertrain Systems for Net-Zero Transport

The transport sector continues to shift towards alternative powertrains, particularly with the UK Government’s announcement to end the sale of petrol and diesel passenger cars by 2030 and increasing support for alternatives. Despite this announcement, the internal combustion continues to play a significant role both in the passenger car market through the use of hybrids and sustainable low carbon fuels, as well as a key role in other sectors such as heavy-duty vehicles and off-highway applications across the globe. Building on the industry-leading IC Engines conference, the 2021 Powertrain Systems for Net-Zero Transport conference (7-8 December 2021, London, UK) focussed on the internal combustion engine’s role in Net-Zero transport as well as covered developments in the wide range of propulsion systems available (electric, fuel cell, sustainable fuels etc) and their associated powertrains. To achieve the net-zero transport across the globe, the life-cycle analysis of future powertrain and energy was also discussed. Powertrain Systems for Net-Zero Transport provided a forum for engine, fuels, e-machine, fuel cell and powertrain experts to look closely at developments in powertrain technology required, to meet the demands of the net-zero future and global competition in all sectors of the road transportation, off-highway and stationary power industries

A study of flame development with isooctane alcohol blended fuels in a optical spark ignition engine

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel UniversityThe work was concerned with experimental study of the turbulent flame development process of alcohol fuels, namely ethanol and butanol, in an optically accessed spark ignition research engine. The fuels were evaluated in a single cylinder engine equipped with full-bore overhead optical access operated at typical stoichiometric part-load conditions with images captured using high-speed natural light imaging techniques (or chemiluminescence). The differences in flame development between the fuels was analysed to understand better the impact of high and low alcohol content fuels on combustion. Advanced image analysis, in conjunction with Ricardo WAVE simulation, allowed for the conclusion that the faster burning exhibited by ethanol was the result of the marginally higher laminar burning velocity providing a faster laminar burn phase and accelerating the flame into the turbulent spectrum thus reducing bulk flame distortion and better in-cylinder pressure development. Such physical reactions are often over-looked in the face of chemical differences between fuels. A further study into the variation of maximum in-cylinder pressure values was conducted focussing on iso-octane and ethanol. This study identified two phenomena, namely “saw-toothing” and “creep” in which cluster of cycles feed into one another. From this it became clear that the presence of high pressure during the exhaust process had a large influence on the following cycles. This is another often overlooked phenomenon of direct cycle-to-cycle variation whereby incylinder pressures during blowdown can dictate the duration, load or stability output of the following cycle. Finally the work investigated the impact on flame development of alcohol fuels when the overlap duration was altered. While the engine produced counterintuitive figures of residual gas, ethanol was confirmed as having greater synergy with EGR by displaying less impacted combustion durations c.f. iso-octane. Care should be taken however when analysing these results due to the unique valve configuration of the engine.Thomas Gerald Gray Charitable Trust Scholarship Scheme and from the School of Engineering and Desig

Simulation and numerical modelling of three-phase flow in automotive high-pressure fuel injectors

In the last 20 years the automotive industry has managed an impressive reduction in emissions, in agreement to relevant regulations. One key component in achieving lower emissions is the fuel injector nozzle. This PhD Thesis aims to present an experimentally validated computational fluid dynamics (CFD) method able to better describe the flow developing inside Diesel and gasoline fuel direct injection nozzles. The compressible Navier-Stokes equations are numerically solved considering the vertical motion of the injector’s needle valve. A homogenous three-phase (liquid, vapour and air) barotropic equation of state linking the variation of density and pressure is implemented into the utilised flow solver. This model is able to capture cavitation and its collapse as well as the air entrainment inside the injector taking place in between successive injection events. The flow turbulence is modelled using LES, in order to better understand the details of the physical processes, and URANS, as a suitable method for industry product development time scales and the available CPU resources. For the case of Diesel fuel injection, highspeed visualisations of a transparent nozzle tip replica are used to validate the proposed methodology. The numerical simulations describe the interaction between the vortex flow and cavitation formation that take place simultaneously with air entrainment from the surrounding environment into the injector’s sac volume during the injection and the dwell time between successive injections. The experimentally observed flow phenomena are well predicted by the simulation model, namely, the compression of pre-existing air bubbles inside the injector’s sac volume during the injector opening, cavitation vapour condensation and air suction after the needle closure. In the case of Gasoline direct injection (GDi) nozzles operated with ethanol (E100) fuel, emphasis is put on the prediction of erosion sites. E100 represents a challenge to the durability of the fuel injection system components since it can result in corrosion which is further enhanced by cavitation induced erosion as a result of the collapse of vapour structures. CFD predictions for both the flow development and the locations prone to cavitation erosion inside GDi injectors are reported. The CFD simulations predict the flow structures leading to the observed erosion locations in the nozzle. Three cavitation erosion indices reported in literature are evaluated against new experimental data of erosion damage. Scanning electron microscope erosion images are found to correlate well with the accumulated erosive power predicted by the simulation

Powertrain Systems for Net-Zero Transport

The transport sector continues to shift towards alternative powertrains, particularly with the UK Government’s announcement to end the sale of petrol and diesel passenger cars by 2030 and increasing support for alternatives. Despite this announcement, the internal combustion continues to play a significant role both in the passenger car market through the use of hybrids and sustainable low carbon fuels, as well as a key role in other sectors such as heavy-duty vehicles and off-highway applications across the globe. Building on the industry-leading IC Engines conference, the 2021 Powertrain Systems for Net-Zero Transport conference (7-8 December 2021, London, UK) focussed on the internal combustion engine’s role in Net-Zero transport as well as covered developments in the wide range of propulsion systems available (electric, fuel cell, sustainable fuels etc) and their associated powertrains. To achieve the net-zero transport across the globe, the life-cycle analysis of future powertrain and energy was also discussed. Powertrain Systems for Net-Zero Transport provided a forum for engine, fuels, e-machine, fuel cell and powertrain experts to look closely at developments in powertrain technology required, to meet the demands of the net-zero future and global competition in all sectors of the road transportation, off-highway and stationary power industries

THIESEL 2022. Conference on Thermo-and Fluid Dynamics of Clean Propulsion Powerplants

The THIESEL 2022. Conference on Thermo-and Fluid Dynamic Processes in Direct Injection Engines planned in Valencia (Spain) for 8th to 11th September 2020 has been successfully held in a virtual format, due to the COVID19 pandemic. In spite of the very tough environmental demands, combustion engines will probably remain the main propulsion system in transport for the next 20 to 50 years, at least for as long as alternative solutions cannot provide the flexibility expected by customers of the 21st century. But it needs to adapt to the new times, and so research in combustion engines is nowadays mostly focused on the new challenges posed by hybridization and downsizing. The topics presented in the papers of the conference include traditional ones, such as Injection & Sprays, Combustion, but also Alternative Fuels, as well as papers dedicated specifically to CO2 Reduction and Emissions Abatement.Papers stem from the Academic Research sector as well as from the IndustryXandra Marcelle, M.; Payri Marín, R.; Serrano Cruz, JR. (2022). THIESEL 2022. Conference on Thermo-and Fluid Dynamics of Clean Propulsion Powerplants. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thiesel.2022.632801EDITORIA