PhD Research Project Proposal
“CFD Modelling of Down-Sized GDI Engines: an Investigation of Control Strategies for
Fuel Economy and Minimisation of Soot Emissions”
Dr Fabrizio Bonatesta
Department of Mechanical Engineering and Mathematical Sciences
Oxford Brookes University
Introduction
The wider adoption of the Gasoline Direct Injection (GDI) engine is threatened by ever more stringent limits on Particulate Matter (PM) emissions. The development and optimisation of engine and combustion control strategies to effectively minimise the production of soot, must carefully consider the co-existing effects on engine thermal efficiency and fuel economy. In
GDI engines, thermal efficiency appears to be constrained by pumping losses and incomplete cylinder filling; auto-ignition and knock tendency are further crucial issues especially in down-sized, high power-density platforms. The Variable Valve Timing (VVT) technology has been demonstrated to have a sizeable influence on fuel efficiency; VVT in combination with external Exhaust Gas Recirculation (EGR) may also serve the purpose of combustion optimisation for the reduction of PM formation. Multi-dimensional engine modelling can be used effectively to assess such influences on in-cylinder soot formation and to determine whether soot reduction and improved efficiency can be gained simultaneously across the wider engine running envelope. The proposed research project will contribute towards an improved understanding of PM mechanisms in modern downsized GDI engines. The project will investigate potential approaches to gain efficiency savings from existing technologies, and to delay or avoid the prospect of adoption of
Gasoline Particulate Filters.
Background and Project Goals
The main aim of the proposed PhD programme is to develop a comprehensive
Computational Fluid Dynamics (CFD) model of a modern gasoline direct injection engine, which includes reliable mechanisms for soot production and which can be used for engine strategy optimisation.
At present, very limited work has been published in the area of modelling soot formation in gasoline direct injection engines [1-4]. The techniques developed and results presented are not satisfactory in terms of both models reliability and transportability. The subject area is new as only recently consumers and organisations have realised the hazardousness of ultrafine particulate matter emissions from GDI engines [5]; moreover, there are inherent difficulties associated to modelling GDI in-cylinder processes [6], as well as to extending soot models originally developed for diesel combustion to GDI theoretically-homogeneous combustion [3, 4].
In recent years, research staff at the Department of Mechanical Engineering and
Mathematical Sciences has worked in the field of GDI engine modelling using CFD software
Star-CD. The work has focused on combustion modelling using the ECFM-3Z model [7], and on in-cylinder soot mechanisms using the Soot Sectional Method [8]. The proposed PhD research work aims
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to extend the previous work to cover the latest engine technology currently being developed by engine manufacturers world-wide. The project will focus on modelling a EURO 6 GDI engine, featuring spray-guided technology, which reportedly brings measurable advantages in terms of soot formation [9]. Specific engine strategies will be investigated, which combine
VVT technology and external EGR to minimised soot production and increase thermal efficiency. The project will implement the latest ECFM-CLEH Enthalpy-Limited combustion models [8], enabling full customisation of the Soot Sectional Method to deliver useful models of soot particle mass, size and number density distributions. The proposed research work has potentials to define the state-of-the-art in soot modelling in modern gasoline direct injection engines; the project will facilitate the establishment of long-term industrial collaborations, as well as leading to research council and EU bids for funding of a type that require established capabilities and appropriate under-pinning research.
Project Description
Full-cycle CFD models of a Ford spray-guided GDI engine will be developed from CAD models and experimental engine data will be used as input and boundary conditions for the simulations, and for calibration purposes. The simulations will include fuel spray, spray-wall interaction and liquid film formation, air-fuel mixture preparation, combustion and soot formation/oxidation modelling. An initial set of calibrated simulations will then be modified to examine the effects of VVT and external EGR on fuel efficiency, according to a strategic map of operating points to reflect real-world drive cycles. The effects on soot formation and emission will be investigated in parallel, via customisation and calibration of the Soot
Sectional Method. The examined engine strategies will incorporate conventional VVT and external EGR settings, but the flexibility of the simulation environment will enable exploring extreme settings beyond what is currently feasible experimentally. The CFD work will be supported by parallel experimental projects carried out on a fully-instrumented Ford 3cylinder Eco-Boost engine available at OBU. Engine-out, size-resolved, soot particles number density distributions will be acquired using the Differential Mobility Spectrometer
DMS-500 by Cambustion and also used to support the investigation.
Deliverables
This project has three main deliverables:
1. Creation of calibrated CFD models of the complete cycle of a spray-guided down-sized
GDI engine;
2. Assessment of the combined influence of VVT and external EGR on soot formation and emission, as well as on thermal efficiency;
3. Improved insight into relevant soot mechanisms and identification of engine control strategies to minimise soot emissions.
The CFD project will also deliver a comprehensive analysis of spray evolution, wall-wetting, air-fuel mixture preparation and combustion, according to a strategic map of operating points.
Project Details
The offered studentship is for a “PhD direct” research project of the duration of two years, starting in September 2015. The studentship is open only to Home/EU students who have recently completed a Master or MPhil degree in an area closely related to the proposed research topic. E xtensive
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previous research experience in the field of CFD modelling of GDI engines and soot modelling is essential.
References
1. Etheridge, J., Mosbach, S., Kraft, M., Wu, H., Collings, N. Modelling soot formation in a
DISI engine. Proceedings of the Combustion Institute, 33(2): 3159-3167, 2011.
2. Naik, C. V., Liang, L., Puduppakkam, K., Meeks, E. Simulation and Analysis of In-Cylinder
Soot Formation in a Gasoline Direct-Injection Engine Using a Detailed Reaction Mechanism.
SAE Technical Paper 2014-01-1135, 2014.
3. Jiao, Q., Reitz, R. D. Modeling of Equivalence Ratio Effects on Particulate Formation in a
Spark-Ignition Engine under Premixed Conditions. SAE Technical Paper 2014-01-1607,
2014.
4. Jiao, Q., Reitz, R. D. The Effect of Operating Parameters on Soot Emissions in GDI
Engines. SAE International Journal of Engines, 8. (2015-01-1071), 2015.
5. Bonatesta, F., La Rocca, S., Hopkins, E., Bell, D. Application of Computational Fluid
Dynamics to Explore the Sources of Soot Formation in a Gasoline Direct Injection Engine.
SAE Technical Paper 2014-01-2569, 2014.
6. Bonatesta, F., Chiappetta, E., La Rocca, A. Part-load particulate matter from a GDI engine and the connection with combustion characteristics. Applied Energy, 124: 366-376, 2014.
7. Colin, O., Benkenida, A. The 3-Zone Extended Coherent Flame Model (ECFM3Z) for computing premixed/diffusion combustion. Oil & Gas Science and Technology, 59(6): 593-
609, 2004.
8. Star-CD Methodology Manual, Version 4.20, CD-Adapco, 2013.
9. Choi K, Kim J, Myung CL, Lee M, Kwon S, Lee Y, et al. Effect of the mixture preparation on the nanoparticle characteristics of gasoline direct-injection vehicles. Part D: J Auto, 226(11):1514–24,
2012.