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Novel multizone thermodynamic model and specialised software for rapid optimisation of working process strategies and design parameters of Internal Combustion Engines run on advanced biofuels

Final Report Summary - BIO-GREEN-IC-ENGINE (Novel multizone thermodynamic model and specialised software for rapid optimisation of working process strategies and design parameters of Internal Combustion Engines run on advanced biofuels)

International Energy Agency’s Energy Technology Perspectives 2010 (IEA, 2010c) BLUE Map Scenario sets out cost effective strategies for reducing greenhouse-gas emissions by 50% by 2050 from 2005 levels. The BLUE Map Scenario envisages biofuels to contribute significantly to reduction of emissions by increasing from 2-3% of total transport energy supply today to 27% by 2050. The scenario suggests that a considerable share of the required volume will come from advanced biofuel technologies.

Currently, the existing engines from major manufacturers in the EU area can operate on blends with biofuel fractions up to 5% (biodiesel) and 20% (bioethanol) without significant modifications and consequences for the engine performance and emission levels. However, very intensive R & D works are being carried out by all major IC engine manufacturers on the development of engine designs for transport and power applications which will be capable to work on blends with up to 100% of biofuel. Similar works are being conducted on retrofitting second-hand motors.

The main challenge in the R & D works will be satisfaction of EU regulations on emission levels. Intensive fundamental theoretical and experimental research is required to achieve these targets. One of barriers in conducting theoretical part of investigations is a limited number of available specialised software dedicated to accurate modelling of the operation of IC engines on different biofuel blends and which would allow engineers to rapidly optimise the operation and design of the engine including the investigation of the injection strategy and combustion phases and optimisation of the engine part geometry to achieve the highest possible efficiency and satisfactorily level of emissions in accordance with current and future EU regulations. Specialised CFD software packages, which are used for accurate modelling of IC engines operation, are computationally intensive and to carry out a complete CFD multi-parameter optimisation of engines would be an excessively time consuming procedure.

For optimisation of IC engine usually thermodynamic modelling based approach is deployed. In such models IC engines are split into significantly fewer control volumes and ordinary differential equations are used to describe the flow and heat transfer processes in each control volume, i.e. the lump parameter modelling approach is applied. Because of a number of assumptions made during the simulations these types of models fail to provide a very accurate description of all the physical processes in the engine, but using an array of correction coefficients it is possible to produce the engine performance predictions within an acceptable accuracy. The advantage of such models is that they do not impose high requirements on computational resources yet they consider the interaction and the mutual effect of in-cylinder processes, the flow in the inlet and exhaust manifolds, the flow in turbo- or superchargers and the operation of a fuel injection system. Thus, lump parameter models of IC engines can be more easily adapted for the solution of the formal optimization problem.
Several software packages, built around the thermodynamic models of IC engines, are commercially available. At present a number of single- and multi-zone thermodynamic models exist which utilise various approaches to split the fuel spray and analyse combustion process inside the cylinder. At the top end of such thermodynamic models complex methods for the computation of the heat release process are used.

The objective of this Marie Curie “Bio-Green-IC-Engine” project has been the development of the advanced multi-zone combustion thermodynamic model for the simulation of IC engines which are run on conventional fuels, advanced biofuels and their blends.

Such the model splits fuel spray in a number of zones (up to 10), which differ from each other by thermodynamic parameters and evaporation conditions, and then takes into account the impingement of the fuel spray upon the walls of the engine combustion chamber (the piston bowl, walls of the cylinder liner, head of the cylinder) and formation of additional zones (up to 4) with fuel on the walls. Evaporation and combustion in such zones take place in less favourite conditions and these are reasons for deterioration of the engine’s performance and for high level emissions.

The following are main features of the enhanced thermodynamic model developed in the framework of “Bio-Green IC Engine”:
• In addition to catalogue of conventional diesel and petrol fuels, extensive database of advanced biofules has been created for modelling of IC engines. This includes physical and chemical properties of biofuels, e.g. RME, SME, biofule blends B5, B10, B20 etc., bio-ethanol and bio-methanol;
• The capability of using a number of independent fuel injection systems with various geometry of fuel injectors and their operational parameter for supplying different types of fuels into the cylinder. A combined strategy for multi-stage injection process for each type of fuel can be optimised to achieve the highest possible engine performance.
• Three-dimensional non-CFD modelling of evaluation of fuel sprays, supplied by independent fuel injection systems, and for visualisation of the fuel spray evolutions;
• Capability of thermodynamic modelling of dual-fuel diesel engines, operating on bio-methanol or bio-ethanol ignited with a pilot injection of diesel or biodiesel fuel. Previously this type of engines have been modelled using only CFD approach.
The above enhanced thermodynamic model has been incorporated into previously existed specialised software, Diesel-RK, for rapid optimization of biofuel engine design parameters and organization of its working process in order to achieve the highest possible efficiency and to satisfy NOx, CO, PM and smoke emission levels.

Using this approach a concept of novel Z-engine has been investigated with a split compression process. In such engines the first stage of the compression takes place outside of the cylinder (external piston compressor) with the second stage carried out in the cylinder. Due to such the organisation of the compression process the injected fuel evaporation takes place at low pressure and high temperature conditions, making it possible to realise the HCCI process, which reduces emissions to levels which are achieved at modern engines with after treatment systems.

The results of the project improve the technological and industrial practice related to manufacturing IC engines and their fuel supply systems to operate on conventional and advanced biofuels or their blends. A wide range of diesel and gasoline engine configurations can be evaluated in terms of engine part geometry and its operating parameters in order to increase the engine efficiency by improving combustion and to reduce emissions when using mixtures or pure conventional and bio-fuels. The enhanced modelling software can be used for industrial, research and educational purposes across EU countries.