In order to develop, in the short and long terms, Internal Combustion (IC) engines featuring extremely low specific fuel consumption and CO2 emissions as well as high intrinsic limits in pollutant emission production, researchers and manufacturers have to comply with EURO VI and the even more stringent future anti-pollution regulations, in addition to the European strategy (GUCE: L202 dated 10.8.2000) for CO2 emission and fuel consumption reduction in automotive engines. The concept and control of mixture formation and combustion processes in these engines require deep review, innovation and substantial enhancement of the knowledge.
The research project, involving five Research Units (RUs), Polytechnics of Torino and Milano, Universities of Lecce, Napoli and Pisa, was aimed at studying new and fuel neutral combustion systems for IC engines featuring very low pollutant emissions, with the main objective to give a substantial contribution to the development of 'intrinsically clean' propulsion systems. It was also intended to contribute to the knowledge of the thermo-fluid-dynamic processes in the combustion chamber and of their dependence on engine design and operation parameters.
In particular, it was planned to study the combustion system of electronically controlled diesel engines with compression ignition of premixed air-fuel charge approaching the Homogeneous Charge Compression Ignition (HCCI) concept. Such a combustion mode was recently shown to have the potential of drastically reducing both nitrogen oxides (NOx) and particulate matter (PM) emissions, while retaining at same time the high efficiency of the most advanced diesel engines. The research was also oriented at developing downsized Spark-Ignition (SI) engines fuelled by Natural Gas (NG), featuring tumble-assisted high-turbulence combustion chambers. The investigation of single engine components (such as turbochargers) was also planned for steady-state and transient operations. In addition, it was intended to enhance the scientific and technological knowledge in the field and to promote qualified scientific formation at university level as well as technological transfer to the Industry.
Specific attention was paid to:
- the application of non-conventional multiple injection strategies with innovative injection systems, capable of actuating a high number of shots in each engine cycle;
- closed-loop combustion control;
- correlations of combustion and emission-formation processes under steady-state and transient engine operations.
The optimal use of NG as a nonconventional fuel was addressed in addition to its integration with the following technologies:
- engine downsizing
- electrically assisted turbo-charging
- high-turbulence combustion chambers with Exhaust Gas Recirculation (EGR)
- flexible control of intake and exhaust processes by variable valve timing.
The numerical and experimental techniques, which were developed for the analysis of 3D non-stationary thermo-fluid-dynamics processes in IC engines, has
The above mentioned goal will be interpreted in different ways by the different RUs, as can be inferred from their proposals, but with strong homogeneity and integration of competence. The scheduled main research activities, as well as the experimental and theoretical-numerical investigation tools, that are described in the proposals, belong to consolidated research streams developed within previous MUR-COFIN programmes.
These activities and their methodologies deal with the development, the integration and the application of advanced experimental and numerical techniques for the analysis of phenomena especially in LDI (Lean Direct Injection)-HCCI systems, featuring fuel direct injection in the combustion chamber, retarded ignition with respect to top dead centre, and highly-premixed charge formation assisted by high-turbulence organised in-cylinder air flows (swirl, tumble and/or squish). It was intended to pay specific attention to the following topics:
- application of non-conventional multiple injection strategies with innovative injectors capable of actuating a high number of shots in each engine cycle and promoting fuel atomisation
- closed-loop control of combustion and its correlation to emissions under steady-state and dynamic operations.
The research activities were basically oriented to the following two main subjects, which were extended by additional complementary activities developed by some of the involved RUs, with the following main scientific and technical results achieved:
1. Tumble-assisted combustion systems for CNG downsized high-boost SI engines
In the literature, there is a lack of basic knowledge about the correlation amongst thermo-fluid-dynamic processes, performance and emissions for the development of small-displacement turbocharged CNG engines with high power density. In fact, the analysis of the processes in NG engines has only recently gained a significant impulse [1-9].
Torino (TO) RU has contributed to the development and assessment of a new SI ‘downsized’ turbocharged CNG engine built at Fiat Research Centre (CRF). The engine features a high-turbulence combustion system with: two intake ducts, displacement of 1400 cc and compression ratio of 11:1. The turbocharger is electrically assisted so as to minimise the turbolag.
A further contribution to methodologies for in-cylinder combustion diagnostics has been given by developing and applying quasi-dimensional multizone models, which were integrated with a CAD procedure for the simulation of the average surface of the burned-gas front in order to evaluate the main flame combustion parameters, such as the mean gas speed of the burned gas, for which there is a lack of experimental data in the literature, especially in NG engines.
Milano (MI) RU developed and applied a new CFD combustion model in order to simulate the performance of the engine fuelled with either NG or H2-NG mixtures and consequently to predict the distribution of the chemical species in the engine chamber for its optimisation.
Napoli (NA) RU was involved with the experimental and numerical study of electrically-assisted turbochargers for a better control of the combustion, so as to drastically reduce the turbolag during engine transient operations.
2. High-turbulence combustion systems for automotive HCCI direct-injection engines
The premixed-charge compression-ignition combustion in IC engines represents an attractive approach, which is under investigation with different fuels. It offers the potential for achieving the high efficiency of the most recent diesel engines with electronically-controlled injection and a drastic reduction in pollutant emissions, o
- The project emphasised the technical implications of results in the development of more efficient and less pollutant IC engines for passenger cars.
- The project outlined technical issues for an environmentally-friendly automotive transport.