Photo Credit: VKA


MTZ Project Reports: CNG DI Combustion Processes in Combination with High-load EGR and the Miller Process

Compressed Natural Gas (CNG) represents a short- and medium term addition to the fuel portfolio for turbo-DI spark ignition engines, as it is readily available worldwide and can contribute significantly to greenhouse gas reduction due to the low C/H ratio. As part of the FVV research project No. 1202, a homogeneous stoichiometric combustion process with direct natural gas injection in combination with high-load exhaust gas recirculation was investigated at RWTH Aachen University and Otto von Guericke University Magdeburg.

The focus of the research project was on the overall evaluation of the homogeneous stoichiometric combustion process in combination with high-load Exhaust Gas Recirculation (EGR) and Miller valve control. The project was carried out at the Institute for Combustion Engines (VKA) at RWTH Aachen University and the Institute for Mobile Systems (IMS) at the Otto von Guericke University (OVGU). Fundamental mixture for mation investigations were carried out both in a low-pressure injection chamber and on a motored, optically accessible single-cylinder research engine. In addition, the investigations were numerically supported. The findings were transferred to a geometrically identical thermodynamic single-cylinder research engine and supplemented by numerical investigations. The experiments were transferred to a Ford multi-cylinder engine, the results of which were finally incorporated to a 0-D/1-D engine model. The numerical and ther modynamic results of the investigation are presented in this article.

A selection of the research work, as presented here, comprised various experimental and numerical investigations in order to evaluate the potential of natural gas direct injection. The optical investigations provide a fundamental increase in knowledge of direct gas injection and valuable input for the validation of the developed 3-D CFD injector model. A lateral injection increases the tumble level significantly compared to central injection, both at an early and at a late injection timing. An early central injection even counteracts the complete tumble motion development. The engine investigations in particular provide detailed knowledge about propagation and the mixture formation of CNG injection. The thermodynamic investigations on the single-cylinder engine showed that EGR has a limited potential in influencing the location of the center of combustion due to a limited peak pressure. The multi-cylinder engine investigations with high-load EGR showed a high NOx reduction potential with slight efficiency advantages up to n = 4000 rpm. The peak pressures could not be reduced with the same center of combustion. The findings in this study show that the use of CNG as a fuel, together with corresponding engine modifications, has great potential in many respects. A monovalent CNG powertrain could represent an extremely low CO2 or neutral technology, in particular with the addition or exclusive use of regeneratively produced methane.

Project profile

The FVV in the MTZ and ATZ magazine

Results from Industrial Collective Research are accessible to all interested parties and thus final reports of FVV research projects will be presented to the public at our conferences in spring and autumn. In order to further promote the transfer of knowledge and the expansion of the prime movers innovation network, we publish articles on individual projects with particularly interesting new insights in the world's leading specialist magazines for the engine and vehicle industries. MTZ / ATZ and FVV have been working together successfully in this field for many years.

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