engleski

Improved Autoignition Modeling for 3D CFD Simulation of Diesel Ignited Large Gas Engines

Natural gas is currently a promising fuel for combustion engines that makes it possible to obtain efficient power generation with relatively low environmental impact. Diesel-gas dual fuel operation is especially interesting because it combines the safety and reliability of the basic diesel concept with great flexibility in the choice of fuel. The large engines used for power generation and locomotive and marine propulsion pose different challenges in the development process than engines for the automotive industry. Because there are fewer prototypes in the development and field test phases, it is necessary to have simulation tools that accurately predict the combustion process in order to reduce costs and development time. Furthermore, the use of simulation methods is essential to development due to the increased number of degrees of freedom of dual fuel combustion concepts. 3D-CFD simulation is a tool that is able to meet the challenges of predicting the complex combustion process as well as providing spatial and time resolved information about the process that furthers understanding of the physical phenomena involved. The combustion process of the diesel ignited gas engine combines different combustion regimes, namely premixed and diffusion combustion, as well as autoignition processes. One combustion model in the 3D-CFD framework that is capable of simulating all the required combustion regimes is the Extended Coherent Flame Model with the 3 zones approach (ECFM-3Z). Previous papers have already introduced viable approaches to 3D-CFD simulation of a diesel ignited gas engine with the ECFM-3Z. A very important factor for predicting combustion in these engines is ignition delay. The two fuels influence each other, and good numerical modeling of ignition delay is imperative to accurate prediction of the overall combustion process. This paper focuses on improving ignition delay modeling of diesel ignited gas engines. The challenges of modeling when two different fuels are involved are stated and possible solutions are provided. Two-stage ignition methods are described along with improvements in ignition delay modeling of the diesel ignited gas engine. Both of the described ignition modeling approaches are used in the Extended Coherent Flame Model with the 3 Zones approach (ECFM-3Z). The predictive capability of the models is investigated using data from single cylinder engine (SCE) tests conducted at the LEC. The results are discussed and further steps for development are identified.

Dual fuel combustion, ECFM-3Z, diesel ignited gas engine, 3D-CFD, numerical modeling, experimental validation

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