NUMERICAL STUDIES OF PREMIXED DUAL FUEL COMBUSTION

Activity: Examinations and supervisionSupervisor activities

Description

Master thesis by Abdul Kadim Kilic and Serife Köysüren

Abstract:

The dual-fuel (DF) combustion concept is one of the promising strategies for modern automotive and marine engines to achieve lower emission levels. A premixed DF engine operates by having a pilot diesel injection to ignite the lean premixed natural gas in the engine. Experimental studies on premixed DF combustion with micro pilot diesel fuel are limited. Hence, the underlying mechanism are still not well-understood. The current thesis contains a three dimensional (3D) computational fluid dynamic (CFD) study using the Simcenter STAR CCM+ software to investigate the ignition characteristics of the premixed DF combustion. Large eddy simulation (LES) is used for the turbulence modelling in this study. Initially, the spray and combustion models were validated using the Sandia Spray A case by means of the experimental spray and combustion characteristics. The obtained numerical combustion and spray model were then implemented for the DF simulation by modelling the injection of pilot diesel fuel into a constant volume bomb with a premixed methane-air mixture. The adaptive mesh refinement (AMR) is implemented in order to increase the computational efficiency using a minimum cell size of 0.25mm. N-Dodecane fuel is used as a pilot diesel surrogate fuel here. Two reduced n-dodecane chemical mechanisms are being tested. Model validation is carried out by comparing the liquid penetration length (LPL) of the inert diesel spray to the measured data. The predicted ignition delay time (IDT) in the pure diesel case and the DF case are also validated against the experimental data. A reasonable agreement between the CFD results and measurements for the LPL and IDT is achieved for the validation case Spray A, hence showing robust numerical modelling setup. The LPL for the pure diesel case in the actual case study showed only to deviate with 6% from the experimental data. Ignition happened both mechanisms for the pure diesel case. The results obtained for the DF case using methane in the ambient gas composition showed to delay the IDT compared to pure diesel case which is in agreement with the literature.
Period1 Apr 2021