ILASS – Europe 2013, 25 th European Conference on Liquid Atomization and Spray Systems, Chania, Greece, 1-4 September 2013 1 Investigation of Fuel Injection Strategies for Partially Premixed Compression Ignition Combustion in Two-Stroke Marine Diesel Engines Emmanouil Pananakis 1 , Panagiotis Kontoulis 1 , Christos Chryssakis 2 and Lambros Kaiktsis 1 1: Division of Marine Engineering, Department of Naval Architecture and Marine Engineering, National Technical University of Athens, Greece 2: Maritime Transportation, Research and Innovation Department, DNV, Norway Abstract The implementation of multiple-injection strategies in marine Diesel engines may partially contribute to compliance with emission regulations, while also maintaining a high engine performance. The present computational study investigates the possibility of implementing Partially Premixed Compression Ignition (PPCI) combustion in two-stroke marine Diesel engines. In particular, the concept is implemented in terms of pilot fuel injection with proper orientation of the spray jets, and tested by Computational Fluid Dynamics (CFD) simulations in a large two-stroke marine Diesel engine operating at full load. An early fuel injection is accompanied by long ignition delay, thus allowing fuel-air premixing. In the present study, a different orientation of fuel injection is considered for pilot and main injection, which can be implemented in practice in terms of twin needle injectors. A CFD parametric study of spray pilot injection angles is first performed, aiming at a proper fuel-air mixing, while also avoiding spray wall impingement. Next, the entire spray injection profile (pilot and main injection) is optimized, by coupling the KIVA-3 CFD code with an optimization code based on evolutionary algorithms. Here, multi-objective optimization is performed, aiming at minimizing simultaneously the engine nitric oxides (NOx) emissions and Specific Fuel Oil Consumption (SFOC). Solutions are evaluated against a reference operation mode, characterized by continuous injection. Both an unconstrained and a constrained optimization problem are considered, the latter complying with the engine maximum pressure limit, while also maintaining the work output of the reference mode. The algorithm converges to Pareto optimal solutions. For the unconstrained problem, several solutions are characterized by NOx reduction slightly higher than 20% and SFOC reduction of the order of 3%. For the constrained problem, reductions up to 18% in NOx emissions are attained, without a SFOC penalty. Optimal solutions are further characterized by visualizations of the computed reactive flow fields and assessment of the associated engine thermal loads. Introduction The environmentally friendly and efficient operation of two-stroke marine Diesel engines is dependent on air charging, fuel-air mixing, ignition and combustion processes. Engine optimization is associated with minimizing Specific Fuel Oil Consumption (SFOC), emissions and thermal loads. To this end, understanding of in-cylinder flow and combustion processes is essential. Among different approaches, the concept of Partially Premixed Compression Ignition (PPCI) appears as a promising candidate for the reduction of pollutant emissions from large marine engines. PPCI is associated with the use of multiple injection events (e.g. pilot and main injection) within an engine cycle; a precise shaping of injection profile is enabled by common rail injection systems. In the context of PPCI, the timing of pilot injection is well advanced before Top Dead Center (TDC), allowing enough time for fuel-air premixing. This contributes to minimization of pollutant emissions formation, due to the low levels achieved for the local values of both equivalence ratio and temperature. PPCI has been investigated mostly for engines of the automotive industry. In particular, Lechner et al. [1] employed PPCI by implementing early pilot injection in a four-stroke high speed Diesel engine, in conjunction with heavy Exhaust Gas Recirculation (EGR) rates. Their study, including both experiments and CFD analysis, has demonstrated that a substantial reduction in both nitric oxides (NOx) and soot emissions is feasible, at the expense of increased SFOC. Motivated by its longer ignition delay times, Struckmeier et al . [2] utilized Light Cycle Oil (LCO) in an experimental two-stroke medium size Diesel engine operated with split injection, thus attaining a PPCI mode with reduced NOx emissions. Engine optimization can utilize the advances in both CFD and optimization methods, in particular evolutionary algorithms. Engine optimization studies coupling CFD and optimization tools are nowadays feasible, both for the small (automotive) [3] and the large (marine) engines [4]. In particular, the study of [4] has shown that, in a large two-stroke marine engine operating at full load, optimization of the injection profile consisting of pilot and main injection can result in gains in SFOC of the order of 2% accompanied by NOx