Manipulating Heat Release Features to Minimize Combustion Noise

Changes in combustion noise, eciency, and emissions are investigated as responses to boundary conditions and injection scheduling parameters of closely-coupled multiple-pilot strategies. The eects of pilot injection separation times, mixture dilution, and injection pressure are investigated. In order to minimize combustion noise, the heat release rate (HRR) should be as linear in its buildup as possible. Through low injection pressure, high dilution ratio, and close-coupling of the pilot injections, combustion noise can be minimized. It is possible to have too much mixture dilution or dwells which are too short, however. This causes excessive blending of combustion events which tends to increase combustion noise. Noise minimization though HRR shaping has also been achieved through injection rate shaping. Based on the learnings from each investigation, triple and quadruple pilot injection strategies are created for lowest possible combustion noise. The investigations also reveal the relative extent to which emissions, noise, and eciency are aected by each control parameter so that compromises in each response can be understood.