Pre-mixed diesel combustion has the potential of offering high thermal efficiency with low emissions; however, this may result in loud combustion noise because of the high maximum rate of pressure rise. Combustion noise and thermal efficiency work in a trade-off relation, and it has not been possible to achieve high thermal efficiency with low combustion noise, so far. Our laboratory has worked on combustion noise simulations calculated from the heat release history, and it is now possible to calculate a heat release shape for high thermal efficiency with low combustion noise. In this article, the objective of the research is the reduction of combustion noise by multiple fuel injections with high indicated thermal efficiency for a wide range of engine speeds and loads. The engine employed in the simulations and experiments is a supercharged, single-cylinder direct-injection diesel engine, with a high-pressure common rail fuel injection system. The heat release is approximated by Wiebe functions, and the combustion noise and indicated thermal efficiency are calculated in simulations. The engine operational range was divided into 12 conditions, four engine speed conditions each at three engine load conditions, and the optimum heat release shape for low combustion noise with high indicated thermal efficiency was calculated by a genetic-based algorithm method. The parameters for the genetic-based algorithm simulation were the number of injections, each injection timing, the heating value in each heat release, and the combustion period of each injection. The optimum heat release shape is a delta triangle (Δ)-shaped heat release (the heat release increase in the expansion stroke) with a high degree of constant volume for all conditions; however, the optimum number of heat releases and the injection timing are different depending on the engine speed and load conditions. The simulated results were confirmed by engine tests.

中文翻译：

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在较宽的速度和负载运行范围内优化柴油发动机的燃烧噪声和热效率

预混合柴油燃烧具有提供高热效率和低排放的潜力；然而，由于最大压力上升率很高，这可能会导致很大的燃烧噪音。燃烧噪声和热效率处于一种折衷的关系中，到目前为止，还不可能在低燃烧噪声的情况下实现高热效率。我们的实验室致力于根据热释放历史计算出燃烧噪声模拟，现在可以计算热释放形状以实现高热效率和低燃烧噪声。在本文中，研究的目标是通过多次燃油喷射降低燃烧噪音，并在广泛的发动机速度和负载范围内具有高指示热效率。模拟和实验中使用的发动机是增压的，单缸直喷柴油机，高压共轨燃油喷射系统。热释放由 Wiebe 函数近似，燃烧噪声和指示热效率在模拟中计算。将发动机运行范围划分为12种工况，4种发动机转速工况，每种工况在3种发动机负荷工况下，采用遗传算法计算出低燃烧噪声、高指示热效率的最佳放热形状。基于遗传算法模拟的参数是喷射次数、每次喷射正时、每次放热的热值和每次喷射的燃烧周期。最佳的放热形状是三角形（Δ）形放热（膨胀冲程中放热增加），在所有条件下都具有高度的恒定体积；然而，最佳放热次数和喷射正时因发动机转速和负载条件而异。发动机试验证实了模拟结果。