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A computational and experimental study on combustion processes in natural gas/diesel dual fuel engines.

机译：天然气/柴油双燃料发动机燃烧过程的计算和实验研究。

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摘要

Natural gas/diesel dual fuel engines offer a path towards meeting current and future emissions standards with lower fuel cost. However, numerous technical challenges remain that require a greater understanding of the in-cylinder combustion physics. For example, due to the high compression ratio of diesel engines, substitution of natural gas for diesel fuel at high load is often limited by engine knock and pre-ignition. Additionally, increasing the natural gas percentage in a dual fuel engine often results in decreasing maximum load. These problems limit the substitution percentage of natural gas in high compression ratio diesel engines and therefore reduce the fuel cost savings. Furthermore, when operating at part load dual fuel engines can suffer from excessive emissions of unburned natural gas. Computational fluid dynamics (CFD) is a multi-dimensional modeling tool that can provide new information about the in-cylinder combustion processes causing these issues.;In this work a multi-dimensional CFD model has been developed for dual fuel natural gas/diesel combustion and validated across a wide range of engine loads, natural gas substitution percentages, and natural gas compositions. The model utilizes reduced chemical kinetics and a RANS based turbulence model. A new reduced chemical kinetic mechanism consisting of 141 species and 709 reactions was generated from multiple detailed mechanisms, and has been validated against ignition delay, laminar flame speed, diesel spray experiments, and dual fuel engine experiments using two different natural gas compositions. Engine experiments were conducted using a GM 1.9 liter turbocharged 4-cylinder common rail diesel engine, which was modified to accommodate port injection of natural gas and propane. A combination of experiments and simulations were used to explore the performance limitations of the light duty dual fuel engine including natural gas substitution percentage limits due to fast combustion or engine knock, pre-ignition, emissions, and maximum load. In particular, comparisons between detailed computations and experimental engine data resulted in an explanation of combustion phenomena leading to engine knock in dual fuel engines.;In addition to conventional dual fuel operation, a low temperature combustion strategy known as reactivity controlled compression ignition (RCCI) was explored using experiments and computations. RCCI uses early diesel injection to create a reactivity gradient leading to staged auto-ignition from the highest reactivity region to the lowest. Natural gas/diesel RCCI has proven to yield high efficiency and low emissions at moderate load, but has not been realized at the high loads possible in conventional diesel engines. Previous attempts to model natural gas/diesel RCCI using a RANS based turbulence model and a single component diesel fuel surrogate have shown much larger combustion rates than seen in experimental heat release rate profiles, because the reactivity gradient of real diesel fuel is not well captured. To obtain better agreement with experiments, a reduced dual fuel mechanism was constructed using a two component diesel surrogate. A sensitivity study was then performed on various model parameters resulting in improved agreement with experimental pressure and heat release rate.
机译：天然气/柴油双燃料发动机提供了一条以更低的燃料成本达到当前和未来排放标准的途径。但是，仍然存在许多技术挑战，需要对缸内燃烧物理学有更多的了解。例如，由于柴油发动机的高压缩比，在高负荷下用天然气代替柴油燃料常常受到发动机爆震和预点火的限制。另外，增加双燃料发动机中的天然气百分比通常会导致最大负载降低。这些问题限制了高压缩比柴油发动机中天然气的替代百分比，因此降低了燃料成本节省。此外，当在部分负荷下运行时，双燃料发动机会遭受未燃烧天然气的过量排放。计算流体动力学（CFD）是一个多维建模工具，可以提供有关导致这些问题的缸内燃烧过程的新信息。在这项工作中，已经开发了用于双燃料天然气/柴油燃烧的多维CFD模型。并在各种发动机负载，天然气替代百分比和天然气成分中得到验证。该模型利用降低的化学动力学和基于RANS的湍流模型。从多种详细的机理中产生了由141个物种和709个反应组成的新的降低的化学动力学机理，并已针对使用两种不同天然气成分的点火延迟，层流火焰速度，柴油喷雾实验和双燃料发动机实验进行了验证。发动机实验是使用GM 1.9升涡轮增压4缸共轨柴油发动机进行的，该发动机经过改装以适应天然气和丙烷的进气口喷射。实验与模拟相结合，用于探索轻型双燃料发动机的性能局限性，其中包括由于快速燃烧或发动机爆震，预点火，排放和最大负载而导致的天然气替代百分比的局限性。特别是，通过对详细计算和发动机实验数据的比较，得出了导致双燃料发动机爆震的燃烧现象的解释。除了常规的双燃料操作外，一种低温燃烧策略称为反应性可控压燃（RCCI）通过实验和计算进行了探索。 RCCI使用早期的柴油机喷射产生反应性梯度，导致从最高反应性区域到最低反应性的阶段性自动点火。事实证明，天然气/柴油RCCI在中等负荷下可产生高效率和低排放，但在常规柴油发动机的高负荷下尚未实现。以前使用基于RANS的湍流模型和单组分柴油燃料替代物对天然气/柴油RCCI进行建模的尝试显示出比实验放热率曲线中观察到的燃烧速率大得多的燃烧速率，因为无法完全捕获真实柴油的反应梯度。为了与实验更好地吻合，使用两组分柴油替代品构造了简化的双燃料机制。然后对各种模型参数进行了敏感性研究，从而提高了与实验压力和放热速率的一致性。

著录项

  • 作者

    Hockett, Andrew.;

  • 作者单位

    Colorado State University.;

  • 授予单位 Colorado State University.;
  • 学科 Mechanical engineering.;Automotive engineering.
  • 学位 Ph.D.
  • 年度 2015
  • 页码 249 p.
  • 总页数 249
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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