EAGER: Investigating Super-Heated Urea for NOx Reduction for Low Temperature Combustion Engine Application

氮氧化物（NOx）是柴油发动机的主要污染物之一，它对健康和环境的影响有据可查。通过废气清理和燃烧优化，已经作出了认真的努力来减少它们。有趣的是，效率和污染之间往往存在权衡。该项目将开发并演示一种大大改进的尾气后处理方法，以减少氮氧化物，特别是在低温燃烧状态下运行的发动机。具体的重点将是开发和测试一种新型系统，通过对目前用于柴油发动机的柴油排气液（DEF）进行过热加热，以低成本降低氮氧化物。该项目不仅将开辟新的研究领域，而且将直接影响发动机的燃烧和能源效率。氮氧化物已经成为一个重要的问题，因为越来越多的人关注燃油经济性，促使发动机燃烧更少的燃料，从而在更低的温度条件下运行。这样的低温操作导致了更冷的排气，而混合动力系统打开和关闭发动机只会加剧这个问题。此外，无法降低高浓度氮氧化物也限制了柴油发动机的运行窗口。该项目将研究通过向发动机排气流中注入过热尿素来减少非平衡态氮氧化物。这一想法的核心是，随着温度升高，化学反应速度加快，商用柴油废气（DEF）（尿素与水）的氮氧化物还原能力急剧上升。新系统在注入前对尿素进行微波加热（至1200 K），使其更具反应性，实验证明，在商用锅炉中，在这种温度下，氮氧化物的减少率高达96%。实验测试将用于测量各种尿素喷射情况下的排气成分，计算机建模将用于提取与实验观察行为相对应的化学反应速率。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nitrogen oxide (NOx) is one of the major pollutants from diesel engines and has its own well-documented health and environmental impacts. Serious efforts have been devoted to reducing them through exhaust clean-up and combustion optimization. Interestingly, there are often trade-offs between efficiency and pollution. This project will develop and demonstrate a greatly improved exhaust after-treatment methodology for NOx reduction, particularly for engines operating at low-temperature combustion regimes. The specific focus will be on developing and testing a novel system for low-cost NOx reduction by super-heating the diesel exhaust fluid (DEF) currently used on diesel engines. The project will not only open up new areas of research, but also directly impact engine combustion and energy efficiency.NOx has become an important problem because the increased focus on fuel economy has driven engines to burn less fuel and consequently operate at a lower temperature condition. Such low-temperature operations have led to colder exhaust, with hybrid systems that turn the engine on and off only exacerbating this problem. Additionally, the inability to mitigate high levels of NOx has limited the operational window for diesel engines. This project will investigate non-equilibrium NOx reduction through injection of super-heated urea into an engine exhaust stream. Central to this idea is the steep rise of NOx reduction capacities of commercial diesel exhaust fluid (DEF), urea with water, with rising temperature because of higher chemical reaction rates. The new system uses microwave heating of the urea (to 1200 K) prior to injection to make it much more reactive, with experimentally proven NOx reduction of up to 96% for such temperatures in commercial boilers. Experimental testing will be used to measure the exhaust composition for various urea injection cases while computer modeling will be employed to extract the chemical reaction rates that correspond to experimentally observed behaviors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.