PM emissions from mixing-controlled combustion in natural gas fueled engines

柴油发动机为加拿大人民和工业提供了必不可少的动力。这种主力技术是省油和高度可靠的。然而，柴油发动机在其废气中排放大量的气态氮氧化物（NOx）和颗粒物（PM），这些排放物与不利的健康影响有关，包括心肺和免疫系统反应以及肺癌风险。2012年6月，国际癌症研究机构（IARC，世界卫生组织的一部分）将柴油发动机废气指定为人类致癌物（1型），媒体对此进行了广泛报道，这是一个令人高度关注的例子。由于日益关注柴油废气排放对健康的影响，2010年实施了非常严格的重型柴油发动机废气排放标准。通过不断改进发动机燃烧系统，改变柴油成分（例如去除硫），以及使用附加的尾气后处理设备，包括颗粒过滤器、氧化催化剂和氮氧化物吸收器，这些标准都得到了满足。然而，如果能在发动机源头减少排放，那么后处理的必要性就会最小化，甚至消除。后处理会带来燃油罚款。解决这个问题的关键在于减少颗粒物的排放。燃烧产生的颗粒排放的主要来源是扩散（混合控制）燃烧过程。几十年来对扩散火焰的基础研究使人们对烟尘的形成过程有了基本的了解，但仍有许多问题有待解决。减少油烟形成的工业解决方案是实施越来越高的燃油喷射压力，以增强燃油的雾化、汽化和混合。然而，目前的燃油喷射器正在接近喷射压力的实际极限。使用天然气作为燃料可以减少发动机的颗粒物排放。与传统柴油相比，天然气燃料的价格非常低，因此目前人们对天然气燃料的发动机有着极大的兴趣。以柴油式混合控制燃烧方式燃烧天然气确实会产生PM排放，但排放量低于柴油燃料。这里提出的研究将研究高压直接注入天然气，以尽量减少PM排放。此次调查将使用光学单缸研究引擎和高速数码相机。实验将采用辉光塞点火，因此可以使用100%的天然气燃料。研究的重点将是通过探索通过使用椭圆喷嘴、多次喷射和非常规气体喷射模式来增强气缸内燃料气体混合的方法，从而减少PM排放。PM排放较低的发动机可以带来可观的健康红利。

Diesel engines provide essential motive power to Canada’s people and industries. This workhorse technology is fuel efficient and highly reliable. However, diesel engines emit significant quantities of gaseous oxides of nitrogen (NOx) and particulate matter (PM) in their exhaust and these emissions are associated with adverse health effects, including cardiopulmonary and immune system responses and lung cancer risk. The widespread press coverage of the designation in June 2012 of diesel engine exhaust as carcinogenic to humans (Type 1) by the International Agency for Research on Cancer (IARC, part of the World Health Organization) is an example of heightened concern. Increased concerns about the health effects of diesel exhaust emissions resulted in the implementation of very stringent heavy-duty diesel engine exhaust emission standards in 2010. The standards have been met by making incremental engine combustion system improvements, changes to diesel fuel composition (e.g. the removal of sulfur), and through the use of add-on exhaust aftertreatment devices including particulate filters, oxidation catalysts and NOx absorbers. Yet the need for aftertreatment, which imposes a fuel penalty, would be minimized or even eliminated if emissions could be reduced at the engine source. The key to the problem lies in minimizing particulate emissions. The primary source of combustion generated particulate emissions is the diffusion (mixing-controlled) combustion process. Decades of fundamental research with diffusion flames has provided a basic understanding of the soot formation process but there is still much to be resolved. The industry solution to reducing soot formation has been to implement higher and higher fuel injection pressures to enhance fuel atomization, vaporization and mixing. However, current fuel injectors are approaching the practical limit for injection pressure. Use of natural gas as a fuel can reduce engine PM emissions. There is tremendous interest in natural gas fueled engines at present due to its very low price compared to conventional diesel fuel. Combustion of natural gas in diesel-style mixing-controlled combustion does generate PM emissions, but at a lower rate than with diesel fuel. The research proposed here will investigate high pressure direct injection of natural gas for the purpose of minimizing PM emissions. An optically accessible single-cylinder research engine and a high speed digital camera will be used in the investigation. Experiments will utilize glow plug ignition, so as be able to use 100% natural gas fuel. The focus of the research will be on reducing PM emissions by exploring means of enhancing in-cylinder fuel gas mixing through the use of elliptical gas nozzles, multiple injections and un-conventional gas injection patterns. Engines with lower PM emissions could pay a substantial health dividend.