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

柴油发动机为加拿大的人民和工业提供了必要的动力。这种主力技术是燃油效率和高度可靠的。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相关，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）将柴油发动机废气定为对人类致癌物（1型），这一广泛的新闻报道是引起高度关注的一个例子。对柴油机废气排放对健康影响的日益关注导致在2010年实施了非常严格的重型柴油机废气排放标准。通过逐步改进发动机燃烧系统、改变柴油燃料成分（例如脱硫）以及通过使用附加排气后处理装置（包括颗粒过滤器、氧化催化剂和NOx吸收剂），这些标准已经得到满足。然而，如果可以在发动机源头减少排放，则对后处理的需求将被最小化甚至消除，后处理会造成燃料损失。问题的关键在于最大限度地减少颗粒物排放。燃烧产生的颗粒排放物的主要来源是扩散（混合控制）燃烧过程。几十年来对扩散火焰的基础研究提供了对烟灰形成过程的基本了解，但仍有许多问题需要解决。减少烟灰形成的工业解决方案是实施越来越高的燃料喷射压力以增强燃料雾化、汽化和混合。然而，目前的燃料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PM排放。目前，由于天然气燃料发动机与传统柴油燃料相比价格非常低，因此对天然气燃料发动机有极大的兴趣。天然气在柴油式混合控制燃烧中的燃烧确实产生PM排放，但其速率低于柴油燃料。 这里提出的研究将调查高压直接喷射天然气的目的，最大限度地减少PM排放。一个光学可访问的单缸研究引擎和高速数码相机将用于调查。实验将利用电热塞点火，以便能够使用100%天然气燃料。研究的重点将是通过使用椭圆形气体喷嘴、多次喷射和非常规气体喷射模式来探索增强缸内燃料气体混合的方法，从而减少PM排放。PM排放量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.