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。这项主力技术既省油，又高度可靠。然而，柴油发动机在其废气中排放大量的氮氧化物(NOx)和颗粒物(PM)，这些排放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。媒体对2012年6月国际癌症研究机构(IARC，世界卫生组织的一部分)将柴油发动机尾气列为对人类致癌(1型)的广泛报道就是一个高度关切的例子。 对柴油尾气排放对健康影响的日益关注导致2010年实施了非常严格的重型柴油发动机尾气排放标准。通过对发动机燃烧系统进行渐进式改进，改变柴油组成(例如，去除硫)，以及通过使用附加的废气后处理设备，包括微粒过滤器、氧化催化剂和NOx吸收器，已达到这些标准。然而，如果能够从发动机源头减少排放，那么对后处理的需求将被最小化，甚至消除。后处理是对燃料的惩罚。解决问题的关键在于将颗粒物排放降至最低。 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已经对碳烟的形成过程有了基本的了解，但仍有许多问题需要解决。减少碳烟形成的行业解决方案一直是实施越来越高的燃油喷射压力，以增强燃油雾化、汽化和混合。然而，目前的喷油器正在接近实际喷油压力的极限。 使用天然气作为燃料可以减少发动机的PM排放。天然气发动机由于其价格比传统柴油低，目前引起了人们的极大兴趣。天然气在柴油式混合控制燃烧中的燃烧确实会产生PM排放，但其排放速率低于柴油。 本文提出的研究将研究高压直喷天然气，以最大限度地减少PM排放。调查中将使用一台可光学访问的单缸研究发动机和一台高速数码相机。实验将利用辉光塞点火，从而能够使用100%的天然气燃料。研究的重点将是通过探索通过使用椭圆形气体喷嘴、多次喷射和非传统气体喷射模式来增强气缸内燃料气体混合的方法来减少PM排放。 PM排放较低的发动机可能会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.