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

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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.