Impact of fuel and lubricant oil on particulate emissions in direct injection spark ignition engines: A comparative study of methane and hydrogen

Internal combustion engines play a critical role in the global transportation system and the use of alternative fuels, such as methane and hydrogen, offers a promising way for ensuring their sustainability in the future. The best way to exploit the gaseous fuels properties is through the direct injection that allows to enhance the efficiency and to prevent backfire issues. On the other hand, this injection strategy causes a high interaction of the lubricant oil in the combustion process and hence high level of particle emissions despite the low/zero carbon content in the fuels. An experimental study was conducted on a spark-ignition engine powered by directly injected methane. This study involved both physical and chemical characterization of emissions, with the aim of providing an in-depth analysis of the hazardous pollutants emitted. Additionally, it sought to identify their origins, whether from the fuel or lubricating oil. Experimental results show that a higher concentration of particles is produced at higher engine speed. In this condition, which has a more significant environmental impact, a comparison between methane and hydrogen-fueled engine operating under similar conditions was performed, revealing that hydrogen engine produces more particles with a smaller size.