Alternative Fuels for Particulate Control in CI Engines

It is widely known that diesel combustion in a compression ignition (CI) engine produces and emits a significant amount of particulate matter (PM) which contributes to degradation in both health and environment. The origin of the soot formation depends on several factors, however, the main source of the soot emissions is the combustion of the diesel fuel itself. To circumvent this issue, studies have been conducted to explore and exploit the advantages of fuels with a lower sooting tendency. Around the world, the utilization of oxygenated biodiesels, such as fatty acid methyl esters (FAME), have been increasing to allow the reduction of PM emissions alongside the net CO2. Due to the FAMEs oxygen content, the fuel is oxidized more readily during the combustion process and thus emitting a significantly lower engine out concentration of PM emission than that of commercial diesel fuel. The utilization of the lighter alcohol fuels, methanol and ethanol neat and blended, is a good option to reduce the soot to zero levels. The reduction of soot to near zero levels introduces another advantage; the soot-NOx trade-off diminishes completely when utilizing exhaust gas recycling (EGR). The issue, however, is that the PN emission of nucleation mode particles is high when utilizing such fuels while ignition is hard to achieve with high octane number fuels in a CI engine.