An evaluation of cetane sensitivity in low-temperature combustion and options to compensate for market cetane variation

Abstract

A single-cylinder engine was used to assess the sensitivity of emissions, noise and fuel consumption to variation in cetane number when operated in low temperature combustion both with and without the application of compensation strategies. Without compensation, changes in cetane caused greater variability in all of the parameters studied when operated in low temperature combustion as compared to conventional diesel combustion. Correcting combustion phasing was explored by adjusting three different parameters: start of injection timing, burnt gas fraction and intake manifold temperature. None of these methods were able to achieve substantially equivalent combustion and emissions across all fuels evaluated. Large variations in hydrocarbon and particulate emissions were observed when start of injection was adjusted to correct combustion phasing. Adjusting the burnt gas fraction caused large differences in nitrogen oxides and noise, particularly with low cetane fuels. Finally, intake manifold temperatures low enough to reach the target combustion phasing with the higher cetane fuel were unachievable, suggesting that this method would not be viable as a production solution. It was concluded that the most effective way to ensure robust combustion and emissions in low temperature combustion is to reduce ignition delay variability by refining the fuel specification, either through tighter control over the cetane number range or by shifting the fuel specification toward higher cetane number, where ignition delay is less sensitive to changes in cetane rating.