..phi..-Sensitivity of Gasoline/Oxygenate Blends in an Advanced Compression Ignition Engine

Advanced compression ignition (ACI) engines have shown the potential to improve internal combustion engine efficiency while drastically reducing levels of nitrogen oxides (NOX) and particulate matter, including soot, in the exhaust. However, achieving high loads and control over ACI engines requires improvement of fuel ..phi..-sensitivity relative to standard gasoline. Ideally, improving fuel ..phi..-sensitivity will go hand-in-hand with reducing fuel carbon intensity. This study identifies three potential low-carbon fuels that can be blended with gasoline for use in ACI engines: methyl pentanoate, 1-pentanol, and 2-pentanol. These fuels have been tested in approximately 30% blends with gasoline at three different speed/load conditions in a medium-duty CI engine. Two different ..phi..-sensitivity metrics were developed. The first metric ("Type 1") evaluates the change in ignition timing with respect to the start-of-injection timing of the final injection in a multi-pulse ACI injection schedule. According to this metric, 1-pentanol increased ..phi..-sensitivity by 57%, 2-pentanol by 56%, and methyl pentanoate by 21% over the baseline gasoline. The second metric ("Type 2") determines how far combustion phasing, in terms of degrees of engine rotation, could be advanced before a limit of engine ringing intensity was reached. According to this metric, 1-pentanol allowed 1.03 degrees of advance, 2-pentanol 0.83 degrees, and methyl pentanoate only 0.20 degrees. For both metrics, these results are the average of three speed/load engine conditions, and for the methyl pentanoate, the standard deviation across these three conditions was larger than the average ..phi..-sensitivity improvement. This leads to the conclusion that methyl pentanoate does not offer any significant ..phi..-sensitivity benefits, while the pentanols do. Both 1-pentanol and 2-pentanol are thus fuels of interest for further study as low-carbon blendstocks for ACI engines.