Impact of aromaticity and cetane number on the soot-NOx trade-off in conventional and low temperature combustion

This paper investigates whether or not two persistent diesel dogmas, namely “the higher the cetane number (CN) the better” and “the lower the aromaticity the better”, still ring true when a compression ignition engine is operated in the low temperature combustion (LTC) regime. The transition from conventional, high temperature combustion (HTC) to LTC is realized in a step-wise approach by increasing the level of exhaust gas recirculation, reducing the compression ratio and by lowering intake pressure. The fuel matrix spans a range of both aromaticity and CN. All experiments are conducted on a modified DAF heavy-duty compression ignition engine.Two main conclusions can be drawn from the results. First, at equal aromaticity, there is no discernible benefit of a high CN with respect to the soot-NOx trade-off in the HTC mode. In fact, when operating in the LTC regime, a high CN even results in a penalty in aforementioned trade-off. Second, at equal CN, increased aromatic content always has a negative impact on the soot-NOx trade-off, irrespective of combustion mode. Accordingly, our results demonstrate that, with respect to the soot-NOx trade-off, the first and second dogma is valid in neither and both of the combustion modes, respectively.