Autoignition of diesel-like fuels under dual operation with H2

The partial replacement of diesel fuel with gaseous fuels in diesel engines allows for reducing soot, increasing the renewable fraction of the fuel and decreasing CO2 emissions. Hydrogen is a promising alternative; since it is a non-carbon compound, it can be produced from renewable sources and it has suitable combustion properties. However, the use of hydrogen in diesel engines could require some modifications on the engine calibration. Among the different phenomena involved in diesel combustion, autoignition significantly affects the engine efficiency. This work analyzes the autoignition behavior of diesel and biodiesel fuels under a H2-rich ambient. Two different liquid fuel replacements (10% and 20% by energy) have been tested in a constant-volume combustion chamber. Three different chamber temperatures (535°C, 602°C, and 650°C) and equivalence ratios (0.4, 0.6, and 0.8) have been checked. Results show that, in the case of diesel fuel, hydrogen delays autoignition and reduces the combustion rate, the latter caused by a higher fuel dilution with air. The influence of H2 in the autoignition of biodiesel is less significant. A reduction in the OH radicals pool appears as the main reason for retarding ignition. The lower pressure peaks with hydrogen suggest unburnt hydrogen to be relevant.