Low temperature autoignition of diesel fuel under dual operation with hydrogen and hydrogen-carriers

While electrification of light duty vehicles is becoming a real solution to abate local pollutant as well as greenhouse gases emission, heavy duty applications (such as long distance, freight and maritime transport) will keep requiring fuel-based propulsion systems. In these sectors, dominated by compression ignition engines, research on alternative biofuels and new combustion modes is still highly necessary. Dual-fuel combustion appears as a very promising concept to replace conventional diesel fuel by sustainable ones. Among the latter, hydrogen-derived fuels (the so-called electrofuels or e-fuels) are maybe the most interesting. This work addresses the effect of partial substitution of diesel fuel by hydrogen and hydrogen-carriers (ammonia and methane) on the autoignition process under low temperature conditions. Tests were carried out in a constant volume combustion chamber at different temperatures (535, 600 and 650 °C) and pressures (11, 16 and 21 bar). While the cool flames timing and intensity was only slightly affected by the low reactivity fuel energy content, the main ignition was delayed, this effect being much more noticeable for ammonia, followed by hydrogen and finally methane. Kinetic simulations showed a clear competition for active radicals between both fuels (diesel and low reactivity fuel). The combustion duration also increased with the hydrogen or hydrogen-carrier content, which greatly points to the need of modifications in the injection strategy of compression ignition engines operating under dual mode. A correlation was proposed for estimating the autoignition delay time for dual-fuel lean combustion at low temperature.