Autoignition of sustainable fuels under dual operation with H₂-carriers in a constant volume combustion chamber

The expected increase in the use of environmentally friendly liquid fuels in medium and heavy-duty compression ignition engines (for both off-road and transport applications), together with the well-documented benefits of hydrogen-carriers to decrease energy dependence and to achieve a neutral-carbon economy (internal combustion engines highly contributing to the global CO₂ emissions), have motivated this work. The autoignition characteristics of different alternative diesel-type fuels (hydrotreated vegetable oil, advanced biodiesel and blends of conventional diesel fuel with polyoxymethylene dimethyl ether and 1-butanol) under dual-fuel operation with H₂, NH₃, and CH₄ were studied in a constant volume combustion chamber at 535 and 600 °C. The high reactivity fuel was replaced by the gaseous fuel up to 40 % by energy. The main ignition delay time was significantly affected not only by the type of low reactivity fuel, with ammonia considerably retarding autoignition, but also by the nature of the liquid fuel, biodiesel being the less sensitive to the presence of the H₂-carrier fuel. Results also proved that the higher the reactivity of the diesel-type fuel (quantified through the cetane number), the lower the influence of the gaseous fuel on the autoignition time.