BRUSSELS — The war against Iran is exposing a critical weakness for Europe’s militaries: it imports over 90 percent of the crude converted to jet fuel, which could leave aircraft grounded in a prolonged crisis. Thanks to the war in Iran, kerosene spiked to an all-time high of $1,795 per ton on March 19, more than double what it was before the U.S. and Israeli strikes began. One solution would be to ramp up the production of synthetic sustainable aviation fuel, known as eSAF, made by combining