Light distillate fuels for transport

The fuels best suited to vehicular transport are those in the liquid phase that lend themselves to both long-term storage and efficient combustion. Petroleum-derived gasolines, kerosines and gas oils suit spark-ignition, gas-turbine and compression-ignition engines respectively. Storage requirements include upper limits on volatility, viscosity and freezing point, lower limits on flash point, and adequate thermal stability. For piston engines of both types the most important fuel factor is spontaneous ignitability, which controls combustion knock, whereas gas-turbine combustors require a more general range of properties. Throughout transport, the dominant factor is emission reduction to alleviate environmental pollution. Special high-performance fuel components have been employed in motor racing, but conventional unleaded 'pump' fuel is now specified for reasons of safety, cost and fair competition. The future may bring supplementation of conventional-type fuels from non-petroleum sources, plus substitutes based on compounds of C, H, O and N, including perpetually available bio-derived fuels.