What effect does a fuel heater have on fuel being fed into a gas-turbine engine?

A fuel heater functions primarily to prevent ice formation in fuel filters, which is crucial for the operation of gas-turbine engines. As fuel is exposed to low temperatures, especially at high altitudes, water present in the fuel can freeze and turn into ice. This ice can clog fuel filters, leading to fuel starvation for the engine and potentially causing failure. By heating the fuel, the fuel heater ensures that any water in the fuel remains in a liquid state, thus preventing ice from forming and allowing for uninterrupted fuel flow to the engine.

The other options do not accurately reflect the primary function of a fuel heater in this context. While fuel heaters may have secondary effects related to flow and combustion efficiency, their main purpose is to manage temperature to prevent icing, which is a critical safety and operational concern for gas-turbine engines.