Preheating

Preheating is the deliberate warming of an object or substance before it is used, operated, or processed. The goal is to bring temperatures closer to the intended operating condition, reduce defects from rapid temperature changes, and improve performance or efficiency. Preheating is applied across mechanical, chemical, and culinary contexts.

In engines and fuel systems, preheating commonly involves warming the engine or intake air prior to starting, using block heaters or glow plugs. This reduces cold-start wear, improves starting reliability, lowers emissions, and can shorten warm-up time. Diesel engines often rely more on preheating in cold weather to achieve reliable ignition.

In fabrication and materials science, preheating refers to warming metals before welding or forming. Preheating lowers thermal gradients, reduces the risk of cracking or distortion, and can slow the cooling rate to control residual stresses. Interpass heating and controlled cooling are typical practices for sensitive alloys.

In culinary contexts, ovens are preheated to the target cooking temperature before food is placed inside. This ensures even cooking and consistent results, though it adds time and energy use to the process.

In industrial processes, preheating feeds, combustion air, or gases can improve energy efficiency and reduce thermal shock to equipment. For boilers, preheating feedwater reduces thermal stresses and lowers the energy required to generate steam, contributing to overall process efficiency.