Firewall (engine)

Cutaway drawing of the 1934 Citroen, showing the firewall

Firewall of an aircraft's engine nacelle

In automotive engineering, a firewall is the part of the bodywork that separates the engine from the driver and passengers.

It is most commonly a separate component of the body, or in monocoque construction, a separate steel pressing, but may be continuous with the floorpan or its edges may form part of the door pillars.

The name originates from steam-powered vehicles. The firewall would separate the driver from the fire heating the boiler.

In aviation, a firewall on an aircraft serves a similar purpose to that of a motor vehicle. In single-engine aircraft it is the part of the fuselage that separates the engine compartment from the cockpit. "Put the throttle to the firewall" refers to setting the engine to run at maximum speed. In most multi-engine propeller aircraft the firewall typically divides the nacelle from the wing of the aircraft, or divides the nacelle into two zones.