Intercooler . An air-to-air heat exchanger installed between a turbosupercharger and the carburetor. Intercoolers decrease the temperature of compressed air to prevent detonation.

Interference angle (poppet valve dimension ). The difference between the valve seat and the valve face angles. Normally, the valve seats are ground with between 0.5º and 1º greater angle than the valve face. This allows the face to touch the seat with a line contact that provides the best sealing.

Interference fit . A type of fit used when assembling certain mechanical devices. The hole is made smaller than the part that fits into it. The material containing the hole is heated to expand the hole, and the part that fits into the hole is chilled to shrink it. The parts are assembled, and when they reach the same temperature their fit is so tight they will not loosen in service.

Internal-combustion engine . A form of heat engine in which the fuel and air mixture is burned inside the engine to heat and expand the air so it can perform useful work.

Internal timing . The adjustment of the breaker points of a magneto so they will begin to open at the time the magnet is in its E-gap position.

Interpole . A field pole in a compound-wound DC generator used to minimize armature reaction. Interpoles are located between each of the regular field poles, and their coils are in series with the armature winding so all of the armature current flows through them. The magnetic field produced by the interpole coils cancels the distortion caused by the armature field and allows the brushed to remain in the neutral plane where there is no potential difference between the commutator segments. Keeping the brushes in the neutral plane minimizes sparking.

Inverted engine . An inline or V-engine in which the cylinders are mounted below the crankshaft.

Iridium . A very hard, brittle, highly corrosion-resistant, whitish-yellow, metallic chemical element. Iridium is used for the fine-wire electrodes in spark plugs that must operate in engines using fuel with an exceptionally high lead content.

Iso-octane . An organic compound used as the high reference fuel for rating the antidetonation characteristics of aviation gasoline (CH ) CHCH C(CH ). 3 2 2 3 3

Isothermal change . A physical change that takes place within a material in which heat energy is added to or taken from the material as needed to keep its temperature constant.

Jet fuel . Fuel designed and produced to be used in aircraft gas turbine engines.

Jet propulsion . A method of propulsion by accelerating a relatively small mass of air through a large change in velocity.

Jeweler’s file . A small, fine-cut, metalworking file used by jewelry manufacturers.

Joule . A measure of energy. In terms of electrical energy, one joule is equal to one watt-second.

Journal (bearing ). A hardened and polished surface on a rotating shaft that rides in a plain bearing.

Kerosene . A light, almost colorless, hydrocarbon liquid obtained from crude oil through the fractional distillation process. Kerosene is the base for turbine engine fuel.

Kevlar . The registered trade name by DuPont for a patented aramid fiber.

Kinematic viscosity . The ratio of the absolute viscosity of a fluid to its density. Kinematic viscosity is measured in centistokes.