Nacelles are streamlined enclosures used primarily to house the engine and its components. They usually present a round or elliptical profile to the wind thus reducing aerodynamic drag. On most single-engine aircraft, the engine and nacelle are at the forward end of the fuselage. 

Nacelles are nothing but the housing for the aircraft engines as they protect the gas turbine from foreign object ingestion (FOI). They are designed with the objective of delivering air efficiently and with minimum distortion to the fan and also expand the gases in the exhaust system with maximum efficiency. Aircraft nacelles commonly include the following components: Engine cowlings such as inlet and fan cowls are designed to protect aircraft engines and reduce parasitic drag, including form drag and skin friction drag.

An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines. Examples of engines used in aviation include: Piston Engine. Turbojet Engine. “Aircraft engine” means an engine used, or intended to be used, to propel an aircraft, including a part, appurtenance, and accessory of the engine, except a propeller. Electric planes use batteries to power an electric motor instead of jet fuel to power an engine. They need a motor that can turn electric power into mechanical energy — and they need a battery. Compares electric planes to its traditional fuel-powered equivalent.