Automotive engine

(mechanical engineering) The fuel-consuming machine that provides the motive power for automobiles, airplanes, tractors, buses, and motorcycles and is carried in the vehicle.

The component of the motor vehicle that converts the chemical energy in fuel into mechanical energy for power. The automotive engine also drives the generator and various accessories, such as the air-conditioning compressor and power-steering pump. See also Automotive climate control; Automotive electrical system; Automotive steering.

Otto-cycle engine

An Otto-cycle engine, the dominant automotive engine in use today, is an internal combustion piston engine that may be designed to operate on either two strokes or four strokes of a piston that moves up and down in a cylinder. Generally, the automotive engine uses four strokes to convert chemical energy to mechanical energy through combustion of gasoline or similar hydrocarbon fuel. The heat produced is converted into mechanical work by pushing the piston down in the cylinder. A connecting rod attached to the piston transfers this energy to a rotating crankshaft. See also Gasoline; Internal combustion engine; Otto cycle.

Engines having from 1 to 16 cylinders in in-line, flat, horizontally opposed, or V-type cylinder arrangements have appeared in production vehicles. Increased vehicle size and weight played a major role in this transition, requiring engines with additional displacement and cylinders to provide acceptable performance. See also Engine.

In many automotive engines, the camshaft, which operates the intake and exhaust valves, has been moved from the cylinder block to the cylinder head. This overhead-camshaft arrangement allows the use of more than two valves per cylinder, with various multivalve engines having three to five. Some overhead-camshaft engines have only one camshaft, while others have two camshafts, one for the intake valves and one for the exhaust valves. A V-type engine may have four camshafts, two for each bank of cylinders.

Most engines have fixed valve timing, regardless of the number of camshafts or their location. Variable valve timing can improve fuel economy and minimize exhaust emissions, especially on multivalve engines. At higher speeds, volumetric efficiency can be increased by opening the intake valves earlier. One method drives the camshaft through an electrohydraulic mechanism that, on signal from the engine computer, rotates the intake camshaft ahead about 10°. Another system varies both valve timing and valve lift by having two cam lobes, each with a different profile, that the computer can selectively engage to operate each valve. Computer-controlled solenoids for opening and closing the valves will allow elimination of the complete valve train, including the camshaft, from the automotive piston engine while providing variable valve timing and lift.

Alternative engines

Alternative engine designs have been investigated as replacements for the four-stroke Otto-cycle piston engine, including the two-stroke, diesel, Stirling, Wankel rotary, gas turbine, and steam engines, as well as electric motors and hybrid power plants. However, only two engines are in mass production as automotive power plants: the four-stroke gasoline engine described above, and the diesel engine. See also Diesel engine; Rotary engine; Stirling engine.