Power System

Power System

Gasoline internal-combustion engines power most automobiles, but some engines use diesel fuel, electricity, natural gas, solar energy, or fuels derived from methanol (wood alcohol) and ethanol (grain alcohol).

Most gasoline engines work in the following way: Turning the ignition key operates a switch that sends electricity from a battery to a starter motor. The starter motor turns a disc known as a flywheel, which in turn causes the engine’s crankshaft to revolve. The rotating crankshaft causes pistons, which are solid cylinders that fit snugly inside the engine’s hollow cylinders, to move up and down. Fuel-injection systems or, in older cars, a carburetor deliver fuel vapor from the gas tank to the engine cylinders.

The pistons compress the vapor inside the cylinders. An electric current flows through a spark plug to ignite the vapor. The fuel mixture explodes, or combusts, creating hot expanding gases that push the pistons down the cylinders and cause the crankshaft to rotate. The crankshaft is now rotating via the up-and-down motion of the pistons, permitting the starter motor to disengage from the flywheel.

Engine

The basic components of an internal-combustion engine are the engine block, cylinder head, cylinders, pistons, valves, crankshaft, and camshaft. The lower part of the engine, called the engine block, houses the cylinders, pistons, and crankshaft. The components of other engine systems bolt or attach to the engine block. The block is manufactured with internal passageways for lubricants and coolant. Engine blocks are made of cast iron or aluminum alloy and formed with a set of round cylinders.

The upper part of the engine is the cylinder head. Bolted to the top of the block, it seals the tops of the cylinders. Pistons compress air and fuel against the cylinder head prior to ignition. The top of the piston forms the floor of the combustion chamber. A rod connects the bottom of the piston to the crankshaft. Lubricated bearings enable both ends of the connecting rod to pivot, transferring the piston’s vertical motion into the crankshaft’s rotational force, or torque. The pistons’ motion rotates the crankshaft at speeds ranging from about 600 to thousands of revolutions per minute (rpm), depending on how much fuel is delivered to the cylinders.

Fuel vapor enters and exhaust gases leave the combustion chamber through openings in the cylinder head controlled by valves. The typical engine valve is a metal shaft with a disk at one end fitted to block the opening. The other end of the shaft is mechanically linked to a camshaft, a round rod with odd-shaped lobes located inside the engine block or in the cylinder head. Inlet valves open to allow fuel to enter the combustion chambers. Outlet valves open to let exhaust gases out.

A gear wheel, belt, or chain links the camshaft to the crankshaft. When the crankshaft forces the camshaft to turn, lobes on the camshaft cause valves to open and close at precise moments in the engine’s cycle. When fuel vapor ignites, the intake and outlet valves close tightly to direct the force of the explosion downward on the piston.

Engine Types

The blocks in most internal-combustion engines are in-line designs or V designs. In-line designs are arranged so that the cylinders stand upright in a single line over the crankshaft. In a V design, two rows of cylinders are set at an angle to form a V. At the bottom of the V is the crankshaft. In-line configurations of six or eight cylinders require long engine compartments found more often in trucks than in cars. The V design allows the same number of cylinders to fit into a shorter, although wider, space. Another engine design that fits into shorter, shallower spaces is a horizontally opposed, or flat, arrangement in which the crankshaft lies between two rows of cylinders.

Engines become more powerful, and use more fuel, as the size and number of cylinders increase. Most modern vehicles in the United States have 4-, 6-, or 8-cylinder engines, but car engines have been designed with 1, 2, 3, 5, 12, and more cylinders.

Diesel engines, common in large trucks or buses, are similar to gasoline internal-combustion engines, but they have a different ignition system. Diesels compress air inside the cylinders with greater force than a gasoline engine does, producing temperatures hot enough to ignite the diesel fuel on contact. Some cars have rotary engines, also known as Wankel engines, which have one or more elliptical chambers in which triangular-shaped rotors, instead of pistons, rotate.

Electric motors have been used to power automobiles since the late 1800s. Electric power supplied by batteries runs the motor, which rotates a driveshaft, the shaft that transmits engine power to the axles. Commercial electric car models for specialized purposes were available in the 1980s. General Motors Corporation introduced a mass-production all-electric car in the mid-1990s.

Automobiles that combine two or more types of engines are called hybrids. A typical hybrid is an electric motor with batteries that are recharged by a generator run by a small gas- or diesel-powered engine. By relying more on electricity and less on fuel combustion, hybrids have higher fuel efficiency and fewer toxic emissions. Several automakers have experimented with hybrids and in 1997 Toyota became the first to announce plans for mass-production of a hybrid vehicle.

Fuel Supply

The internal-combustion engine is powered by the burning of a precise mixture of liquefied fuel and air in the cylinders’ combustion chambers. Fuel is stored in a tank until it is needed, then pumped to a carburetor or, in newer cars, to a fuel-injection system.

The carburetor controls the mixture of gas and air that travels to the engine. It mixes fuel with air at the head of a pipe, called the intake manifold, leading to the cylinders. A vacuum created by the downward strokes of pistons draws air through the carburetor and intake manifold. Inside the carburetor, the airflow transforms drops of fuel into a fine mist, or vapor. The intake manifold delivers the fuel vapor to the cylinders, where it is ignited.

All new cars produced today are equipped with fuel injection instead of carburetors. Fuel injectors spray carefully calibrated bursts of fuel mist into cylinders either at or near openings to the combustion chambers. Since the exact quantity of gas needed is injected into the cylinders, fuel injection is more precise, easier to adjust, and more consistent than a carburetor, delivering better efficiency, gas mileage, engine responsiveness, and pollution control. Fuel-injection systems vary widely, but most are operated or managed electronically.

High-performance automobiles are often fitted with air-compressing equipment that increases an engine’s output. By increasing the air and fuel flow to the engine, these features produce greater horsepower. Superchargers are compressors powered by the crankshaft. Turbochargers are turbine-powered compressors run by pressurized exhaust gas.

Exhaust System

The exhaust system carries exhaust gases from the engine’s combustion chamber to the atmosphere and reduces, or muffles, engine noise. Exhaust gases leave the engine in a pipe, traveling through a catalytic converter and a muffler before exiting through the tailpipe.

Chemical reactions inside the catalytic converter change most of the hazardous hydrocarbons and carbon monoxide produced by the engine into water vapor and carbon dioxide.

The conventional muffler is an enclosed metal tube packed with sound-deadening material. Most conventional mufflers are round or oval-shaped with an inlet and outlet pipe at either end. Some contain partitions to help reduce engine noise.

Car manufacturers are experimenting with an electronic muffler, which uses sensors to monitor the sound waves of the exhaust noise. The sound wave data are sent to a computer that controls speakers near the tailpipe. The system generates sound waves 180 degrees out of phase with the engine noise. The sound waves from the electronic muffler collide with the exhaust sound waves and cancel each other out, leaving only low-level heat to emerge from the tailpipe.

Cooling and Heating System

Combustion inside an engine produces temperatures high enough to melt cast iron. A cooling system conducts this heat away from the engine’s cylinders and radiates it into the air.

In most automobiles, a liquid coolant circulates through the engine. A pump sends the coolant from the engine to a radiator, which transfers heat from the coolant to the air. In early engines, the coolant was water. In most automobiles today, the coolant is a chemical solution called antifreeze that has a higher boiling point and lower freezing point than water, making it effective in temperature extremes. Some engines are air cooled, that is, they are designed so a flow of air can reach metal fins that conduct heat away from the cylinders.

A second, smaller radiator is fitted to all modern cars. This unit uses engine heat to warm the interior of the passenger compartment and supply heat to the windshield defroster.