Classification of Engine

ABOUT YOUR CAR

Have you ever opened the hood of your car and wondered what was going on in there? A car engine can look like a big confusing jumble of metal, tubes and wires to the uninitiated. You might want to know what's going on simply out of curiosity. Or perhaps you are buying a new car, and you hear things like "3.0 liter V-6" and "dual overhead cams" and "tuned port fuel injection." What does all of that mean?

The engine provides the power to drive the vehicle's wheels. All automobile engines, both gasoline and diesel, are classified as internal-combustion engines because the combustion or burning that creates energy takes place inside the engine.

The biggest part of the engine is the cylinder block. The cylinder block is a large casting of metal that is drilled with holes to allow for the passage of lubricants and coolant through the block and provide spaces for movement of mechanical parts. The block contains the cylinders, which are round passageways fitted with pistons. The block houses or holds the major mechanical parts of the engine. The cylinder head fits on top of the cylinder block to close off and seal the top of the cylinder. The combustion chamber is an area into which the air/fuel mixture is compressed and burned. The cylinder head contains all or most of the combustion chamber. The cylinder head also contains ports through which the air/fuel mixture enters and burned gases exit the cylinder. The valve train is a series of parts used to open and close. the intake and exhaust ports. A valve is a movable part that opens and closes the ports. A camshaft controls the movement of the valves. Springs are used to help close the valves. The up-and-down motion of the pistons must be converted to rotary motion before it can drive the wheels of a vehicle. This conversion is achieved by linking the piston to a crankshaft with a connecting rod. The upper end of the connecting rod moves with the piston. The lower end of the connecting rod is attached to the crankshaft and moves in a circle. The end of the crankshaft is connected to the flywheel.

Engine Construction

Modern engines are highly engineered power plants. These engines are designed to meet the performance and fuel efficiency demands of the public. The days of the heavy, cast-iron V8 engine with its poor gas mileage are quickly drawing to a close. Today, those engines have been replaced by compact, lightweight, and fuel-efficient engines . Modem engines are made of light weight engine castings and stampings; non-iron materials (for example, aluminum, magnesium, fiber-reinforced plastics); and fewer and smaller fasteners to hold things together. These fasteners are made possible through computerized joint designs that optimize loading patterns. Each of these newer engine designs has its own distinct personality, based on construction materials, casting configurations, and design.

These modern engine-building techniques have changed.
How engine repair technicians make a living.

Today's automotive engines can be classified in several ways depending on the following design features:

Operational cycles. Most technicians will generally come in contact with only four-stroke engines . However, a few older cars have used and some cars in the future will use a two-stroke engine.

Number of cylinders. Current engine designs include 4-,5-,6-, B-, 10-, and 12-cylinder engines.

Cylinder arrangement. An engine can be flat (opposed), in-line, or V-type. Other more complicated designs have also been used.

Valve train type. Engine valve trains can be either the overhead camshaft (OHC) type or the camshaft in block over head valve (OHV) type. Some engines separate camshafts for the intake and exhaust valves.

These are based on the OHC design and are called dual overhead camshaft (DOHC) engines. V-type DOHC engines have four camshafts-two on each side.

Ignition type.

There are two types of ignition systems: spark and compression. Gasoline engines use a spark ignition system. In a spark ignition system, the air/fuel mixture is ignited by an electrical spark. Diesel engines, or compression ignition engines, have no spark plugs. An automotive diesel engine relies on heat generated as air is compressed to ignite air/fuel mixture for the power stroke.

Cooling systems. There are both air-cooled and liquid cooled engines in use. Nearly all of today's engines have liquid-cooling systems.

Fuel type. Several types of fuel currently used in automobile engines include gasoline, natural gas, diesel and propane. The most commonly used is gasoline.