engines can be classified in several ways depending on the following
- Operational cycles.
Most technicians will generally come in contact with only four-stroke
cycle 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 3-, 4-, 5-, 6-, 8-, and 12-cylinder
- 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 overhead 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 ¨C two on each side.
- Ignition type. There
are twp 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 the heat generated as air is compressed to ignite the
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 in gasoline.