Small Engine Construction and Principles of Operation - Part I

After reading this, you will be able to:

* Explain simple engine operation.
* Know the qualities of gasoline that make you're mower an efficient small engine.
* Know why gasoline is atomized in the small engine.
* Know the basic components of your small engine and know the function of each part.

GASOLINE ENGINES

A gosoline-fueled ingine is a mechanism desinged to transform the chemical energy of burning fuel into mechanical energy. In operation, it controls and applies this energy to mow lawns, cut trees, propel tractors, and perform many other laborsaving jobs. A gasoline engine is an internal combustion engine. Gasoline is combined with air and burned inside the engine. In its simplest form, an engine consists of a ported cyliner, piston, connecting rod, and crankshaft.
The piston is a close fit inside the cylinder, yet it is free to slide on the lubricated walls. One end of the connecting rod is attached to the poston; the other end is fastened to an offset crankpin, or jouranl, of the crankshaft. As the piston moves up and down, the connecting rod forces the journal to follow a circular path, rotating the crankshaft.

SIMPLE ENGINE IN OPERATION

When the engine is cranked, gasoline is atomized (reduced to minute particles) and mixed with air. This mixture is forced through an intake port and into the cylinder, where it is compressed by the piston on the upstroke and ignited by an electrical spark. Combuston forces the piston down to rotate crankshaft. Burning rapidly, the heated gases trapped within the cylinder (combustion chamber) expand and apply pressure to the walls of the cylinder and to the top of the piston. This pressure drives the piston downward on the power stroke, causing the crankshaft to turn. As the piston and connecting rod push the crankshaft journal to the bottom of the stroke, the pressure of the burned gases is released through an exhaust port. Meanwhile, a fresh air-fuel charge enters the cylinder and the momentum of the power stroke turns the crankshaft journal through bottom dead center (BCD) and into the upstroke on another power cycle. Tommorow: Gasoline - The Hydrocaarbon Fuel in Small Engines.