Basic Properties of an Internal Combustion Engine By: Todd Conrado Why is it important to understand the operation of engines? Why is it important to understand the operation of engines? • General knowledge. • Understanding what your working with. • To be a better technician. • To be able to troubleshoot more efficiently. The Basics • Internal combustion engines are a direct descendent of external combustion engines. • The switch over to internal combustion was difficult but resulted in much greater efficiency, smaller engine size, ease of use, and adaptability. The basics • Today’s modern engines are relatively safe, efficient, inexpensive, and easy to refuel. Engines and Potato Guns • To understand the basic idea of how an internal combustion engine works, it is helpful to have a good mental picture of how “internal combustion” works. A good example is the potato gun. Engines and Potato Guns • Say you take an enclosed cylinder and place a small amount of gasoline in it. • You then take a potato and seal the end of the cylinder. • Now you ignite the fuel. • What happens? Engines and Potato Guns • Correct - The potato is expelled out the cylinder with great force. • This small amount of fuel produced a tremendous amount of force. This is the energy harnessed by the internal combustion engine. Engines and Potato Guns • The internal combustion engine uses the basic principles behind the potato canon. • To be more efficient though the engine needs to perform the loading operations automatically. It does this through the operation cycles. Engine Cycles • The vast majority of engines use the four stroke cycle (Otto Cycle) to convert gasoline into motion. • The four strokes are – Intake – Compression – Power – Exhaust Engine Cycles • The potato in our example is replaced by the piston. • The piston is connected to the crankshaft by the connecting rod. • As the crankshaft rotates it actuates the valves in effect reloading the cannon. Intake Stroke • The piston starts at the top of the cylinder and moves downward. • The intake valve opens allowing a fresh charge of mixed fuel and air into the cylinder. • This is the intake stroke. Compression Stroke • Once reaching bottom the piston moves back up. • The intake valve closes sealing the mixture inside the cylinder. • The mixture compresses making the soon to come explosion more powerful and efficient. • This is the compression stroke. Power Stroke • When the piston reaches the top of its stroke the fuel mixture is ignited by the spark plug. • The gasoline charge in the cylinder explodes with great power. • This is the power stroke Exhaust Stroke • Once the piston reaches the bottom of its stroke the piston again moves upward. • The exhaust valve opens and the burnt gasses are forced out of the cylinder. • This is the exhaust stroke and the engine is ready to begin the cycle again. The basis for understanding • All engines need three basic functions to operate. • They are – Fuel – Ignition – compression • The Four Cycle process provides these three functions continuously and automatically for efficient engine operation. Key Points • Internal Combustion is combustion inside the cylinder. • The cycle order is – Intake – Compression – Power – Exhaust • The basic parts of the internal combustion engine.
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