Understanding Compression Strokes
A compression stroke is one of the operating phases of an internal combustion engine. In a typical four-stroke internal combustion engine, the compression stroke constitutes the second of four movements of the engine piston in the sequence of intake, compression, power and exhaust. During the compression stroke phase, air and fuel are compressed together in the engine.
Other People Are Reading
-
How the Piston Moves
-
The piston reaches the compression stroke phase after the intake phase and the piston has gone as far down as it can go. As the compression phase begins, the piston reverses and moves upward. The intake and exhaust valves close and the cylinder is sealed. As the piston travels upward, the mixture of air and fuel in the cylinder becomes compressed. This compression increases the pressure in the cylinder and prepares it for the power phase.
Effects
-
The compression stroke phase increases the pressure and temperature of the air/fuel mixture. No heat is transferred to the mixture during compression, but the pressure and the volume work together to produce an increase in temperature according to the laws of thermodynamics. As the volume of the air/fuel mixture decreases, the pressure and temperature increases.
-
The Process in Diesel Engines
-
The operation of a diesel-powered engine works a little differently than in a gas-powered engine. In a diesel engine, the fuel is not mixed with the air entering the cylinder during the intake stroke. During the compression stroke phase, only air is compressed, and the compression ratio is much higher. The air can reach temperatures of up to 1000 degrees Fahrenheit. At the end of the compression stroke phase, the fuel is injected into the cylinder, where the high temperature of the air causes it to ignite spontaneously.
Compression Testing
-
Testing the compression stroke of an engine is a standard way to gauge the condition of a car engine's parts. Testing occurs when the engine is warm, with the ignition disabled and spark plugs removed. The testers crank the engine and read a tester meter connected to the cylinder as the engine turns over 6 to 8 compression strokes. A reading of 135 PSI means the engine is working perfectly, while 85 PSI or lower means it is in poor condition.
-
References
- Photo Credit Aeronautical piston engine image by Andrew Breeden from Fotolia.com
