#15 Car Engines – The 4 Stroke Cycle

A car’s engine basically functions as the brain behind all the mechanics. It enable the power generated by the engine’s cylinders to be transferred to the car’s rear wheels. Here, we take a closer look at one of the cylinder in the engine compartment and learn how it works in the famous 4 Stroke Cycle.

1) Intake Stroke

ü  The piston located in the cylinder descends, enable air into the cylinder through an open intake valve.

ü  The fuel is injected into the cylinder from fuel injector.

ü  The image below demonstrates how the intake stroke work.

2) Compression Stroke

ü  Now, all the valves are closed, the piston comes up.

ü  In the process, the fuel and air mixture is compressed.

ü  The compression of the mixture creates power and efficiency that run the car.

ü  The image below demonstrates how the compression work.

3) Power Stroke

ü  The spark plug located at the top of the piston ignites a spark.

ü  The spark creates a downward force for the piston to go to the bottom of the cylinder again.

ü  Generally, the smaller the cylinder, the smoother the explosion produced by the spark.

ü  The image below demonstrates how the power work.

4) Exhaust Stroke

ü  The piston return to the top again.

ü  This time force the spent fuel-air mixture (wastes) out through the open exhaust valve.

ü  The image below demonstrates how the exhaust work.

 The Full Model

After looking at how one cylinder works in the engine systems, we now take a closer look at a basic 4 cylinders engine configurations.

The Engine Full Scale Model

The moment the piston in the cylinder moves up and down, it turns the crank beneath it so that the crank will produce a continuous rotation about the crankshaft (see picture). The car’s power is delivered from the crankshaft and eventually to the wheels. Note that the crank for each cylinder does not rotate at the same feat; it has to be counterweights to produce a balanced spin.

The timing belt helps to synchronize the rotation of the crankshaft and the camshafts. This is to ensure the engine’s valves open and close at proper times during each cylinder’s intake and exhaust strokes. (One full crankshaft revolution is equivalent to the complete 4 Stroke Cycle)

Basic and Common Engine Configurations

1) V-Twin

ü  Two-cylinder arrangement.

ü  Mostly used in vehicles that utilize smaller horsepower.

ü  For instance, most Harley-Davidson motorcycles have this type of configuration.

A spotted V-Twin in a Harley-Davidson

2) Flat Four

ü  Known as inline-4 cylinder as four cylinders are arranged in flat, opposing configuration.

ü  Neat and require less space compared to the V-shaped arrangements.

Flat Four Engine Arrangement

3) V6

ü  Have six opposing cylinders arranged in a ‘‘V’’ shape.

ü  Suitable for performance cars; commonly the SUVs, MPVs and sport cars.

ü  Believed to be able to deliver more power from the car’s engine.

The V6 Engine

4) V8

ü  Have eight opposing cylinders arranged in a ‘‘V’’ shape.

ü  Suitable for super-performance cars; commonly the muscle-car applications or heavy duty engines.

The V8 Engine Model

After discussing the working principle of the cylinders in a car’s engine, we see the variables that capable to bring the most out of the engine’s package. In other words, the horsepower output.

Increase displacement. More displacement in the engine increases the overall power output. For each revolution, more gas (fuel) is burnt. The increase of combustion release more power to the wheels.

Increase the compression ratio. Higher compression ratios in a car will produce more power. This indicates a more complete fuel-air mixture compression. Higher-octane gasolines are designed for cars with high compression ratios.

Maximize the fuel-air mixture in each cylinder. For any given size of cylinder, the maximum of fuel-air mixture would generate more power just like how you increase the cylinder’s size. This application is commonly seen in turbochargers and superchargers. ( I will discuss about the turbochargers and superchargers’ applications in future post)

Cool the air in the engine. The compression process raise the air’s temperature. A hotter air expands less for combustion to take place, hence, rob the engine of its power. An intercooler helps compressed air that passes through it to cool before entering the cylinder.

Summary

The Camshaft

To sum it up, a car engine consists of multiple cylinders to produce power for the wheels. The intake, compression, power and exhaust strokes constitute the basic principle of The 4 Stroke Cycle we discussed today. In addition, the most common types of engine configurations are being discussed and compared. Lastly, ways and methods to improve the engine’s power output are examined.

In the next automotive article, we will look at another part of the car’s engine which is closely related to The 4 Stroke Cycle – The camshafts. Stay tuned!

Sources: www.auto.howstuffworks.com

               www.animagraffs.com

By: Vincent Ti