Internal Combustion Engines & Engine Oil

Table Of Contents

How an internal combustion engine works:

All internal combustion engines operate on a theory called the Otto Cycle of events, named after Nikolaus Otto, who invented it in 1867. It occurs in 4 repeating steps or cycles:

  • Intake
  • Compression
  • Combustion (or power)
  • Exhaust

The fuel and air are drawn into the engine cylinder by the piston moving down while the intake valve is open. When the piston starts moving up, both intake and exhaust valves are closed. The piston moving up compresses the air and fuel mixture. The air and fuel mixture is then ignited with a spark plug (in regular gasoline engines), creating combustion. The extreme heat creates high pressure forcing the piston down. Next, the exhaust valve opens. The piston goes back up exhausting the exhaust gas. Then the cycle is repeated.

C: Crankshaft

E: Exhaust camshaft I: Inlet camshaft

P: Piston

R: Connecting rod S: Spark plug

V: Valves (Red: exhaust, Blue: intake) W: Cooling water duct

Cross section of a cylinder in a combustion engine.

Here is a decent animation of the Otto cycle on YouTube: . (ln the illustration above, the intake is on the right and the exhaust is on the left, but in the YouTube animation the intake is on the left and the exhaust is on the right)

The process of combustion is the conversion of chemical energy (gasoline) into heat energy (combustion) which is converted into reciprocating energy (pumping of the pistons). The pistons turn a crank shaft via a connecting rod. As the piston goes up and down during combustion it rotates the crankshaft. The crankshaft turns reciprocating energy into rotational energy. This energy is eventually transferred to the wheels through the drivetrain, which we will discuss later in Chapter 9.

An illustration showing pistons (gray) in their respective cylinders (blue) and a crankshaft (red). As the pistons go up and down the crankshaft is rotated. This image is animated at

ln a diesel engine there are no spark plugs. The fuel is ignited based on compression alone. The compression is higher on a diesel engine, which generates enough heat to cause the combustion.

A hybrid vehicle uses an electric motor and battery for assisting propulsion along with the internal combustion engine. The internal combustion engine generates electricity to recharge the batteries. Also, the batteries are recharged when braking to a stop.

Engine Oil

Sample of motor oil

The purpose of engine oil is to form a film of lubrication between all moving parts of an internal combustion engine to reduce friction and wear. Choosing the right engine oil for your vehicle and changing the oil during regularly-scheduled maintenance intervals will keep the engine running smoothly over time. The recommended oil type and specification for your vehicle can be found in the owner's manual. Another place to find it is on the oil fill cap. lt will be based on the ambient temperature where you live. There are two engine oil codes that the owner’s manual will specify, an APl and an SAE.

All oil has an APl code which stands for American Petroleum lnstitute. lt's a service rating for the quality, cleanliness, and types of detergents in the oil. The code will always be two letters.

The SAE is the viscosity or thickness of the oil. Modern oil is multi-viscosity oil. The SAE may be something to the effect of 5W-30. The first number-letter combo (5W) indicates the viscosity or thickness of the oil when it is cold. The second number is the viscosity at the engine operating temperature. Before they had multi-viscosity oil there was only single-viscosity oil (such as SAE 30), which in cold weather was extremely thick. Trying to pour it into your engine would be like pouring honey, but more importantly it would be hard to pump the oil and lubricate the engine. That's why older engines had to be warmed up before you could drive them.

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