OTTO CYCLE: How does an internal combustion engine work?

The Otto Cycle: What is it? Have you heard it before?Engines are all around us—in automobiles, motorbikes, boats, and, of course, airplanes. However, how do they operate? And how does a combustion engine operate in our aeroplanes?

This is where the Otto Cycle, which powers most internal combustion engines, enters the picture. Before we go too far, though, watch this instructional video that provides a visual summary of everything we're about to discuss. Have fun!

What is the Otto Cycle?

Thermodynamically, internal combustion engines that use electric spark ignition employ the Otto cycle.

All of the energy produced by the engine, which originates in the internal chamber intended for this purpose, is the cause of its moniker.

The German engineer Nikolaus Otto created this cycle, which has been in operation for just over 145 years since 1876.

Two-stroke and four-stroke engines are the two types of engines found in the Otto cycle. The discrepancy is determined by how many rotations the crankshaft makes, but don't worry—we'll give you all the details in the following lines.

Diagram of the four-stroke Otto Cycle engine

The Otto cycle's diagram is built on four phases, which match the four processes it uses to produce electricity. They are as follows:

Admission

During this stage, the fuel and oxygen mixture can enter the cylinder thanks to the piston's downward movement. The exhaust valve is closed and the intake valve is open.

Furthermore, the fuel is a gas when it enters the cylinder rather than a liquid. As a result, its combustion qualities are greatly enhanced.

Compression

Both valves close when the piston reaches the lowest point in the cylinder, at which point it begins its upward stroke.

The power produced by an engine increases with the compression ratio it produces.

Expansion

The maximum pressure is obtained when the cylinder reaches its top. Both valves are closed during this phase, which is the only one where work is generated.

In diesel engines, the mixture ignites because of the high temperature and pressure created during compression, whereas in Otto Cycle engines, the spark is produced by the spark plug.

The piston begins its rapid downward stroke after the mixture has burned.

Escape

It is the Otto cycle's last phase. When the cylinder rises once more, the exhaust valve is open, allowing the combustion-generated gases to be released.

The intake phase is restarted when the exhaust valve closes when the piston reaches the top of the cylinder.

Two-stroke Otto Cycle vs. four-strike

Two-stroke Otto cycle engines are also available, as we have already discussed. Let's examine the differences between them and the 4-stroke ones.

The first thing to remember is that the crankshaft rotates 180 degrees each time the piston passes inside the cylinder.

Since the piston in a four-stroke engine completes four full strokes, the crankshaft completes two full revolutions.

The procedure is drastically altered with the 2-stroke engine, though, as it is only divided into two stages rather than four.

The combustion and exhaust processes, as well as the intake and compression processes, are all completed simultaneously in this kind of engine. As a result, the crankshaft makes just one revolution rather than two, and the number of piston strokes inside the cylinder is cut in half.

Small motorcycles and outboard engines are examples of two-stroke motors.

Otto Cycle efficiency

Since internal combustion engines generate a lot of power with high efficiency, you are already aware that they operate using the Otto cycle.

A balanced ratio of fuel to air entering the engine is necessary for an Otto Cycle engine to run at peak efficiency.

Its stoichiometric ratio, which is the most precise, is 14.7 parts air to 1 part fuel. This ratio is known as the lambda factor.

It is for this reason that we have to reduce the mixture as we fly higher.

Formula for power in the Otto Cycle

The following is the formula that describes how Otto cycle engines work:

Work = (U2-U1) + (U4-U3) = +4 -5 = -1 = W1-2 + W 3-4

One must remember that the explosion process is the only one that produces work; all other processes deduct energy. This is demonstrated by the work created formula, where each negative sign denotes an energy loss.

Another consideration is that an engine produces more power the more compression it has. The volume loss inside the cylinder from the bottom dead center to the top dead center is known as the compression ratio.

Indeed, we are aware of your thoughts. It's a little unclear. However, let's use a more straightforward comparison:

Consider filling a syringe with air until the needle reaches the tenth mark. Then, shut off the inlet and push the plunger until it reaches 1, achieving a compression ratio of 10. That's easier.

Atkinson Cycle vs. Otto Cycle

Because of its great efficiency and low fuel consumption, the Atkinson cycle is increasingly being used in the development of hybrid vehicles.

The Atkinson cycle and the Otto cycle vary primarily in that the Atkinson cycle reduces compression by having the intake valve close later.

Additionally, the pressure within the cylinder is equivalent to atmospheric pressure when the cycle is finished, however this pressure is significantly higher in Otto cycle engines.

Generally speaking, Atkinson engines' lower compression ratio results in both a longer service life and reduced fuel use. But compared to an Otto cycle engine, they produce a lot less power.

Nikolaus Otto, the inventor of the internal combustion engine

On June 10, 1832, Nikolaus Otto was born in Cologne. Because to his creation of the first four-stroke engine in 1872, this German inventor is remembered as one of the most significant engineers in human history.

Despite lacking a strong educational foundation, Otto rose to fame in 1864 when he and Eugen Langen established the NA Otto & Cie, the first engine factory in history.

Personally, Gustav Otto, who co-founded BMW with Karl Rapp in 1917, was the son of Nikolaus Otto.