These days, basically every internal combustion engine you'll find in a car uses a four-stroke combustion cycle. But who was it exactly that came up with this cycle, and how exactly does a four-stroke engine work?
While the second one of these questions will require a more in-depth explanation, the first question is easy to answer. The four-stroke engine was invented in 1876 by Nicolaus Otto, a German inventor.
In this article, we'll be going over the history of the four-stroke engine and its creator, and we'll also explain the difference between two- and four-stroke engines as well as the differences between the different kinds of four-stroke cycles.
Who Was Nicolaus Otto?
First, though, a little bit of background on the man who came up with this engine design.
Nicolaus Otto was born on June 10th, 1832, as the youngest of six children. As a young man, Otto had always been interested in science and technology, but his first job was something a lot more mundane; he worked as a grocery salesman, travelling throughout Western Germany and selling colonial goods like sugar, coffee, tea, and rice.
It took quite a while for Otto to get into the business of engine design. His first real attempt at this happened in 1860 after he learned of the engine that French inventor Jean Joseph Étienne Lenoir had invented. Lenoir's design was the first truly successful internal combustion engine design.
Initially, Otto sought to replicate Lenoir's design, and his first engine design was basically the same as Lenoir's but created to run on liquid fuel instead of coal gas. However, his patent didn't end up going through.
While Lenoir's engine worked reasonably well overall and was very quiet when running, it suffered from one pretty significant issue in that it was very inefficient. This was because Lenoir's engine didn't compress the air/fuel mixture before combusting it, leading to incomplete combustion.
After trying to copy Lenoir's design, Otto set out to improve upon it. He'd previously learned of the concept of fuel compression and wanted to try and make an engine that utilized it. In 1862, Otto produced his first attempt at a four-stroke engine, but his design was flawed and the engine broke after running for only a few minutes.
After a few more years of reworking his engine design, Otto was starting to run low on funds, and reached out to industrialist Eugen Langen to provide him with the capital needed to design a successful engine. Their company, named NA Otto ; Cie, was the first company in the world founded solely to design and manufacture internal combustion engines.
Otto's company started seeing its first real success in 1872, when it brought on Gottlieb Daimler as technical director and Wilhelm Maybach as head of engine design. Daimler, in turn, was responsible for hiring two engineers named Franz Rings and Herman Schumm.
Ultimately, it was the design created in 1876 by Otto, Rings, and Schumm that would be the first truly successful four-stroke engine, and the engine that would be the template for almost every other four-stroke engine in the future.
Four-Stroke Versus Two-Stroke Engines
We've talked at length about the history of the four-stroke engine now, but perhaps you're not entirely aware of what a four-stroke engine is. You may have also heard the term "two-stroke" engine used before and wondered if there's a difference between two- and four-stroke engines.
Basically, the difference between a two-stroke engine and a four-stroke engine is the number of strokes each piston in the engine needs to make to complete a full combustion cycle. Four-stroke engines, as the name suggests, complete the combustion cycle in four strokes, while a two-stroke engine completes it in two.
In a four-stroke engine, the first stroke is the intake stroke, where air and fuel enter the combustion chamber. The second stroke is the compression stroke, which compresses the air/fuel mixture. The third stroke is the actual combustion stroke, and the fourth stroke is the exhaust stroke.
In a two-stroke engine, on the other hand, the intake, exhaust, and combustion strokes are the same stroke, while the compression stroke is its own separate stroke. As the piston descends in the cylinder following combustion, exhaust gas is forced out of the cylinder while the air/fuel mixture is simultaneously being sent in.
The advantage of two-stroke engines is that they usually have a higher power-to-weight ratio than four-stroke engines, and they're a bit easier to maintain because they contain fewer moving parts. However, two-stroke engines are a lot dirtier than four-strokes, and also require more regular maintenance.
Otto Cycle Versus Atkinson Cycle Versus Diesel Cycle
While Otto's four-stroke cycle is the one used in the majority of cars today, it's not the only four-stroke cycle that exists. The other four-stroke cycles that are sometimes used in modern engines are the Atkinson cycle and the Diesel cycle.
The Atkinson cycle was invented by British inventor James Atkinson in 1882 and was designed to provide more fuel efficiency than an Otto cycle engine at the cost of slightly reduced power at low speeds. While Atkinson's engines weren't successful at the time, his design would later be used in many hybrid cars.
The Atkinson cycle only has one key difference compared to the Otto cycle. In an Otto cycle, during the compression stroke, the intake valves remain closed the entire time to provide as much compression as possible.
In an Atkinson cycle, however, the intake valve remains open for a short time during the compression stroke, so some of the air/fuel mixture gets pushed back up into the intake manifold. However, because the piston doesn't have to work as hard to achieve compression due to the decreased pressure in the cylinder, this helps the engine run more efficiently.
The fuel that gets pushed back up into the intake manifold returns to the combustion chamber during the next cycle, so no fuel is actually wasted in this process.
The other cycle is the Diesel cycle, which as you can probably guess is used on diesel fuel engines. The Diesel cycle is essentially the same as the Otto cycle, except for the fact that the air/fuel mixture in a Diesel cycle engine is combusted entirely through the heat and pressure generated by compression.