In this article we will discuss a topic much discussed in the automotive field. The differences between the Otto engine and the Diesel engine. For starters we will start with a little history to know how these two engines first appeared.
Let’s start with the Otto engine. This engine was invented by Nikolaus August Otto in 1854, but more importantly, Nikolaus Otto invented the Otto engine cycle, in fact he first invented the internal combustion engine. The Otto engine cycle consists of 4 strokes:
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Time 1, downhill intake, where fuel and air enter the combustion chamber. (the inlet valve is in the open position and the outlet valve in the closed position)
Time 2, adiabatic compression, the piston compresses the mixture. (both valves are closed)
Time 3, combustion and expansion, when the compressed mixture is ignited by the spark plug and the piston is pushed down. (both valves are closed)
Time 4, the exhaust, the gases resulting from the combustion chamber are released. (the intake valve is closed and the exhaust valve is open).
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With the diesel engine, things are about the same, only with a few changes. For the beginning the diesel engine was invented by Rudolf Christian Karl Diesel (former German engineer and inventor).
The diesel engine is very similar to the gasoline engine, except that the fuel is ignited due to the high temperature created by compressing the air needed for combustion and not by using an auxiliary device (as in the case of the Otto engine that uses an electric spark plug).
Compressing a gas inevitably leads to an increase in its temperature, this being the method by which fuel is ignited in diesel engines. The air is sucked into the cylinder and is compressed by the piston at a ratio of 25 to 1, i.e. its volume is reduced 25 times.
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When the piston almost reaches the end of the upper stroke, the diesel is sprayed inside and thanks to the very high temperature (somewhere at 700-900 C) it ignites instantly. Combustion of the mixture (air and diesel) leads to an increase in the temperature and pressure acting on the piston, pushing it down, thus producing mechanical work.
We talked a lot about their history and how they work, now let’s move on to the differences between fuels. What is the difference between gasoline and diesel? Well, both gasoline and diesel are extracted from oil, but by different methods of refining.
Specifically during combustion, gasoline is combined with air to create vapors, which once ignited produce power (gasoline molecules are smaller than diesel because it is more refined). While for diesel (which is less refined), the engine needs higher compression and higher temperatures to burn (diesel molecules are larger and therefore burn harder) and excess diesel that cannot be burned will be eliminated on evacuation in the form of “black smoke”.
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Even though it may not seem like it, the two engines are very, very similar in operation. That is, the biggest difference between the two is how the fuel is ignited.
As I said above, for gasoline the mixture is ignited by a spark produced by a spark plug and for diesel engines the mixture is ignited by compression. Another difference between the two is the power and strength they develop.
Diesel engines produce more power, which is why they are especially useful when it comes to heavy weights, which is why in the beginning they were mostly used on commercial cars, which carried heavy weights.
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Gasoline engines have more horsepower, so they will have more rotations and thus a higher acceleration. Usually, the big car manufacturers offer both engine variants.
They will drive differently, for this reason it is recommended to buy a car equipped with a diesel engine only if you plan to do many km on highway or constant driving. The advantages of a diesel engine are high torque and low consumption, which makes it more profitable in the long run if you do many km.
So mainly the differences between the two engines are: the way the fuel is ignited, the power or force they develop and the purpose for which they are used.
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