Diesel Engine 101: Getting to Know the Basics
09 Mar 2022
Diesel engines are the most common type of combustion engine used in cars, boats, and trucks. They are used for generating electricity, as well as providing propulsion. They are also used for industrial applications, as well as in trains, such as locomotives.
The diesel engine was invented by Rudolf Diesel. The diesel engine, in fact, a compression-ignition engine (CI engine), is one in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder as it is compressed. This contrasts with spark plug-ignition engines such as gasoline engines or gas engines that burn their fuel outside the cylinder, such as those which use natural gas or liquid petroleum gas.
Diesel engines work by compressing only air, or air plus residual combustion gasses from the exhaust (known as exhaust gas recirculation or EGR). Air is inducted into the chamber during intake and compressed during compression. This increases the temperature of the air inside to a degree so high that atomized diesel fuel injected into it ignites.
With fuel being injected right before combustion, dispersion of particles is uneven- this is called heterogeneous mixture. You can control torque by adjusting λ - instead of throttling intake air, you alter how much fuel gets injected in order to produce desired results; usually, there's a high concentration on λ which has certain effects on your engine performance.
A Brief History of the Diesel Engine
The diesel engine has been around since the late 19th century. The idea of a diesel engine is credited to a German named Rudolf Diesel, who had the goal of inventing a car that didn't require a gasoline engine. Rudolf Diesel conceptualized the diesel engine in 1893, with the very first prototype built later that same year. Diesel engines are usually designed as either two-stroke or four-stroke cycles and have been mainly used to replace stationary steam engines. In the 1910s, diesel started being used in submarines and ships. They were later put into locomotives, buses/trucks, heavy equipment for agricultural use - even electricity generation plants! At the time, however, there was no way to convert it into practical, roadworthy transportation. That wouldn't happen until 1924. In the meantime, Rudolf Diesel became intrigued by the possibilities of the diesel engine and began work on a new prototype, but he sadly passed away before he could finish it. The 1930s saw diesel cars becoming popular (but only in America), but it wasn’t until the 1970's that their use on American roads really began to take off. According to Konrad Reif (2012), half of the newly registered diesel cars in Europe come from European Union countries. The world's largest diesel engines are 14-cylinder, two-stroke marine diesel engines that have a peak power of 100 MW each.How Does a Diesel Engine Work?
In diesel engines, the operating cycle starts with clean air being drawn into the cylinder, not a fuel-air mixture as in a conventional gasoline engine. The motion of the piston compresses the air, heating it to a high temperature. When the piston nears the top of the cylinder, fuel is injected under high pressure through a number of precisely machined holes in the tip of the fuel injector. The fuel enters the engine in the form of a fine spray and the surface of each droplet quickly begins to vaporize on its path through the hot air. Spontaneous ignition takes place without the need for a spark and rapid expansion of the combusting mixture increases the pressure in the cylinder, forcing the piston down and powering the vehicle. When the piston is close to its lowest position, the exhaust valve starts to open and the exhaust stroke then drives the spent gasses out of the combustion chamber and the cycle starts again. In conventional gasoline engines, a mixture of fuel AND air is drawn into the cylinder, compressed by the motion of the piston, and ignited by a spark as the piston nears the top of the cylinder. The resulting combustion generates pressure which forces the piston down to power the vehicle.What Makes the Diesel Engine So Popular?
The diesel engine has the highest thermal efficiency, or efficacy, of any internal combustion engine. This means that it does not waste a lot of fuel or energy. It is able to maintain this high level of effectiveness because it operates with a lean burn- which allows for more heat dissipation. And its wide expansion ratio enables it to do all this without creating excess pollution in return. Unburned fuel isn’t present when valves overlap (therefore, no fuel goes from intake to exhaust). Diesel engines also have a small efficiency loss when compared to non-direct injection cars that rely on unburned fuel going from intake/injection directly into the exhaust. Low-speed diesel engines (used in ships and other applications where weight isn't an issue) have been shown to be up to 55% efficient. A combined cycle gas turbine (Brayton and Rankin cycles) can be efficient too; however, due to their mass and dimensions, they are impractical for vehicles such as cars or boats since they weigh so much!A Final Word About Diesel Engine Basics
The diesel engine is much more efficient and cleaner than an engine that runs on gasoline or natural gas. These engines are used in many industries, especially large trucks and boats. The best way to think of a diesel engine is that it is like a gasoline engine, but instead of using a spark to ignite the fuel, the fuel ignites by compression. While diesel engines are more expensive to buy, they save money over the lifetime of the engine because they are more efficient and last longer.
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