Despite being a continuation of the gasoline engine, the diesel engine is among the most efficient and potent engines. Diesel engines are used as mechanical engines, power generators, and mobile drives.
They are used to power locomotives, construction equipment, automobiles, and other industrial applications. Internal combustion engines, such as diesel, heat the air in the cylinder by a process called “adiabatic compression,” a form of mechanical compression, and then ignite the fuel.
In this reading, we’ll explore what a diesel engine is, its diagram, applications, parts, types, and how it works!
Let’s get started!
What Is a Diesel Engine?
A diesel engine is a powerful, efficient, and reliable form of an internal combustion engine. It uses the heat generated by compressing air in the cylinder to ignite the fuel, resulting in higher efficiency and lower emissions.
This process, known as compression ignition, also allows the diesel engine to produce more torque than a gasoline engine of the same size. The diesel engine is also known as a compression-ignition or CI engine, named after the founder Rudolf Diesel.
Rudolf Diesel was a student of Polytctechnikum in Munich, where he attended the lectures of Carl von Linden. The diesel engine exists as the engine with the highest thermal efficiency, either with the internal or external combustion engine. This occurs due to the very high expansion ratio and inherent lean burn, which enables heat dissipation by the excess air.
Parts Of a Diesel Engine
A diesel engine consists of multiple components that work together to convert chemical energy into mechanical energy. The primary components include:
Block
The block is where all the parts for the basic internal combustion process are contained. The block has an open space for each cylinder, where the combustion happens.
Piston
The pistons create the bottom of the combustion chamber; they move up and down in the cylinder while the engine is working. The movement creates the compression of the air, which leads to combustion.
Cylinder head
The cylinder head closes the top of the open space in the block to reach the chamber where combustion happens.
Fuel Injector
The fuel injector gets fuel inside the cylinder in order to burn. It sprays fuel in very precise patterns with highly controlled timing.
Valves
The valves help in allowing fresh air in and the leftover gases out. There are usually two valves for taking in air and two for the exhaust for each cylinder.
Crankshaft
The crankshaft transfers the up-and-down part of the combustion process into a rotational motion.
Connecting rod
These connect to a piston at the bottom arm and carry the force of the combustion to the crankshaft.
Camshaft
The camshaft’s revolutions control the timing of opening valves and fuel injection by lobes on the shaft that set them into motion.
Diagram Of a Diesel Engine
Applications
Applications of the diesel engine in vehicles and industrial generators have been increasingly high over the years. However, the gasoline (petrol) engine can somehow serve some purposes of this so-called diesel engine of higher cost.
Passenger Cars
Diesel is quite known for larger trucks, bigger cars, and now smaller bigger cars like the superminis. Smooth operation, as well as high low-end torque, are deemed important for passenger cars and small commercial vehicles.
The use of electronically controlled fuel injection has improved smooth torque generation, making the manufacturer produce high-end luxury vehicles with diesel engines. Passenger car diesel engines usually have between three and ten cylinders and a displacement ranging from 0.8 to 5.0 litres. Modern powerplants are usually turbocharged and have direct injection.
Locomotives
Diesel locomotives appeared first in 1913, were built for continuous operation, and may require the ability to use poor-quality fuel in some situations. Some locomotives use a two-stroke diesel engine, but many modern diesel locomotives are designed for diesel-electric locomotives.
The diesel engine is used to power an electric generator that in turn powers electric traction motors with no mechanical connection between the diesel engine and traction. Diesel engines have eclipsed steam engines as the prime mover on all non-electrified railroads in the industrialized world.
Watercraft
The requirements for marine diesel engines vary based on their application. mass usage of the diesel engine in the military and medium-size boats are suitable for medium-speed four-stroke diesel engines.
These engines usually contain up to 24 cylinders and have power outputs in the one-digit megawatt region. Diesel engines for trucks may be used on small boats. while, large ships use extremely efficient, low-speed two-stroke diesel engines.
They can reach efficiencies of up to 55%. Unlike most regular diesel engines, two-stroke watercraft engines use highly viscous fuel oil. Submarines are usually diesel-electric.
Stationary Diesel Engine
Stationary diesel engines are commonly used for electricity generation but also for powering refrigerator compressors or other types of compressors or pumps. Usually, these engines run permanently, either with mostly partial load or intermittently, with a full load.
Stationary diesel engines powering electric generators that put out alternating current usually operate with an alternating load but fixed rotational frequency. This is due to the mains’ fixed frequency of either 50 Hz (Europe) or 60 Hz (United States).
The engine’s crankshaft rotational frequency is chosen so that the mains’ frequency is a multiple of it. For practical reasons, this results in crankshaft rotational frequencies of either 25 Hz (1500 per minute) or 30 Hz (1800 per minute).
Non-road Diesel Engine
The applications of non-road diesel engines are common for construction equipment. It offers better usability, such as fuel efficiency, reliability, and ease of maintenance. However, high power output and quiet operation are negligible. Therefore, mechanically controlled fuel injection and air cooling are still very common.
The common power outputs of non-road diesel engines vary a lot, with the smallest units starting at 3 kW and the most powerful engines being heavy-duty truck engines.
Aviation
The applications of diesel engines in aircraft existed before World War II. However, in the late 1970s, there have not been any applications of the diesel engine in aircraft.
In 1978, Karl H. Bergey suggested that “the likelihood of a general aviation diesel in the near future is remote.” In recent years (2016), diesel engines have found use in unmanned aircraft (UAV) due to their reliability, durability, and low fuel consumption.
Finally, in early 2019, AOPA reported that a diesel engine model for general aviation aircraft is “approaching the finish line.”
Types of Diesel Engine
The types of diesel engine are two-stroke and four-stroke engines. Diesel engines are designed to operate on either the two- or four-stroke cycle.
In the typical four-stroke-cycle engine, the intake and exhaust valves and the fuel-injection nozzle are located in the cylinder head. Often, dual valve arrangements—two intake and two exhaust valves—are employed.
The use of two-stroke cycles can eliminate the need for one or both valves in the engine design. Scavenging and intake air are usually provided through ports in the cylinder liner.
Exhaust can be either through valves located in the cylinder head or through ports in the cylinder liner. Engine construction is simplified when using a port design instead of one requiring exhaust valves.
How Does a Diesel Engine Work?
A diesel engine takes air, compresses it, and then injects fuel into the compressed air. Compressed air naturally ignites fuel due to its high temperature. Initially, only air is introduced into the combustion chamber. The air is then compressed at a ratio between 15:1 and 23:1, depending on the type of diesel engine and its application. The air temperature rises as a result of the high compression.
When the compression stroke is almost at its peak, fuel is now injected into the heated air. All these take place in the combustion chamber on top of the piston. The fuel injector helps in injecting fuel into the combustion chamber in small droplets and is distributed evenly.
The compressed air creates extreme heat, causing the fuel to vaporize from the surface of the droplets. The vapor is then ignited using the same heat in the combustion chamber. The vaporization of the droplets continued until they were completely burnt.
The combustion occurs at a substantially constant pressure during the initial part of the power stroke. When combustion is complete, the combustion gases expand as the piston descends further; the high pressure in the cylinder drives the piston downward, supplying power to the crankshaft.
Advantages
Diesel engines have several advantages over other types of engines, especially gasoline engines. Here are some of the key benefits:
- It has the highest effective efficiency of all combustion engines.
- The diesel engine can combust a huge variety of fuel.
- Low fuel costs. That is, it is economical.
- It has a high energy density.
- Good lubrication properties.
- Low risk of catching fire, as flammable vapor is not produced.
- Injection of fuel directly into the combustion chamber has no intake of air restriction apart from the air filters.
- Diesel engines have very good exhaust-emission behavior.
Disadvantages
Even though diesel engines have many benefits, they also have some disadvantages when compared to gasoline engines and other types of engines. Here are the key drawbacks:
- Cars with diesel engines usually cost more than a standard vehicle.
- The cost of diesel fuel is expensive in most geographic regions.
- Diesel engine maintenance and repair cost more.
- You may not have as much access to the fuel that you need with diesel.
- The new diesel fuel doesn’t have the same lubricating qualities.
- It is difficult to start a diesel engine in cold weather.
- They make much more noise than their gasoline counterparts.