How Do Diesel Engines Work?

The diesel engine working principle was completed by the inventor, Rudolf Diesel, in 1892, and the first prototype was created in 1897. In the years following, he continued to work on improving his theory, and others soon realized the potential of this invention and started making their own versions. One of the people to recognize the importance of the diesel engine was Clessie Lyle Cummins. In 1919, He founded Cummins Engine Company with a goal of improving diesel technology and producing the world’s finest engines. Thanks to his vision, Cummins Inc. is now a global leader, producing advanced diesel engines for applications ranging from heavy-duty trucks and consumer pickups to industrial mining and oil drilling.

How does a diesel engine work?

Rudolf Diesel built his internal combustion engine based on the Carnot cycle, an idealized model of how a theoretical engine could maximize efficiency. In reality, this model doesn’t work since factors like friction make maximal efficiency impossible. However, the diesel engine applies this theoretical principle in a very practical way. 

In general, a diesel engine works by using a piston to compress air to increase the temperature in the cylinder and then injecting atomized diesel fuel into this cylinder. When the fuel comes into contact with the high temperature, it ignites, creating energy that drives the piston down transferring energy to the crankshaft and through the powertrain. This process is repeated over and over again at a high speed, making a diesel engine a powerful piece of technology. Different types of diesel engines will have varying compression ratios. The compression ratio of the diesel engine impacts how much power the engine puts out. The higher the ratio, the more power is generated. 

One common question about how diesel engines work is; why don’t diesel engines have spark plugs? The simple answer is that a diesel engine doesn’t need spark plugs because the fuel is ignited by the compression of air. Don’t get confused because there are certain parts of a diesel engine called “glow plugs.” When comparing a glow plug to a spark plug, you’ll find their purpose is different. A spark plug is used to ignite fuel in a gasoline or natural gas engine. The glow plug does not ignite the fuel but is basically a small heater that helps with heating up the compressed air in the cylinder. Glow plugs, among other key advantages to diesel engines, are especially useful when starting a cold engine. 

How does a diesel engine work step-by-step?

In order to understand the step-by-step process, let’s take a look at the diesel engine components and functions. 

• Block - As the foundation of the modern diesel engine, 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. 
• Pistons - The pistons create the bottom of the combustion chamber, moving up and down in the cylinder while the engine is working. The movement of the pistons creates the compression of the air that 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. This head can be one unit to cover all the cylinders or multiple units that cover a section. 
• Valves - With the cylinder closed by the piston at the bottom and the cylinder head at the top, there needs to be a way to allow fresh air in and the leftover gasses out. This is where the valves come in. There are usually two valves for taking in air and two for the exhaust for each cylinder. 
• Fuel Injectors - Now, there needs to be a way to get fuel inside the cylinder, so there is something to combust. These components are a complex part of the process, spraying fuel in very precise patterns with highly controlled timing. 
• Camshaft - Rather than relying on an electrical system for opening valves and fuel injection, most engines use a mechanical process. The camshaft’s revolutions control the timing of these events by lobes on the shaft that set them into motion. 
• Connecting Rods - These pieces connect to a piston head at the bottom arm and carry the force of the combustion to the crankshaft. 
• Crankshaft - The crankshaft transfers the linear motion of combustion (the up-and-down part of the combustion process) into a rotational motion. 

Each piston moves in sync with one other piston to create balance in the engine. With a 4-stroke diesel engine, these parts all come together to produce the combustion event in four stages. These stages are:

• Intake stroke: The piston moves down to the bottom of the cylinder, creating negative pressure that draws air from the open intake valve to fill the cylinder with air.
• Compression stroke: The intake and exhaust valves are closed, and the piston moves from the bottom to the top, compressing air to create heat. At the end of this stroke, fuel is injected into the chamber.
• Power stroke: Ignited by the heat of the compressed air, the fuel explodes, driving the piston down and creating the power stroke that transfers energy to other parts of the engine. 
• Exhaust stroke: The exhaust valve is opened, and the piston moves from the bottom to the top, pushing out all of the exhaust from the combustion event.

Cummins: Diesel engines for today and tomorrow

At Cummins, you’ll find the most powerful and reliable engines on the market today, that continue to evolve through key innovations. With a wide range of sizes and specifications, you’ll find a diverse engine lineup that will fit your specific needs, whatever they are. Find your perfect Cummins engine today. Cummins’ commitment to creating dependable engines with peak performance shows in their dedication to tomorrow’s engines. Cummins is always innovating and testing new ideas to bring you the best in diesel engine technology, following in the footsteps of Clessie Cummins and Rudolf Diesel.