How Does a Diesel Engine Work?

Close-Up of Diesel Engine

Even if you understand the basic differences between diesel and gas-powered vehicles, you still might wonder about what’s actually going on beneath the hood! How does a diesel engine work, anyway, and what accounts for the benefits they offer over internal combustion engines? The most important thing to note is that diesel fuel is almost always ignited automatically within the cylinder, without the use of a spark plug.


Diesel Combustion: From Start to Finish

Most diesel engines utilize the same 4-stroke combustion cycle that one could observe with gasoline engines, with a caveat: diesel engines compress air at much higher levels, and when air is compressed, it heats up. Since the air in diesel-engine cylinders is higher than diesel fuel’s “auto-ignition” temperature, no spark plug is required to get you moving.

So, how does a diesel engine work? Here’s the whole process, as it would occur in a 4-stroke cycle:

  • Stroke 1: Air Intake – The opening of the intake valve allows fresh air to enter the combustion chamber. The piston moves down as air enters.
  • Stroke 2: Compression – The piston compresses the air in the cylinder by moving back up. Compression ratios from 15:1 to 25:1 are the most common.
  • Stroke 3: Combustion – When the air is compressed enough at a high enough temperature, fuel is injected into the cylinder, where it immediately combusts. This creates the power which is channelled through the crankshaft to move the vehicle forward. It also pushes the cylinder back down.
  • Stroke 4: Exhaust – A fourth and final stroke pushes the exhaust out of a second valve to make room for more fresh air.

Compare Diesel vs. Gas Engines: Diesel and gas-powered engines are generally regarded as different tools made for different jobs. While neither can be said to be better than the other, diesel engines are generally more efficient, longer-lasting, and capable of producing much more torque than other internal combustion engines. That means diesel is preferred in many industries near Racine.


2-Stroke vs. 4-Stroke Diesel Engines

Not all diesel engines work in exactly the same way. One of the most common variations has to do with the combustion cycle. Here’s how that works out in practice:

  • How Does a 2-Stroke Diesel Engine Work? – With a 2-stroke combustion cycle, air intake and exhaust output can both occur through ports in the cylinder liner, rather than through dedicated valves. (Some two-stroke cycles utilize one valve, but not the other.) This simplifies the engine construction even further, resulting in reduced weight. In some cases, 4-stroke diesel engines weigh up to twice as much as 2-stroke diesel engines.
  • How Does a 4-Stroke Diesel Engine Work? – The absorption of air through the valve requires the piston to move up and down one more time than it would in a 2-stroke cycle–but this also means that fuel is only burnt with every four strokes, rather than with every other. 4-stroke engines are generally much more efficient than 2-stroke diesel engines for this reason.

Engines with cylinders of less than 600 mm (24 inches) in diameter might use either 2-stroke or 4-stroke combustion cycles. In engines with larger cylinders, a 2-stroke design offsets the added weight and reduces the risk of knocking.

There’s a world of difference between the various diesel engines on the market today. Compare the most popular diesel engines with the Lynch Truck Center before you take your next truck out on the roads of Milwaukee and Northern Chicago.

Explore Diesel Engines and Diesel Vehicles with Our Team!

Are you ready to find a new commercial vehicle with a high-powered diesel engine? Perhaps you’d like to do more research on heavy-duty vehicles before you commit to a particular model! Either way, you can count on the Lynch Truck Center to point you in the right direction. No matter where you’re headed, we’ll help you get there.


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