Diesel Engines: Understanding the Basics
While less than 5% of US passenger cars are diesel-powered, diesel engines are the workhorses of agriculture, construction, drilling, forestry, industry, mining, transportation and shipping. They power everything from buses and combines to bulldozers, excavators, semi-trailer trucks, ships and trains.
Diesel and gas-powered engines are classified as internal combustion engines. In both instances, chemical energy is converted into mechanical energy. This occurs when fuel is channeled into the interior of the engine where it ignites to produce energy that’s converted into power to make a vehicle or machine move.
There are other differences, but the most important distinction between gasoline and diesel engines is this: Gas engines rely on a spark plug to ignite the fuel and create combustion. Diesel engines feature a compression ignition (CI) system that in very basic terms produces combustion using:
- Super-heated air. Air is pumped into a compact cylinder where it’s quickly and forcefully compressed by the piston. This rapid, powerful compression causes the air to instantly heat to a high temperature, typically between 500 and 1000 degrees F.
- Fuel injection. A fine mist of fuel is injected (sprayed) into the cylinder, where the super-heated air causes it to instantaneously ignite without the need for a spark plug or other fire source.
- Energy. When the air ignites, it produces energy that pushes the piston out of the cylinder. This transfers power from the cylinder to the piston, through the crankshaft and gears to turn the wheels and make your vehicle go.
When a diesel engine is running, the CI process is repeated over and over again producing the steady stream of energy required to power vehicles, equipment and machines.
Diesel engines offer significant advantages. The fundamental design is simpler and more straightforward, comparatively speaking, so there are fewer parts to maintain or replace. The compression process is forceful and effective, which burns fuel more completely and produces more energy to make the most of every drop. This effect is maximized because diesel fuel is denser than gasoline, so each gallon produces roughly 30% more energy on average. The dense fuel also acts as a better lubricant, which reduces friction and helps diesel engines last longer.
Diesel engines also have a few drawbacks. They perform best at the steady speeds required for highways, but can seem sluggish in stop-start city driving. Because diesel fuel is less refined, it contains more energy potential but produces more emissions, so in spite of improvements, many diesel-powered vehicles continue to fall short of their gas-powered counterparts.