Diesel Engines Explained


The basic distinction between a diesel engine plus a gasoline engine is that in the diesel engine, the fuel is sprayed into the combustion chambers through fuel injector nozzles just when the air in each chamber is placed under such great pressure that it’s hot enough to ignite the fuel spontaneously.

Following is a step-by-step view of what happens when you start up a diesel-powered vehicle.

You turn the true secret in the ignition.

Then you delay until the engine builds up enough heat in the cylinders for satisfactory starting. (Most vehicles have a little light which says “Wait,” but a sultry computer voice may do the same job on some vehicles.) Turning the key begins an activity in which fuel is injected into the cylinders under such high pressure it heats the atmosphere in the cylinders all by itself. The time it takes to warm things up has been dramatically reduced – probably no more than 1.5 seconds in moderate weather.

In the event the combustion chamber is preheated, so manufacturers originally installed little glow plugs that worked from the battery to pre-warm the environment in the cylinders when you first started the engine, diesel fuel is less volatile than gasoline which is easier to start. Better fuel management techniques and higher injection pressures now create enough heat to touch from the fuel without glow plugs, but the plugs are still inside for emissions control: The additional heat they give helps burn the fuel more efficiently. Some vehicles still need these chambers, others don’t, but the results are still the same.

Glow plugs provide extra heat to get rid of fuel more efficiently.

Glow plugs provide extra heat to shed fuel more efficiently.

A “Start” light goes on.

When you see it, you step on the accelerator and turn the ignition key to “Start.”

Fuel pumps provide you with the fuel from the fuel tank for the engine.

On its way, the fuel passes through a couple of fuel filters that clean it before it can reach the fuel injector nozzles. Proper filter maintenance is especially important in diesels because fuel contamination can clog up the tiny holes from the injector nozzles.

A diesel fuel filter.

A diesel fuel filter.

The fuel injection pump pressurizes fuel into a delivery tube.

This delivery tube is called a rail and keeps it there under constant high pressure of 23,500 pounds per square inch (psi) or even higher while it delivers the fuel to every cylinder at the proper time. (Gasoline fuel injection pressure may be just 10 to 50 psi! ) The fuel injectors feed the fuel as a fine spray to the combustion chambers of the cylinders through nozzles controlled from the engine’s engine control unit (ECU), which determines the strain, when the fuel spray occurs, how long it lasts, and also other functions.

Anatomy of a fuel injector.

Anatomy of a fuel injector.

Other diesel fuel systems use hydraulics, crystalline wafers, as well as other methods to control fuel injection, and more are developed to produce diesel engines that are even more powerful and responsive.

A common rail fuel injection system.

A typical rail fuel injection system.

Thefuel and air, and “fire” meet in the cylinders.

While the preceding steps get the fuel where it needs to go, another process runs simultaneously to get the air where it needs to be for the final, fiery power play.

On conventional diesels, the air is available in through an air cleaner that’s quite much like those in gas-powered vehicles. However, modern turbochargers can ram greater volumes of air into the cylinders and may provide greater fuel and power economy under optimum conditions. A turbocharger can increase the power on a diesel vehicle by 50 percent while lowering its fuel consumption by 20 to 25 %!

Combustion spreads from the smaller amount of fuel that’s placed under pressure in the precombustion chamber towards the fuel and air in the combustion chamber itself.