How Does a Diesel Engine Start?

February 23, 2022 5:29 pm Published by Leave your thoughts

Diesel engines are extremely complex. When you start the vehicle, there are various processes that must take place for the diesel engine to start.

How does a diesel engine start? Understanding the process can help you to troubleshoot problems and know when it’s time to look for a particular part or service.

What is a Diesel Engine?

First, it’s important to know that how a diesel engine starts is different from a standard spark-plug ignition. It is an internal combustion engine that ignites the fuel through mechanical compression. As such, it is also known as a compression-ignition (CI) engine.

A traditional gas engine relies on a spark-plug ignition that uses a mixture of air and fuel.

How Does a Diesel Engine Start?

A diesel engine, at first glance, looks similar to a gas engine. They share many of the same components, and both work using a four-stroke cycle.

Now, the way in which the fuel is ignited is one of the main differences

A diesel engine achieves ignition through the compression of air. Most compression ratios for a diesel engine is 20:1. In a gas engine, the ratio would only be 9:1.

The compression of the air is critical as it will heat the air up. The temperate is high enough that it will ignite the fuel spontaneously as opposed to needing a spark.

The amount of air that is drawn in per stroke of the engine is the same with a diesel engine. The same amount of air is always drawn in. The air goes through an unthrottled inlet tract, and it is only closed through an inlet valve.

Gas engines have variable amounts of air due to the varying throttle openings. It’s also why there is either a carburetor or butterfly valve in place (diesel engines have neither of these).

When the fuel has been spontaneously ignited, it allows the engine to power up. When the piston finishes the induction stroke, the inlet valve will close.

The piston is then carried around with the momentum of the flywheel – and is being powered by the other pistons. The piston reaches the top of the cylinder and compresses the air.

A carefully measured amount of diesel fuel is injected into the combustion chamber of the engine once the piston reaches the top position.

Then, the heat from the compression fires the fuel and air mixture. This will cause everything to burn and expand. The force moves the piston down, which, in turn, rotates the crankshaft.

Once the engine is fully powered, all of the processes happen consistently to maintain ideal performance. When the piston moves along the cylinder on the exhaust stroke, it also allows the exhaust valve to open.

This pushes all of the expanded and burned gases to move out of the engine compartment and out of the vehicle through the exhaust pipe. After the exhaust cycle is completed, the cylinder receives a new charge of fresh air.

Various Components to Improve the Start and Performance

There are all sorts of components that you can add to your diesel engine. Many of these will impact the way in which your engine starts – and it can play a role in the performance of the engine, too.

A turbocharger, for example, is a common aftermarket part to put on your diesel engine. This type of air pump will compress the air at higher pressures.

The compressed air blown into the engine can lead to higher performance, higher speeds, and even a faster start – but only if everything is working properly.

If there are issues with the air compression, it can lead to problems where your engine won’t start or there is a rough idle when the engine starts to run.

When you want to make upgrades to your diesel engine, there are OEM and aftermarket fuel pumps, fuel ignitors, and more. It can help you to achieve a smoother start and help you to get the most out of your diesel engine.

Whether you’re riding around on a farm, in construction zones, or down the highway, you need your engine to perform at top levels at all times.

Getting Help with Engine Starts

Your diesel engine is a complex machine – as you can tell with the process in which it starts and operates.

When you find that you’re experiencing various symptoms (loud sounds, burning smells, backfires, and misfires, and more), it’s a sign that there’s something going on with your engine.

Diagnosing the problem so that you can make a repair or replace a part is absolutely critical.

Listen to the way in which your diesel engine starts. If there are problems, contact us.

At Thompson Diesel, we have over 30 years of experience working with diesel engines and fuel systems. We can make recommendations and provide the services you need.


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