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Have you ever looked at a truck or large piece of machinery and wondered where its power comes from? The answer is simple: diesel engines.
From passenger cars and trucks to railroad locomotives, farming equipment, and even cargo ships, diesel engines power some of the vehicles our world relies on most. Diesel engines are often favored for their efficiency and durability, especially when compared with gasoline engines.
Keep reading to learn all about these incredible engines — what they are, how they work and what diesel technicians need to know to be successful.
Diesel engines, like gas engines, are internal combustion engines that convert chemical energy into mechanical energy. This process moves pistons up and down inside cylinders, which then leads to the motion that turns the wheels of a vehicle.
Through a series of small combustions (or explosions), diesel engines convert fuel to energy. They are used in many different types of equipment and vehicles, including:
There are several reasons diesel engines are chosen over gas engines for certain applications. These include:
Diesel engines are robust. They are made up of several different parts, and each part must work correctly to power the engine. Below is a breakdown of some of the most important components of these engines.
The fuel system consists of the fuel tank, water separator, feed pump (low-pressure), filter, high-pressure pump, injector nozzle and cylinder. Essentially, the fuel tank stores the fuel, then a low-pressure pump pulls the fuel from the tank through a filter/water separator, then pushes the fuel through another filter. From there, fuel pressure is stepped up via a high-pressure pump, whether it is an injection pump or a unit injector.
The lubrication system plays an important role in the engine. It reduces wear and tear of rubbing surfaces by placing a film of oil between parts, reduces the power required to overcome friction, and removes heat from the pistons and other parts in the engine. It also separates the cylinders and piston rings.
In this system, air flows into the cylinder bore through the air cleaner, which prevents dust from entering. The turbocharger compresses air from the air filter, and the intake manifold takes the air from the turbocharger to the inlet port. Finally, the intake valve allows air to pass into the cylinder bore, and a camshaft controls when the valve opens and closes.
In this system, exhaust gas is passed through the diesel particulate filter, which traps solids in the exhaust stream. These solids, or particulates, are carbon and ash. The filter will need to undergo a cleaning process called regeneration periodically to convert the carbon into carbon dioxide through exposure to high temperatures.
The gas then passes through the selective catalyst reduction system, which removes the oxides of nitrogen with the help of diesel exhaust fluid. There is also an exhaust gas recirculation valve, cooler and mixer in this system. All of this equipment is there to reduce harmful emissions.
The cooling system helps maintain proper engine temperature, which allows all of the parts to work correctly. It keeps oil and engine components at the right temperature, which in turn helps protect the cylinder head, cylinders, valves and pistons. There are two different types of cooling used in internal combustion engines: air cooling and water cooling. While gas engines can use either method, diesel engines use water cooling exclusively.
The electrical system is made up of the alternator, starter motor and battery. The starter motor, which is powered by the battery, rotates the flywheel, which rotates the crankshaft. This is what causes the pistons to move in the cylinders. The piston compresses the air in the cylinder to create heat, which ignites fuel injected into the cylinder.
So how does a diesel engine turn fuel into power? Diesel engines operate using the same four strokes as gas engines:
Diesel engines do not use spark plugs to ignite the fuel mixture. The higher compression ratio in the engines produces enough heat to ignite the mixture. Additionally, diesel fuel itself allows for combustion without the use of a spark plug.
A key difference between diesel and gas engines is fuel management. Gas engines control the flow of air into the cylinder. By increasing airflow, gasoline increases by default. Diesel engines directly control fuel flow into the cylinder, and more fuel equals more engine speed.
To overcome the existing air pressure in the combustion chamber, diesel engines need to generate a significant amount of fuel pressure. The pictured diesel engine relies on a pressurizing fuel pump and a high-pressure common rail system to create, maintain and deliver fuel at precisely the correct time.
The high-pressure common rail sits under the valve cover. It distributes fuel to the individual cylinders via the fuel injectors. Unused fuel cools down in the fuel cooler before the return line transports it back to the fuel tank.
It’s important for diesel technicians to know diesel engines inside and out. Understanding how each of the different components work together is what allows technicians to diagnose, repair and maintain these engines.
Because of their many benefits, diesel engines are here to stay — and as with anything in the transportation industry, they will likely continue to evolve and improve. Today’s diesel techs must be able to keep up with these changes to stay relevant.
Being able to work on diesel engines has the potential to provide a variety of career opportunities, whether it be in a dealership, repair shop, truck stop or even the railroad industry. Skilled diesel techs can take their skills to many different industries, including:
In some cases, diesel techs are able to learn skills on the job, but many employers prefer candidates who have completed a postsecondary training program, like the Diesel Technology program at Universal Technical Institute (UTI).
Students who train at UTI can learn everything from truck brakes and chassis to fuel systems, preventive maintenance, and transportation refrigeration. They also dive into diesel engines — learning the principles of operation of four-stroke engines, diesel combustion fundamentals and other characteristics unique to these powerful engines.
UTI’s Diesel Technology program is designed to be completed in just 45 weeks7 and is available at campus locations nationwide. Classes begin every three weeks, so you can get started and prepare for your dream career sooner.1
To learn more, visit our program page and request information to get in touch with an Admissions Representative today.
Diesel engines are used in wide variety of fields today. Learn more about their history and when they were invented here!
Are you interested in training to become a diesel technician? Click here for a 2023 guide on career outlook and median annual diesel mechanic salary.
What is a mobile diesel mechanic, and how do you become one? Find out in this career guide.
1) UTI is an educational institution and cannot guarantee employment or salary.
2) For program outcome information and other disclosures, visit www.uti.edu/disclosures.
7) Some programs may require longer than one year to complete.
Universal Technical Institute of Illinois, Inc. is approved by the Division of Private Business and Vocational Schools of the Illinois Board of Higher Education.
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