Skip navigation
10_Domenico8.jpg Photo: File photo

You and your rig: How well do you really know it?

From the combustion cycle to aftertreatment systems: Understanding all aspects of the modern diesel truck

Today’s heavy-duty trucks consist of multiple components that work together to operate more efficiently and cleaner. When it comes to optimizing vehicle performance, understanding the complex mechanisms and processes that exist in fuel and engine systems is a fundamental first step.

Those in the trucking industry are cognizant of how important proper maintenance techniques are to the bottom line, but can be less aware of just how sophisticated fuel and engine systems are – a crucial step in developing a smart maintenance plan. Additionally, today’s modern diesel trucks have progressed substantially over the years to balance demands for emissions control and fuel economy, which has led to higher sensitivities to maintenance issues.

Equipment downtime adds up quickly for fleets when it can cost between $448 and $760 per day, per truck, according to By looking closely at the fuel’s journey from tank to tailpipe, fleet operators can access a much fuller picture of what it takes to keep today’s diesel trucks running like new.

Breaking down the combustion cycle

Understanding the complexity of each step in the combustion cycle is important in helping fleet owners identify proper maintenance practices based on the engine’s integration with other vehicle systems.

Most modern commercial truck engines today use a high pressure common rail fuel injection system. Through this system, diesel fuel is sprayed into the combustion cylinder near the end of the compression stroke to then trigger the combustion cycle. Today’s injection systems are capable of multiple injections to deliver the right amount of fuel into the cylinder at the right timing. The extremely high injection pressure ensures good fuel atomization and promotes air entrainment into the spray. This leads to more complete combustion, which can result in higher efficiency and less emissions out of the engine.

The diesel injection system is not only critical for diesel combustion, but also can create challenges for maintenance. Deposits can form both inside the injector and inside the tiny nozzle holes, which impair injection timing and quantity, fuel atomization and fuel-air mixing. This deterioration of performance leads to efficiency loss and emissions increase or even early replacement of the injector.

The intricacies of the combustion cycle make the quality of diesel fuel paramount to the success of the entire system. As a result of the high pressure common rail injection system, there is a greater need for diesel fuel that is more thermally and oxidatively stable. This is because a portion of the fuel that is waiting to be sprayed into the combustion cylinder typically ends up being recirculated back into the tank under a much higher pressure and temperature after being in the rail. Diesel fuel without sufficient thermal and oxidative properties can result in the formation of harmful particulates that can plug filters and injectors, leading to potential corrosion of critical engine and fuel system components.

Beyond combustion: aftertreatment systems

In addition to optimal performance and efficiency, today’s trucks have widely adopted aftertreatment systems to meet stringent emission regulations. Designed to reduce emissions out of the engine, the aftertreatment system includes a diesel oxidation catalyst (DOC), selective catalytic reduction (SCR), and diesel particulate filters (DPF). The aftertreatment systems also demand higher quality diesel fuel. Ultra-low sulfur (less than 15 ppm) diesel fuel is often required for today’s trucks. High sulfur content can cause aftertreatment systems to become much less effective at removing emissions and increase particulate loading for the DPF.

The aftertreatment systems are influenced by what is happening in the engine. As the injection system deteriorates with deposit buildup, the engine out emissions will increase. Higher NOx can require more diesel emission fluid (DEF) consumption and higher PM can result in more often DPF regeneration. The more frequent DPF regeneration could shorten DPF life due to increased thermal stress and cause maintenance challenges.

Selecting the right fuel

A proactive practice that can prevent or delay maintenance issues down the line is selecting a diesel fuel option pre-blended with additives that enables maintenance benefits in addition to its performance and attributes.

Considering today’s demands of modern diesel trucks, a well-designed diesel fuel could provide better protection to engine and aftertreatment systems of a heavy-duty vehicle the minute it enters the tank.

ExxonMobil’s 2019 Outlook for Energy: A Perspective to 2040 reveals heavy-duty vehicle growth is  expected to be the largest sector by volume as the global transportation-related energy demand continues to rise. In response, diesel engine technology will become even more sophisticated, and the demand for higher quality diesel and a more intelligent approach to proactive maintenance will also rise.

Now more than ever, fleet operators will need to focus on how holistic changes to vehicle and engine design will carry implications for a smarter approach to proactive maintenance and ultimately, the bottom line.

Henning Hoeft is global commercial fuels marketing advisor for ExxonMobil


TAGS: Trucks
Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.