Supporters of the exhaust aftertreatment systems utilized in today’s diesel engines are hard to come by. Issues such as diesel particulate filters becoming clogged or leaking, recurring failures of NOx, EGT, and pressure differential sensors, sticking EGR valves, ruptured EGR coolers, and numerous other complications plague these systems. So, what’s the reasoning behind their existence? They are needed to comply with progressively stricter emissions standards imposed by the government since the early 2000s. Although these diesel emissions regulations have resulted in the introduction of devices like DPFs, EGRs, SCRs, and DOCs—which many enthusiasts struggle to appreciate—they have also ushered in significant advancements in engine technology.
To mitigate particulate matter, NOx, and hydrocarbons, innovative technologies in turbocharging, fuel injection systems, injectors, and transmissions have been developed. These advancements have led to heavy-duty pickup trucks that excel in drivability, generating over 1,000 lb-ft of torque while also achieving impressive fuel efficiency for their size. This article delves into the high-tech innovations that, while initially designed to combat emissions, have enabled modern diesel trucks to accelerate with a vigor more akin to sports cars rather than their hefty frames. From high-pressure common-rail injection to variable geometry turbos and 10-speed automatics, these technologies have allowed leading manufacturers to meet—and even exceed—government emissions standards.
PM And NOx—The Main Focus Of Emissions Regulations
Particulate matter (PM) ranks as one of the most significant pollutants emitted by diesel engines, and the Environmental Protection Agency (EPA) has targeted it since the early 1990s. Starting in 1994, the PM standard was revised downward to 0.10 g/bhp-hr from the previous 0.25 g/bhp-hr, tightened further to 0.01 g/bhp-hr in 2007, and sits at a remarkable 0.005 g/bhp-hr today. Nitrogen Oxide (NOx) also constitutes a major pollutant that the EPA has sought to reduce. Initially set at 4.0 g/bhp-hr in 1998, the federal NOx standard has gradually been decreased to 0.035 g/bhp-hr.
High-Pressure, Direct Injection Fuel Systems
Diesel engine builders, such as Cummins, International/Navistar, and GM/Detroit Diesel, managed to meet the 1994 PM standard without major modifications to their injection systems. However, the more stringent regulations established in 2007 demanded significant changes. With the PM emissions cap drastically reduced to just 10 percent of previous limits, manufacturers embraced high-pressure common-rail injection starting in the early 2000s—both GM and Cummins preemptively implemented it in 2001 and 2003, respectively. This advanced fuel injection technology employs extremely high pressure, in conjunction with electronic, solenoid-controlled injectors, to improve fuel atomization within the cylinder, thereby lowering PM emissions.
Fast-Firing, Multi-Event Fuel Injectors
The high-pressure common-rail diesel injection system integrates a high-pressure fuel pump with a high-pressure rail and electronically managed injectors. These common-rail injectors are capable of rapid operation, executing five or more injection events per combustion cycle—within each power stroke. Typically, you’ll find two pilot injections (to mitigate noise), a primary injection, and two post-injections (for heat management and PM control). The precision in fuel quantity and flexible injection timing are crucial in minimizing emissions, which make common-rail injectors significantly superior to the older mechanical pop-off models.
Variable Geometry Turbochargers
Previously, operating a diesel engine under heavy load at low RPM often resulted in noticeable turbo lag. Such conditions typically led to incomplete combustion, manifesting as smoke (indicating elevated PM levels) from the exhaust. However, the advent of variable geometry turbocharging in the diesel truck sector has virtually eliminated this lag. A VGT functions similarly to a much smaller turbo during acceleration, enabling quick torque build-up and consistent boost pressure availability. Not only does a VGT enhance drivability, but it also plays a vital role in managing emissions.
10-Speed Transmissions
Today’s automatic transmissions, such as Ford’s 10R140 TorqShift and GM’s 10L1000 Allison, both featuring ten gear ratios along with advanced electronic systems, serve to minimize particulate matter (PM) emissions, similar to the role of variable geometry turbochargers (VGT). By ensuring that the engine operates within its optimal power band at all times, they prevent scenarios where the engine has to struggle under heavy loads at low RPM. Beyond addressing emission standards, these modern 10-speed automatic transmissions also enhance fuel efficiency by allowing the engine to run at lower RPMs during highway travel.
The introduction of exhaust gas recirculation (EGR) on diesel engines in the early 2000s marked a challenging time for emissions control. As manufacturers sought to comply with the stringent 0.20 g/bhp-hr NOx standard during the 2007-2010 transition, increasing EGR levels became the go-to approach. However, the implementation of selective catalytic reduction (SCR) in 2011, which utilizes diesel exhaust fluid (DEF) to significantly reduce NOx emissions, changed the landscape. SCR’s effectiveness in lowering NOx emissions allows engine manufacturers to reduce the amount of harmful EGR while enhancing horsepower and torque outputs.
Lighter, Stronger Blocks
It’s important to note that emissions regulations did not mandate a shift in the materials used for engine crankcases. Despite this, both Ford and Cummins have transitioned from traditional cast-iron blocks to compacted graphite iron (CGI) for various advantageous reasons. CGI offers increased strength and reduced weight compared to cast iron, allowing these manufacturers to continue their competitive torque advancements while simultaneously lowering vehicle weight. A lighter truck requires less fuel to operate, which in turn leads to decreased carbon emissions.
In summary, the advancements discussed have enabled today’s heavy-duty diesel trucks, which weigh around 8,000 pounds, to achieve the same fuel efficiency of 16 to 19 mpg that was common three decades ago. These trucks now boast double the horsepower and nearly triple the torque while generating significantly fewer tailpipe emissions. With power outputs ranging from 400 to 500 hp and torque ratings of 1,075 to 1,200 lb-ft, these vehicles can easily tow enormous weights of 30,000, 35,000, or even 40,000 pounds. These remarkable power figures that adhere to emissions standards and substantial towing capacities have been made possible through innovations such as VGT, high-pressure common-rail injection, and cutting-edge transmissions.
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