Technicians have been asking and we’ve been listening. That’s why we decided to cover this topic in depth as we know there are many struggles around it in the industry. There is a lot said about aftertreatment systems, but we couldn’t find a compiled source of reliable information about it.
The evolution in Heavy Duty Trucks and in everything Diesel, has made it so that Diesel Particulate Filters have become the norm. But that was not always like that. There were times, some technicians would say “The Good Old Times” where DPF’s and aftertreatment systems did not exist. Times where everything was so much simpler and fixing a truck depended on your mechanical knowledge and of the experience you had. How times have changed.
The Environmental Protection Agency (EPA) got involved and it started passing proposals first, and then laws. These laws have changed trucking forever. Nowadays every truck needs a DPF Filter, a solid Aftertreatment System, and its DEF Fluid. The difficulty here is that all of this is electronically controlled, requiring sensors, calibrations, pressure, and temperature checks. This all means that for undertaking almost every repair we now need a computer.
The Environmental Impact of Diesel Engines
In a perfect world we would all wish to breathe the cleanest air. However, most of our human interactions generate emissions. In fact, transportation has been always a huge generator of pollutant elements. However, in order to control this huge impact, the authorities have set up more and more strict regulations. Regulations with the aim of controlling emissions to the limit and pushing technology to generate cleaner engines.
In the US, the regulations come from the Environmental Protection Agency (EPA). This authority’s main goal is to care for the environment, and for this, the EPA has determined certain standards that engine manufacturers must meet. These vary from one type of vehicle to another and are updated periodically. Over the last 40 years, despite the exponential growth of the GDP (Gross Domestic Product), the growing population and the increase of both energy consumption and vehicle miles traveled, emissions of C02 and other common pollutants have been controlled to be tied to the lower percentage possible.
Furthermore, apart from regulations, technology has been also the gear towards the cut on emissions. In the following graphs, we see the percentage of reduction in the last 30 years as technology has made machines more efficient. These have been reached in part thanks to the development of different mechanisms like the Aftertreatment System.
Heavy-duty vehicles—commercial trucks and buses—were by far the largest contributors worldwide, accounting for 76% of the total excess NOx emissions. The US is actually among the 5 markets that contribute the most on NOx production toping altogether 90% of emissions in that category.
But Why NOx Now?
But why are we now focusing particularly over NOx? Well, NOx is generated on every combustion and combustion is actually the driver of the engine. Every time diesel is burnt inside the engine, Nitrogen is generated. This element gets along perfectly with the Oxygen present in the air and join forces. This combination ends up becoming a very irritant gas that is what we call NOx (Nitrogen + Oxygen). This composition makes its way through the exhaust and is released into the atmosphere. Once it reaches the atmosphere, NOx reacts with sunlight and produces Ozone (O3), another unhealthy pollutant. The accumulation of this in busy areas is what causes that brownish smog that cover some major cities mostly in hot days.
All these elements that are combined in the air we breathe. And they have very harmful effects on our health and the environment. In fact, it is estimated that 1,100 deaths were caused from excess diesel NOx in 2015. For the United States, heavy-duty diesel vehicles caused 10 times the impact of light-duty diesel cars. It makes sense, with a vast territory to deliver goods and a fragile railway system, diesel trucks are king.
To tackle this massive public health and environmental issue, there are all kind of mechanisms aiming towards the reduction of emissions thrown into the air. Technological developments along with targeted legislation are strategically helping in this attempt to reduce the NOx impact. New vehicles must meet the strictest of standards and different mechanisms have been put in place to cut down the emissions.
What Are the Main Pollutants?
Nitrogen (N) and oxygen (O) are present separately in the ambient air and by themselves can be harmless. Consequently, both elements are present in the air fuel mixture that is combusted inside of the engine. Knowing this, it is easy to see that it would be impossible to design an internal combustion engine that does not produce NOx when it burns fuel.
The amount of NOx created during combustion varies with peak combustion temperature. The higher the temperature, the more NOx generated, thus the reason the EGR was created. Once the NOx is generated, it reacts with atmospheric chemicals originating SOOT, also called particulate matter (PM). This is what blackens the smoke that goes out the exhaust. In recent years, the amount of NOx and PM liberated to the atmosphere have seen a huge reduction.
Taking this into account, while electric alternatives are gaining ground slowly but surely, when it comes to heavy duty, the industry has leaned on technology to reduce NOx to its very limit. There are many efforts devoted to the reduction of the total amount of NOx and PM generated. And the same goes for the removal of NOx from the exhaust.
Some answers to this issue have been high-pressure common rail fuel injection systems, electronically controlled injector solenoids, and advanced turbocharging. As technology has taken a lead role in the development of engines, legislation took control of the range. Little by little the reduction started taking place and kept going to current levels.
How OEMs are using Technology to Make Reductions
Back in 1985, EPA started to determine the maximum NOx amounts that were allowed to be exhausted to the air. In 1989, PM were also added to the regulation list. Since then, the limitations have been set to meet stricter parameters.
For off highway engines, EPA distinguishes 4 tiers. By 2015, when final Tier 4 regulations were fully applicable, PM and NOx emissions had been reduced 99% compared to 1996 levels. From 2019, Tier 5 adds even stricter limitations. After Tier 4 Final, Tier 5’s aim is reducing these harmful emissions to zero making emphasis on eliminating very fine particle of soot. On the technological side, there aren’t many expectations on what manufacturers will deliver over 2022 when this new level of restrictions could be enforced.
For the purpose of delivering cleaner exhaust and meeting environmental standards Diesel Particulate Filters (DPFs) were introduced to diesel engines in the year 2007. However, there is more than a filter in the exhaust system. The whole aftertreatment system of the vehicle has made possible the achievement pointed out by EPA who states that new heavy-duty trucks and buses are roughly 99 percent cleaner than 1970 models.
The Birth of the Aftertreatment System
The original purpose of the exhaust system was to route exhaust gases from the engine in a safe manner. The goal was to get the exhaust safely directed to the environment, while also providing the reduction of combustion noise. However, over time, increasing concern on public health issues would cause tension. It emphasized the harmful components that this process was sending straight out to the atmosphere and that we have learnt about in the previous sections.
To tackle this situation other responses were created. This is how the idea of treating those gases inside of the vehicle before they exit to the atmosphere came about. And this is in fact how the aftertreatment systems came to life. An aftertreatment system is a method or device for reducing harmful exhaust emissions from internal-combustion engines. In other words, it is a device that cleans exhaust gases to ensure the engines meet emission regulations. And this is how aftertreatment systems were born.