One thing is clear—the air we breathe is getting cleaner, thanks to years of work by engine and equipment manufacturers, prodded by the government, the environmental agencies, and the Clean Air Act.

A brief history in clean air developments

Since the middle of the 20th Century, the U.S. government—and other governments around the world—have been working to clean the air. In 1955 the U.S. Congress passed the Air Pollution Control Act, the first time the government formally identified air pollution as a national problem and pollution as a risk to the public’s health and welfare. It also marked the beginning of funding to research methods to improve air quality.

Eight years later, Congress passed the original Clean Air Act of 1963, setting standards for emissions on stationary sources of pollution, such as power plants and steel mills. In 1965 an amendment to the Clean Air Act called the Motor Vehicle Pollution Control Act set the first federal emission reduction standards for automobiles, starting with 1968 models.

EPA is established

Another major milestone for a cleaner environment was the creation of the Environmental Protection Agency (EPA), which took place in 1970 during the Clean Air Act extension. EPA was established—in part—to help enforce the regulations set forth by the amended Clean Air Act. The rewritten version of the Act set new national standards for ambient air quality and “new-source” performance standards that strictly regulated emissions of a new source (e.g., automobiles, factories) entering an area.

Also, parts of the Clean Air Act extension were new standards for hazardous emissions from motor vehicles, including carbon monoxide, hydrocarbons, nitrogen oxides, lead, and particulate matter. These emissions are still of primary concern today and a large part of the emission standards—such as Interim Tier 4 and Final Tier 4—that are required for the future.

To combat the hazardous emissions from motor vehicles, the automotive manufacturing industry incorporated the catalytic converter in 1975 as a method to reduce automobile emissions. It soon became a regular part of a vehicle exhaust system, and has been adopted in other forms of transportation, such as buses, trains, and airplanes, to name a few.

1977 amendment

The next significant update to the Clean Air Act was in 1977. Among the amendments was the creation of the New Source Review, which was responsible for helping older facilities (power plants, manufacturing plants, and more) that were previously grandfathered in to the Clean Air Act to undergo environmental testing and install pollution controls during facility expansions. The 1977 amendment also, for the first time, set standards for lead in gasoline used in vehicles, such as automobiles and light trucks.

1990 amendment

The last noteworthy amendment to the Clean Air Act happened in 1990, placing emphasis on prohibiting leaded gasoline after 1995; addressing acid rain, ozone depletion, and toxic air pollution; and creating a national permits program, known as “emissions trading.” This was done to encourage companies to minimize air pollution with incentives for meeting air quality regulations. Companies could purchase emission credits to emit specific volumes of air pollution—or trade permits with other companies—but they were not allowed to exceed a cap.

Shortly after the 1990 amendments, new emission standards were announced for cars and light trucks setup as a two-tier system that started in 1994 and was completed in 2010. Meanwhile, heavy-duty trucks and buses also followed new emission requirements. The final tier for cars, light trucks, heavy-duty trucks, and buses is comparable to Tier 4 standards for nonroad equipment. Construction equipment was the last category required to meet the air quality controls, but now the nonroad equipment is entering the final phases of EPA emission standards to virtually eliminate any harmful pollutants.

EPA standards for nonroad equipment

Understanding exactly how the EPA emission standards impact nonroad equipment can be difficult to understand, and even more challenging is determining what manufacturers are doing to their equipment to make it compliant with EPA regulations. The rest of this article will attempt, on a high level, to explain the implications of EPA nonroad emission standards and the technologies available to help manufacturers meet Interim Tier 4 and Final Tier 4 regulations.

Health benefits. First and foremost, cleaner air is good for everyone. That may sound like common sense, but research shows that remarkable health improvements, especially respiratory, have been made because of changes to clean air standards. Studies show that efforts taken by the EPA have reduced air pollutants, mostly the two worst ones: particulate matter (PM) and nitrogen oxides (NOx). By the end of 2010, the EPA estimated that NOx emissions would be reduced by about a million tons per year. That’s the equivalent of removing 35 million passenger cars from the roads. Even better, by the year 2030, the EPA estimates that annually, cleaner air will prevent 12,000 premature deaths, 8900 hospitalizations, and 1 million lost work days.

However what exactly has the EPA been doing since the first clean air nonroad diesel rules took effect in 1995? The EPA’s primary goal was to create a national program designed to reduce harmful emissions from nonroad diesel engines. To do so, they encouraged equipment manufacturers to implement engine and fuel controls to eliminate or minimize PM and NOx levels from diesel engine exhaust. Let’s take a look at the four individual tiers since they took effect.

Tier 1. Tier 1 was the first set of emission standards adopted and regulated by the EPA for new nonroad diesel engines. The goal of Tier 1 was to reduce NOx emissions from nonroad diesel engines by approximately 30%. The time frame for construction equipment was 1998 to 2004, depending on the engine horsepower. For some manufacturers, meeting the Tier 1 requirements meant some simple modifications to the engine combustion system. It changed how diesel fuel burned in the engine cylinders.

Tier 2. In 2004 the next step in nonroad diesel regulations took effect. The goal of these regulations was to reduce NOx, PM, and hydrocarbons. Tier 2 lasted from 2004 through 2007. Again, equipment manufacturers met these requirements. In some machines, Tier 2 standards were achieved by incorporating a direct fuel injection design (known as direct injection). Additional methods were implemented to help meet the Tier 2 requirements. Direct injection was helpful in improving fuel efficiency and lowering overall operating costs for some equipment owners. Direct injection improved engine heat rejection to the machine’s cooling system, therefore some engines operated at cooler temperatures to improve the engine’s life in most machines.

Tier 3. In 2008 the EPA Tier 3 regulations took effect. These emission regulations applied only to equipment with engines greater than 75 hp. In one example, Bobcat equipment with lower horsepower engines jumped from Tier 2 to Interim Tier 4 or Final Tier 4. The goal of Tier 3 targeted NOx again—to reduce it by approximately 37% compared to Tier 2. To meet the Tier 3 regulations for machines between 75 and 100 hp, Bobcat implemented a cooled exhaust gas recirculation (CEGR) process.

Interim Tier 4 and Final Tier 4. These are the final steps the EPA is implementing as part of its non-road diesel rules to curb emissions. Deadlines needed for compliance vary the most among the tiers at this point. They began in 2008 with Interim Tier 4 and will continue through 2015 when the Final Tier 4 regulations are complete.

The good news is that some machines are already Interim Tier 4 (25 to 75 hp) or Final Tier 4 (under 25 hp) compliant. This is the case with machines with engines that are less than 75 hp because the emission standards were less stringent. These machines have particulate matter reductions of 50% and comply with the low-sulfur and ultra-low sulfur diesel fuel requirements. Other machines with diesel engines that have horsepower ranges between 75 and 100 will not become Interim Tier 4 compliant until 2012 and Final Tier 4 compliant until 2015.

Tier 4 technologies. Now that we’ve looked at the history of the EPA emission standards, it’s time to review the technologies available to manufacturers to reach Tier 4 compliance. This is a comprehensive list of the available technologies, at a high level, and not necessarily how equipment manufacturers will reach Tier 4 compliance.

Engine manufacturers identified the fuel injection system as a major focus point to help meet the EPA nonroad diesel engine emission levels for Tier 4. Fuel injection systems affect the diesel engine’s fuel consumption, torque, noise, and emission levels.

High-pressure common-rail fuel system (HPCR). The fuel injection system is a major area of focus for advancement toward clean-operating diesel engines. HPCR is an advanced fuel-injection design that regulates fuel pressure and injection timing.

Fuel pressure. The pump applies extreme pressure to fuel (22,000 to 34,000 psi). The common rail stores pressurized fuel. The injectors deliver fuel to the engine.

Injection timing. The electronic control unit (ECU) precisely controls the injector to allow multiple fuel injections during each combustion cycle.

HPCR benefits. Extreme pressure transforms fuel into extremely fine mist as it leaves the injectors. Fuel mist combusts (burns) more thoroughly. Lower operating costs: When fuel combusts more thoroughly, less is needed to make the engine run. The result is improved fuel economy. Cleaner exhaust: When fuel combusts more thoroughly, less of it is left over in the exhaust after combustion. The result is cleaner exhaust. When fuel is injected multiple times during each combustion cycle, the combustion lasts longer to create more energy and lower peak engine cylinder pressure. Better performance: Creating more energy during combustion results in more torque output from the engine. More operator comfort: Lower peak engine cylinder pressure reduces engine noise levels.

After-treatment systems. The good news for nonroad engine manufacturers is this: Car and light-duty truck manufacturers complied with EPA regulations years earlier and developed technologies that have been tested in nonroad engines. These after-treatment systems take the diesel engine exhaust that has already been created by the engine and clean it further by using one or a combination of the following: catalytic oxidation, heat, filtering, and diesel exhaust fluid (DEF).

DOC/DPF Systems. These after-treatment devices use filtering, heat, and catalytic oxidation to lower emissions in diesel engine exhaust. They’re commonly combined with one another in a single canister. Together they lower many emissions but, most importantly, they reduce particulate matter.

The diesel oxidation catalysts (DOC). Engine exhaust is transformed by the DOC to reduce particulate matter. The DOC is a special catalyst that reacts with engine exhaust upon contact. The reaction transforms particulate matter emissions in the exhaust into harmless substances such as water and carbon dioxide.

The diesel particulate filter (DPF). Engine exhaust is filtered by the DPF to reduce particulate matter. The DPF is a special “ceramic wall flow” filtration system that further separates particulate matter from the engine exhaust.

DPF regeneration. To keep the DPF clean and working efficiently, the high temperature of the exhaust itself is used to burn accumulated particulate matter off of the DPF. This DPF cleaning process is called “regeneration.” See Figure 3.

Selective catalyst reduction (SCR). Engine exhaust is transformed by SCR to reduce NOx. SCR uses an ammonia and DEF. Combining exhaust with DEF causes it to react with a SCR catalyst. This reaction turns harmful NOx into harmless nitrogen and water vapor.