Tech2Tech: Tier 4 diesel emissions standards: Are you ready?

By Dave Worden

In this article, I will delve into the new Tier 4 emissions standards and then look at some of the technology being implemented. Specifically, I will touch on a new Tier 4 engine that was introduced by Kohler at GIE+EXPO 2011.


The following notes are excerpts taken from the U.S. Environmental Protection Agency (EPA) website at Hopefully, they will give you a better understanding of the rules and regulations:

Clean Air Rules of 2004

These rules address ozone and fine particle pollution, nonroad diesel emissions, and power plant emissions of sulfur dioxide, nitrogen oxides (NOx) and mercury. The EPA has adopted a comprehensive national program to reduce emissions from future nonroad diesel engines by integrating engine and fuel controls as a system to gain the greatest emission reductions. To meet these emissions standards, engine manufacturers will produce new engines with advanced emission-control technologies similar to those already expected for highway trucks and buses. Exhaust emissions from these engines will decrease by more than 90 percent. Because the emission-control devices can be damaged by sulfur, the EPA is also adopting a limit to decrease the allowable level of sulfur in nonroad diesel fuel by more than 99 percent.

Quick overview of the Tier 1-3 standards

Tier 1 for new nonroad (or off-road) diesel engines were adopted in 1994 for engines over 37 kW (50 hp.) to be phased in from 1996 to 2000.
In 1996, a Statement of Principles (SOP) pertaining to nonroad diesel engines was signed between EPA, the California Air Resources Board (CARB) and engine makers.
On Aug. 27, 1998, the EPA signed the final rule reflecting the provisions of the SOP. The 1998 regulation introduced Tier 1 standards for equipment under 37 kW (50 hp.) and were increasingly more stringent.
Tier 2 and Tier 3 standards for all equipment with phase-in schedules from 2000 to 2008. The Tier 1-3 standards were met through advanced engine design, with no or only limited use of exhaust gas aftertreatment (oxidation catalysts). Tier 3 standards for NOx + hydrocarbons (HC) are similar in stringency to the 2004 standards for highway engines; however, Tier 3 standards for particulate matter (PM) were never adopted.
Tier 4 standards. On May 11, 2004, the EPA signed the final rule introducing Tier 4 emission standards, which are to be phased in from 2008 to 2015. The Tier 4 standards require that emissions of PM and NOx be further reduced by about 90 percent. Such emission reductions can be achieved through the use of control technologies — including advanced exhaust gas aftertreatment — similar to those required by the 2007-2010 standards for highway engines.

All of the previously mentioned information is to give you, the technician, a little better understanding of how the diesel engine has evolved. For manufacturers, service centers and you, the technician, what does the new standard mean?

Frequently asked questions

Question (Q): Once the Tier 4 engines hit the market, can I still order a Tier 3 engine?

Answer (A): According to federal law and EPA regulations, depending on the machine, manufacturers will only be able to produce the Tier 4 engines after the established deadlines. However, equipment dealers can sell inventories of engines and equipment from the previous generation technology (Tier 3) until the inventory is depleted. Each engine and equipment OEM may have different technology and transition plans, so it will be important to understand these requirements.

Q: Do these engines require a different fuel?

A: Yes! New Tier 4 generation engines and equipment will require the use of ultra-low sulfur diesel (ULSD) fuel, which has no more than 15-parts-per-million (ppm) sulfur. This fuel has been used since 2006 in on-highway vehicles. Older off-road machines and engines can continue to use the higher sulfur fuels that will be available in diminishing quantities.

Q: Will additional dealer diagnostic equipment be needed?

A: Technicians will need to have a general familiarity with electronically controlled engines, exhaust aftertreatment control devices, the concept and practice of measuring backpressure, along with the general exhaust equipment maintenance and operation. New operator warning lights and dashboard indicators will likely be included. Some Tier 4 engines/machines may use particulate filter technology that could require periodic maintenance and cleaning and/or removal. Then again, some manufacturers will use Selective Catalyst Reduction (SCR) technology, so service employees will need to be trained in the general aspects of SCR technology. Training on the safe handling, storage, disposal and dispensing of diesel exhaust fluid, including its material safety data sheet (MSDS), is also strongly suggested.

Q: Are any additional technician training and certifications needed? Do the new engines require additional maintenance?

A: Some new Tier 4 engines may have additional or different maintenance requirements as compared to previous generations of equipment. You will need to check with your specific manufacturer. It would further be to your advantage to attend any and all training programs whether they are held at the manufacturer’s facility or at a regional location. These new requirements could include changes in the types of engine oil, the frequency of recommended oil changes, and the types of air filters and fuel filters along with routine maintenance on the exhaust particulate filter systems. For engines that use SCR technology, they will have to be periodically filled with Diesel Exhaust Fluid (DEF), which could occur at a maintenance interval or while on the job site, depending on manufacturer design, machine use and other factors. Equipment that uses diesel particulate filters will require exhaust filter maintenance at intervals typically of 3,000 to 4,500 hours.


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 Figure 2


 Figure 3


 Figure 4


 Figure 5


 Figure 6New terminology

There will be many new features and designs introduced by various manufacturers. Following are a few of them and some notes regarding their functions.

High-Pressure Common Rail (HPCR) fuel system: An advanced fuel injection design that regulates fuel pressure and injection timing (see Figure 1).
Diesel Oxidation Catalysts (DOC) and Diesel Particulate Filters (DPF): DOC/DPF systems are highly effective at reducing particulate matter (PM) contained in engine exhaust.
Selective Catalyst Reduction (SCR)*: Engine exhaust is transformed by SCR to reduce nitrogen oxides (NOx). SCR uses an ammonia- and water-based liquid called Diesel Exhaust Fluid (DEF). Combining exhaust with DEF causes it to react with a SCR catalyst. This reaction turns harmful NOx into harmless nitrogen and water vapor.

* Widely used in Europe on heavy-duty trucks and in some U.S. stationary industrial and power generation settings, SCR technology was introduced to the U.S. for mobile on-road and off-road applications in 2010.

Additional notes

Some Tier 4 engines will include use of cooled exhaust gas recirculation (EGR). EGR is a technique that recirculates a portion of the exhaust gases back into the combustion chamber which has the effect of lowering the combustion temperature and reduces the formation of NOx. This system will normally add manifolds and plumbing around the engine.

Kohler Company and its new Tier 4 engine

Kohler acquired Lombardini in 2007 and has since been working on developing new technologies, as well as building new engines — not just updating older units.

Kohler has built from the ground up a Tier 4 emissions-compliant engine without a Diesel Particulate Filter (DPF). By using Kohler’s exclusive direct-injection system, cooled exhaust gas recirculation (EGR) (see Figure 2), diesel oxygenated catalyst (DOC) and the high-pressure common rail fuel system, Kohler achieved better atomization of the fuel and improved the fuel consumption, resulting in reduced emissions.

The benefits

An Electronic Control Unit (ECU) with a fuel mapping program monitors and manages the engine’s power output and fuel system for peak efficiency. Using an efficient turbocharger, 4-valve cylinder head, a special combustion chamber design, a cooled electronic exhaust gas recirculation (EGR) and a diesel oxygenated catalyst (DOC), you get the following:

Low cost of ownership
Limited maintenance
Compact sizing for equipment manufacturers
No heat management issues

Enhanced performance

The engine’s fuel mapping program within the Electronic Control Unit (ECU) (see Figure 3) monitors and manages the engine’s power output in varying conditions by injecting fuel multiple times into the combustion cycle to maximize torque and power when needed most.

Other features of the new diesel engine include less noise and vibration, making it Kohler’s quietest diesel model, as well as a heavy-duty crankcase for increased durability to extend the life of the engine.

Other unique features

Waste gate turbine (see Figure 4)
Liquid-cooled EGR (see Figure 5)
Clean lines and balance in a compact design (see Figure 6)
Cost savings: The direct-injection system offers equipment owners the ability to save up to $1,400 on fuel and $116 on oil per year — when compared to indirect-injection diesel engines with diesel particulate filters and based on 1,000 hours of annual operation at $3.75/gallon of diesel fuel and $4.10/quart of oil.

As you can see, this new engine series offers a lot of features and benefits, and you can rest assured that more Tier 4-compliant engine technology will be coming and it will be up to the technicians to stay on top of this technology.

In closing, I would like to leave you with a few thoughts:

Laws of life: No job is too small to botch!
Problem solving: In the Chinese language, the meaning of “crisis” is a composite of two words: one meaning “danger” and the other meaning “opportunity.” Working on engines can be a danger but an opportunity to conquer.
The future: The trouble with the future is that it keeps getting closer and closer!








Dave Worden has 40 years of extensive experience in the outdoor power equipment industry at the dealer, distributor and manufacturer levels. After beginning his career as a service technician for a dealership, he made the jump to a Central Distributor. There, he continued to work in the service department before he was promoted to educational director, representing Briggs & Stratton, Kohler, MTD and Tecumseh. He then moved up to the manufacturer level, serving as a territory manager for McCulloch Corp., a training specialist for Kohler Co. Engine Division, and a general manager for a manufacturer-owned dealership. In addition to being a contributing writer for OPE magazine, Worden is currently a program director for SkillsUSA.


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