Diesel Emissions—The Final Cut?

TECH TALK
Diesel Emissions—The Final Cut?
By Dan Marty

The latest emission regulations from the U.S. EPA, known as Tier 4 Final, are now in effect for all EPA classified diesel engine power categories. However, we are still a long way from having all the dust settle on this subject in the concrete cutting industry. Many are still wondering “What effect will this latest round of pollution controls have on our operations and profits? Can these limits be met and how? Why they are necessary?” Let’s start with the last question first.

Clearing the Air
Diesel engines are one of the largest sources of fine particulate matter (PM)—particles so small that several thousand of them could fit in the period at the end of this sentence. Diesel exhaust also contains ozone-forming nitrogen oxides (NOx), hydrocarbons (HC) and other toxic air pollutants. In addition to environmental and possible climate effects, these pollutants cause lung damage and aggravate existing respiratory diseases such as asthma and COPD. Nationwide, particulate matter—including the fine particles in diesel exhaust—causes 15,000 premature deaths every year. Diesel exhaust is also thought to be a likely human carcinogen [Diesel Exhaust in the United States (EPA420-F-03-022, June 2003)].

In the U.S., diesel engine emissions have been progressively regulated for almost 40 years. For most of that time, the regulations governed primarily on-highway engines in trucks and buses, but in 1998 non-road engines were also brought under the scope of these regulations. Canada enacted a parallel inclusion the next year, and established an agreement to align each of their standards with those from the U.S. in each succeeding tier. Similar standards were enacted in European and Japanese regulatory phases.

The inclusion of non-road diesel engines, which included construction equipment like concrete saws and hydraulic power packs along with other off-highway vehicles, was designed to capture a larger percentage of the remaining emissions in the face of diminishing returns from further on-road controls. However, the complexities of thousands of machine and operating variables for off-highway engines required an extended phase in period for 19-56kW Tier 4 off-highway engine standards (2008-2012 Tier 4 Interim). The Tier 4 Final standards require emissions of PM to be further reduced by 90% and NOx/HC by up to 37% beyond the Tier 4 Interim standards.

In addition, the EPA created a Transition Program for Equipment Manufacturers (TPEM) program. This was created in an effort to provide original equipment manufacturers (OEMs) with some flexibility in complying with the regulations. TPEM allows the use of limited quantities of previous tier engines over a limited period of time in consideration of existing stocks of engines and the difficulties of producing and incorporating compliant engines in equipment designs. Participation in the program is voluntary, but most equipment manufacturers have needed this provision to cover some or all of their production in recent years. Participating OEMs and engine manufacturers who provide the noncompliant engines are required to keep records and submit reports of their activities under the program.

Picking a Path
As the emissions standards have tightened, the methods used by the engine manufacturers have grown more complex and diverse. Nevertheless, most manufacturers achieve Tier 4 Final compliance by selecting all or several of the technologies from a common portfolio originally developed for on-road applications, often choosing different combinations for different power ranges and/or applications. The selections made by manufacturers impact equipment performance and operator experience, so it will be helpful to understand the basics of each approach. The latest emission reducing technologies include:

Ultra Low Sulfur Diesel Fuel & Low Ash Oil – A requirement for all Tier 4 engines (and thus a barrier to emission regulation in many developing countries), ultra low sulfur diesel fuel (ULSD) and low ash oil are essential to the sulfur-sensitive catalytic processes used to minimize soot and ash particulates and NOx.

Combustion Chamber Redesign – Combustion chambers have been reshaped and rearranged to optimize in-cylinder combustion, promoting more complete burning of fuels while reducing NOx producing hotspots. While some engine manufacturers have revised existing engine platforms, others have resorted to clean sheet designs to meet Tier 4 Final standards.

EGR/Cooled EGR – Exhaust Gas Recirculation, used by most engine manufacturers to meet Tier 3 emissions, gets a boost from additional cooling to reduce combustion temperatures and NOx further while increasing charge density and power, albeit at the cost of increased heat rejection loading.

High-Pressure Common Rail Fuel Injection & ECM – Introduced to meet Tier 4 Interim requirements, nearly all diesel suppliers now combine high-pressure common rail (HPCR) fuel injection (up to 26,000 psi) with an Electronic Control Module (ECM) and a network of sophisticated sensors to meet the stricter Tier 4 Final standards. HPCR fuel injection improves atomization and fuel mixing and ECM controls improve fuel efficiency and increase power while reducing HC, NOx and PM emissions. ECM controls also provide added protection and convenience through safe operating control limits and on-board diagnostic tools.

Exhaust Aftertreatments – One, two or all three of the following methods can be combined to fine-tune the emissions remaining after the above modifications are implemented:

• DOC – A diesel oxidation catalyst (DOC) contains materials that oxidize unburned hydrocarbons when exhaust gases flow through it. DOCs are generally maintenance free, with a service life intended to match that of the engine.
• DPF – A diesel particulate filter (DPF) is designed to capture particulate matter from the exhaust flow. A DPF generally requires either active or passive regeneration to burn off collected PM with supplier specific operating and/or service requirements.
• SCR – Selective catalytic reduction (SCR) injects a urea and deionized water “reducer” fluid (DEF) into the exhaust flow to initiate reactions in a catalytic chamber that reduce NOx produced by high temperatures in PM optimized combustion. DEF tanks need to kept clean and be refilled in proportion to fuel use.

An Engine/Equipment System
Tier 4 Final engine changes required equipment manufacturers to significantly revise existing models. Engine compartments have been rearranged, become more crowded and in some cases expanded to fit new and/or larger exhaust aftertreatment systems, DEF tanks (where SCR is used), electronic control systems and component protection. Re-specifications are due to higher operating temperatures and pressures, the inclusion of new or larger cooling systems that address increased heat loading and, in some cases, entirely new engine models that replace engine families discontinued due to noncompliance. Wiring harnesses have grown and become more sophisticated to accommodate more sensors and new control network protocols. Control panels have been similarly rearranged and expanded to include digital gages, informational display screens and electronic engine controls.

Recognizing that actual emissions are a function of the engine and the operating application, Tier 4 Final regulations uniquely cover not just diesel engines, but also the equipment in which they are installed. For the first time, the OEM is required to certify and label equipment as complying with the latest EPA standards and certain engine installation instructions. OEMs must annually report and maintain records of all new and replacement engine installations, including engine and equipment serial numbers, assembly or shipping dates and shipping destinations, subject to selective enforcement audits and penalties up to $37,500 for each piece of equipment found non-compliant. There are separate enforcement provisions for equipment owners, repair centers and aftermarket parts suppliers as well.

Cut to the Chase
The implementation of Tier 4 Final engines in concrete cutting equipment will directly impact CSDA contractors. New equipment will be more expensive to purchase, more complex in construction and less forgiving of abuse and neglect in service. On the other hand, Tier 4 Final engines promise lower operating costs due to improved fuel efficiency, higher performance with extended service intervals and longer service life due to clean combustion. They also feature improved controls, accurate diagnostics for reduced downtime and preemptive operational controls and maintenance warnings. Furthermore, if work involves public sector jobs and/or jobs for universities and other large organizations that have adopted Tier 4 standards, or if in a non-compliance zone that the EPA has determined has poor air quality, expect contract preference, and possibly the outright requirement, to be given to Tier 4-compliant machines.

Most normal concrete cutting operations will not be significantly affected, but integration of Tier 4 Final equipment into contractor fleets involves some important considerations. They include:

• Consulting with an equipment supplier to select Tier 4 compliant equipment that best matches operational requirements with the lowest total operating costs.
• Familiarizing operators with the new technologies, controls, monitoring systems, new display symbols and alarms.
• Updating service parts and supplies to include low ash oil and any other items specifically required by new equipment.
• Ensuring equipment service providers are trained in the engine maintenance and repair requirements of the specific engine models and technologies being used.

The most important thing for owners and operators to remember is that Tier 4 Final engines and equipment (and associated serialized records) must be used and maintained in compliant condition and configuration. Contractors need to follow all operating and service instructions, using only compliant ULSD fuel, low ash oil, clean and dry DEF (if SCR is installed) and approved emission-related components for maintenance and repairs. This will help achieve peak performance, minimize operating costs and avoid costly shutdowns and penalties. Remember—employee health and the company’s bottom line depend on it.

Additional Resources

www.dieselforum.org General info on off-road diesel engines, equipment, retrofitting, etc.

www.clean-diesel.org Diesel fuel standards and timeframes.

www.epa.gov/otaq/nonroad-diesel.htm U.S. EPA information and regulations for non-road engines.