Fabrizio Mozzi & Joseph Feldman, Cummins Power Generation, USA
The EU has established a series of increasingly strict regulations for off-road, portable diesel powered equipment. As the chart below indicates, most of the EU’s Stage IIIA emissions regulations take effect in January 2011. The requirements for 34–69 kVA generators take effect in January 2012. In the US, the Environmental Protection Agency (EPA) has established similar requirements known as Tier 4 Interim (or T4i).
These EU and EPA regulations primarily affect portable diesel generator sets (18–550 kVA) and other non-road and industrial engines. Typically, a portable, non-stationary set is considered to be either a rental set, or a unit that is moved more than twice a year from a defined location. At the present time, the EU does not regulate emissions from stationary diesel generator sets used for prime, peak shaving, load shedding or emergency standby power.
The four main constituents in diesel exhaust that the new regulations have been designed to address are:
- Nitrogen oxides (NOx) – NOx is a combustion by-product that combines in the atmosphere to create ozone and smog. It is controlled by reducing the combustion temperature inside the cylinder.
- Hydrocarbons (HC) – Essentially unburned fuel, HC also contribute to ozone and smog production. HC is a minor constituent in diesel exhaust. It is controlled by improving combustion efficiency.
- Carbon monoxide (CO) – CO is also a minor constituent of diesel exhaust. It is controlled by improving combustion efficiency.
- Particulate matter (PM) – PM is made up of soot particles in diesel exhaust from unburned carbon. It is controlled by optimizing the combustion temperature and improving combustion efficiency.
To meet Stage IIIA targets for 2011, NOx and PM levels need to drop 98 per cent below unregulated levels, and some 40 per cent from the previous phase of regulations. These two reductions are especially challenging because most engine modifications that decrease NOx tend to increase PM.
Meeting Stage IIIA and T4i Requirements
Engine makers have been busy working on product innovations and enhancements to satisfy these ever-stricter requirements for both the EU and the USA. Cummins Power Generation has been working closely with the EU and supports its efforts to strengthen emissions regulations for non-road and stationary diesel engines. In fact, Cummins Power Generation was the first manufacturer to offer generator sets meeting Stage IIIA requirements.
|The QSX15 engine features Cummins Power Generation’s PowerCommand controls Source: Cummins|
In order to meeting these new emission standards, Cummins has been focusing first on existing electronic-controlled engine platforms and new in-cylinder design enhancements, applying a number of modifications to fuel systems, after-treatment and overall design.
Cooled exhaust gas recirculation (EGR) recycles and cools a portion of the inert gases of the exhaust stream as they mix with incoming engine air. The Cummins short-loop EGR system routes the exhaust gas directly back to the cylinder. Combustion temperatures are thereby reduced, and therefore so is NOx. The cooling also increases the density of the charge air, boosting power.
Variable Geometry Turbocharger allows the effective aspect ratio of the turbo to be altered as conditions change. The optimal aspect ratio at low engine speeds is very different from that at higher engine speeds. Varying the angle of the vanes reduces the turbo lag at low speeds without compromising the boost at higher speeds.
|The cooled exhaust gas recirculation system Source: Cummins|
The direct flow air filter is mandatory for the current Tier 4 Interim and it also allows the integration of a mass air flow sensor into the housing of the filter for Tier 4 Final. It has a pre-cleaner, primary and secondary filter elements. There is also a dust ejector valve.
A redesigned and more durable electronic control module (ECM) has sensors and microprocessor-based controls that improve fuel efficiency and power output while decreasing both NOx and PM emissions. These controls manage fuel quantity, injection timing and turbo boost pressure, and they take into account load, temperature, barometric pressure, fuel energy content, and even engine wear. The result is optimal combustion.
While for the EU market most of the modifications apply to the inner section of the engines, in order to meet the more stringent US EPA regulations for Cummins mid-range and heavy-duty engines, the company has developed an integrated PGI Harness for its power generation interface (PGI). It has connections for engine, after-treatment and service data built in. The ultra-clean exhaust eliminates visible smoke and soot, and its thermal insulation reduces surface temperatures. It operates together with the EGR to make up an integrated emissions system.
The high-pressure common rail fuel system plays a big role in meeting the new requirements for emissions in both the EU and the United States. Increasing fuel pressures up to 1800 bars (26 000 psi), along with the retardation of injection timing, reduces NOx without increasing PM or HC. Alterations to nozzle design and injection systems themselves can have an impact as well. For example, multiple injection events per cycle improve fuel atomization and penetration of the combustion chamber, boosting fuel efficiency while reducing PM.
To reach the Tier 4 levels of PM for the USA market, after-treatment of exhaust gas is required, since it can reduce emissions by a substantial margin. For its lead products, like the QSB7 and QSL9, Cummins has developed a regenerating diesel particulate filter (DPF) with selective catalytic reduction (SCR) that removes PM from the exhaust gas. Cummins offers a wide variety of horizontal and vertical designs, as well as side inlet and side outlet configurations for the DPF.
Integrated Design and Manufacturing
To comply with these coming EPA and EU requirements, Cummins has integrated components from its own technology portfolio. The engine combustion technologies were developed specifically to work with both the cooled EGR and the after-treatment filter. The company believes this approach minimizes space and installation impact while optimizing performance, reliability and emission control.
For OEM customers a Coolpac integrated cooling solution is available. The idea is to save customers both time and resources by designing products that comply with the new standards. The Coolpac option includes a radiator, air cleaner and PM filter exhaust after-treatment (for the USA market only), reducing the OEM’s engineering requirements.
Looking Forward to Stage IV and Tier 4 Final
Cummins’ Tier 4 Interim/Stage IIIB technology path for 2011 across the 174–751 hp (130–560 kW) power category will continue to combine cooled EGR, variable geometry turbocharging and a high-pressure common rail fuel system with integrated Cummins particulate filter after-treatment and direct flow air filtration.
With just a few years before the introduction of Stage IV and Tier 4Final requirements in 2014, Cummins will apply an incremental technology approach, which will be more easily incorporated on the interim product platforms and help to reduce installation complexity.
A Cummins engine equipped with Coolpac Source: Cummins
Meeting these emission requirements in both the EU and the US has involved building on the proven success of its compliant engines and has required the contributions of many design and manufacturing engineers, as well as countless discussions with customers. Cummins strives to continue earning the business and trust of customers with products that meet or exceed these strict environmental standards.
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