At the Conexpo trade show in Las Vegas, the Tognum subsidiary MTU Detroit Diesel displays one of its Series 900 engines that is Tier 4i compliant using selective catalytic reduction (SCR) technology. Diesel engine manufacturer MTU Friedrichshafen has already demonstrated the experience and expertise necessary to offer its customers EPA Tier 4i compliant engines when these off-highway emission standards take effect on January 1, 2011.

The versatile Series 900 and Series 500 engine families were the ideal candidates for the use of selective catalytic reduction (SCR) to meet upcoming Tier 4 interim emissions regulations. "These engines have established themselves as the premier engines in their power class," said Scott Jenkins, Director of C&I Sales for MTU's North American division, MTU Detroit Diesel. "And they have proven to perform just as well with SCR."

Emissions reduction often works in opposition, explained Gerhard Kramer, Director, Application Center Industrial for MTU. For example, reducing particulate matter often increases the output of oxides of nitrogen (NOx), and vice-versa. "As designed, the Series 900 and Series 500 engines exhibit low particulate matter emissions," said Kramer. "To comply with NOx limiting values, an SCR system is added."

An SCR system works by injecting urea into the exhaust stream where it reacts with nitrous oxides to produce harmless nitrogen and water. This reaction takes place when the urea and exhaust gases pass over a catalyst material in the SCR unit. Urea consumption varies with duty cycle and other factors but is not expected to exceed five percent of fuel consumption. As a rule of thumb, fuel consumption compared to Tier 3 engines is reduced by a similar amount, so that total consumption of liquids remains the same.

The SCR system itself consists of engine-mounted hardware, urea lines, electrical wiring and a catalyst unit somewhat larger than a muffler. The catalyst unit is used instead of the standard muffler.

SCR is a proven technology already found in a wide range of applications. Some 200,000 on-highway versions of Series 900 and Series 500 engines have already been sold and are operating satisfactorily. In Europe, all major truck manufacturers have adopted this technology. Urea will likely also be required for diesel engines to meet the on-highway 2010 emissions standards in North America, so the delivery infrastructure is being built out rapidly. Urea is non-toxic and requires no special handling. Service trucks will refill off-highway equipment with urea at the same time as they refuel that equipment.

"Other emissions reduction technologies have merit and MTU has experience with all of them," said Jenkins. "Our philosophy is to match the best technology to the needs of the specific engine, and in this case SCR was by far the best choice. We wanted to take these proven engine families with state-of-the-art designs, and bring them into compliance with the next round of emissions standards without compromising the benefits the engines. SCR allowed us to do that optimally by adapting the existing on-highway technology for industrial use."

Inline four- and six-cylinder Series 900 engines have ratings from 120 to 322 bhp (90 to 240 kW), while V-configuration six- and eight-cylinder Series 500 engines cover ratings from 349 to 644 bhp (260 to 480 kW). OEMs appreciate the compact size of the Series 900, while end users praise the engines' performance characteristics, reliability and low cost of operation. More than a half-million Series 900 engines are in service today.

The same SCR technology will also be used in the related 460 inline six-cylinder engine, which covers a power range from 348 to 483 bhp (260 to 360 kW).

MTU Detroit Diesel
MTU Detroit Diesel, Inc. is the North American regional headquarters of MTU Friedrichshafen GmbH, one of the world's most important providers of diesel engines and drive and propulsion systems for ships, heavy-duty land and rail vehicles, and decentralized power plants. Under the brand names MTU and Detroit Diesel, it offers a complete line of power solutions from 30 to 12,200 bhp (20 to 9,100 kW) for applications in the marine, rail, power generation, oil and gas, agriculture, mining, construction and industrial, and defense markets. MTU Detroit Diesel is part of the Tognum MTU Engines division.

Tognum is one of the world's leading suppliers of high speed diesel engines and complete propulsion systems for ships, heavy land and rail vehicles and of industrial drive systems as well as decentralized power plants, set-up in the two divisions mtu Engines and Tognum Onsite Energy Systems and Components. Its product portfolio includes diesel engines in the power range from 20 to 9,100 kW, gas engine systems, gas turbines and fuel cells and is one of the most modern and comprehensive in its sector. In addition, the group develops and manufactures custom-made electronic control and monitoring systems for its engines and propulsion systems.

Sales of the Tognum Group amounted to more than EUR 2.8 billion in 2007. By the end of 2007, the Group employed approximately 8,200 personnel worldwide. It maintains a global sales and distribution network including 22 subsidiaries, more than 130 distribution partners and 1,100 authorized dealers.