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What Tier 4 Means for Asphalt Contractors

The U.S. government first took action against air pollution in the mid-fifties, with the Air Pollution Control Act of 1955. The act recognized air pollution as a national problem and provided federal funding to improve air quality. Then in the sixties, the Clean Air Act of 1963 set emission standards for stationary sources such as power plants, steel mills and the like – and identified motor vehicle exhaust as a problem.

The Tier rating program started in the U.S. in 1996 to reduce nitrogen oxide (NOx) and particulate matter (PM) in diesel engine exhaust. The Environmental Protection Agency (EPA) says off-road diesel engines affected by the Tiered rating system account for 47% of diesel particulate emissions and one-fourth of NOx emissions from mobile sources nationwide. The EPA estimates that by 2030, controlling these emissions will annually prevent 12,000 premature deaths, 8,900 hospitalizations, and one million work days lost.

The staggered Tier system of regulations recognizes that it becomes increasingly complex for diesel engine manufacturers to meet more and more stringent exhaust emission standards. Compared to Tier 3, Tier 4 reduces NOx and particulate emissions by 90 percent. In certain areas of high pollution, the exhaust air from the diesel engine could be cleaner than the intake air.

Tier 4 is being implemented in two stages, Tier 4 Interim (T4i) and Tier 4 Final (T4f). Stage IIIB is the European Union’s equivalent to T4i, and Stage IV is equivalent to T4f.

Since Jan. 1, 2011, manufacturers have been required to use T4i engines in all equipment for the U.S. and European Union countries in machines over 174 hp and under 751 hp with the exception of some “Flex Credits” that may be used. Tier 4 Final will be implemented for the majority of equipment on Jan. 1, 2014.

Tier 4i engines require ultra low-sulfur diesel fuel (ULSD) because of the emission control equipment that is used. This fuel has been required in the U.S. since 2010, but that is not the case in the rest of the world. ULSD is not available everywhere in the world.

“In the Tier 3 days, we could design and build a machine and ship it anywhere in the world,” says Dave Swearingen, Roadtec vice president, engineering. “Now one machine platform needs to be designed for a T4i engine for the U.S./Europe/Japan, and we need another platform for an engine that can use the higher sulfur fuels in countries with less stringent emission rules. We designate those engines as an LRC engine, for Less Regulated Countries.”

Better planning needed

“All U.S. manufacturers are going to basically double the number of models that we manufacture,” says John Irvine, Roadtec vice president of Sales and Marketing. “We have to forecast the demand for each type of engine that we need – and so will everyone else – and that is going to make the availability of machines tougher for LRC and Tier 4 regions.

“Forecasting the number of engines that we can get is becoming more difficult in view of the long lead times that are developing for engines,” says Irvine. “The upshot is that it’s going to take excellent planning on the part of ourselves and our customers to secure the availability of new equipment.

“Lead times will be lengthened,” says Irvine. “Getting engines, especially as the new Tier 4 Interim engines are introduced, has been challenging at best.”

Across the roadbuilding equipment industry, the overall price of machines is rising by 5 percent to 10 percent as a result of Tier 4, says Irvine. Larger engines are more expensive, so the price increase is higher for them.

Will fuel economy drop? Not so, say the major engine manufacturers. Both Caterpillar and Cummins say Tier 4 engines will boast fuel economy improvements of five percent on average.

Larger space claim

A T4i engine involves a larger space claim than the previous Tier 3 because of the higher cooling requirements and the after-treatment module.

“Combining the larger space claim – and still providing the degree of service access we feel is necessary – was quite a challenge, especially on compact machines like pavers,” says Swearingen.

“For that reason, on some machines we raised deck and hood heights to maintain or even improve service access,” Swearingen says. “As the machine size increases, the T4i space claim represents less of the overall volume available. That being said, all T4i installations caused some change in the machine envelope.”

The difference between T4i and Tier 4 Final (T4f) engines is that selective catalytic reduction (SCR) is applied with T4f engines. With SCR, a fine mist of a urea-water mixture is sprayed into the hot exhaust stream. Yes, a urea tank will be required for a T4f engine. The urea-water mixture, also called Diesel Exhaust Fluid, breaks down into ammonia during a chemical reaction called hydrolysis. The NOx and ammonia pass into the SCR element where a catalytic reaction takes place, converting the NOx into harmless nitrogen and water vapor.

In addition to using ultra-low sulfur diesel fuel, a Tier4i engine features changes to both the engine and exhaust after-treatment hardware. For one thing, the engine is controlled electronically. A high pressure common rail fuel system ensures fine fuel atomization to help reduce particulate matter emissions. A smart turbocharger(s) is used to control the ratio of exhaust that gets recirculated back to the engine inlet.

Smarter machines

As the engines get smarter, so do the machines. Electronic engines allow an OEM to customize engine speeds and torques to match the application. The machine side electronics are getting smarter to make operation easier and more productive for the end user.

While machines with CAN networks have been around for some time, Roadtec decided that T4i was a good time to introduce it into the company’s milling products. (CAN stands for controller area network, and a CAN bus is a vehicle standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer.)

Swearingen says one of the benefits of a CAN-networked machine is diagnostic capability, which can be done on-board or remotely.

“Our T4i-powered milling machines have a system that allows a customer or the factory to remotely log onto a machine and view and/or trouble-shoot functions, control systems, engine operation and faults, grade and slope controls, see machine location and maintenance status.

On a T4i engine, cooled exhaust gas recirculation cools a portion of the exhaust gas and reintroduces it to the intake manifold. Lower combustion chamber temperatures reduce the amount of NOx that is generated. And crankcase ventilation filter is applied; crankcase blow-by is now included in overall emissions. The crankcase ventilation system includes a filter.

In post-engine after-treatment, a diesel oxidation catalyst is used to control carbon monoxide, hydrocarbons and the soluble organic fraction of particulate matter. A diesel particulate filter (DPF) removes particulates, or soot, from the engine exhaust.

A T4i engine also employs both passive and active regeneration, which is the method of removing particulates from the DPF. With passive regeneration, the exhaust temperature is high enough to keep the DPF clean.

But with active regeneration, a device is used to raise the exhaust to a high enough temperature to clean the DPF.

Like it or not, Tier 4 is here to stay. Fewer people will go to an early grave or get sick over air pollution. So take heart, the smog is going away.