Coming soon: higher emission restrictions for off-road diesel engines

Sunday, April 3, 2011

Since 1996, U.S. environmental regulations have used a tier system to regulate emissions from 'off-road' diesel engines. Expect a new set of regulations covering carbon particulate matter and nitrous oxides in 2011

by RALPH WINFIELD

Up until 1994, "off-road" diesel engines, which include all farm diesel engines, were not regulated. The U.S. Environmental Protection Agency (EPA) had set lower diesel emission standards under the Clean Air Act of 1970 for "on-road" diesel engines.

The Act initially regulated emissions from automobiles and then highway trucks and buses. Over the ensuing 16 years, the emission standards became increasingly more stringent, using a "tier" or stepped system.

The Tier 1 standard was phased in from 1996 to 2000. The more stringent Tier 2 and Tier 3 standards were phased in from 2000 to 2008. Many of you will recall the race to build as many highway trucks as possible in 2007 to beat the more stringent standards that were to come. Some diesel engine manufacturers were under pressure just to meet the Tier 3 standards.

The EPA's first major effort was to get sulphur out of diesel fuel. Diesel fuel used to contain about 3,000 parts per million (ppm) of sulphur. The regulations required that the level be reduced to 500 ppm in 2007 and to 15 ppm by 2010. I am sure that most of you remember the lubricity concerns of the diesel injection manufacturers when the first major sulphur reduction was imposed. Fortunately, with the help of the oil companies, that hurdle was surmounted.

You may also remember from your high school chemistry that when sulphur reacts with oxygen it produces sulphur dioxide. When water is added, the new mix is sulphuric acid.

The other two components of concern to the EPA and environmentalists are unburned fuel that produces carbon particulate material and the oxides of nitrogen – primarily NO2.

Hence, the black smoke plume that used to emanate from the neighbour's combine or tractor. In some cases, it allowed you to locate Charlie in the field!

The primary cause of the particulate material (carbon) emissions was incomplete combustion of the injected diesel fuel. If the fuel was not broken down into small enough particles or there was insufficient air (oxygen) for the amount of fuel injected, black exhaust smoke would occur.

So what's ahead?
We have seen tremendous improvements in fuel injection technology in the last 10 years. This included significant increases in injection pressures to do a much better job of atomizing the higher quality diesel fuel that became available. Usually, this involved electronic injection technology.

Further reductions in particulate matter emissions can now be achieved by use of particulate filters. These filters will require regular operator attention to ensure adequate regeneration (or replacement) of the filters, as necessary.

The new Tier 4 "interim" standards applicable for 2011 require a 90 per cent reduction in particulate matter emissions compared to the Tier 3 requirement of 2008. Similarly a 50 per cent reduction is required of the nitrous oxides (NOx) levels permissible in the Tier 3 requirements.

Basically two approaches are appearing as methods to reduce NOx levels. The first requires no added material. It utilizes exhaust gas recirculation (EGR), a technology that has been used on our gasoline-powered vehicles for a number of years. What this means is that a portion of the exhaust gas is added back into the intake air stream of the engine. For turbocharged and after-cooled engines (which includes many of our large diesel engines), the system is somewhat complex but provides the required reduction. John Deere is using this technology.

The other methodology is to introduce a urea solution into the exhaust gas just before it enters a type of catalytic converter, thus the term Selective Catalytic Reduction or SCR. The exhaust heat turns the urea into ammonia, which reacts chemically with the NOx to produce water and nitrogen gas, both of which are normal components of our environment. Sisu diesel engines used by AGCO utilize this technology and so does Case IH with their FPT engines.

As the engineers for various engine manufacturers experiment and look to the future, other techniques will likely come forward.

Do remember that the 2011 timing of the Tier 4 "interim" or 4A emission control requirements is just another step. The full Tier 4 or 4B requirements are mandated for 2014.

If you are interested in further details of the EPA requirements and the ISO standards being developed for components, do an Internet search using the words "Tier 4 Diesel Engines." You will get about 148,000 results! BF

Agricultural engineer Ralph Winfield farms at Belmont in Elgin County.