The California Air Resources Board (ARB) and the US Environmental Protection Agency (EPA) have presented preliminary proposals aimed at closing compliance loopholes for medium- and heavy-duty diesel engines using SCR-based NOxemissions control systems for 2011 and later model years.
SCR is currently the primary NOx control strategy for heavy-duty on-road engines. On Tuesday, ARB held a public workshop, with EPA’s participation, to discuss the SCR system attributes that will be evaluated during staff’s review of an application for certification.
ARB and EPA have approved 2010 and 2011 model year heavy-duty engines with SCR that are designed with certain strategies affecting operation and detection of malfunctions. While most manufacturers have developed warning signals for the operator to become aware of low diesel exhaust fluid (DEF, the term for any SVR reductant) volume and malfunctions, the agencies now say they expect manufacturers to do a better job of assuring that vehicles are not allowed to operate out of compliance for significant periods of time due to operators’s actions or inactions or equipment deficiencies or failures.
Navistar International Corporation, which relies on advanced EGR technology for 2010 compliance instead of SCR, and which has been vocal in its opposition to the use of SCR for compliance (“a license to pollute”) presented independent test findings showing that new commercial vehicles that must contain liquid urea to meet federal NOx emissions standards continue to operate effectively when urea is not present. In other words, there is no operational mechanism to forestall cheating. At such times, Navistar said, the vehicles throw off levels of NOx as much as 10 times higher or more than when urea is present.
The research was conducted by EnSIGHT, an independent environmental consulting firm, using two long-haul vehicles and one heavy-duty pickup, all of which use Selective Catalytic Reduction (SCR) technology that relies on liquid urea to clean up NOx emissions after they leave the engine.
EnSIGHT’s research showed that when liquid urea was not present, there was little or no effect on the vehicles’ operations. This included long periods of time when the vehicles’ urea tanks were empty or were refilled with water instead of urea. One truck tested appears to operate indefinitely with water and as a result without any functioning SCR NOx control. That truck has accumulated more than 13,000 miles with its SCR NOx emission control turned off.
European research also has shown that even with a full tank of liquid urea, the SCR NOx emission control system does not turn on when exhaust temperatures are not hot enough, Navistar said. This occurs during stop-and-go traffic. That means that there is frequently no SCR NOx control when these trucks are operating in urban areas as well as in any other congested traffic situation.
One of the main goals of the proposal presented by ARB staff at the workshop is to require minimal engine operation when the SCR system is no longer able to dose. Key elements of implementing such an inducement would include:
- An indication of reductant level for the operator
- Inducement initiated early enough so that final inducement is engaged prior to noncompliance due to low reductant
- Any driver inducement should account for safety concerns
- Notify operator of low level at least 2 times prior to final inducement
Inducements could be left up to the manufacturer, but could include options such as a 5 mpg limit, no power, or idle only. The system should allow for diagnostics and restart after refill.
The proposal is also addressing reductant quality, tampering, repeat offenses, self healing, delegated assembly, maintenance intervals, freeze protection, infrastructure, and unregulated pollutants.