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Off-road diesel engines remain one of the most significant contributors to the overall oxides of nitrogen (NOX) inventory and the California Air Resources Board (CARB) has indicated that reductions of up to 90% from current standards may be necessary to achieve its air quality goals. In recognition of this, CARB has funded a program aimed at demonstrating emission control technologies for off-road engines. This program builds on previous efforts to demonstrate Low NOX technologies for on-road engines. The objective was to demonstrate technologies to reduce tailpipe NOX and particulate matter (PM) emissions by 90 and 75%, respectively, from the current Tier 4 Final standards. In addition, the emission reductions were to be achieved while also demonstrating a 5 to 8.6% carbon dioxide (CO2) reduction and remaining Greenhouse Gas (GHG) neutral with respect to nitrous oxide (N2O) and methane (CH4).

Eco-driving algorithms enabled by Vehicle to Everything (V2X) communications in Connected and Automated Vehicles (CAVs) can improve fuel economy by generating an energy-efficient velocity trajectory for vehicles to follow in real time. Southwest Research Institute (SwRI) demonstrated a 7% reduction in energy consumption for fully loaded class 8 trucks using SwRI’s eco-driving algorithms. However, the impact of these schemes on vehicle emissions is not well understood. This paper details the effort of using data from SwRI’s on-road vehicle tests to measure and evaluate how eco-driving could impact emissions. Two engine and aftertreatment configurations were evaluated: a production system that meets current NOX standards and a system with advanced aftertreatment and engine technologies designed to meet low NOX 2031+ emissions standards.

Accelerated aging of automotive gasoline emissions catalysts has been performed on bench engines for decades. The EPA regulations include an accelerated aging cycle called the Standard Bench Cycle (SBC) that is modeled on the RAT-A cycle developed by GM Corp. and published in 1988. However, this cycle cannot be used for diesel aftertreatment components because it is based on stoichiometric operation, whereas diesel engines typically operate under excess air (lean) conditions. The need for accelerated aging cycles for diesel emissions systems can be illustrated by considering that the full useful life (FUL) requirement in the United States for an on-highway truck is 435,000 miles, and an off-road application may be 8,000 hours. With the recent CARB Omibus legislation, the durability duration will be increasing for on-road applications by as much as 80 percent in the next decade.

The commercial vehicle industry continues to move in the direction of improving brake thermal efficiency while meeting more stringent diesel engine emission requirements. This study focused on demonstrating future emissions by using an exhaust burner upstream of a conventional aftertreatment system. This work highlights system results over the low load cycle (LLC) and many other pertinent cycles (Beverage Cycle, and Stay Hot Cycle, New York Bus Cycle). These efforts complement previous works showing system performance over the Heavy-Duty FTP and World Harmonized Transient Cycle (WHTC). The exhaust burner is used to raise and maintain the Selective Catalytic Reduction (SCR) catalyst at its optimal temperature over these cycles for efficient NOX reduction. This work showed that tailpipe NOX is significantly improved over these cycles with the exhaust burner.

Despite considerable progress over the last several decades, California continues to face some of the most significant air quality problems in the United States. These continued issues highlight the need for further mobile source NOX reductions to help California and other areas meet ambient air quality targets mandated by the U.S. EPA. Beginning in 2014, the California Air Resources Board (CARB) launched a program aimed at demonstrating technologies that could enable heavy-duty on-highway engines to reach tailpipe NOX levels up to 90% below the current standards, which were implemented in 2010. At the same time, mandated improvements to greenhouse gas emissions (GHG) require that these NOX reductions be achieved without sacrificing fuel consumption and increasing GHG emissions.

Commercial vehicles require fast aftertreatment heat-up in order to move the SCR catalyst into the most efficient temperature range to meet upcoming NOX regulations. Today’s diesel aftertreatment systems require on the order of 10 minutes to heat up during a cold FTP cycle. The focus of this paper is to heat up the aftertreatment system as quickly as possible during cold starts and maintain a high temperature during low load, while minimizing fuel consumption. A system solution is demonstrated using a heavy-duty diesel engine with an end-of-life aged aftertreatment system targeted for 2027 emission levels using various levels of controls. The baseline layer of controls includes cylinder deactivation to raise the exhaust temperature more than 100° C in combination with elevated idle speed to increase the mass flowrate through the aftertreatment system. The combination yields higher exhaust enthalpy through the aftertreatment system.

With the conclusion of the California Air Resources Board (CARB) Stage 1 Ultra-Low NOX (ULN) program, there continues to be a commitment for identifying potential pathways to demonstrate 0.02 g/bhp-hr NOX emissions. The Stage 1 program focused on achieving the ULN levels on the heavy-duty regulatory cycles utilizing a turbo-compound engine which required the integration of novel catalyst technologies and a supplemental heat source. While the aftertreatment configuration provided a potential solution to meet the ULN target, a complicated approach with a greenhouse gas (GHG) penalty was required to overcome challenges from low temperature exhaust. A subsequent Stage 2 program was concerned with the development of a new low load test cycle and evaluating the trade-off between GHG and tailpipe NOX on the Stage 1 ULN solution.

Recently conducted work has been funded by the California Air Resources Board (CARB) to explore the feasibility of achieving 0.02 g/bhp-hr NOX emissions for heavy-duty on-road engines. In addition to NOX emissions, greenhouse gas (GHG), CO2 and methane emissions regulations from heavy-duty engines are also becoming more stringent. To achieve low cold-start NOX and methane emissions, the exhaust aftertreatment must be brought up to temperature quickly while keeping proper air-fuel ratio control; however, a balance between catalyst light-off and fuel penalty must be addressed to meet future CO2 emissions regulations. This paper details the work executed to improve catalyst light-off for a natural gas engine with a close-coupled and an underfloor three-way-catalyst while meeting an FTP NOX emission target of 0.02 g/bhp-hr and minimizing any fuel penalty.

The 2010 emission standards for heavy-duty diesel engines in the U.S. have established a limit for oxides of nitrogen (NOx) emissions of 0.20 g/bhp-hr., a 90% reduction from the previous emission standards. However, it has been projected that even when the entire on-road fleet of heavy-duty vehicles operating in California is compliant with the 2010 emission standards, the upcoming National Ambient Air Quality Standards (NAAQS) requirement for ambient particulate matter and ozone will not be achieved in California without further significant reductions in NOx emissions from the heavy-duty vehicle fleet. Given this, there is potential of further reduction in NOx emissions limit standards for heavy duty engines in the US. Recently there have been extensive studies and publications focusing on ultra-low NOx after treatment technologies that help achieve up to 0.02g/bhp-hr. at tailpipe [1].

It is projected that even when the entire on-road fleet of heavy-duty vehicles operating in California is compliant with 2010 emission standards of 0.20 g/bhp-hr, the National Ambient Air Quality Standards (NAAQS) requirements for ambient ozone will not be met. It is expected that further reductions in NOX emissions from the heavy-duty fleet will be required to achieve compliance with the ambient ozone requirement. To study the feasibility of further reductions, the California Air Resources Board (CARB) funded a research program to demonstrate the potential to reach 0.02 g/bhp-hr NOX emissions. This paper details the work executed to achieve this goal on the heavy-duty Federal Test Procedure (FTP) with a heavy-duty natural gas engine equipped with a three-way catalyst. A Cummins ISX-12G natural gas engine was modified and coupled with an advanced catalyst system.

The classical approach to prepare engine exhaust emissions control systems for evaluation and certification is to condition the fresh parts by aging the systems on an engine/dynamometer aging stand. For diesel systems this can be a very lengthy process since the estimated service life of the emissions control systems can be several hundred thousand miles. Thus full useful life aging can take thousands of engine bench aging hours, even at elevated temperatures, making aging a considerable cost and time investment. Compared to gasoline engines, diesel engines operate with very low exhaust gas temperatures. One of the major sources of catalyst deactivation is exposure to high temperature [ 1 ].

The 2007 emission standards for both light-duty and heavy-duty diesel vehicles remain a challenge. A level of about 90% NOx conversion is required to meet the standards. Technologies that have the most potential to achieve very high NOx conversion at low temperatures of diesel exhaust are lean NOx traps (LNTs) and Selective Catalytic Reduction (SCR) of NOx using aqueous urea, typically known as Urea SCR. The LNT has the advantage of requiring no new infrastructure, and does not pose any new customer compliance issues. However, Urea SCR has high and durable NOx conversion in a wider temperature window, a lower equivalent fuel penalty, and lower system cost. On a technical basis, Urea SCR has the best chance of meeting the 2007 NOx targets. This paper reviews the results of some demonstration programs for both light-and heavy-duty applications.