Helmut Theissl’s research while affiliated with AVL LIST GMBH and other places

GHG and CO2 legislations in US, Europe and China demand a reduction of emissions in the range of 25 to 30% for heavy commercial vehicles in the current decade. To meet these challenging targets, a further increase of the efficiency of the internal combustion engine is one of various optimization parameters. AVL develops engine concepts to increase the brake thermal efficiency (BTE) to 50%, focusing on base-engine improvements. This requires a spec. fuel consumption below 170 g/kwh. This article shows AVL’s research results, which are based on the testing results of a single cylinder research engine and on 1D-thermodynamic simulations. From these results, challenges for design and friction requirements are derived. Finally, the strengths and weaknesses of diesel engine concepts with the potential for 50% BTE are discussed.

In April 2019, the California Air Resources Board (CARB) released its white paper on the ultra-low NOx standard for heavy-duty diesel engines (HDDE)[1]. AVL has been conducting research on how to meet these new limits and to address the continuing challenge of cold start emissions from HDDE, including incorporating • Advanced thermal management strategies to accelerate exhaust aftertreatment system (EAS) warm-up • Close-coupled selective catalytic reduction (ccSCR) system upstream of the current Euro VI or EPA 2013 EAS To date, the most of the work done has been in simulation, with the intent of evaluating control strategies. This paper will describe the following results: • Effect of thermal management strategies on EAS warm-up • Control strategy for ultra-low NOx incorporating ccSCR • Interactions between ccSCR system and on-board diagnostics (OBD) requirements The interaction between NOx control and reduced fuel consumption or CO2 emissions will be discussed. AVL recommendations and next steps will also be discussed. [See https://cleers.org/cleers-workshops/workshop-presentations/entry/2100/] 1. California Air Resources Board, “California Air Resources Board Staff Current Assessment of the Technical Feasibility of Lower NOx Standards and Associated Test Procedures for 2022 and Subsequent Model Year Medium-Duty and Heavy-Duty Diesel Engines.” California Air Resources Board Report No, 2019.

For current and prior emission legislations, the focus of the development process was strongly influenced by achieving the limited emissions components like nitrogen oxide (NOx), particulates, etc. In future, the focus will be on improving the thermal efficiency and consequently reducing CO2 emissions. For the already existing greenhouse gas legislation in the USA as well as the discussed CO2 regulation in Europe, both measures on the vehicle (aerodynamics, tire rolling resistance, axle efficiency …) as well as measures on the power train will be mandatory to achieve the future limits. As an example: For the second phase of the greenhouse gas engine standards in the US there will be a reduction of up to 6.1% respectively, 5.1% considering same weighting factor in RMC for MY2027 compared to MY2017 required.

Commercial vehicles require continual improvements in greenhouse gas emissions to meet upcoming emission regulations and fleet fuel economy needs. Challenges for future emission standards require technologies for engine exhaust temperature management to deal with low engine load operation for optimal aftertreatment performance. The proposed ultra-low NOx emission standards of 10% of today’s US level (0.2 g/hp-hr) is challenging and requires significant temperature management strategies including heat-up strategies during the cold part of the emission cycle. Heavy duty commercial vehicle applications requires a heat source on the order of 30 kW to achieve aftertreatment temperatures for sufficient NOx reduction. There are technologies that can provide such high heat loads in a short period of time. A diesel exhaust burner is an option for fast heat-up at the expense of fuel economy. Variable valve actuation (VVA) solutions are effective for aftertreatment temperature management including early exhaust valve opening, intake valve closing modulation and cylinder deactivation. Further steps of emission legislation focus on in-service operation, including NOx emission reduction during low load operation. Such low engine load operation may result in exhaust temperatures between 100°C and 250°C, where NOx aftertreatment systems are not effective. Thus, technologies are needed to raise the exhaust temperature under such conditions. The use of VVA to vary the air-excess ratio in the cylinder is a fuel efficient method to increase exhaust temperature under low load conditions. Methods of intake air throttling are capable measures such as cylinder deactivation and Miller cycle. Cylinder deactivation during low load engine operation shows a marked increase in exhaust temperature by approximately 100°C which moves aftertreatment systems to a more optimal region, typically significantly above 250°C while also offering fuel economy benefits. The addition of a high efficiency boosting system enables Miller cycle operation to improve fuel economy. Thus, the use of VVA is a leading technology combining the future requirements to simultaneously reduce NOx and fuel consumption. This paper will show the benefits of variable exhaust valve opening, intake valve closing modulation with and without boosting, and cylinder deactivation for meeting future emission regulations and fuel economy needs. Finally, solutions combining VVA and engine braking are provided.

Upcoming most stringent legislations for greenhouse gas emissions (GHG) as well as for criteria pollutant emissions will confront the commercial vehicle industry with new challenges. The recently concluded 2nd phase of GHG regulation in North America demands a GHG reduction of up to 27% of for model year 2027 (MY2027) depending on the individual application. This regulation includes a dedicated reduction of CO2 emissions from engines, e.g. in the magnitude of 5% for heavy heavy-duty tractor applications. At the same time, the California Air Resources Board (CARB) announced plans to introduce a 90% reduction of nitrogen oxide (NOx) emissions compared to current levels (EPA10). In addition, EPA announced plans to lower the nationwide NOx standard. In Europe, a reduction of NOx emission limits is a possible development for the future. A mandatory CO2 declaration for heavy-duty vehicles will be in force in the EU from 2018. Based on the outcome of the monitoring, CO2 limits could follow at a later stage.