Meeting 2025 CAFE Standards for LDT with Fuel-Efficient Diesel Powertrains - Approaches and Solutions 2017-01-0698

In view of changing climatic conditions all over the world, Green House Gas (GHG) saving related initiatives such as reducing the CO₂ emissions from the mobility and transportation sectors have gained in importance. Therefore, with respect to the large U.S. market, the corresponding legal authorities have defined aggressive and challenging targets for the upcoming time frame. Due to several aspects and conditions, like hesitantly acting clients regarding electrically powered vehicles or low prices for fossil fuels, convincing and attractive products have to be developed to merge legal requirements with market constraints. This is especially valid for the market segment of Light-Duty vehicles, like SUV’S and Pick-Up trucks, which are in high demand. The modern DI Diesel engine has gained an increasing market share in the recent 25 years in the European market and has converted from a niche application to an established, highly appreciated propulsion system in the Light-Duty vehicle segment, covering passenger car as well as light commercial applications. In vehicle classes with high market penetration this low CO₂ concept offers a substantial contribution to minimized GHG emissions from the transportation sector. The current Diesel engine portfolio provides an average advantage of ≥20% reduction in CO₂ emissions in contrast to gasoline-powered applications, while best-in-class installations achieve already now the stringent CO₂ demands of 2020/21 for Europe. For the end consumer the fuel consumption behavior in real day usage is much more relevant, where Diesel powered vehicles typically offer even a further attractive attribute, due to the quite flat fuel consumption characteristics over the entire engine map. Therefore, modern and hence fuel efficient Diesel powertrains represent a promising technology to support also the U.S. market regarding compliance with tight upcoming CAFE standards, particularly for larger vehicle applications.

This paper provides an overview of core technologies which on one hand support meeting the ambitious fuel economy figures for SUV’s and Pick-Up trucks in the weight range from 5,000 to 8,500 lbs considering a 6-cylinder design with ∼3.3 L displacement, but also regarding compliance with the extremely challenging future CARB LEVIII / EPA Tier 3 emission standards. In addition, the question whether an in-line arrangement for 6-cylinder engines provides a substantial benefit for meeting low CO₂ numbers and simultaneously lowest tailpipe emissions versus the very compact and attractive Vee-type layout due to better charging conditions and easier realization of closed-coupled exhaust aftertreatment system positioning, will be analyzed and clarified.

The paper will conclude with an outlook on accompanying transmission and vehicle measures to meet the upcoming fuel economy targets.