Despite all the hype about electrification, internal combustion engines (ICEs) are likely to dominate the commercial vehicles market for several years. But these engines will have to advance using an array of technologies, including the adoption of some electrified systems.
Engines must meet increasingly stringent emissions regulations while providing performance needed by truckers and off-highway users. Meeting those requirements will require a lot of R&D in many areas, according to five experts who discussed “ICE Powertrain Efficiency” at the recent SAE COMVEC Technology Connection conference.
The panelists all agreed that diesels will dominate the commercial market, especially in heavy-duty vehicles, for the foreseeable future. Meeting regulations and market requirements will necessitate pushing many different technologies. Jonathon White, Executive Director of Cummins Engine Business, detailed some of the many advances being developed through the U.S. Energy Department’s SuperTruck II program.
“We’ve demonstrated 55% brake thermal efficiency (BTE), that’s definitely achievable in a production vehicle,” White said. “We do need to look at mild electrification and engine-off cruising. There are a lot of technologies used in passenger cars that we haven’t used yet.”
Panelists focused on a range of engine technologies that provide small percentage improvements but can add up to offer significant advances.
“We can gain a 2-3% improvement in combustion performance from increasing the compression ratio, the peak firing pressure and the air-fuel ratio,” said Michael Franke, Director of Commercial Engines at FEV North America Inc. “Reducing thermal losses with waste heat recovery systems and thermal insulation can provide another 3-4% improvement.”
Franke described an integrated turbocompounding / electrification and supercharging (ITES) that can be embedded in engines to improve efficiency. He explained that if ITES is combined with other technologies such as peak firing pressure, engines can be downsized to provide total fuel-economy savings of as much as 11%.
Panelists also agreed that electric motors and batteries are another tool that can help them build more efficient powertrains.
“We need to start decoupling elements in the engine and powertrain,” said Philip Stephenson, General Manager of the PACCAR Technical Center. “Water pumps, air-conditioning and other pumps now run at constant speeds. People are starting to go with electronic components for things like water pumps. There’s no need for the parasitic draw of a water pump, it’s only needed at certain times. There are a lot of opportunities to use energy storage like batteries to augment engines.”
The trade-offs continue to become more complex as engineers adjust building blocks that include air management, combustion, and friction and parasitics. Adjusting one parameter impacts others, which can alter cost and reliability. Reducing exhaust gas recirculation (EGR) increases engine-out NOx, which forces changes in the selective catalytic reduction (SCR) system. All changes have to be made with an eye towards reliability and long lifetimes.
“Any time you make changes to the fundamental architecture, there are durability concerns,” Stephenson said. “Uptime is key. A system that gives you a 1-2% improvement is not good if it’s in the shop an additional 1-2% of the time.”
Slowing engine speed on highways is another way to meet looming requirements. Stephenson noted that cruising-speed rpm levels have declined from 1,500 to 1,100 rpm. Some researchers are working on three-digit rpm ratings.
Constantly-evolving regulations are also expanding the number of critical parameters engineers must address. Regulators are pressing for reduced NOx as well as lower carbon dioxide. That moved start-ups and cold-temperature operations into the spotlight.
“We need very fast combustion during warmup,” said Brent Keppy, Manager of Commercial Vehicle Powertrains at Robert Bosch LLC. “At cold temperatures, you need to minimize NOx. We’re looking at injection pressures of 2,500 bar or more for low temperatures. At higher engine temperature on the highway, you want maximum efficiency, so you may not need high pressure.”
Connectivity and diagnostics
The many parameters in powertrain design aren’t the only factors being employed to meet new constraints. Panelists said a holistic effort that includes factors like aerodynamics and connectivity will be necessary to meet requirements made by regulators who in some cases are banning ICEs for passenger cars. Connectivity systems can leverage GPS and maps to provide input on upcoming hills and other roadway conditions so engines can rev up or down.
“The amount of data gives us the opportunity to do custom operation of the powertrain,” said Christian Weiskirch, CTO at Traton Group (formerly known as Volkswagen Truck & Bus). “You can see how the vehicle’s running and where it is so you can use the right combination of technologies for operations.”
Cellular and Wi-Fi links can also help in the off-highway world. On large worksites, it can be quite beneficial for vehicles to know what other vehicles are doing.
“In the off-highway world, productivity is more important than engine efficiency,” Keppy said. “Connectivity becomes important; it lets machines talk to each other, providing a lot of areas for advances.”
Aftertreatment and diagnostic systems are also critical elements in the drive to trim emissions. Aftertreatment systems can vary widely depending on engine sizes and styles. Diagnostic systems that monitor powertrain elements can help ensure that vehicles meet requirements over the lengthy lifetime of commercial vehicles.
“With different aftertreatment systems, you need to have good on-board diagnostic systems so you can spot errors when they happen,” Keppy said. “Diagnostics help us keep these systems in line as vehicles age.”
He also noted that aftertreatment systems need to be compact so they can be placed close to the engine. Many technologies rely on heat to reduce emissions and remove particulates, so they must be small enough to fit in cramped engine compartments.
Hope for harmonization
The underlying driver for many engine developments—regulations—got a lot of attention during the panel. The experts noted that regulations being made in several states and countries must all be met.
There’s concern that regulations will vary substantially, making it difficult to design powertrains that can be used on vehicles sold globally. While panelists all expressed hope for harmonization, they are preparing for the possibility that regulators won’t work to set common goals. Software is a preferred choice over hardware, but software can only work if the difference between requirements is relatively minor.
“Everyone wants to work on one solution,” Stephenson said. “If we don’t have that, we can try to achieve a solution using common hardware and do the changes using calibration. If that’s not possible, we’ll have to go to different hardware modules.”Continue reading »