It is undeniable that developments in battery electric trucks are generating a lot of excitement as the commercial vehicle industry focuses on reducing its negative impact on the environment. But don’t forget that changes to diesel engines also bring important ecological gains and contribute to decarbonization. The reality is that diesel engines have become increasingly cleaner over the past 20 years and, according to the Diesel Technology Forum, 49% of all diesel-powered commercial vehicles in the United States are now powered by clean diesel technology. .
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Two of the latest diesel technologies that Jacobs Vehicle Systems has been working on to reduce NOx and CO2 emissions, for example, are variable valve actuation (VVA) and cylinder deactivation (CDA) are two of the most promising ways to achieve the twin goals of increased fuel efficiency and reduced emissions.
Two-stage VVA adjusts valve openings and closings (early or late valve closes) in real time and allows for optimization of valve timing at two operating points. Intake valve pre-closing works by using a main pre-closing profile event with auxiliary valve movement disabled. The intake valve late close works with the late close cam profile activated on the auxiliary rocker arm, which keeps the valve open longer.
An early-opening cam profile on the auxiliary rocker arm, or a lost motion system that is operated on demand with engine oil, is how early exhaust valve openings occur. This allows the engine and aftertreatment system to warm up faster, which improves emissions because it keeps the aftertreatment system warm during light load operation.
VVA integration has little impact on motor overload design and precisely tunes the motor over all of its operating ranges.
CDA has been used for decades in passenger cars, but is relatively new to trucking. CDA works by deactivating the valves of the engine cylinders. For overhead camshaft engines, its hydraulically actuated mechanism is integrated into a collapsing valve bridge system. For block cam engines, a folding push rod system is used. As many cylinders as needed can be deactivated, improving combustion efficiency during low torque demand.
The components used for the CDA are identical to those of Jacobs’ high density engine brake and therefore have a long history of durability. To ensure that cylinder shutdowns are optimally managed, Jacobs has partnered with Tula Technology Inc., a specialist in internal combustion controls. Tula’s Dynamic Jump Fire (DSF) combined with Jacobs’ CDA means that decisions about which cylinders to deactivate are made individually and with each rotation of the engine, to best meet torque demands and eliminate vibration.
Independent test results have shown that using three-cylinder deactivation results in a 6% drop in CO2 and 8% in NOx during the hot FTP cycle. Under the low load conditions of the LL cycle, CO2 dropped by 12% and NOx by 77%.
Emissions are improved with CDA due to higher exhaust temperatures. Even when the engine is running at light load, aftertreatment temperatures are maintained. CDA improves fuel economy due to increased load on cylinders that are still operating.
New CARB low NOx regulations for 2024 and 2027 include further reductions in NOx emissions from diesel engines, and the EPA is expected to set similar targets for 2027. CDA is a technology that will help industry meet these standards while further improving energy efficiency.
Even as fleet managers start integrating more electric vehicles into their fleets, diesel-powered vehicles will continue to dominate the market for the foreseeable future. Added to these figures are vehicles that are developed using renewable fuels. Compressed natural gas, liquefied natural gas, propane, renewable diesel and other alternative fuel sources are increasingly emerging as viable options. Diesel options should be considered as a way to ensure today’s truck exhaust is as free of harmful emissions as possible as fleets move towards more sustainability-conscious operations.