Fuel efficiency and climate impacts of soot-free heavy-duty diesel engines
Despite following somewhat different technological pathways, HD diesel engine designs in the United States and the European Union have converged on a similar package of design elements in order to meet EPA 2010 and Euro VI emission standards—high-pressure variable fuel injection, cooled EGR, and an aftertreatment system of DOC, DPF, SCR, and ASC in series. In isolation, some of these technologies, specifically EGR and DPF systems, can negatively impact engine efficiency, resulting in a fuel consumption penalty. However, the introduction of SCR systems to soot-free engine designs has allowed designers to calibrate engines for more efficient operations and thereby offset some of the penalties associated with other control technologies. Furthermore, electronic engine controls, better fuel injection systems, and other engine developments fully offset any fuel consumption penalties introduced by modern emission control systems.
Comparisons of soot-free HD diesel engines and vehicles with engines certified to prior emission standards indicate that improvements in emissions control did not come at the detriment of fuel consumption. Furthermore, overall decreases in non-CO2 climate pollutant emissions have improved the overall climate emissions performance of modern HD diesel engines compared to older diesel engines. However, long-term fuel consumption trends for HD vehicles in Europe and the United States also indicate that the real-world fuel efficiency of commercial fleets has been relatively stagnant over time. These trends indicate that complementary efficiency and GHG emission standards are important and necessary to meaningfully reduce CO2 emissions from HD diesel vehicles.