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Downsized, Boosted Gasoline Engines in the U.S

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Downsized, Boosted Gasoline Engines in the U.S TECHNICAL BRIEF NO. 5 | DECEMBER 2016 SERIES: U.S. PASSENGER VEHICLE TECHNOLOGY TRENDS WWW.THEICCT.ORG ©2016 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION Downsized, Boosted Gasoline Engines In the U.S. market, automakers are is required to support and house the Even though it has been less than leveraging advances in technology to engine, auto bodies can be lightened, five years since the technology dramatically shrink engines without compounding the benefits. assessments conducted by the compromising performance. This Environmental Protection Agency will help the industry reduce carbon The technologies making this possible (EPA) and the National Highway emissions and improve fuel economy aren’t all new. They include refinements Traffic Safety Administration (NHTSA) in response to market and regulatory on turbochargers, which have been to inform the 2017–2025 CAFE and greenhouse gas vehicle emissions demands since smaller, more efficient around almost as long as internal engines consume less fuel. standards, major improvements combustion engines, and application that were not anticipated in those of the more efficient Miller cycle Capitalizing on these technological assessments are already in production. developments means automotive with variable valve timing, patented In still more cases, automakers have engineers can reduce the number of almost 60 years ago. But some are already announced production cylinders in an engine to three from new, such as direct gasoline injection, plans for vehicles that incorporate four or to four from six, potentially cooled exhaust gas recirculation, technology whose efficiency benefits cutting fuel consumption by more and improvements in materials and the EPA and NHTSA did not take into than 30% in each case with much of electronic controls. Another significant account for the rulemaking. Figure the cost of necessary new technology 1 illustrates these improvements trend has been an explosion in offset because fewer cylinders and by comparing the turbocharger- development of 48-volt e-boosting valve-train components are needed. related cost and benefit estimates systems, or electric supercharging. Downsizing the power plant also from the rulemaking to updated reduces the weight of one of the These devices increase the ability to cost assessments and one possible heaviest components of a vehicle, run smaller engines at lower speeds, pathway for new technologies that decreasing the work necessary to burning less fuel, and pave the way to the agencies did not anticipate: move it. And, because less structure low-cost 48V hybrid systems. Miller cycle, variable-geometry ABOUT THIS SERIES Under efficiency standards adopted in 2012, the U.S. passenger vehicle fleet must achieve an average fuel economy of 49.1 miles per gallon in 2025, or 54.5 mpg as measured in terms of carbon dioxide emissions with various credits for additional climate benefits factored in. While the fleet-average targets may change—the regulation provides for recalculating the fuel economy targets annually based on the mix of cars, pickups, and SUVs actually sold—they will still represent an average energy-efficiency improvement of 4.1% per year. Automakers have responded by developing fuel-saving technologies even more rapidly and at lower cost than the U.S. EPA and NHTSA projected in 2011–2012, when the supporting analyses for the 2017–2025 rule were developed. In particular, innovations in conventional (as opposed to hybrid or electric) power trains and vehicle body design are significantly outpacing initial expectations. These technical briefs highlight the most important innovations and trends in those conventional automotive technologies. For other papers in this series, as well as the more detailed technology surveys on which these briefs are based, go to www.theicct.org/series/us-passenger-vehicle-technology-trends. 1225 I Street NW, Suite 900, Washington DC 20005 | [email protected] | www.theicct.org | @TheICCT BEIJING | BERLIN | BRUSSELS | SAN FRANCISCO | WASHINGTON DOWNSIZED, BOOSTED GASOLINE ENGINES turbochargers (VGTs), e-boost, and 35% +e-boost 48V systems. Variable compression ratio is not included in the figure, +e-boost but that is yet another pathway that +48V +VGT Nissan will soon put into production. 30% -2-stage turbo In summary, advances in downsized +48V +VGT engines give every indication that -2-stage turbo they will exceed the best technology projections available at the time the 25% 2022–2025 fuel economy and CO2 +Miller cycle emission standards were finalized, and enable significant additional +Miller cycle reductions in fuel consumption and 1 20% 2-stage turbo carbon emissions. 2-stage turbo TURBOCHARGERS cooled EGR cooled EGR AND EFFICIENCY 15% 1-stage+GDI The key to engine downsizing without significant loss of performance is 1-stage+GDI increasing the intake air pressure above atmospheric with boosting Percent reduction in fuel consumption 10% technology. This is usually accomplished with a turbocharger, a turbine-driven device that forces extra air into an engine’s cylinders. Internal 5% combustion engines produce power in proportion to the amount of air that ICCT, V6 to I4 EPA/NHTSA, V6 to I4 flows through them. Turbochargers ICCT, I4 to I3 EPA/NHTSA, I4 to I3 increase engine power by raising the 0% intake air density, increasing the mass ($500) $0 $500 $1,000 $1,500 $2,000 flow of air and fuel to the engine. Direct Manufacturing Cost Smaller engines equipped with turbochargers can deliver maximum Figure 1. Comparison of ICCT/supplier and EPA/NHTSA 2012 costs and benefits of power at lower engine speeds than turbocharging and downsizing technologies. naturally aspirated engines, which Until recently, turbochargers only air flows through the intake valves. rely solely on ambient air pressure were primarily used to elevate the Evaporation of the injected fuel creates within and around the engine to performance of sporty vehicles, due a cooling effect, reducing compression provide the oxygen necessary for fuel to efficiency compromises caused temperatures and, as a result, knock combustion. The boost in power is by side effects of the older systems, and early detonation. This also allows larger at low engine speeds than at higher engine speeds, which means knock and early detonation. But valve timings that promote clearing that for the same maximum power, improvements in materials used in exhaust gases from the cylinder during turbocharged engines will accelerate turbochargers, electronic controls, high-load operation, further reducing faster and climb steeper hills without and the introduction of gasoline direct charge temperatures while increasing having to downshift, and provide injection (GDI) have transformed the the amount of air compressed in the more towing capability. use of this technology. cylinder. With GDI, the compression ratio in the turbocharged engine can Previous fueling systems combined the be higher, improving engine efficiency. 1 This technical brief is based on Aaron Isenstadt, John German, Mihai Dorobantu, air and fuel before the mixture entered David Boggs, Tom Watson, Downsized, the combustion chamber. Gasoline Turbochargers are driven by exhaust gas boosted gasoline engines (ICCT: Washington, DC, October 28, 2016). http://www.theicct. direct injection (GDI) systems inject the pressure. This recovers some exhaust- org/downsized-boosted-gasoline-engines fuel directly into the cylinder so that gas energy that would otherwise be 2 ICCT TECHNICAL BRIEF NO. 5 | DECEMBER 2016 DOWNSIZED, BOOSTED GASOLINE ENGINES lost out the tailpipe. But there is a delay 30.0% between opening of the throttle and building up of boost pressure, a result of the inertia of the turbo. This “turbo lag” 25.0% s is especially noticeable at low engine le Combined speeds and is generally mitigated by sa e running the engine at higher speeds cl 20.0% and with automatic transmissions that hi ve allow engine revolutions and flow rate r to rise rapidly. ge 15.0% ssen Use of low-weight materials for turbine pa or compressor wheels and lower friction w ne 10.0% bearing systems, such as ball bearings, of Cars can decrease the lag in turbo response. Trucks e Two-stage boosting systems can also ar reduce response lag, by combining Sh 5.0% a small turbine with fast response and a larger turbine for higher power, although these systems are higher cost. 0.0% 2003 2005 2007 2009 2011 2013 2015 2017 The benefits of engine downsizing are Model Year already appearing in the U.S. market. Turbocharged vehicles jumped to Figure 2. Market share of turbocharged light-duty vehicles. (Source: U.S. EPA, “Light- 22% of sales in 2016 from 3.3% in Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 2010 (Figure 2). Most automakers 1975 Through 2016” 2016). https://www.epa.gov/sites/production/files/2016-11/ in the U.S. market offer downsized documents/420r16010.pdf gasoline engines, and all of the world’s ten largest auto companies on gasoline spark-ignition engines. intake manifold pressure from the produce engines capitalizing on By timing intake-valve closing so boost system, compensating for the these technologies. Based on product that it occurs early or is delayed, the shorter compression stroke. planning estimates, the market share Miller cycle decouples expansion for downsized, boosted engines will and compression. This creates a All turbocharger manufacturers are continue to increase. higher expansion ratio relative to developing Miller-cycle engines. The the compression ratio, which has German engineering consultancy FEV several efficiency benefits. The higher GmbH estimates that the Miller cycle NEW DEVELOPMENTS expansion ratio increases the work improves geometric compression In writing fleet fuel-economy rules for extracted from combustion. It also ratio from 10.0:1 to 12.0:1 and 2017–2025, federal regulators took reduces the risk of knock, allowing a reduces fuel consumption by 3.9%– some of these developments into higher compression ratio for increased 5.7% compared with a downsized, account, such as cooled exhaust-gas engine efficiency. This is because turbocharged engine with variable recirculation. However, they did not some of the compression work takes valve lift and timing.
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