sign in sign up
<<
Home , Compression ratio, Engine downsizing, Miller cycle, Turbocharger

TECHNICAL BRIEF NO. 5 | DECEMBER 2016

SERIES: U.S. PASSENGER VEHICLE TECHNOLOGY TRENDS

WWW.THEICCT.ORG ©2016 INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION

Downsized, Boosted 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 , 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 , 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 Capitalizing on these technological assessments are already in production. developments means automotive with variable , 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 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 - 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 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 , 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 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 without significant loss of performance is 1-stage+GDI increasing the air 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 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 . 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 . 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 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

or wheels and lower friction w pa 10.0% bearing systems, such as ball bearings, ne Cars can decrease the lag in turbo response. e of

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 . 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 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. For its EA211 anticipate three significant advances: place outside the cylinder in the TSI evo engine family, scheduled to Miller cycle, e-boost, and variable turbocharger, where the incoming air go into production in Europe late in compression ratio. These technologies goes through an and enters 2016, used the Miller are being enabled, in part, by in- the cylinder at a lower temperature. cycle along with a variable-geometry cylinder flow improvements for knock turbocharger and other in-cylinder limitation, , and The tradeoff is that the Miller cycle improvements, and claims that it will higher injection pressure. can decrease specific engine power see an efficiency improvement of and torque, which must be offset with 10%. will also offer vehicles with higher boost and effective Miller-cycle engines, starting with the MILLER CYCLE intercooling. Miller-cycle engines A4 in the 2017 model year. now The Miller cycle is a special variant of achieve the greatest benefits when offers a 2.5L turbocharged version the Otto used they rely on significant amounts of of its I4 SKYACTIV-G, designed to

ICCT TECHNICAL BRIEF NO. 5 | DECEMBER 2016 3 DOWNSIZED, BOOSTED GASOLINE ENGINES

replace V6 engines in SUVs and other @2000rpm larger vehicle classes. As shown in Improved in mechanical friction and pumping loss by downsizing, V6 to I4 Figure 3, this engine achieves a 23% reduction in fuel consumption over the naturally aspirated Mazda used previously. V6 3.7L Improved by cooled EGR (Current Large-SUV)

Further refinements in advanced valve Improved by controls are likely to result in additional Predecessor improvements in the efficiency and 2.3L TC (Mid-SUV) performance of Miller-cycle engines.

Because of gains in knock resistance BSFC (g/kWh) and efficiency provided by the Miller cycle, automakers will probably increase production of downsized, New Large-SUV turbocharged, high-compression- SKYACTIV-G 2.5T SKYACTIV-G 2.5 ratio engines like VW’s and Mazda’s.

0 100 200 300 400 500 E-BOOSTING AND 48-VOLT Torque (Nm) HYBRID SYSTEMS Figure 3. Reduction in fuel consumption of SKYACTIV-G 2.5T. (Source: Ichiro Hirose Perhaps the most significant (2016). Mazda 2.5L SKYACTIV-G Engine with New Boosting Technology. Presented at development in downsized, the 37th International Vienna Motor Symposium, 28-29 April 2016.) turbocharged engines is an explosion in development of 48V e-boosting— systems can also capture regenerative only about 40% of the cost. Examples i.e., electric supercharging—systems. braking energy. And the 48V-hybrid include Ricardo’s prototype 1.0L These systems increase the electrical design enables more robust start-stop HyBoost engine, which demonstrated system voltage to 48 volts from 12, systems, in which the engine is shut off dramatically increased torque providing power for a small electric at higher speeds and the 48V-system compared with a baseline 2009 Ford compressor motor within or external maintains power to all electronics and Focus 2.0L, 4-cylinder engine while to the turbocharger. These either electrical devices. Enhanced - eliminating turbo lag. Efficiency directly boost the engine or spin up generators make restarting the engine jumped to 59 mpg from 39 mpg with a the turbocharger faster to greatly quick and seamless. 40g–50g reduction in CO2 on the New reduce turbo lag, without losing the European Driving Cycle, which is less benefit of waste- recovery. This The major turbocharger stringent than the U.S. certification increases the ability to downsize the manufacturers, including BorgWarner, test cycles. Valeo is working on engine and also allows the engine to Hitachi, Valeo, and Honeywell, all have all types of microhybrid and mild- run at lower speeds (down-speeding). e-boost prototypes under consumer hybrid systems, which are claimed E-boost also enables the use of larger evaluation. The first e-boost system to be more cost-effective than full turbines with lower backpressure and is in production on the Audi V8 hybrids, diesels, or plug-in hybrids. higher efficiency. diesel SQ7. This engine integrates a Their electrically driven compressor compressor driven by a 48V electric reduces fuel consumption 7%–20% A larger battery delivers the power motor with a more conventional when used with regenerative braking. needed for the e-booster. As with turbocharger system, eliminating the IDTechEx estimated that mild-hybrid conventional hybrid vehicles, the need for a two-stage turbocharger systems could reduce CO2 emissions availability of the additional electrical system. Audi has said this V8 will by 15%–20%, or half to three-quarters power from the battery allows consume about the same amount of as much as full hybrids; the company automotive engineers to replace fuel in operation as a V6 diesel. projects that sales will mechanical pumps and accessories begin in 2017, and anticipates that with more efficient electrical systems, The 48V e-boost systems typically manufacturers will sell more than 300 reducing engine losses. By simply realize at least 60% of the efficiency of million such vehicles by 2030. AVL adding a small motor/generator, these deeper hybridization/electrification at estimates that nearly 300,000 mild

4 ICCT TECHNICAL BRIEF NO. 5 | DECEMBER 2016 DOWNSIZED, BOOSTED GASOLINE ENGINES

hybrids will be produced annually in North America in 2020. 2000 rpm/ WOT HIGH

VARIABLE COMPRESSION RATIO 2000 rpm/ BMEP = 2 bar Higher compression ratios improve efficiency, but at high engine loads they 100 BSFC [%] increase detonation, which is especially a problem for boosted engines. Variable compression ratio (VCR) allows for a VCR high compression ratio to be used at light loads, when detonation is not a LOW problem, and a low ratio at heavy loads 8 CRbase 14 for increased power. Compressionratio(CR) [-]

Engineering research into VCR Figure 4. Fuel-consumption dependence on compression ratio under part and full-load engines dates to the early 1970s, with operation conditions. (Source: Kleeberg et al. Two-Stage Variable Compression Ratio no production applications. However, (VCR) System to Increase Efficiency in Gasoline Powertrains. Presented at Automotive yearly patent filings related to VCR World Megatrends USA 2014, 18 March 2014.) technology increased rapidly after 2000, from fewer than 25 filings EGR system would reduce fuel ratio. While VCR allows for higher annually before that year to more than consumption by 4.2% to 6.2% on the compression ratios than the Miller 100 in 2013, signaling an upsurge in U.S. combined cycles. This is mostly cycle, it does not offer the efficiency VCR research and investment. due to optimizing compression ratio benefits of increased expansion. VCR during part and full loads, as shown does have one significant benefit over The idea behind all VCR systems is in Figure 4. Miller cycle: it allows performance to to change the size of the combustion be completely maintained at lower chamber depending on engine load. Nissan/Infiniti plans to introduce the engine speeds, whereas Miller cycle While there have been attempts to first VCR application in a production must add boost to maintain low-end create this effect by moving cylinder turbocharged engine, the I4 VC-T for torque. VCR may thus be a competitor heads or changing the the 2017 model year—well ahead of to Miller cycle concepts in the long radius, recent innovations have the moment when FEV and others run, offering manufacturers more focused on raising/lowering the had anticipated that technology to options for improving efficiency while position at top-dead-center go into production. Nissan’s engine maintaining performance. (TDC) within a fixed cylinder . has been in development for nearly 20 years. Its compression ratio varies FEV is developing a two-step VCR continuously between 8.0:1 and 14.0:1 CONSUMER DEMAND system, which uses an eccentric using a crankshaft-mounted linkage bearing on the . The that smoothly raises or lowers the Turbocharged engines offer system uses gas and mass forces to piston head via a control rod. Nissan’s performance benefits that are highly change the compression ratio and 2.0L VC-T engine is expected to use valued by some drivers, in addition hydraulically fix the position of the VCR as well as Miller cycle to achieve to the efficiency improvements. connecting-rod length-adjusting the highest efficiency at any load. The The Ford 3.5L EcoBoost engine mechanism. FEV estimates that the engine achieves a 21% reduction in offered on the F150 pickup cost of a two-step VCR system will fuel consumption compared with its dramatically illustrates consumer be significantly lower than for a fully 3.5L V6 predecessor. response to downsized, boosted variable system while still delivering power plants. In the first model year more than 80% of the potential The benefits of incorporating the use with the EcoBoost option (2011), reduction in fuel consumption. The of Miller cycle and VCR into engine Ford originally projected that 20% of consultancy also estimated that designs will likely overlap, as both customers would pay the additional two-step VCR with a low-pressure increase geometric compression $595 for the smaller 3.5L EcoBoost

ICCT TECHNICAL BRIEF NO. 5 | DECEMBER 2016 5 DOWNSIZED, BOOSTED GASOLINE ENGINES

engine over the standard 5.0L V8. In naturally aspirated SUVs. The total Hyundai, Mazda, and Subaru appear reality, 45% of F150 customers did so, number of vehicles in the study was committed to improved naturally and sales of the optional EcoBoost V6 also relatively small, making it difficult aspirated engines for a substantial were higher than of the standard 5.0L to derive valid statistical results. portion of their fleet, at least in the V8.2 Certainly consumers valued the Still, the findings suggest that while near term. greater of the smaller turbocharged engines may consume engine, but what most buyers sought slightly more fuel in real-world driving On the other hand, significant technical was the higher torque at low rpm and than naturally aspirated engines, the developments in turbocharged higher towing capacity. effect is likely below half of a mile per gasoline engines not evaluated for gallon—too small for most customers the rulemaking are already being The upside is that the performance to notice. implemented in the fleet, which benefits make consumers more will significantly improve efficiency accepting of the technology. The over the agencies’ projections. downside is that if customers routinely IMPLICATIONS Most important of these are Miller- use the additional power from the FOR THE MIDTERM cycle engine designs, 48V e-boost turbocharger to accelerate faster, systems, and variable compression real-world efficiency gains might not EVALUATION ratio. In addition, for the technologies be as great as if their driving habits Auto-industry component suppliers considered in the rulemaking, supplier were to remain unchanged. agree that engine downsizing is one estimates of costs are lower and of the most important pathways to their estimates of fuel-efficiency Recent findings from researchers at improving the fuel efficiency of future benefits are higher. See Figure 1, the University of Tennessee suggest vehicles. For example, BorgWarner above, for a graphical comparison that in actual, everyday driving, estimates that, thanks to boosting, of turbocharger-related cost-benefit gasoline turbocharged vehicles fall by 2019–2020 3-cylinder engines will estimates by the EPA and NHTSA short of their fuel economy label sell at more than twice the rate of for the 2017–2025 ruling to only one values by only 1.7% more than naturally today; 4-cylinder engines will expand of several possible new-vehicle- aspirated vehicles, or roughly 0.4 their market share by 13 percentage design pathways deploying new mpg for the average vehicle. The points; and 6-cylinder and 8-cylinder technologies—Miller cycle, variable- researchers compared in-use fuel engines will lose share. Honeywell geometry turbochargers, e-boost, economy reported by consumers and BorgWarner both project that and 48V systems—that the agencies on fueleconomy.gov with the fuel the market share for turbocharged economy values on the vehicles’ engines will reach about 40% by 2020. did not anticipate at all. Monroney stickers, the window labels In short, although turbocharging is giving various vehicle specifications However, these projections fall short not penetrating the fleet as rapidly and ratings that all new vehicles are of the estimates in the government’s as predicted in the rulemaking, in required to display. The slightly higher 2017–2025 rulemaking, which the less than five years since the shortfalls reported for turbocharged projected that turbocharged engines would account for 64% of sales in 2021. rulemaking technology assessments vehicles were primarily attributable to In part, the differential likely reflects the U.S. vehicle market has already turbocharged pickup trucks, whose improvements in naturally aspirated seen turbocharging and related drivers reported missing the mileage engines that were not anticipated in technologies that were unanticipated ratings by 6% more than owners of the 2017–2025 rulemaking.3 Toyota, in the rulemaking go into production, naturally aspirated pickups. That data on top of significant cost reductions subset was particularly small, only in efficiency improvements from 67 vehicles. The 542 turbocharged 3 For details on the agencies’ pessimistic projections for naturally aspirated technologies that were evaluated SUVs did not fall short more than engines, contrasted with actual trends and technology developments indicating that for the rule. Bottom line: Advances those engines will be an important part in boosted, downsized engines 2 The 5.0L V8 engine had a sales rate of about of the fleet mix through 2025, see Aaron 40%. A naturally aspirated 3.7L engine was Isenstadt, John German, Mihai Dorobantu, show every indication of exceeding standard on some base models (sold mostly Naturally aspirated gasoline engines and projections and enabling significant to commercial fleets), and there was a 6.2L cylinder deactivation (ICCT: Washington, reductions in fuel consumption and V8 option. These two engines account for DC 2016). http://www.theicct.org/naturally- the balance of F150 sales, or about 15%. aspirated-gas-engines-201606 carbon emissions.

6 ICCT TECHNICAL BRIEF NO. 5 | DECEMBER 2016