The 1.4-liter solution for 2016 fuel economy

  • 14-Dec-2009 09:58 EST
ecoboost`.JPG

Left: Turbocharging with direct injection (Ford EcoBoost example) increases BMEP in the best operating area (green) for BSFC. Right: Higher BMEP from 2000-5000 rpm with a turbo/DI gasoline engine translates to nearly double the specific torque at 2000 rpm, over 30% more specific power at 5500 rpm.

As automakers plan for greater vehicle efficiency, will engines of 1.4-L displacement become the "new" 2.4-L engines?

The 2.3 to 2.5-L four-cylinder gasoline engine has been the popular displacement range for midsize cars sold in the U.S., and for sound reason. When mated to a six-speed automatic transmission, engines of this size typically deliver 22 city/33 highway (26-mpg combined) fuel economy with good performance.

However, such levels of fuel efficiency fall significantly short of the U.S. EPA's proposed fuel economy regulations for 2016. The new regs now under discussion call for a 35.5 mpg (6.63 L/100 km) fleet average. Cars delivering 40 mpg combined and higher (5.9 L/100 km) likely will be needed to meet the average, even if trucks' 26 mpg (9.0 L/100 km) average is factored in.

The 35.5 mpg standard isn't absolute. There will be some fuel economy credits for other greenhouse-gas-abatement technologies, such as low-leak air-conditioning systems and changing to new refrigerants such as R-1234yf.

The 2016 requirement is leading to some vehicle downsizing, and changing from body-on-frame SUVs to unit-body crossovers. Hybrids and diesels, with a sprinkling of battery-electrics, will help the fleet averages. But the cost-effective approach that carmakers have publicly identified for their future high-volume vehicle programs is a 1.4-L gasoline four-cylinder.

1.4-L programs in the works

Various automakers have announced 1.4-L programs in development, with direct injection (DI) for most applications. Some of the engines will be boosted. Included among them are the following: 

General Motors' naturally aspirated 1.4-L will power the onboard generator in the Volt hybrid. Non-hybrid compact sedans will get a turbocharged DI variant rated at 140 hp/104 kW;

Volkswagen will offer a 1.4 turbo in the Golf and Jetta, and an even smaller displacement (1.2-L) turbo engine in the Polo;

Chrysler will use a Fiat-developed 1.4-L four with the company's Multiair (oil-pressure-operated) variable valve timing/lift system.

Other companies have made it clear a 1.4-L four is coming. Mark Perry, Director of Product Planning for Nissan Americas, told AEI that Nissan may adapt a Renault-developed turbocharged four from its 1.3-1.5-L family.

Ford is downsizing engines, though it is starting from the opposite direction with turbocharged 3.5-3.7-L V6s in place of larger V8s. Ford reportedly also has a 2.3-L four coming to replace older V6s, even in pickups.

The 1.4-L displacement isn't just a "round number." In C-segment and smaller vehicles, it could deliver the expected 40-mpg fuel economy with such moderate-cost technologies as DI, variable valve timing and lift, and intake valve throttling (eliminating the throttle plate).

Six-speed automatic transmissions will provide some help, and there's a significant total improvement (up to 10-15%) with dual-clutch (DCT), CVT, and possibly eight-speed planetary alternatives.

The DCT reportedly does better in the European driving cycle, with the less-expensive CVT very close to it in the Japanese and U.S. cycles. Though less costly, the CVT lacks the sporty character of the DCT, according to Dr. Hermann Middendorf, head of development for VW's small four-cylinder gasoline engine family.

Boosting BMEP

To provide satisfactory acceleration, particularly under load, the 1.4-L four requires boosting. An exhaust turbocharger is the closest approach to "free" power, as it has no parasitics. The turbocharger system hardware certainly isn't free, but engineers note that among the many fuel efficiency technologies available to automakers it offers higher value than even an assist-type hybrid system as used by Honda.

Boosting a 1.4-L four provides a significant torque improvement over larger naturally aspirated engines. Dr. Middendorf said VW's 1.4-L turbo, rated at 122 kW/164 hp, produces up to 15% more low-end torque than the company's 2.5-L five-cylinder (125 kW/167 hp).

Turbocharging a small-displacement DI gasoline engine expands the operating area with good BSFC (brake-specific fuel consumption—the rate of fuel used divided by power developed), compared with enlarging a naturally aspirated engine.

Further, turbo/DI greatly increases the rpm range of peak BMEP (brake mean effective pressure—the measurement of work output independent of displacement), noted Dan Kapp, Ford's Director of Advanced Powertrain Engineering. High BMEP translates to nearly doubling the engine's specific torque and a 33% increase in specific power.

These factors mean there's an opportunity to downsize the engine for greater fuel economy while maintaining acceptable engine performance. In its work with EcoBoost (turbocharged direct-injected) engines, Ford found it could reduce engine displacement by 33% for the same power and more torque, while the engine operated more in its BSFC "sweet spot," Kapp explained.

Smaller four-cylinder turbocharged gasoline engines also could satisfy some premium vehicle power demands at moderate extra cost with two-stage turbocharging (as used in some diesels) or even twincharging (addition of a small on-demand supercharger to a single turbo). The latter design has been installed on VW's European 1.4-L four-cylinder Golf for five years and on the Japan market Nissan March 1.0-L four since the mid-1980s.

The 2.4-L displacement will continue to have applications, engineers explain. Direct-injection versions that produce 200 hp (149 kW) and more will continue to be developed. As the 1.4-L turbo takes hold, the 2.4-L DI could be turbocharged to produce approximately 275 hp (205 kW) and higher, to replace the V6.

At this point in time, the naturally aspirated DI version can achieve the 35 mpg bogey in highway use but comes up short on the city/highway average.

However, with improved vehicle aerodynamics, mass reduction techniques, alternative transmissions, and various degrees of hybridization, it could come close—and hold off the march toward a 1.4-L future.

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