Automobile Manufacturers Pursue a Variety of Strategies to Improve Fuel Economy
February 25, 2013
The auto industry has plenty of incentive to improve vehicle efficiency. In August of 2012, the Obama Administration finalized new fuel efficiency standards that will increase fuel economy for cars and light trucks to an unprecedented 54.5 miles per gallon (MPG) by Model Year 2025. “When combined with previous standards set by this Administration,” the White House said in an announcement, “this move will nearly double the fuel efficiency of those vehicles compared to new vehicles currently on our roads.” The Administration says the new standards “will save consumers more than $1.7 trillion at the gas pump and reduce U.S. oil consumption by 12 billion barrels.”
What measures will be used to comply with these aggressive new standards for vehicle efficiency? The White House's announcement doesn't go into much detail but does make mention of “advanced gasoline engines and transmissions, vehicle weight reduction, lower tire rolling resistance, improvements in aerodynamics, diesel engines, more efficient accessories, and improvements in air conditioning systems.”
These technology targets fit into the U.S. Department of Energy's (DOE) explanation of “where the energy goes” when a car moves down the road. Consumption of energy varies depending on whether you're talking about city or highway driving, but DOE says that combined city and highway driving place the following energy requirements on the fuel usage for an automobile:
- 70-72 percent -- Engine losses, mostly thermal losses from things like the radiator and exhaust heat
- 17-21 percent -- Power to the wheels, dissipated through wind resistance, rolling resistance and braking
- 5-6 percent -- Parasitic losses through things like the water pump and alternator
- 5-6 percent -- Drivetrain losses
The large percentage of energy consumed in the engine naturally leads automakers to focus on improving the efficiency of the engine.
A 2011 report from the National Academy of Sciences (NAS) details a number of technologies for improving fuel economy that are commercially available now and can be implemented in the short-term, that is, the next five years out from the study period, which was 2009-2010.
Given the market penetration of spark-ignition (SI) gasoline engine technologies, NAS believes improvements in this area offer the greatest short-term potential for improvement of fuel economy. Also, SI engine technologies have the attractive attribute that they are subject to improvements in “small, incremental steps,” says the report. The most important areas for improvement are “friction reduction, reduced pumping losses through advanced valve-event modulation, thermal efficiency improvements, cooled exhaust gas recirculation, and improved overall engine architecture, including downsizing.”
Such an incremental approach allows manufacturers the flexibility “to create packages of technologies that can be tailored to meet specific cost and effectiveness targets, as opposed to developing diesel or full hybrid alternatives that offer a single large benefit, but at a significant cost increase.”
NAS also highlights these technologies for reducing fuel consumption:
- Cylinder deactivation is an effective technology, especially for six- and eight-cylinder overhead valve engines. Cylinder deactivation essentially shuts off some of an engine's cylinders during light-load operation, reducing fuel consumption by four to 10 percent at an incremental retail price equivalent (RPE) of $550.
- Stoichiometric direct injection involves controlling precisely the amount of gasoline used in the cylinders in a fuel-injection engine, optimizing the amount of gasoline used. This technology offers a 1.5 to 3 percent fuel reduction at an incremental RPE of $230 to $480.
- A combination of downsizing and turbocharging produces a smaller, more efficient engine without sacrificing power. This approach can reduce fuel consumption by 2 to 6 percent. The incremental RPE can vary widely, says NAS, from almost nothing to $1,000.
In early 2012, I attended a lecture at North Carolina State University (NCSU) in Raleigh by Amory Lovins, chairman and chief scientist at the Rocky Mountain Institute (RMI). Lovins spoke on his current theme of “Reinventing Fire,” the title of his Oct. 2011 book proposing “Bold Business Solutions for the New Energy Era.” During that talk, Lovins passed around a sample of carbon fiber in the form of a hollow hemisphere shaped like a helmet. It was extraordinary to hold and feel this strong yet incredibly light-weight material and to imagine how it might be used to replace heavy body parts in automobiles.
During his lecture, Lovins said, “Epidemic obesity has made our autos heavy, and carbon fiber composites can make autos simpler, lighter and cheaper to build.”
In a recent interview, RMI transportation consultant Josh Agenbroad told me more about the potential for vehicle light-weighting. He acknowledged that there's value in designing engines for greater fuel efficiency. But think how much more leverage you gain by making the vehicle lighter, he urged:
It's true that a lot of energy -- 70 percent or more -- is lost due to the inefficiency of the engine. But the best way to avoid these losses is to reduce the amount of energy that must be produced by such an inefficient device in first place -- for example, by making the vehicle lighter. More than two-thirds of the energy required to move a vehicle is due to its weight, as opposed to drag and rolling resistance.RMI is focusing much of its investigative work right now on carbon fiber, because of its physical properties.
If you cut the weight in half, then you need only half as much mechanical energy to power the vehicle. You basically can halve the engine as well.
In the big picture, electrification represents one of the more important strategies for improving vehicle efficiency.
At the lecture I attended last year, RMI's Lovins said he thinks vehicle light-weighting and electrification should go hand-in-hand:
The engine gets smaller, and that makes electric batteries more affordable, and the costs fall. They can also be charged easier. Three interlocking technologies will make it possible: advanced materials, electric propulsion, and manufacturing... This shift in autos is as game-changing as moving from the typewriter to the computer. Lighter cars makes affordable the electrification of the auto industry.RMI's Agenbroad tells me that “Electricity is about the same price as gasoline in energy equivalent, but the electric power train is two or three times more efficient than the internal combustion engine.”
DOE says that electric vehicles (EVs) “convert about 59 to 62 percent of the electrical energy from the grid to power at the wheels,” compared to conventional gasoline vehicles, which “only convert about 17 to 21 percent of the energy stored in gasoline to power at the wheels.” EVs offer the added environmental benefits of quieter operation and no tailpipe emissions.