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NRC report finds significant number of near-term technologies could greatly reduce fuel consumption in passenger cars

Various combinations of commercially available technologies could greatly reduce fuel consumption in passenger cars, sport-utility vehicles, minivans, and other light-duty vehicles over the next 15 years without compromising vehicle performance or safety, according to a newly published report by the Committee on the Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy of the US National Research Council (NRC).

According to its estimates, adopting the full combination of improved technologies in medium and large cars and pickup trucks with spark-ignition engines could reduce fuel consumption by 29% at an additional cost of $2,200 to the consumer. Replacing spark-ignition engines with diesel engines and components would yield fuel savings of about 37% at an added cost of approximately $5,900 per vehicle, and replacing spark-ignition engines with hybrid engines and components would reduce fuel consumption by 43% at an increase of $6,000 per vehicle.

In 2007 the National Highway Traffic Safety Administration (NHTSA) requested that the US National Academies provide an objective and independent update of the technology assessments for fuel economy improvements and incremental costs contained in the 2002 National Research Council (NRC) report Effectiveness and Impact of Corporate Average Fuel Economy (CAFE) Standards.

NHTSA also asked that the NRC add to its assessment technologies that have emerged since that report was prepared. To address this request, the NRC formed the Committee on the Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy. The statement of task directed the committee to estimate the efficacy, cost, and applicability of technologies that might be used over the next 15 years.

The report, Assessment of Technologies for Improving Light Duty Vehicle Fuel Economy estimates the potential fuel savings and costs to consumers of available technology combinations for three types of engines: spark-ignition gasoline, compression-ignition diesel, and hybrid.

While each technology on its own has benefits, and is often considered independently, there can be positive and negative interactions among individual technologies, and so the technologies must be integrated effectively into the full vehicle system, the report says.

Committee’s estimates of effectiveness (shown as a percentage) of near-term technologies in reducing vehicle fuel consumption. Benefits highlighted in green are incremental to those obtained with preceding technologies shown in the technology pathways. Source: NRC. Click to enlarge.

Integration requires that other components of the vehicle be added or modified to produce a competitive vehicle that can be marketed successfully. Thus, although the fuel consumption benefits and costs discussed here are compared against those of representative base vehicles, the actual costs and benefits will vary by specific model. Further, the benefits of some technologies are not completely represented in the tests used to estimate corporate average fuel economy (CAFE). The estimate of such benefits will be more realistic using the new five-cycle tests that display fuel economy data on new vehicles’ labels, but improvements to test procedures and additional analysis are warranted.

Given that the ultimate energy savings are directly related to the amount of fuel consumed, as opposed to the distance that a vehicle travels on a gallon of fuel, consumers also will be helped by addition to the label of explicit information that specifies the number of gallons typically used by the vehicle to travel 100 miles.

—“Assessment of Technologies”

Spark-ignition technologies. Spark-ignition (SI) engines will continue to be the primary source of propulsion for light-duty vehicles in the United States over the time frame of the report (next 15 years). There have been and continue to be significant improvements in reducing the fuel consumption of SI engines in the areas of friction reduction; reduced pumping losses through advanced valve-event modulation; thermal efficiency improvements; cooled exhaust gas recirculation; and improved overall engine architecture, including downsizing, the report says.

An important attribute of improvements in SI engine technologies is that they offer a means of reducing fuel consumption in relatively small, incremental steps. This approach allows automobile manufacturers 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. Because of the flexibility offered by this approach, and given the size of the SI engine-powered fleet, the implementation of SI engine technologies will continue to play a large role in reducing fuel consumption.

—“Assessment of Technologies”

The committee identifies cylinder deactivation as one of the more effective in reducing fuel consumption; this feature is most cost-effective when applied to six-cylinder (V6) and eight-cylinder (V8) overhead valve engines, and typically reduces fuel consumption by 4 to 10% at an incremental retail price equivalent (RPE) increase of about $550. Others include:

  • Stoichiometric direct injection typically affords a 1.5 to 3 percent reduction in fuel consumption at an incremental RPE increase of $230 to $480, depending on cylinder count and noise abatement requirements.

  • Turbocharging and downsizing can also yield fuel consumption reductions.

    Downsizing is an important strategy applicable in combination with technologies that increase engine torque, such as turbocharging or supercharging.

  • Downsizing simultaneously reduces throttling and friction losses because downsized engines generally have smaller bearings and either fewer cylinders or smaller cylinder bore friction surfaces. Reductions in fuel consumption can range from 2 to 6% with turbocharging and downsizing, depending on many details of implementation.

    This technology combination is assumed to be added after direct injection, and its fuel consumption benefits are incremental to those from direct injection. Based primarily on an EPA teardown study, the committee’s estimates of the costs for turbocharging and downsizing range from close to zero additional cost, when converting from a V6 to a four-cylinder (I4) engine, to almost $1,000, when converting from a V8 to a V6 engine.

  • Valve-event modulation (VEM) can further reduce fuel consumption and can also cause a slight increase in engine performance, which offers a potential opportunity for engine downsizing. There are many different implementations of VEM, and the costs and benefits depend on the specific engine architecture. Fuel consumption reduction can range from 1% with only intake cam phasing, to about 7% with a continuously variable valve lift and timing setup.

    The incremental RPE increase for valve-event modulation ranges from about $50 to $550, with the amount depending on the implementation technique and the engine architecture.

The committee considered variable compression ratio, camless valve trains, and homogeneous-charge compression ignition. However, it concluded that because of questionable benefits, major implementation issues, or uncertain costs, it is uncertain whether any of these technologies will have any significant market penetration in the next 10 to 15 years.

Compression-ignition technologies. The committee found that replacing a 2007 model year SI gasoline power train with a base-level compression-ignition (CI) diesel engine with an advanced 6-speed dual-clutch automated manual transmission (DCT) and more efficient accessories packages can reduce fuel consumption by about 33% on an equivalent vehicle performance basis. It estimated the incremental RPE cost of conversion to the CI engine is about $3,600 for a four-cylinder engine and $4,800 for a six-cylinder engine.

  • Advanced-level CI diesel engines, which are expected to reach market in the 2011-2014 time frame, with DCT (7/8 speed) could reduce fuel consumption by about an additional 13% for larger vehicles and by about 7% for small vehicles. Part of the gain from advanced-level CI diesel engines comes from downsizing.

  • The estimated incremental RPE cost of the conversion to the package of advanced diesel technologies is about $4,600 for small passenger cars and $5,900 for intermediate and large passenger cars.

An important characteristic of CI diesel engines is that they provide reductions in fuel consumption over the entire vehicle operating range, including city driving, highway driving, hill climbing, and towing. This attribute of CI diesel engines is an advantage when compared with other technology options that in most cases provide fuel consumption benefits for only part of the vehicle operating range.

—“Assessment of Technologies”

The committee found that market penetration of CI diesel engines will be strongly influenced by both the incremental cost of CI diesel power trains above the cost of SI gasoline power trains and by diesel and gasoline fuel prices.

Further, while technology improvements to CI diesel engines are expected to reach market in the 2011-2014 time frame, technology improvements to SI gasoline and hybrid engines will also enter the market. Thus, competition between these power train systems will continue with respect to reductions in fuel consumption and to cost. For the period 2014-2020, further potential reductions in fuel consumption by CI diesel engines may be offset by increases in fuel consumption as a result of changes in engines and emissions systems required to meet potentially stricter emissions standards.

—“Assessment of Technologies”

Hybrid vehicle technologies. For the most basic hybrid systems that reduce fuel consumption by turning off the engine while the vehicle is at idle, the committee pegged the fuel consumption benefit at up to about 4% at an estimated incremental RPE increase of $670 to $1,100. The fuel consumption benefit of a full hybrid may be up to about 50% at an estimated incremental RPE cost of $3,000 to $9,000 depending on vehicle size and specific hybrid technology.

A significant part of the improved fuel consumption of full hybrid vehicles comes from the complete vehicle redesign that can incorporate modifications such as low-rolling-resistance tires, improved aerodynamics, and the use of smaller, more efficient SI engines, the committee noted.

In the next 10 to 15 years, improvements in hybrid vehicles will occur primarily as a result of reduced costs for hybrid power train components and improvements in battery performance such as higher power per mass and volume, increased number of lifetime charges, and wider allowable state-of-charge ranges.

...A number of different lithium-ion chemistries are being studied, and it is not yet clear which ones will prove most beneficial. Given the high level of activity in lithium-ion battery development, plug-in hybrid electric vehicles will be commercially viable and will soon enter at least limited production. The practicality of full-performance battery electric vehicles (i.e., with driving range, trunk space, volume, and acceleration comparable to those of vehicles powered with internal-combustion engines) depends on a battery cost breakthrough that the committee does not anticipate within the time horizon considered in this study.

However, it is clear that small, limited-range, but otherwise full-performance battery electric vehicles will be marketed within that time frame. Although there has been significant progress in fuel cell technology, it is the committee’s opinion that fuel cell vehicles will not represent a significant fraction of on-road light-duty vehicles within the next 15 years.

—“Assessment of Technologies”




Some pretty sobering estimates here.

It is more comforting to assume MPG improvement technology, hybrids and BEVs will penetrate the marketplace by costing less as they mature.

This claims they come at a hefty price no matter what.

A 29% improvement for the ICE for $2200 is OK.

But I believe the hybrid delta will soon be less than $6000.

And maybe the CI diesel (is there any other kind of diesel) numbers are based on BMW prices.

I may be wrong but now I feel better.


This is a summary of what we have been reading about on here for a while. It comes down to what do you pay for what you get. Even the average consumer looks at payback here.


The only way this will succeed for that much money is if you outlaw all the other cars

6000 dollars buys alot of gas


If one drives a 20 mpg car and drives 20,000 miles per year and gas sells for $6 per gallon, then $6000 for fuel lasts one year. Once you look at it that way, trading hardware for energy sounds like a bargain.


If you compare a Toyota Matrix to a Prius, and adjust for features and options, the hybrid premium comes out under $1500.. and the Prius engine gets diesel like efficiency of 38% already. The Prius engine is also cheap, no DI or turbo.


I recall Toyota stating that the "hybrid premium" was $2000 and falling, and that was some years ago. Toyota ought to know. The assumptions of the NRC study should be checked carefully to see if they had errors, or even attempted to spike hybrids.


There is a big performance difference between the Toyota Matrix and Prius. 2 seconds slower on 0-60 and 1/4 mile is a lot slower also. For this reason the Prius is boring and not for every one.

So if you put something cheaper, more efficient, and less powerful in the Matrix (like the FIAT twin air?), the price premium will be bigger and the MPG difference smaller.


Surprised that nobody did the ratios:

.013% per dollar for SI
.006% per dollar for Diesel
.007% per dollar for Hybrid

SI wins in a landslide, in that it's twice as cost-effective to improve current, cheaper engines than to have a wholesale switchover to other engines/technologies. Obviously, one can argue the inputs but this is worth looking at.


Good info (% per dollar).
SI does win.

Their assumptions/inputs seem to be at least in the ballpark and in agreement with many semi-impartial studies.

Toyota DOES know - They SAY "EVs make a profit" etc.
But they make only a few hybrid models.
Actions speak much more honestly than words.

Gas is not $6/g.
And the non-SI vehicle's energy will be far from free.

I can recall no credible study that says any EV makes simple financial sense for the buyer.

Wait I take that back, I meant to exclude the state and federal buyers.

I can recall no credible study that says any EV makes simple financial sense for the average buyer spending his own money (except maybe, sometimes, IF you include state and federal rebates).


Gasoline may not cost $6 per gallon yet in the U.S. but it does somewhere. (think the U.K.)


Actually MOST of the time IF you include the Fed and State (eg CA) rebate on the Leaf or Volt - there is financial gain. It helps to factor in the cost of your TIME, fighting traffic and congestion to get to the gas station.

Let's not forget that an EV refuels itself overnight while (most) sleep. This means never stopping at the gas station again (rarely with Volt.) I value my time and time NOT spent commuting to gas stations and pumping gasoline is valuable in hard cash. Ownership over 10 years at 520 refuelings x $17.50 (value of time) = $9,100.00.

Not to mention the positive health result from NOT inhaling gasoline (benzine - BTEX, etc) fumes. Ultimately another gain from converting the light transport fleet to non-polluting electric.

Henry Gibson

Simple actions by the driver can also improve performance. The US government shows itself to be not interested in fuel savings by allowing extra high motorway speeds as does Germany. ..HG..


an EV refuels itself overnight

That is a BIG deal, whether EV, CNG, H2 or what, it is looking at the price displayed on the pump go up every second while you are filling that drives the idea home.


The Senate is proposing to cut the $6B/year subsidy for ethanol and promote the sale of electrified vehicles instead. That would be a wise move because gas price would go up and EVs price would go down.

Raising gas price progressively to $6+/gallon and progressively doubling electrified vehicles direct and indirect subsidies could change the ball game.


It also could have other effects on the economy, for every action there is a reaction.


This is a poor website overall. The solution is not to pay 6 000$ more for cars with less drivability like suggested by this website. The solution is audi windmill e-gas and hydrogen put in car that cost less. It cost less because you can keep your car longer because it wear less and also it don't pollute so no need to change for a new car.


Thanks for your input a.b. that helped a lot.


Less driveability? I find a smaller turbodiesel more driveable than a gasser. It doesn't have the top end, but the torque peak is right in the range of cruising RPM so it almost never needs e.g. downshifting on hills.

I have been putting a lot of miles on a V6 minivan lately, and would cheerfully trade it's 3.3 liters for a 2.0 TDI.


s/it's/its/ Yes, I know the difference.


I find that a 1.8L supercharged is able to pull without downshifting. It produces 189 hp and 190 foot pounds of torque, that is more than enough for a 3200 pound car.


IME, it takes more than 200 ft-lb to pull 6000 lb up a grade while maintaining less than 2000 RPM. Turbodiesels can do that in 2 liters or less.

Most modern cars are overpowered (even minivans), but don't have good low-end torque for starting and towing. Turbodiesels do. I understand that turbo-DISI engines are similar (e.g. Ecoboost), and I would like to see one or the other become standard.


Requirements makes the difference. The majority could do with 4 or 5 passenger (under 3000 lbs) cars and have no need for tractors. One could always rent a pick up truck to haul heavy cargo when needed.


Most people COULD make do with a 3000 pound 7 passenger vehicle, but they believe it is their RIGHT to drive a 6000 pound vehicle with one person in it and burn TWICE as much fuel. Your "freedoms" end when you harm others by using twice as much fuel and driving the prices up for everyone.

Stan Peterson

I would make the observation that many of these technologies are already adopted by the auto & truck manufacturers. So the possible future improvements are not that large.

Diesel or CI engines still need extensive engineering to make them clean enough to sell in NAFTA. Unless of course, continually adding to the Air pollution is acceptable, as is the reigning toxic regulations in Europe.

I note that ther are several automotive technologies that are NOT listed here, that have large fuel economy implications. We will see several variations in the next five years. Principally these are categorized as HCCI or PCCI, mixed Otto/Diesel operation, and perfected low temperature Diesel combustion.

Meanwhile America's Air is growing increasingly Clean; having exceeeded the Air quality for every county in the USA, thought to represent "Clean Air" at the First Earth Day in 1970.

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