Noticed engines getting smaller recently?

You're not alone. "Downsizing", as it's called, involves using a smaller engine to do the work of a larger alternative--usually through turbocharging--while enjoying the fuel efficiency benefits associated with its size.

Engineering firm Ricardo thinks this will continue, and not just in small stages--instead, it says "radical" downsizing will be required to meet fuel efficiency targets like CAFE's 54.5 mpg by 2025.

Conveniently, the company is working on its own 'HyBoost' research project, which looks at achieving the same performance as bigger engines than typical downsized ones compete with, yet still maintaining that small-engine efficiency.

Boosted EcoBoost

The testing compares two fairly familiar engines. The first, in a Ford Focus, a 2.0-litre naturally-aspirated four-cylinder, with 145 horsepower. The second is another Focus development of Ford's tiny 1.0-liter, 3-cylinder EcoBoost unit, here tuned to 160 horsepower. For comparison, the standard EcoBoost Focus produces 125 hp--closer to that of a 1.6-liter atmospheric unit.

Getting this power from the 1.0 is actually fairly straightforward: Put a larger turbocharger on it.

That means instant top-end power boost, and low pumping losses at low revs (the extra effort of exhaust gases having to spin a turbocharger, in this case) meaning better part-load fuel efficiency.

Keeping such a system driveable on a small engine is more complex. A large turbocharger takes more time to "spool up", resulting in little power at lower revs, and a surge as engine speeds rise--something known as turbo lag.

To eliminate this, and provide the engine with low-end response, Ricardo uses an electric supercharger.

This can be brought up to speed in a fraction of a second. It need not be used all the time (more air and fuel at all speeds means lower mpg and higher emissions), but it's there when required--if you need a burst of acceleration at highway speeds, for example.

Electricity for the supercharger is supplied by power from an ultracapacitor, its power supplied simply by the rolling energy of the vehicle.

A stop-start system is also fitted, which stops as soon as the speed reaches zero (whether in gear or not) and re-starts as the driver lifts their foot off the clutch to drive away.

Better efficiency

The upshot of all the technical cleverness is that you get an engine which uses very little fuel at a cruise--because it's still just a 1.0-liter three-cylinder--but has plenty of power and response when required.

Lower emissions too. Where the 2.0-liter benchmark car produces 169 grams of carbon dioxide every kilometer, the HyBoost EcoBoost produces under 100 grams--81 g/km, according to Ricardo's figures. That does include some other changes--longer gearing, tweaks to software and optimizing systems, but it's indicative of the benefits: High power, low consumption.

For the record, those two CO2 figures work out at 32 mpg and 67 mpg respectively--that's U.S. gallons, but calculated on the European fuel economy cycle.

The overall benefit is that the expense and weight associated with diesel or hybrid drivetrains is reduced.

By how much we're not sure--Ricardo provides no figures, but we're guessing there's some extra expense to supercapacitors and electric superchargers.

What it all means for you is that even larger vehicles may substitute their engines for high-boost, electrically-assisted engines to ensure both cruising efficiency and adequate power. That's if they deliver suitable real-world gains--not always the case with small-capacity turbocharged engines.

Since the largest improvements can be made on the least efficient vehicles though, "radical downsizing" may be the best way of hitting those fleet-wide CAFE targets in just over a decade.


Follow GreenCarReports on Facebook, Twitter, Instagram and Google+